Mine gases and ventilation; textbook for students of mining, mining engineers and candidates preparing for mining examinations designed for working out the various problems that arise in the practice of coal mining, as they relate to the safe and effecient operation of mines
In March, 1913, there was started in Coal Age a department entitled "Study Course in Coal Mining,' and each week following that date there have appeared two
Overview
Mine gases and ventilation; textbook for students of mining, mining engineers and candidates preparing for mining examinations designed for working out the various problems that arise in the practice of coal mining, as they relate to the safe and effecient operation of mines is a 1920 historical mining reference by Beard, James T. (James Thom), b. 1855, preserved in the Mountain Man Mining research library. In March, 1913, there was started in Coal Age a department entitled "Study Course in Coal Mining,' and each week following that date there have appeared two…
This 1920 document, Mine gases and ventilation; textbook for students of mining, mining engineers and candidates preparing for mining examinations designed for working out the various problems that arise in the practice of coal mining, as they relate to the safe and effecient operation of mines, is preserved in the Mountain Man Mining Library for research and reference. Original source: archive.org.
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Mine Gases And Ventilation
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Mine Gases And Ventilation
Textbook For Students Of Mining, Mining
Engineers And Candidates Preparing
For Mining Examinations
Designed for Working Out the Varioup Problems That
Arise in the Practice of Coal Mining, as They Relate
to the Safe and Efficient Operation of Mines
By
James T. Beard, C.E., E.M.
8ENIOR ASSOCIATE EDITOB, COAL AGE; FORMEBLY PBINCIPAL SCHOOL OF MINES, INTEB- MATIONAL COBRB8PONDENCE SCHOOLS, AND ASSOCIATE EDITOR MINES AND MlNEB- AL8, 8CRANTON, PA.; PBOFE8SOB OF CHEMI8TBT, SCHOOL OF THX LACKAWANNA; BECBETABY STATE BOARD OF MINE EXAMINERS, IOWA; MEMBER AMERICAN INSTITU'l'E MINING engineers; INSTITUTION OF MINING ENGINEEB8, KNGLAND; MINE INSPEC- TOBS' INSTITUTE OF AMERICA; FELLOW AMEBICAN ASSOCIATION FOB THE ADVANCE- MENT OF SCIENCE.
REVlfeBa AND Enlajigjed
b
McGRAW-HILL BOOK COMPANY. Inc.
New York: 239 West 39Th Street London: 6 & 8 Bouveme St., E. C. 4
T7/3 01
Copyright, 1916, 192
By
James T. Beard
v
i
Preface To Second Edition
Any one who has been closely associated with the practical operation of coal mines will realize quickly the need of technical knowledge relating to the safe and economical production of coal. In no department of the work is this need more urgent than in the ventilation of the mine.
A knowledge of the properties and behavior of' the gases found or generated in the mine, and the means for effecting their safe removal or rendering them harmless are of chief importance, requiring careful study combined with practical experience in the operation of mines.
Experience, without a knowledge of the theory of mining, is little better than is the possession of such knowledge by one who has had no experience in the practical work. Experience and knowledge must go hand in hand.
The problems relating air, gases, ventilation, safety lamps, breathing apparatus, rescue work, gas and dust explosions in mines are treated in a thoroughly practical manner, while at the same time showing their correct solution. Formulas must always play an important part in mine ventilation and their treatment is made as simple as possible.
No effort has been spared to make this volume a standard of ventilating practice. With this end in view, the various constants used have been carefully selected and are those most generally adopted. Particularly is this true of the tables of weight and measures and the conversion tables relating to the common and metric systems given in the Addenda. Their use is recommended.
The present volimie, which replaces the little booklet issued by Cool Age, some time previous, under the same title, will be recognized as a second edition of that handbook, though greatly enlarged by the addition of whole new sections on Safety Lamps, Oils, Breathing Apparatus, Rescue Work and numerous tables, making it a complete treatise on the subject. The author desires to thank those who have generously lent their
vu
viii PREFACE
aid in the work, among whom he would particularly mention James W. Paul, Mining Engineer, Federal Bureau of Mines, and J. T. Ryan, Vice-president and General Manager, Mine Safety Appliances Co., Pittsburgh, Pa.
James T. Bbard.
New York City, June 1920.
Preface To First Edition
In March, 1913, there was started in Coal Age a department entitled "Study Course in Coal Mining,' and each week following that date there have appeared two pages of matter in pocket-book form, which were intended to be later compiled and published as "The Coal Age Pocket Book."
The publication of these weekly pages was not confined to a consecutive order, which gave to that department of CocU Age an increasing and widening interest among readers and students of technical mining subjects. The matter treated was in response to the requests of coal-mining men, who were seeking to know the development of formulas, the explanation of principles, and the most approved and generally adopted methods in the practice of coal miniftg. The requests that have been received from publishers of similar technical matter, asking for the privilege of reproducing many of the pages already published in Coal Age, is sufficient evidence of the technical value of the work.
Recently, so many letters have come from mining men and from several mining classes who have beeii studying the pages as they have appeared each week, askin,g that the matter already prepared be published at once in suitable book form, it has been decided to issue the following sections on the atmosphere, gases and ventilation of mines. Although it is not assumed that these sections are in their final form, they contain much valuable matter that will be appreciated by practical mining men and students of coal mining.
Coed Age particularly commends this work to mining students, engineers, mine foremen, assistant foremen and firebosses, superintendents and managers. The book contains only original matter, prepared at great expense of time and labor, involving much careful research and experiment. The author does not hesitate to say that many of the practical problems in the ventilation of mines, which cannot be solved
X Preface
by the usual methods employed, are easily worked by the potential methods explained fully in these pages. No mine official or mine employee can afford to be without this edition in his reference file or library.
James T. Beard.
New York City, Jvlpy 1916.
Contents
Paob CHAPTER I
Am
The atmosphere — The barometer — Physics of air and gases — Matter — Measurement — Density and volume — Specific gravity — Occlusion, emission, diffusion of gases.
Chapter Ii
Heat 42
Sources and measurement of heat — Chemistry of gases — Thermochemistry — Hy geometry — Steam .
Chapter Iii
Mine Gases 86
Geological conditions — Common mine gases — Hydrocarbon gases — Properties and behavior of mine gases — Methane — Firedamp — Carbon monoxide — Carbon dioxide — Blackdamp — Afterdamp — Inflammable and explosive mine gases.
Chapter Iv
Explosions in mines 116
Definition, gas explosion, dust explosion — Inflammation of gas — Nature and temperature of flame — Explosion of gas — Coal dust, its inflammability and influence; effect of stone dust — Mine explosion, development, causes, mixed lights, electric mine lamps, prevention of mine explosions.
Chapter V
Mine Rescue Work and Appliances 131
Preliminary, entering a mine after explosion, first-aid suggestions — Breathing apparatus, principle, action and requirements in respiration, development, design and testing of breathing apparatus — Types of breathing apparatus, Draeger, Fleuss Proto, Gibbs, Paul — Bureau of Mines, permissible breathing apparatus — Specifications by the Bureau of Mines — First-aid work.
Chapter Vi
Theory op Ventilation 161
Mine ventilation — Problems — Flow of air in airways — Ventilating pressure, how produced and measured, the water gage — Velocity of air currents — Quantity of air, requirements — Work or power on the air — Equivalents in measurement — Examples
xii CONTENTS
for practice — Mine airways — Symbols and formulas — Mine )>(Vtoiitiai methods — Measurement -of air currents — Examples for practice — Tandeni circulations — Splitting the air current — Natural division of air — Examples in natural division — Proportionate division of air, kinds of regulators — Secondary splitting — Theoretical considerations in splitting — Practical problem.
Chapter Vii
Practical Ventilation 248
(conducting air currents, air bridges — General plan of mine — Distribution of air in the mine — Splitting air currents — Systems of ventilation — Systems of mine airways.
Chapter Viii
Mine Lamps and Lighting 268
Principles of construction — Safety lamps, classification and requirements — Characteristic types of lamps — Special types of safety lamps — Piermissible mine safety lamps — Use and care of safety lamps — Testing for gas by indicators — The flame test — lUuminants for safety lamps, oils, etc. — Miner's carbide lamps — Electric mine lamps— Permissible portable electric mine lamps.
Addenda 328
Logarithms — Circular functions, sines and cosines, tangents and cotangents — Squares, cubes, roots and reciprocals of numbers — Circumferences and areas — Denominate numbers — Weights and measures — United States and British systems — Metric systems of weights and measures — Conversion tables — Conversion of compound units.
Index 415
Mine Gases And Ventilation
Section I Air
The Atmosphere — The Barometer — Physics of Air and Gases — Matter — Measurement — Density and Volume — Specific Gravity — Occlusion, Emission, Diffusion OF Gases
Little was known of the aerial envelope that surrounds the earth, until the researches of Cavendish and Priestley in England and Lavoisier in France, in the latter part of the 18th century showed that air was not an element, as had been supposed, but a mechanical mixture of gases.
Up to this time, air and all combustible material was believed to contain a certain substance called ''phlogiston," which escaped as flame when the substance was burned. Both Cavendish and Priestley held this phlogistic theory even after they discovered the complex nature of air. Hence, the name "dephlogisticated air'' was applied to oxygen; while hydrogen was called "inflammable air'' and carbon dioxide "fixed air."
It remained for Lavoisier to expose this fallacy by showing that no matter was lost, but the weight of the products of a combustion was equal to that of the combustibles burned. A large number of carefully made analyses showed a practically constant proportion of the two chief gases of which air is formed. This seemed to suggest that the oxygen and nitrogen of the air were chemically united, although the proportion of each gas did not correspond to its combining power
2 'MlN-e-GA-ES AND VENTILAriON
a8 detrhilned by-tfe* analyses of well-known chemical compounds. The character of air as a mechanical mixture thus became definitely established.
Besides the two principal gases oxygen and nitrogen that constitute, the air we breathe, there are other gases whose presence in the atmosphere is of much vital importance, although their proportion is small. Of these may be mentioned carbon dioxide, water vapor, ammonia, argon and ozone.
Carbon dioxide is most important, because of its toxic effect on the human system. This effect, it is stated on the highest authority, increases with the barometric pressure. Thus, for example, air containing but 1 per cent, carbon dioxide, at a pressure of 4, 5 or 6 atmospheres produces the same effect on the respiratory organs as air containing 4, 5 or 6 per cent, of the gas at a pressure of 1 atmosphere. In other words, the true gage of the effect of this gas in inspired air is the percentage of the gas multiplied by the number of atmospheres.
Water vapor present in the atmosphere breathed has a marked effect on the vital activities and the consequent development of physical energy in the body. In what manner the relative humidity of the inspired air operates to impair the physical force has not been fully explained; but experience has shown that a high degree of humidity in a warm atmosphere or climate has an extremely weakening effect on the human system.
The association of high humidity and temperature marks a comparatively large amount of water per unit volume of air and, to that extent, it may be assumed impairs the respiratory functions of the lungs. The result is to incapacitate men exposed to such conditions and render them wholly or in part unfit to perform the required manual or mental labor. These effects are continually observed in the warm moist atmosphere of deep mine workings and other similar places.
The Respiratory System. — Respiration is the prime means of maintaining the vital action in animal organisms. Its objects are twofold: 1. The oxidation of the organic matter of the animal tissues with the resulting development of vital
Air 3
energy. 2. The removal of the carbon dioxide produced in the process of oxidation. Both of these processes are performed through the medium of the blood.
The Circulation. — Under the action of the respiratory system, the blood flows from the heart into and through the arteries of the body, as water flows through a circulating pipe system under the action of a pump. The pulsations of the heart, corresponding to the strokes of the pump, force the blood through a complex system of arteries and veins to every portion of the body and limbs.
All the blood does not flow in a continuous circuit, but the arteries branch, forming separate channels leading to different parts of the body. The time required to complete a circuit and return to the heart is obviously widely different, varying from 20 or 30 sec. to one-fourth as many minutes. This is of interest in relation to the time required for poison entering the blood to be disseminated throughout the system.
Respiratory Action. — The action known as "breathing'' originates, or, at least, is regulated by a nerve center at the base of the brain from which impulses are transmitted through the spinal column to the respiratory muscles. By this means air enters the air cells of the lungs and oxygen, absorbed therefrom by the red corpuscles (haemoglobin) of the blood, is carried by the circulation to the tissues of the body, where it is consumed with the production of carbon dioxide. This gas is absorbed by the blood and carried back through the-veins to the heart and lungs, where it gives up a portion of its gas, which enters the lungs and is expelled by each succeeding exhalation.
While air expired by a healthy adult, at rest, contains from 2 to 3 per cent, carbon dioxide, careful determinations show a constant production of 5.6 per cent, of this gas in the lungs when the person is at rest.
Quantity of Oxygen Consumed in Breathing. — A man at rest consumes 263 cm.* of oxygen per min., or 263 X 0.06102 16 cu. in. per min. and exhales an equal volume of carbon dioxide. Air exhaled from the lungs contains 2.6 per cent, carbon dioxide, 18.3 per cent, oxygen, 79.1 per cent, nitrogen. In vio-
4 Mine Gases And Ventilation
lent exercise, a man consumes from eight to' nine times the amount of oxygen required when at rest; or, say 128 to 144 cu. in. per min. The exhaled breath may then contain 6.6 per cent, carbon dioxide and only 14.3 per cent, oxygen.
Depletion of Oxygen in Air, Effect on Life. — Air containing 3 per cent, carbon dioxide can be breathed without discomfort, even when the oxygen content has been reduced to 16 per cent.; but 5 per cent, carbon dioxide causes headache, dizziness and nausea, after a short time. When no carbon dioxide is present in the air the oxygen content may fall as low as 14 per cent, before much difficulty is experienced in breathing; but air containing but 10 per cent, is no longer breathable; but will cause death quickly by suffocation.
Composition of Air. — Normal air is composed chiefly of oxygen and nitrogen, which are invariably mixed in the following proportions expressed as percentage by volume and by weight of each of these gases:
Table Showing Composition of Normal Air
By Volume By Weight
Oxygen 20. 9 per cent. 23 .0 per cent.
Nitrogen 79. 1 per cent. 77 . per cent.
Air also contains 0.04 per cent, of carbon dioxide (CO2), together with smaller amounts of argon, ammonia and water vapor. Atmospheric air, it may be said, is never absolutely dry or free of moisture. The term "dry air" in respect to the atmosphere is only a relative expression, meaning that such air is comparatively dry.
Weight of Dry Air, — The weight of dry air, per unit volume, varies directly with the pressure it supports, and inversely as its absolute temperature. There are two formulas for finding the weight of 1 cu. ft. of air, one being expressed in terms of the barometer (5), in inches, and the other in terms of the pressure (p) in pounds per square inch.
Ti u 1.3273 B
By the barometer, w — . . .
By the pressure, w
Air 5
Moisture in Air. — This subject is fully treated under "Hygrometry/* and it is sufficient here to say that the water absorbed or held by the air is an invisible vapor that resembles a gas in its behavior, until a sufficient amount is present to fully saturate the space it occupies. This point of saturation is called the "dew point,'* because at that point any excess of vapor condenses and appears as a mist or cloud. The condensation is more rapid in contact with a cold surface.
Normal Air. — The term ''normal air'' in respect tb its composition refers to air containing a normal percentage of oxygen (20.9 per cent.) as given above. When the percentage of oxygen present is less than normal the air is said to be ''depleted" of its oxygen. This frequently occurs in poorly ventilated places in mines. The depletion of oxygen is the result of the various forms of combustion or oxidation that are constantly taking place in mines, and is also caused by the absorption of oxygen from the air by the coal.
Mine Air. — Except when diluted with other gases, the air in a well-ventilated mine never shows any appreciable depletion of its oxygen content. Even in poorly ventilated places it is exceptional to find less than 20 per cent, of oxygen except where other gases are being generated in considerable volume whereby the air is diluted and the percentage of oxygen correspondingly diminished. This fact has been well established by innumerable tests of mine air made at different mines and under varying conditions of ventilation.
The Atmosphere
The atmosphere is the aerial envelope surrounding the earth. The term is also used to describe the air or gaseous mixture filling any given space; as, for example, the mine atmosphere is the air and gases filling the mine or any portion of the workings.
Atmospheric Pressure. — The weight of the air surrounding the earth causes a pressure, which decreases as the height above the surface increases; and the density of the air decreases in like manner, with the elevation above sea level.
6 Mine Oases And Ventilation
Vftriation of Atmospheric Pressure. — Atmospheric pressure at imy given place varies irregularly with the condition in respect to storms; the storm center being always an area of lower pressure than that surrounding the storm. In this country, a variation of 2 in. of mercury (say 1 lb. per sq. in.) in atmospheric pressure, in 48 hr., is not uncommon.
There is also a regular daily variation, the pressure attaining a maximum about 10 o'clock and a minimum at 4 o'clock, itiorning and evening. There is, likewise, a yearly variation, the general pressure reaching a maximiun, in the northern hemisphere, in January and a minimum in July.
The Barometer
The Mercurial Barometer. — The pressure of the atmosphere is measured by the height of mercury column it will support against a vacuum. The mercurial barometer is a glass tube, about 36 in. long, closed at one end. This is first filled with mercury and then inverted. The open end being immersed in a basin of the same liquid, the mercury in the tube will fall to a height above the surface .of that in the basin, such that the pressure of the atmosphere acting on the surface of the liquid in the basin will support the mercury column in the tube.
Barometric Pressure. — The pressure of the atmosphere' expressed in inches of mercury is called the barometric pressure. For example, at sea level, the atmospheric pressure will commonly support 30 in. of mercury column; or is equivalent to a barometric pressure of 30 in.
Calculation of Barometric Pressure. — One cubic inch of mercury (32°F.) weighs 0.49 lb. A barometric pressure of 30 in., therefore, indicates an atmospheric pressure of
which is the normal pressure at sea level.
Calculation of Water Column. — The height of water column, in feet, the atmospheric pressure will support is found by multiplying the pressure (lb. per sq. in.) by 2.3; or dividing the same by 0.434. Or the barometric pressure, in inches,
Air
multiplied by one and one-eighth will give the equivalent water column, in feet. For example, at sea level,
14.7 X 2.3 33.8, say 34 ft. 30 X 33.75, say 34 ft.
Principle of the Barometer. — In the mercurial barometer the pressure of the atmosphere supports the column of mercury in the tube. The weight of the atmosphere counterbalances the weight of the mercury column, which rises as the atmospheric pressure increases and falls as it decreases. The height of the mercury column is therefore a true index of the pressure of the atmosphere at the surface of the earth, at the moment of taking the observation.
The principle of the balance pressure between the air and the mercury is clearly illustrated in Fig. 1, where a glass tubc) closed at one end, is shown supported in a basin of mercury. The surface of the liquid in the basin is shown as divided into imaginary squares, by lines one inch apart; and the small arrow-heads represent the pressure of the atmosphere exerted on each square inch of surface.
Suppose for a moment, that the column of mercury in the tube is exactly one square inch in cross-section; it is evident, in that case, that the mercury column takes the place of the atmospheric pressure on one square inch of surface; and, since there is perfect equilibrium, its weight is equal to the pressure of the atmosphere per square inch.
Furthermore, whatever the sectional area of the mercury column, it is clear that its weight will always equal the atmospheric pressure for the same area of surface. Hence, the area of mercury column is not important, but its height only.
Fig. 1.
8 Mine Gases And Ventilation
If the weight of one cubic inch of mercury (0.4911 lb.) be multiplied by the observed height of the column of merciu*y measured in inches, the product will be the pressure of the atmosphere, in pounds per square inch, at the place whore the observation was taken. This assumes, that the barometric reading has been reduced to a standard reading, at a temperature of 32 deg. (Fahr.), which must be done when making accurate determinations.
Standard Barometric Readings. — Owing to the fact that the mercury in the tube expands and contracts more rapidly than the glass of the tube, the reading of the barometer will vary slightly for the same pressure, at different temperatures.
In comparing barometric readings taken at different times and at varying temperatures, it is necessary to carefully note the temperature when the reading was taken and reduce the observed reading to a so-called standard reading at 32 deg. F.
Calling the standard reading Hy the observed reading h and the temperature t (Fahr.), the corrected reading is found by the formula,
For example, the standard reading corresponding to 30 in. of barometer, observed at a temperature of 60 deg. is
It is even possible, owing to the more rapid expansion or contraction of the mercury than of the glass, that an observed fall of barometer may correspond to an actual rise in atmospheric pressure, or vice versa, within about 0.4 in.
Description of the Instnunent. — In the illustration, Fig. 2, is shown the common form of the standard mercurial barometer. The glass tube that contains the mercury column is here inclosed in the metal case A, to the bottom of which is attached a somewhat larger casing B. The latter holds a glass cylinder G terminated at the bottom with a chamoisskin bag, the whole forming the basin that holds the mercury.
The entire case AB is hung in a truly vertical position, supported on a substantial base, as shown in the figure. The top
of the mercury column is observed through the opening 0, in the upper end of the case. In this opening, is arranged a sliding vernier V, which can be adjusted, by means of the thumbscrew D, so that its lower edge exactly corresponds with the top of the mercury column. The position of the vernier is then read on the scale S marked on the sidea of the opening in the ease. This scale is graduated in inches, but only extends an inch or two above and an equal distance below the normal barometric reading. The normal reading at sea level is about 30 in,, and the scale extends from 26 to 32 inches.
Before setting the vernier, however, it is necessary to adjust the level of the mercury in the basin so that it corresponds exactly with what would be the zero of the extended scale. To enable this to be done with precision, there is attached to the scale a long rod that extends downward inside the casing. The lower end of the rod is drawn to a fine point that marks the zero of the scale.
To adjust the level of the mercury in the basin, the thumb-screw C is turned. This screw bears against the bottom of the chamois-skin bag and operates to raise or lower the level of the surface of the mercury in the glass cylinder. Theadjustment is complete when the. fine pointed end of f„j 2.
the rod is seen to just prick the surface of the mercury. The point of the rod is observed through the glass cylinder above the surface of the mercury,
A thermometer T is show attached to the metal case. In making accurate observations it is necessary to reduce all readings to standard readings.
The Aneroid Barometer. — -The aneroid barometer consists of a metallic case, having a flexible vacuum box within, which is sensitive to the slightest change in atmospheric pressure.
10 Mine Oases And Ventilation
The corrugated diaphragm forming the back of the vacuum box is supported against the pressure of the atmosphere by a steel spring, and its movement under changes of pressure is communicated to the index hand or needle that registers the pressure on a dial calibrated to read inches of mercury corresponding to the readings of the mercurial barometer under the same pressures (Fig. 3).
The aneroid being portable is very useful in ascertaining quickly differences in elevation of two or more points in mines and on the surface. The dial of mining aneroids has two concentric scales. The inner scale of the aneroid shown in the accompanying figure is graduated to read inches of mercury, while the outer scale reads feet of elevation. It has always been the custom, in firranng the graduation of these two scales, to make the altitude scale read
Air
Ro-
TABLE Showing Atmospheric Pressxtbb at Diffebbnt
Elevations and Cobrespondino DENsmr of Air
FOB Different Temperatures
.S
o .
h
So
level r
Mine Gases And Ventilation
The table on the preceding page is deduced from the determinations of atmospheric density and pressure, under normal conditions, at different elevations above and below sea level, as established by the celebrated British astronomer royal. Sir George Biddle Airy (1840), and the aeronautic observations of Herschel and Glaisher. .
The atmospheric pressures in the third column of the table are the mean of many direct observations taken at diflferent altitudes, under normal conditions, and constitute what are generally known as ''Airy's tables."
The temperatures in the fourth column correspond to the mean observed temperatures, -at different altitudes and are based on a sea-level temperature of 60 deg. F. They are suggestive of the rate of cooling or fall of temperature with respect to increase of altitude.
The following table shows the mean observed temperatures of the atmosphere at different altitudes, the rate of fall (deg. per 1000 ft.) and the estimated average temperature of air column extending from sea level to each respective altitude given :
I'able Showing Relation of Mean
Temperature
to Altitude,
IN THE Atmosphere
Altitude or elevation above sea level, ft.
Mean observed
temperature,
deg. F.
Rate of fall in
temperature,
deg. per 1000 ft.
Mean average temperature of air column, deg. F.
The mean average temperature of air column extending from sea level to any altitude given in the above table makes it possible to calculate the normal barometric pressure for that altitude, by means of the following formula:
Air 13
The application of this formula requires the use of a table of seven-place logarithms or more. It serves to check the temperature observations at these altitudes.
in which
Bh barometric pressure, at altitude h (in.) ; T average absolute temperature of air column, extending from sea level to altitude h (deg. F.); h altitude above sea level (ft.).
The sign ± , in the formula, relates to the altitude h, as being above or below sea level. For altitudes above sea level, the second term within the brackets is negative and the minus ( — ) sign must be used. For altitudes below sea level, this term is positive and the plus (+) sign is employed.
Relation of Drop in Temperature to Altitude. — Approximately, the fall in temperature (t), in the atmosphere, varies as the 1.4 root of the height (h) above the sea level; thus,
Applying this principle and assuming a temperature drop of 6 deg. at an altitude of 1000 ft. above sea level, disregarding the effect of the radiation of heat from the earth, the mean average temperature (/), for any altitude (A), expressed in thousands of feet, can be calculated approximately thus:
This formula assumes a normal sea-level temperature of 60 deg. F., which is the first term in the second member of the equation. The second term of this member accounts for the fall of temperature corresponding to the increase of altitude; while the third term expresses the effect of the radiation of heat from the earth, which varies inversely as the square of the altitude factor A — 2, probably owing to the influence of clouds or vapor in the lower atmosphere.
Example. — Let it be required to find the temperature, at an elevation of 8000 ft. above sea level, corresponding to a normal temperature of 60 deg. at sea level.
14 Mine Gases And Ventilation
Solution. — In this case, the altitude expressed in thousands of feet is /i s 8 ; which substituted in the formula gives :
The mean observed temperature for this altitude as given in the table is 32 deg. F.
Average Temperature of Air Column. — The average temperature of the air column extending from sea level to any altitude h, expressed in thousands of feet, can be calculated with close approximation by the formula
Average temp. 60 —
The mean average air-column temperature, as calculated by this formula, can be used to find the corresponding normal atmospheric pressure by substituting its value, reduced to absolute temperature (T), in the formula
The use of this formula will require a table of seven-place logarithms or more. In the solution of the following example, a ten-place logarithmic table was employed.
Example, — Find the mean average air-column temperature corresponding to a sea-level temperature of 60 deg. F., for an elevation of 12,000 ft. above the sea.
Solution. — In this case, h 12, which gives for the mean average aircolumn temperature
The absolute temperature is 460 39 499 deg.F., abs.
Example. — Calculate the normal atmospheric pressure for ah altitude of 12,000 ft., using the mean average air-column temperature found in the last example, T 499 deg. F. abs.
Solution. — Substituting the given values in the formula gives for the normal atmospheric pressure at this altitude,
The diagram shown on the following page compiles the data relating to average observed temperatures at different elevations, and the calculated heights of the corresponding
Air
water and mercury columns, weight and pressure of air, of interest to the student of atmospheric conditions.
Is
Atmospheric
t
"J
Sj
?
asipoofrho
Iqpoo-
a0472ti98.5
W
2Ta05$U45S.4
a0744
fa/07
H.n4
/6S48
The Differential Method. — The pressure of the atmosphere, per unit area, at any altitude x is due to the weight of aii* column above such point of observation. Air being compressible, any increment of pressure (6px), causes a corresponding minus increment of height {—6x)] and, calUng the unit weight of air ii;* at the altitude x, we have
But the unit weight of air varies with the pressure it supports. Hence, calling this unit weight and pressure at sea
16 Mine Gases And Ventilation
level Wo and poy respectively, and that at any altitude x, Wg, and p,, we have
Wo po Po
Substituting this value in equation 1 and dividing both members of the equation by p„ gives
But, the differential of a quantity divided by the quantity is equal to the differential of its Naperian logarithm.
Hence, 5 log px - 6,; or 5, 5 log p. (4)
Po Wo
Then integrating between the limits a; 0, and x h, remembering that when x 0, p, po; and when x A, p, and subtracting the lower integral from the higher,
Wo
But the unit weight of dry air at sea level, normal atmos- ' pheric pressure (lb. per sq. ft.), is
which, substituted in equation 5, gives for the altitude corresponding to any pressure, under normal conditions,
Or, expressed in common logarithms,
For normal atmospheric pressure, at sea level, po 14.696 lb. per sq. in., and log 14.696 1.1672; hence
Air 17
Physics Of Air And Gases
The volume of any given weight of air or gas depends on two factors — the temperature of the gas and the pressure it supports.
Effect of Temperature. — For any given weight of air or gas, its volume varies directly as its absolute temperature, assuming the pressure remains constant.
Effect of Pressure. — For any given weight of air or gas, its volume varies inversely as the pressure it supports, assuming the temperature remains constant.
Expansion and Contraction of Air or Gas. — Any change in temperature or pressure causes a corresponding change in the volume of the air or gas, as follows:
Increase of temperature causes expansion. Decrease of temperature causes contraction. Increase of pressure causes contraction. Decrease of pressure causes expansion.
Coefficient of Expansion or Contraction. — The coefficient of expansion is the same as that of contraction. This coefficient relates to change in volume due to change in temperature and is practically the same for all gases and air and independent of the pressure.
The coefficient of expansion of air or gas is the ratio of the increase in volume to the original volume, for an increase of one degree in temperature. Since a degree of the Fahrenheit scale is of a degree of the centigrade scale, it is evident that the Fahrenheit coefficient of expansion will be exactly of the centigrade coefficient. These coefficients are as follows: Centigrade, 0.003663; Fahrenheit, 0.002035.
lUustrcUion, — Let it be required to find the increase in volume in an air current of 100,000 cu. ft. entering a mine at a temperature of 32 deg. F. and discharged at a temperature of 68 deg. F.
SoliUion. — The rise in temperature is 68 — 32 =36 deg. F. The increase in volume, calculated by the Fahrenheit scale, is
100,000 X 0.002035 X 36 7326 cu. ft.
Or, since 68 and 32 deg. F. correspond to 20 and deg. C, the rise in temperature is 20 — 20 deg. C, and the increase in volume, calculated by the centigrade scale, is
100,000 X 0.003663 X 20 7326 cu. ft.
18 Mine Gases And Ventilation
Note. — Instead of multiplying by these coefficients, it is possible to divide by their reciprocals, which are
Fahrenheit, nnnonog 491.4, say 492
These numbers, being divisors, show that air or gas expands or contracts of its volume, for each degree rise or fall in temperature (centigrade); or of the san:9 volume for each degree rise or fall in temperature (Fahrenheit). The figures point to what has been called the "absolute zero'' of temperature scales as being 273 deg. below freezing (— 273°C.) or 492 deg. below freezing (-460**F.).
Absolute Zero. — The i-called "absolute zero" of temperature scales is based on the observed rate of expansion and contraction of all gases and air. This rate is practically M73 of the volume, per degree centigrade; or 392 of the volume, per degree Fahrenheit. It is clear that if this rate continued unchanged a fall in temperature of 273 deg. C, or 492 deg. F., below the freezing point of water, would reduce the volume of the gas to zero, when all molecular vibrations would cease, indicating a total absence of heat and pressure.
The absolute zero has therefore been fixed at 273 deg. below the common zero of the centigrade scale ( — 273°C.), which corresponds to 460 deg. below zero on the Fahrenheit scale. The fixing of this point is purely arbitrary, its chiet value being the facility it affords in the calculation of gaseous volumes with respect to temperature.
Absolute Temperature. — Absolute temperatures differ from common temperatures only in being estimated from the absolute zero. Hence the absolute temperature is obtained from the common temperature by adding 273 in the centigrade or 460 in the Fahrenheit scale; thus,
30 deg. C. 273 + 30 303 deg., absolute. 60 deg. F. 460 + 60 520 deg. absolute.
Relation of Volume and Absolute Temperature of Air and Gas. — The law comnonly known as Gay Lussac's or Charles'
Air 10
law makes the volume of all gases and air, under constant pressure, vary directly as the absolute temperature.
This relation is clearly illustrated in Fig. 4, which assumes a volume of 460 cu. ft. of air or gas at deg.F., corresponding to the absolute temperature at that point. It will be observed that this volume expands and contracts exactly as the absolute temperature rises or falls, except at the lowest temperatures approaching the liquefaction of the air or gaw"where the law naturally fails, owing to the changing state, of the matter.
Relation of Volume and Pressure of Air and Gas.-For a constant temperature, the volume of air and gases varies inversely as the pressure supported. In this connection, pressure is often estimated as one, two, three,etc., atmospheres, meaning that the pressure supported by the air or gas is one, two, three, etc., times the normal atmospheric pressure at that place. This is commonly known as Boyle's or Mariotte's law <rf volume.
An "atmosphere" is sometimes incorrectly taken to mean normal sea-level pressure (14.7 lb. per sq. in.). Such a meaning of the term, however, would manifestly limit its application to sea level, or furnish an arbitrary standard inconvenient for use.
The term "free air" relates to atmospheric air at any elevation and for any condition. According to the above rule, when free air is compressed to two, three or four atmospheres its volume is reduced to }4, H or of the original volume, assuming the temperature remains constant. At the same time, the pressure or tension of the air is increased to two,
20 Mine Gases And Ventilation
three or four times the atmospheric or free-air pressure, what-' ever that may have been, assuming always a constant temperature of the air. .
The expansion of air, by the same law, is accompanied by a fall of pressure, the volume ratio being equal to the inverse pressure ratio, for the same temperature. The pressure referred to here is the absolute pressure, or the pressure above a vacuum or zero.
Relation of Absolute Temperature and Pressure of Air and Gas. — For a constant volume, the absolute temperature of air and gases varies directly as the absolute pressure.
Volume, Temperature, Pressure of Air and Gas. — The relation of the volume (v), pressure (p) and absolute temperature for a given weight of air or gas is expressed simply by the following formulas :
Constant pressure Constant temperature Constant volume
The relations of volume, temperature and pressure of air and gas depend on two main conditions: 1. The gas may or may not be free to expand. 2. Heat may or may not be added or taken from the gas.
Addition of Heat. — Two cases may arise, as follows:
(a) If the air is confined (constant volume) the rise in temperature is more rapid, since all the heat is then transformed into heat energy or internal work, and the pressure rises accordingly.
(6) If the air is free to expand (constant pressure) the rise in temperature, for the same addition of heat, is much less rapid. In this case, the air in expanding performs external work against the pressure it supports. A part of the heat added is thus absorbed in doing outside work while the remainder, only, is available for internal work and manifest as heat energy, thus causing a lesser rise of temperature.
Work of Expansion of Air. — When air is expanded by the addition of heat the external work performed can be calculated in two ways, as follows:
1. On a heat-unit basis, by subtracting the heat absorbed.
Air 21
per pound of air, per degree rise in temperature, for constant volume, from the heat, per pound, per degree, for constant pressure; and multiplying this difference, which is the heat converted into external work, by the foot-pounds per heat unit; thus, since 1 B.t.u. 778ft.-lb.,
Heat, per Ib.-deg. (sp. heat, const, pressure) 0.2374 B.t.u.
Heat, per Ib.-deg. (sp. heat, const, volume) 0. 1689 B.t.u.
Heat, per Ib.-deg., available for external work 0.0685 B.t.u.
External work, per Ib.-deg 0.0685 X 778 53.29 ft.-lb.
2. The external work performed in the expansion of air, per pound, per degree, can be calculated, also, very simply by multiplying the volume of 1 lb. of dry air, at 1 deg. F., absolute, and 1 lb. per sq . in. pressure (0.37 cu. ft.), by 144, the number of square inches in 1 sq. ft.; thus, External work, per Ib.-deg. . . . 0.37 X 144 63.28 ft.-lb.
Adiabatic Expansion and Compression. — When there is no addition of heat in the expansion, or no loss of heat in the compression of air or gas, the relations of volume, temperature and pressure follow other laws than those previously given. Such expansion or compression is described as "adiabatic," meaning no passage (of heat) in or out of the gas.
In adiabatic expansion, there being no addition of heat, the increase in volume is at the expense of the internal energy and a fall of temperature is the result, which is accompanied also by a fall of pressure.
In adiabatic compression, there being no loss of heat, the internal energy is augmented by the heat of compression, and the result is an increase of both temperature and pressure.
Adiabatic Formulas. — The following formulas express the relation of volume (v), pressure (p) and absolute temperature (r), for any given weight of air or gas, when expanded or compressed without gain or loss of heat. In actual practice it is only possible to approximate adiabatic expansion or compression :
Pi'
22 Mine Gases And Ventilation
It is important to observe that adiabatic expansion or compression always involves a change in temperature. Where the temperature is maintained constant, by adding heat in expanding, or extracting heat (cooling) in compressing, the change in volume is described as Usothermal" expansion or compression. In practice, it is only possible to approximate isothermal conditions in the expansion or compression of air or gas.
The application of the above formulas necessitates the use of logarithms.
Matter
Definition. — Matter is the tangible substance occup3dng space and endowed with properties that give to it form, motion and other distinguishing characteristics, by virtue of an allpervading or impressed subtle force generally described as electrical.
Divisions of Matter. — Until recently, the ultimate or smallest conceivable division of matter was assumed to be the atom (Dalton, 1808). Later researches of radio-active substances have developed the infinitely smaller particles which have been termed "electrons" (Stoney, 1891) and "corpuscles" (Thomson, 1897). The electron is assumed to be a minute particle of matter having a negative charge of electricity; and its mass is variously estimated at from Ktoo to 3000 of th mass of the atom of hydrogen.
The chemical divisions of matter are the familiar atoms and molecules.
Properties of Matter. — The universal attribute of all matter is that described as "mass," which may be simply defined as amount of matter. By virtue of its assumed electrical state or condition, all matter is endowed with certain tangible and measurable qualities or properties, such as weight, inertia, density, elasticity, cohesion, divisibility, impenetrabiUty, expansion, contraction.
Matter undergoes many changes but is absolutely indestructible.
Law of Attraction. — The universal law of attraction is that every particle of matter attracts every other particle of mat-
Air 23
ter, the force of attraction varying inversely as the square of the distance between the particles.
Terrestrial attraction is the attraction that the mass of the earth exerts on the mass of a body. This is commonly called "gravitation" and the attractive force, the "force of gravity" or simply "gravity."
Form or State of Matter. — All matter exists in one of three different f onns, namely, solid, liquid, or gaseous. The same matter may pass from one form or state to another owing to a change in density.
Molecular State. — The molecular theory assumes that all matter, solid, liquid or gaseous, in respect to its physical condition, is composed of molecules, each complete in itself. It is assumed that these molecules are subject to two opposite or opposing forces known as the "molecular forces" of attraction and repulsion.
Molecular attraction, acting to bind the molecules of matter together, is in obedience to the common law of attraction in all matter.
Molecular Repulsion, acting to drive the molecules of matter apart, is the result of a state of incessant molecular vibration, which produces the effect called "heat."
Solids. — Matter in the soUd state is characterized by a greater or less rigidity of its molecules. The force of molecular attraction is here stronger than that of repulsion, and the molecules are held in a firmer grasp.
Liquids. — 'In the Hquid state, the forces of attraction and repulsion are about evenly balanced, and the molecules move freely among each other.
Gases. — In the gaseous state, the repulsive forces are in the ascendency and the molecules are driven so far apart that the density of the matter is reduced to that of a gas.
Liquids and gases are both fluids, which is a general term applied to any form of matter other than a solid.
Illustration. — Ice, water and steam furnish a good illustration of how the same matter can pass successively from the solid to the liquid and gaseous states. In the passage from one state to another, there is no change in the matter
24 Mine Oases And Ventilation
itself, the difiference being due to the heat condition of the
a
mass.
In the passage from solid to liquid, or from liquid to gas or vapor, heat is given out; and, vice versa, heat is absorbed when a gas or vapor becomes a liquid, or a liquid becomes a solid. The change is thus a heat condition only.
Vapors and Gases.-— The term vapor properly describes the gaseous condition of most substances that, at ordinary temperatures, exist as liquid or solid; or a gas at or near its point of liquefaction. The term thus has a suggestive meaning of the possible liquid or solid state of the substance now in the gaseous state.
The term gas, on the other hand, is a general term that relates solely to the gaseous condition of matter; and is thus more properly applied to those substances that, at ordinary temperatures, exist as gas; although they may be liquefied or solidified by a decrease of temperature and an increase of pressure.
Thus, we speak of air, oxygen, hydrogen, nitrogen, carbon dioxide, methane, etc., as gases," in contrast to steam (water vapor) and the vapors of such volatile hquids and solids as naphtha, benzine, camphor and other similar substances.
Vaporization takes place at all temperatures; and in many instances, a substance will pass directly from the solid to the gaseous condition, without becoming hquid.
Mass, Volume, Density. — Since mass is amount of matter, the mass (M ) of a body is the quantity of matter it contains, which is determined by the volume (F) of the body and the density (D) of the matter. The relation of these elements is expressed by the formula
Then, considering a unit volume (V 1), it is evident that the "unit of mass" is equal to the "unit of density." In other words, whatever is taken as the accepted unit or standard of density is also the unit and standard for the measurement of mass, which is the ultimate unit.
Air 25
Measurement
The valuation and comparison of the various orins and conditions of matter and the estimation of physical phenomena are made by reference to three general standards of measurement, namely, distance force and time. There are many modifications and combinations of these three elemental standards.
Distance. — This includes the measurement of length, surface and voliune, all of which are derived from the same standard of measure.
Force. — All measurement of force is based on the attractive force exerted by the earth on an assumed unit of mass at the surface (sea level), in any given latitude. Mass thus becomes the true unit in this measurement; but being intangible, the adopted unit is the pound, which represents a certain definite mass, taken as the "unit of mass," for purposes of measurement. A force is measured by the effect of its action on a known mass. There are two conditions: 1. Static condition (mass fixed, immovable), foripe applied to a body produces pressure, weight. 2. Dynamic condition (mass free to move) force produces motion, velocity.
Under these two conditions, there are, therefore, two units of force. The unit of measure for static force is the pound, while the unit of measure for dynatmc forces is the force that will produce a unit of velocity in a unit of mass, in a unit of time. In other words, the force that will increase the rate of motion of a unit mass, by a unit distance in a unit time.
Application. — Applying these units of measure, the weight (IT) of a body, expressed in pounds, is the static force (F) acting on the body, due to gravity.
Hence, in statics,
In dynamics, the force (Fi) producing motion is measured by the mass (M) of the body and the velocity (v) produced per unit of time. Hence, in dynamics,
The velocity produced may be constant or accelerated. Constant velocity is the distance passed over in a unit of
26 Mine Gases And Ventilation
time. Acceleration its the gain in velocity per unit of time. A constant force, as gravity, acting on a body free to move produces a uniform acceleration; that is to say the gain in velocity, each unit of time, is constant.
Assuming a falling body, the force producing motion is the weight (W) of the body, and the gain in velocity per unit of time (acceleration due to gravity, g) is the velocity produced in the mass (ilf). Hence, in falling bodies,
and
W
g
which enables the calculation of the mass of a body from its weight.
Hence a force acting to produce motion in a body bears the same ratio to the weight of the body, as the acceleration due to the force bears to the acceleration due to gravity. Or, expressed as a proportion,
Time. — The element of time is important in the estimation of velocity and power. For example, to traverse the same distance in one-half the time will require twice the velocity. Likewise, to perform the same work in one-half the time will require twice the power.
Special Units. — There are numerous other units of limited significance; such as units of capacity, pints, quarts, gallons, barrels, etc.; units of currency, cents, dimes, dollars, etc.; circular units, degrees, radians, etc.; electrical units, amperes, volts, ohms, watts, etc.
Compound Units. — Many units of measure are composed of two or more simple units. The following are examples:
Unit velocity — (distance) -r- (time) Ft. per sec, or ft. per min.
Unit power — (distance) X (force) -r (time). . .Ft.-lb. per min.
Air 27
The above are only given as samples of many similar compound units; such as inch-pounds; miles per hour; gallons per hour; cubic feet per minute; pounds per cubic foot; tons per acre; foot-acres, etc.
All of these, it will appear, are derived from the simple units of distance, force, time, or the special units to which reference has been made.
Energy. — Energy, in physics, is capacity to perform work. It is the vitalizing force that is manifested in matter by the familiar agencies of heat, light, electricity, magnetism, molecular attraction, chemical affinity, etc., all of which are equally convertible, one into the other, without loss.
The physical agencies or forms of energy just mentioned are each and all convertible into mechanical motion, which, again, can be reconverted into heat, light, electricity, and magnetism. This fact gives rise to what is called the mechanical equivalent" in reference to heat.
Forms of Energy. — Energy is of two kinds that dilBfer from each other only in the sense that one (kinetic) is actual and present, while the other (potential) is possible only.
Kinetic energy (E) is the energy possessed by a body by virtue of its motion. The force producing an acceleration (J) in a mass (M), or the "living force" in the body (momentum), is Jiff. The acceleration (J) being uniform or the velocity increasing uniformly, the distance increase, per unit of time is //2, and the work performed in producing this acceleration is stored in the body as "kinetic energy," by virtue of which the body would continue to move at the velocity imparted, till opposed by some force. The energy stored per second is calculated by the formula
Kinetic energy, E Mf Mp
Potential energy is the energy that is possessed by a body by virtue of the position or state in which it is held or restrained so that motion cannot take place till the restraining force is removed. Examples of bodies having potential energy are, a suspended ball, a confined spring, etc.
Mine Cases And Ventilation
A common method of making physical measurements for the estimation of weight, volume, heat, etc., is by reference to some adopted standard. All such measurements are relative and are frequently termed "specific." Such, for example, are specific gravity, specific volume, specific heat, etc. The atomic weight of elements is often called specific weight.
The Elements. — An element is a substance that has not, as yet, been resolved into parts of a different nature and is, therefore, regarded as being composed wholly of one kind of matter or simple, in contrast with a compound, which is composed of two or more elements or kinds of matter.
The following table gives the more important elements,
together with their chemical symbols and specific or atomic
weights:
Table of the More Important Elements International Committee (1910)
Elements
Symbols
Atomic weights
16
Elements
Symbols
Atomic weights
H l
Aluminum. Antimony. .
Argon
Arsenic. ... Barium . . . . Bismuth. . .
Boron
Bromine.. . Cadmium.. Cesium . . . Calcium...
Carbon
Cerium
Chlorine. . . Chromium.
Cobalt
Columbium
Copper ,
Fluorine. . .
Gold .,
Helium... ., Hydrogen. .
Iodine ,
Iridium. . . .
'Iron
Lead
Lithium. . . . Magnesium,
Al
Sb
A
As
Ba
Bi
B
Br
Cd
Cs
Ca
Ce
Cr
Co
Cb
Cu
F
Au
He
H
Ir
Fe
Pb
Mg
Manganese
Mercury
Molybdenum
Nickel
Nitrogen
Osmium
Oxygen
Palladium
Phosphorus
Platinum
Potassium
Radium
Rhodium
Selenium
Silicon
Silver
Sodium
Strontium
Sulphur
Tellurium
Thallium
Tin
Titanium
Tungsten
Uranium
Vanadium
Zinc
Zirconium 6
Mn
Hg
Mo
Ni
N
Os
O
Pd
P
Pt
K
Ra
Rh
Se
Si
Ag
Na
Sr
S
Te
Tl
Sn
: Ti
W
U
Zn
Zr
u.o
Air 29
The preceding table contains only 56 out of the 80 or more elements that have been discovered, many of which are so rare as to be of little practical importance. The values of the atomic weights are given referred both to hydrogen as unity and oxygen as 16. The heavy type indicates the values commonly used in the study of mine gases.
Density And Volume
Density Defined. — The term "density" refers to the amount of matter in a given volume or space. The commonly adopted measure of density is the ratio of the weight of a body to its volume or the space it occupies, as expressed by the formula:
volume
In a general sense, the term density has thus come to mean the weight per unit volume. For example, the density of water is commonly understood to mean its weight per cubic foot (62.4283 lb., max. dens., 4°C.).
Specific or Atomic Volume. — These terms have reference to an assumed unit volume for all gases, which unit is the assumed vo.ume of a single gaseous atom.
Avogadro's Law of Gaseous Volume. — This law may be stated briefly and clearly as follows:
At the same temperature and pressure all gaseous molecules are assumed to be of the same size.
With a few unimportant exceptions, this law applies to all gases, whether simple or compound. It holds true for all mine gases and is important in the calculation of the relative volume of gases concerned in chemical reactions.
Molecular Volume. — Chemical hypothesis assumes that the molecules of simple substances each contain two atoms only, while the molecules of a compound substance may contain any number of atoms, but never less than two. Notwithstanding this multiplicity of atoms, Avogadro's law makes all gases, with a few unimportant exceptions, to contain the same number of molecules, per unit volume, when measured at the same temperature and pressure. In other words, measiu'ed at the
30 Mine Gases And Ventilation
same temperature and pressure, all gaseous molecules are of the same size.
Calculation of Density. — The elements form the basis of all relative measurements with respect to volume, density and weight. For example, the density of air, referred to hydrogen as unity (H 1), can be calculated from the relative weights and volumes of oxygen and nitrogen, which are the chief constituents of air. The composition of pure air, by volume, is practically, oxygen (O), 20.9 per cent.; nitrogen (N), 79.1 per cent. Then, since the atomic weight of oxygen is 16 and that of nitrogen 14, the relative weight of 100 volumes of air, referred to hydrogen as unity, is found as follows:
Oxygen, 20.9 X 16 334.4
Nitrogen, 79.1X14 1107.4
Air, 100 vol's 1441.8
Therefore, one volume of air is 1441.8 -i- 100 14.418 times as heavy as the same volume of hydrogen; or, the density of air referred to hydrogen is 14.418.
The percentage composition of pure air, by weight, is readily calculated from the above figures; thus:
Oxygen, (334.4 X 100) 1441.8 say 23.2 per cent. Nitrogen, (1107.4 X 100) -f- 1441.8 say 76.8 per cent.
Specific Gravity
The specific gravity of a substance — solid, liquid, or gas — is the ratio of the weight of that substance to the weight of another substance taken as a standard, volume for volume;
wt. of unit vol . of su bstanc e
' wt. of unit vol. of standard
Comparison of Standards. — Hydrogen, air and water are the three standards commonly used in the determination of the specific gravity of gases, liquids and solids. The relative densities of these standards are as follows:
Air (dry) is 14.418 times as heavy as hydrogen, at the same temperature and pressure, volume for volume.
Air 31
Water (max. density, 4®C.) is 773 times as heavy as dry air at 32 deg. F., bar. 29.92 in.; and 815 times as heavy as dry air at 60 deg. F., bar. 30 in., volume for volmne.
Standard for Gases. — The standard adopted for gases is air or hydrogen, of the same temperature and pressure as the gas.
Standard for Liquids and Solids. — The standard adopted for liquids and solids is water at maximiun density. Except where great accuracy is desired, the weight of 1 cu. ft. of water is taken as 62.5 lb. Exactly, 1 cu. ft. of pure water, at maximum density weighs 62.4283 lb.; or 1 cu. in. weighs 252.89 grains 0.03613 lb.
Calculation of the Specific Gravity of Gases. — Since air is 14.4 times as heavy as hydrogen, at the same temperature and pressiu'e, the specific gravity of a gas, referred to air as unity, can be calculated by dividing one-half of its molecular weight by 14.4. For example, the molecular weight of carbon dioxide is 44; therefore, 44 2 22, and 22 14.4 1.528. The actual specific gravity is 1.529.
Finding Specific Gravity of Gases. — A glass globe, any convenient size, is first weighed empty (air exhausted), w; then full of air, wi; and, lastly, filled with the gas, w%: the temperature and pressure remaining constant.
Sp. gr,
Wi — w
Finding Specific Gravity of Liquids. — A glass-stoppered bottle is first weighed empty, w] then filled with water w\] and, lastly, filled with the liquid, The specific gravity is then calculated by the above formula for gases. Or, the specific gravity is determined by a graduated float (hydrometer).
Finding Specific Gravity of Solids. — Weight of the solid in air, w] weight immersed in water w\. The weight of the water displaced is then w which has the same volume as that of the solid.
Sv. gr.
w — Wi
Mine Gases And Ventilation
Specific Gravities and Unit Weights op Solids and Liquids
Substance
Alcohol, pure
commercial
Aluminum
rolled
Brick, pressed
common, hard
lignite, brown coal
Coke, loose piled
Concrete
Earth, dry, loose to well rammed . . . moist, loose to well rammed
wet, flowing mud
Gravel, loose
Gypsum, ground or calcined, loose. . . well shaken
Ice ;
rolled
Limestone
Average
specific gravity
Air 33
Pitch 1 . 156 72.0
Platinum 21.6 1348.0
Rosin 1.1 68.67
Sand, dry 100.0
wet. 130.0
Silver 10.6 656.0
Sulphur 2.0 125.0
Tallow 0.94 58.7
Tar 1.0 62.5
Traprock 3.0 187.0
sea, average 1 .028 64. 176
Lb. per cu. ft.
Ash, white 38
Birch 41
Cedar, white 23
red 35
Cherry 42
Chestnut 41
Elm 35
Ebony 76
Hemlock 25
Hickory 53
Mahogany, Spanish 53
Honduras 35
Maple 49
Oak, live 59
white 48
black, jack, etc 35 to 45
Pine, white 25
yellow. Northern 34
Southern 45
Spruce 25
Sycamore 37
Wahiut 37
34 Mine Gases And Ventilation
Specific Gravities and Weights of Oils
Sp. Or. Lb. per Qal.
Animal— lard 0.916 7.64
whale 0.926 7.72
Vegetable— cottonseed 0.923 7.70
olive 0.917 7.65
gasoline 0.700 5.84
naphtha 0.730 6.09
Use of Specific Gravity. — To find the weight of any volume of a substance multiply the unit weight of the standard, by the specific gravity of the substance, and that product by the given volume; or, expressed as a formula,
Wt. unit weight of standard X sp. gr. X vol.
For example, taking the average specific gravity of anthracite coal as 1.5 the weight of this coal underlying 1 acre (43,560 sq. ft.) of land, for a thickness in the seam of 1 ft.; or, as we say, per foot-acre, in long tons (2240 lb.) is
62.5X1.5X43,560 , , 94?; 1823 long tons
Or, taking the weight of 1 cu. ft. of air (60°F., bar. 30 in.) as 0.0766 lb., since the specific gravity of carbon dioxide (CO2) referred to air as unity is 1.529, the weight of 100 cu. ft. of this gas, at the same temperature and pressure, is
Occlusion, Emission, Diffusion Of Gases
Occlusion of Gases. — The occlusion of gases in coal or other solid substances is the result of the absorptive power of the substance for that particular gas. For example, platinum, palladium, gold and other metals, as well as coal (carbon), absorb varying quantities of hydrogen, nitrogen, oxygen, the hydrocarbon and other gases.
Air 35
The most common examples of occlusion are the absorption of hydrogen by platinum; and of methane, nitrogen, oxygen and carbon dioxide by coal and coal dust. The law that governs this absorption is unknown. The occluded gas is often held very strongly by the substance with which, however, it is not combined.
The occluded gases of coal seams were probably produced in the metamorphic processes that formed the coal; and their absorption (occulsion) in the solid formation may have resulted in the oxidation, to a limited extent, of the carbonaceous matter that was being transformed into coal. Such reactions, if taking place in the measures, together with the consolidation that accompanied the formation, would naturally give rise to the observed pressures of occluded gases.
The pressure of occluded gases in coal formations is very variable, depending not only on the conditions attending the occlusion; but to an even greater extent on the impermeability of the infolding strata, which has prevented the escape of the gases from the measures where they are formed.
Transpiration, Emission of Gases from Coal. — The gases occluded in coal exude from its exposed siuf ace in the same manner as perspiration exudes from the pores of the skm. The term ''transpiration'' relates to the motion of a gas through a capillary tube and thus describes the emission of gas from coal.
The velocity of traniiration is according to a different law from that governing the rate of the diffusion of gases. For the same gas, the rate of transpiration varies directly as its pressure or density, and inversely as the length of the tubes through which it must pass. The velocity of transpiration is independent of the material that forms the tube, but is affected by temperature, being less for a higher temperature, and vice versa.
RELATIVE VELOCITY OF OASES (Am - 1) Gas Rel. Veloo. Gas Rel. Veloc
Hydrogen 2.066 Carbon dioxide 1 .237
Olefiant gas 1 . 788 Carbon monoxide 1 . 034
Methane 1.639 Nitrogen 1 .030
Hydrogen sulphide 1 . 458 Oxygen . 903
36 Mine Gases And Ventilation
The above table gives the relative rates or velocities with which the common mine gases transpire, referred to the rate for air as unity. The actual rate of emission of gas from coal, however, will depend chiefly on the pressure of the gas in the coaL Any sudden fall in barometric pressure is always accompanied with an increase in the emission of gas from the coal, but the increase is almost inappreciable.
Diffusion of Air and Gases. — If the molecules of all matter are assumed to be in a constant state of vibration, it naturally follows that the vibratory movement or force will vary with the density of the matter. In the case of fluids — air, gas, or liquid — the molecules are free to move among themselves, which is not true of solids, whose molecules, normally, hold fixed relations to each other.
If the densities of two fluids are equal, the vibratory force is equal in each fluid; and, at the plane of contact of the two fluid bodies, action and reaction are equal between the vibrating molecules and there is no tendency of these fluids to mix. The laws governing the mixture of liquids is not as simple as in the case of gases, owing chiefly to numerous physical properties of liquids that modify and retard the diffusive action. While the diffusion of gases into each other and into air is extremely rapid, the diffusion of liquids is often very slow and in some cases does not take place at all because of the counteracting forces.
Gases of different densities diffuse into each other and into air. The action is extremely rapid and conforms very closely to certain well defined laws. The diffusion of mine gases into the mine air and into the air current is an important feature of mine ventilation.
Law of Diffusion of Air and Gases. — By a similar experiment, showing the diffusion of hydrogen into oxygen, Graham found that for every volume of oxygen that passed into the hydrogen, four volumes of the hydrogen passed into the oxygen, the ratio thus being 4:1, in this case. But, calling the density of hydrogen unity or 1, that of oxygen is 16 and \/i6 4. This and other similar experiments, all confirming the first; led Graham to propound the following law:
Air 37
Graham's Law. — The velocity or rate of diffusion of air and gases varies inversely as the square roots of their densities or specific gravities, density being referred to hydrogen as unity, and specific gravity to air.
This law is simply expressed by the following formulas:
'V density of gas
Vsp. gr. of gas
Experiment. — The diffusion of au* and gases has been shown to take place through certain substances with practically the same rapidity as when they are in direct contact. The diffusion of hydrogen into air is well shown by the following simple experiment. A glass tube, say 18 or 20 in. long, 1-in. bore, is closed at one end with plug of plaster. The tube is first filled with the gas and the open end then immersed beneath the surface of a basin of mercury. At once the mercury is observed to rise slowly in the tube to take the place of the hydrogen that is passing out through the plug and escaping into the air. Investigation shows, however, that while hydrogen has passed out of the tube, some air has passed into the tube, as there remains in the tube a mixture of hydrogen and air.
Blustratioii of Graham's Law. — The relative velocities or rates of diffusion of different gases (hydrogen 1) are calculated from their respective densities referred to hydrogen as unity ; thus,
In like manner, the relative velocities or ratio of diffusion of diflferent gases (air 1) are calculated from their respective specific gravities, referred to air as unity ; thus.
Vo.559
Experiment Showing Effect of Diffusion. — An interesting experiment, showing the relative increase or decrease of the volume of gas contained in a vessel owing to diffusion, is
38 Mine Gases And Ventilation
illustrated in Fig. 5. The velocity of diffusion of methane being greater than that of carbon dioxide, when the latter is contained in the inner jar and the former in the outer belljar the bladder is expanded, because the methane passing into the small jar is greater in volume than the carbon dioxide passing out. Again, the bladder is depressed when the gases change places.
Pio. fi.
Composition Gases. — Gas, like other material substances, is composed of the elements of matter. A simple or elementary gas is composed wholly of one kind of matter; as hydrogen (H), oxygen (0), nitrogen (N), etc.
Many gases, like many solids and liquids, are compound. The molecule of such a gas is formed by the chemical union of two or more atoms of different elements; as methane (CHi), carbon monoxide (CO), carbon dioxide {C0), etc.
A gaseous mixture is a mechanical mixture of different gases, simple or compound. These gases are mixed together in any proportion, but are not chemically united.
Firedamp is a mechanical mixture of a combustible gas or gases with air in such proportions as to render the mixture inflammable or explosive. The term, however, is generally understood to mean an inflammable or explosive mixture
Air 39
of methane (CH4) and air. In English and other foreign textbooks, the term "firedamp" is improperly applied to any mixture of explosive gas and air, without regard to whether the proportions are within the inflammable or explosive limits of the gas. Such a mixture will not inflame or explode and is not, properly speaking, a firedamp mixture.
Percentage Composition by Weight. — By the "percentage composition" of a compound is generally meant the percentage, by weight, (rf each element composing the substance. This is calculated from the ratio of the relative weight of each constituent element to its molecular weight. The term "percentage composition" may refer, however, to the percentage by volume of each constituent element.
For example, a molecule of methane (CH4) contains one -atom of carbon and four atoms of hydrogen. Then, since the atomic weight of carbon is 12 and that of hydrogen 1, the molecular weight of methane isl2-|-(4Xl) 16, and the percentage composition of this gas is calculated as follows:
Carbon (C); atomic weight, 12; relative weight 12
Hydrogen (H4) ; atomic weight, 1 ; relative weight, 4X1=4
Molecular weight of gas 16
The percentage of each constituent element is then :
In like manner, a molecule of carbon dioxide (CO2) contains one atom of carbon and two atoms of oxygen. The atomic weight of carbon being 12 and that of oxygen 16, the molecular weight of carbon dioxide is 12 + (2 X 16) 44, and the percentage composition of the gas is found as follows:
Carbon (C); atomic weight, 12; relative weight 12
Oxygen (0); atomic weight, 16; relative weight, 2 X 16 =32
Molecular weight of gas 44
40 Mine Gases And Ventilation
The percentage composition is then :
Percentage by Volume. — When applied to a gaseous mixture the term "percentage composition'' is usually taken as referring to the percentage by volume of the several gases forming the mixture, unless otherwise stated. The method of making this calculation is given on page 102.
Specific Gravity of Mixtures of Gases. — When different volumes of gases of different densities are uniformly mixed the density of the mixture is determined by dividing the combined weight of the mixed gases by the total volume of the mixture, . which will give the unit weight or the weight per unit of volume of the mixture.
The actual weights of the gases may not be known, but only the volume of each gas and its density or specific gravity. In that case, multiply the density of each gas by its. volume, add the products together and divide the sum by the total volume of the mixture; the quotient obtained will be the required density of the mixture.
Or, in like manner, multiply the specific gravity of each
gas by ts volume, and divide the sum of these products by
the total volume of the mixture, and the quotient obtained
will be the specific gravity of the mixture.
Calcvlaiion. — For illustration, let it be required to calculate the specific gravity of flashdamp, which has a theoretical composition of 1658 volumes of methane (CH4) to each 1000 volumes of carbon dioxide (CO2). The process is as follows:
Volume Sq. gr.
Methane 1658 X 0.559 926.8
Carbon dioxide 1000 X 1.529 1529.0
The specific gravity of the flashdamp is then calculated, in accordance with the above rule, as follows:
Air 41
Calculation Based on the Law of Diffusion of Gases. — If
two gases diffuse into each other, directly, without being diluted with air, the volumes of the gases are inversely proportional to the square roots of their densities or specific gravities. This law makes it possible to calculate the density or specific gravity of such an undiluted mixture of two gases directly from their densities or specific gravities, without reference to their relative volumes. This is accomplished by means of the formula
Va + Vb
in which D density or specific gravity of the mixture; a and b the corresponding densities or specific gravities of the two gases, respectively.
CalculatUm, — For illustration, let it be required to calculate the specific gravity of flashdamp (undiluted mixture of methane and carbon dioxide) directly from the specific gravities of these gases; methane =0.559 and carbon dioxide 1.529. The process is as follows:
Sp.gr. — , . jT= 0.924
V0.559 + V 1.529
Section Ii
Heat
Sources and Measurement op Heat — Chemistry op Gases — THERMocHEBnsTRT — Hygrobcetry — Steam
Definition. — Heat is now understood to be a form of motion. All matter is assumed to be in a state of molecular vibration. The rapidity of the vibration depends on the degree of heating of the mass. The theory assumes that the amplitude of the vibrations or the swing of the molecules is greater as the density of the mass is less. This would lead naturally to the conclusion that pressure, which increases the density of matter, will decrease the amplitude and increase the rapidity of vibration.
Heat is thus assumed to be a form of energy, the amplitude and rapidity of the vibrations being functions, respectively, of pressure and velocity, the factors of energy, in mechanics. The theory is well supported by observed facts, as the blow of a hammer or the friction of rubbing surfaces alike develop heat.
Heat in Bodies. — Assuming that heat is a form of molecular vibration, which varies in different kinds of matter, it is clear that each kind of matter has its own peculiar capacity for heat. This is shown to be the case by the fact that different bodies when exposed to the same source of heat are heated differently. For example, when equal weights of water and mercury are exposed, for the same time, to the same heat it is found that the mercury becomes much hotter than the water. When water and mercury at the same temperature are allowed to cool in the atmosphere, the air absorbing the same heat from each, the mercury is found to cool much quicker than the water. It is evident that the water absorbs more heat and gives out more heat, per pound,
Heat 43
than the mercury, for the same change in temperature. In other words, water has a greater heat capacity.
Temperature. — The temperature of any body or mass of matter is the degree of heat it can radiate or impart to other bodies or matter with which it is in contact; or, in other words, the degree of sensible heat of the body. It is not the amount of heat in the body; as water contains 20 times the quantity of heat contained in an equal weight of mercury, at the same temperature.
The temperature of a body depends on the quantity of heat the body contains, per unit weight, and its heat capacity. A body or matter having a large heat capacity will have a comparatively low temperature.
How Temperature is Measured. Temperature is measured by the thermometer, an instrument so common as to need no description. The principle involved is that the expansion of the liquid contained in the bulb of the thermometer is much mfnified in the capillary stem. Any rise of temperature ia thus clearly indicated by a corresponding rise of the liquid in the stem and a fall of temperature b likewise accompanied by the contraction of the liquid, which drops in the stem.
Two Scales. — There are two principal thermometer scales, the Fahrenheit and the centigrade. These are each calibrated with reference to the melting of ice and boiling of water. As shown in the illustration. Fig. 6, these points are marked 32 and 212 deg., respectively, in the Fahrenheit, and and 100 deg., respectively, in the centigrade scale. Thus, 180 deg. of
Mine Gases And Ventilation
the former correspond to 100 deg. of the latter; or the ratio is 9:5.
Table Showing Cobbbsponding Values of the Fahbenheit Scale FOB Each Five Degbeeb of the Centigrade Scale
F.
F.
F.
F.
F.
+5
Heat
F.
F.
F.
F.
F.
To convert Fahrenheit (F.) readings into centigrade (C) or vice versa, the following formulas are useful :
Example — (a) What are the readings of the Fahrenheit scale corresponding to and — centigrade? SoltUion —
Example — Convert — 4 F. and 50 F. into centigrade readings. Solution —
Readings above zero are plus (+) and those below zero minus ( — ).
46 Mine Gases And Ventila Tion
Sources and Measurement op Heat
Sources of Heat. — In a sense the sun is the original source of most of the heat of the solar system — in other words, the sun is the power house of that system. It may be said that much of the terrestrial hfe and activity emanates from the sun. The source of the sun's heat is understood to be the chemical and possibly electrical activities that are constantly developed in its huge mass and radiating heat, light and electrical energy.
The same chemical and possibly electrical activities are taking place to a less degree in the mass of the earth, creating internal heat. Both the radiated heat of the sun and the internal heat of the earth are natural sources of heat.
Besides these natural or physical sources of heat, there are the mechanical sources of heat, such as friction, impact and pressure. These each develop heat as the result of force applied mechanically.
Sensible Heat. — The heat that is accompanied by a change of temperature when absorbed or given out by a body is called sensible heat," because it is manifest to the senses.
Latent Heat. — When matter passes from the solid to the liquid state, or from the liquid to the gaseous state, the change is always accompanied by the absorption. of a considerable amount of heat, although the temperature remains constant. The heat thus absorbed is called "latent heat, "it being absorbed in performing the work of driving the molecules of matter farther apart than they were in the previous state. This heat is again given out when the matter passes from a gas to a liquid, or from a liquid to a solid.
Chemical Heat. — Theory assumes that chemical heat is the result of the chemical affinity of material atoms for each other, by which they are drawn and held in more or less close contact and union. This condition is in harmony with the notion of "atomic heat," explained elsewhere, and suggests the estimation of the heat of formation, or heat of combination, as the result of chemical union.
In contrast with atomic heat, molecular heat is akin to specific heat and representative of the heat capacity of a substance, or the quantity of heat a particular substance will
Heat 47
absorb, per unit weht, per degree of rise in its temperature.
Theory assumes that all heat of any nature is a vibratory
state of atoms or molecules and, as such, is convertible into
or created by other forms of energy.
The molecular heat of a substance is found by multiplying a gram-molecule (page 54) of the substance by its specific heat.
Combixung Heat. — All matter is assumed to possess a certain definite heat energy peculiar to itself, which is expressed in heat units, per unit weight of substance and called the "combining heat'' of the substance.
Heat of Formation. — In the combining of atoms to form compound molecules, a neutralization of the energies of the combining atoms causes either an evolution or an absorption of heat, the molecule formed then possessing an amount of heat called ''heat of formation'' or "heat of combination."
Heat Due to Friction. — Friction is -caused by one body rubbing against another, whereby a molecular vibration is set up in the two bodies, as manifested by the heat generated.
Heat Due to Impact. — The impact of one body against another likewise sets up a molecular vibration in the bodies, which is manifested by the heat generated.
Heat Due to Pressure. — Pressure applied to a body having a degree of elasticity, or being compressible, forces the molecules of matter closer together, which reduces the intermolecular space and, as a result, there being no loss of molecular energy, the speed of vibration is increased in proportion as the space is diminished and heat is developed.
Transformation of Heat Energy. — Heat energy of any nature, whether chemical or physical, is convertible, without loss, into mechanical energy measured in foot-pounds, which is the "mechanical equivalent of heat."
At each change of state in matter heat is either absorbed and becomes latent in the mass, or is given out and becomes sensible, causing a rise of temperatm-e in the surrounding medium. Heat is absorbed when a solid becomes a liquid or a liquid becomes a gas, the change being one in which the density of the mass is made less. On the other hand, heat is given out when a gas is condensed to a liquid or a liquid to a solid, the density of the mass being then increased.
48 Mine Gases And Ventilation
Heat of Fusion. — The change from a solid to a fluid state is described as liquefaction" when solution takes place, or fusion" if the solid is melted. The heat absorbed in the latter case is called "heat of fusion."
Liquefaction may take place as the result of the absorption of moistiu'e from the air, the substance dissolving either wholly or in part in the water absorbed. Such a substance is said to be deliquescent"
Solution takes place when a solid disappears in a liquid in which it is immersed. The solid is "dissolved," in the liquid, which is called the "solvent."
In any case of liquefaction or fusion heat is absorbed and becomes latent in the liquid, causing a seeming loss or disappearance of heat. When a solid is dissolved in a liquid the liquid is cooled provided no chemical reaction takes place, which might produce heat.
Heat of Vaporization. — The formation of vapor or the change from a solid or liquid to a gaseous state is known as "vaporization" and the heat absorbed and rendered latent in the vapor is called "heat of vaporization" or frequently "heat of evaporation," especially when the vapor is formed by boiling the liquid.
Heat of Condensation. — When a gas or vapor is condensed to a liquid or a liquid is frozen or condensed to a solid the latent heat of the gas, vapor or liquid is given out and appears as sensible heat, which causes a rise of temperature. The heat given out is called "heat of condensation" and is exactly equal to the heat of vaporization or the heat of fusion or liquefaction, as the case may be.
Total Heat in a Body. — By this is meant the total heat absorbed by a body in a given change of temperature or state. For example, the total heat in 1 lb. of water, in passing from ice at 32 deg. F. to steam at 212 deg. F. is as follows:
Latent heat of fusion of ice, from and at 144 B.t.u.
Sensible heat absorbed by water, 32° to 212°F 180 B.t.u.
Latent heat of vaporization, from and at 212°F. . . 970.4 B.t.u.
Total heat absorbed 1294.4 B.t.u.
Heat 49
The total heat of steam at any temperature or pressure is usually estimated from water at 32 deg. F.; thus the total heat in steam (water vapor) at 212 deg. F. is 180 + 970.4 1150.4 B.t.u. This is the heat in steam at atmospheric pres* sure at sea level (14.7 lb. per sq. in.). When steam is generated in a boiler, its temperature increases with the pressure.
Effect of Pressure on Fusion. — Pressure acts to oppose increase of volume. Some substances, as water, for example, expand when passing from the liquid to the solid state and an increase of pressure therefore lowers the freezing point of such substances. The decrease of atmospheric pressure at high altitudes facilitates the formation of ice, though to a less degree than other more potent causes.
On the other hand, some substances, as wax, contract when solidifying, and an increase of pressure then acts to raise the freezing point or point of solidif 3dng. In other words, an increase of pressure acts to assist the melting of wax and similar substances, while it retards that of ice.
Melting Points of Substances. — The melting point of substances depends largely on their purity and treatment. For this reason different authorities often give different values for the same substance. The table on the following page gives the approximate melting points and the heat of fusion, in British thermal units, per pound, for the substances named.
Difference Between Melting and Freezing Points. — The melting point of a substance does not always correspond exactly with its freezing point, even at the same pressure. The melting point of ice is more uniformly constant than the freezing point of water, and for this reason is taken to indicate the zero of the centigrade scale (32**F.).
The solidification of a liquid is generally accompanied with crystallization, and the formation of the crystals is often delayed in a quiet medium, so that the temperature of water free of air may fall as low as 5 deg. F. when perfectly quiet and not freeze. But if the water at this low temperature be stirred or jarred the whole will instantly change to ice or become solid.
Mine Gases And Ventilation
Meltino Points and Hbats of Fusion or SttbstancIss
Substance
Aluminum
Beeswax
Copper
Gold
Ice
Iron, wrought
Lead
Nickel
Platinum
Silver
Spermaceti.'. . . . .
Steel
Sulphur
Tallow
Tin
Zinc
Itingpoint, eg. Fahr.
Heat of fuaion, B.t.u. per lb.
To express heat of fusion in calories per kilogram:
B.t.u. per lb. X cal. per kg.
, Effect of Pressure on Vaporization. — Pressure acts to retard vaporization. An increase of pressure, therefore, raises the boiling point of water and other liquids. For the same reason a decrease of pressure lowers the boiling point of liquids. At an elevation of 10,000 ft. above sea level, under normal atmospheric conditions, pure water boils at 193 deg. F., and at an elevation of 15,000 ft. the boiling point, for the same normal atmospheric conditions, is reduced to 185 deg. F.
Vaporization, Evaporation, Boiling. — Vaporization is a general term relating to the formation of vapor, or the change from a solid or liquid state to a vaporous or gaseous condition, without regard to whether the change is slow or rapid.
The term "evaporation" relates to the slow vaporizing of a solid or liquid that takes place at its surface when the latter is exposed to an atmosphere that is not fully saturated.
Heat 51
The evaporation of a liquid may also be caused by the application of heat.
The term "boiling** refers to the violent ebuUition that takes place throughout the mass of a Uqiiid, caused by the formation of vapor in the liquid and its escape to the surface. Boiling results from the application of heat to the liquid, or may result from a sudden decrease of pressure.
Boiling Points of Liquids. — A liquid boils when raised to such a temperature that the tension of its vapor is equal to the pressure at its surface. At this point the liquid becomes vapor. The term "boiling point," as commonly used, however, refers to atmospheric pressure at sea level, unless otherwise stated. The following table gives both the freezing and the boiling points of a few liquids of interest in mining:
Freezing and Boiuno Points of Liquids
T ;„„; J Freeing Point, Boiling Point,
Deg. Fahr. Deg.. Fahr.
Ammonia ' — 106 140
Linseed oil — 18 697
Mercury -38 . 676
Nitroglycerine 45
Measurement of Heat. — Although heat, as already explained, is a condition of matter and not a tangible quantity, it is possible to measure its intensity or degree through the effect it produces, referred to certain established standards of measurement. The most convenient standard is the heat energy that will cause a rise of one degree in the temperature of a unit weight of pure distilled water at its point of maximum density. This is called a ''heat unit" or "thermal unit'' and is a quantity capable of exact measurement.
Heat or Thermal Units.— There are several heat units in common use, the principal ones being the British unit and the French unit. A third unit that is largely used combines these two units.
The British Thermal Unit. — The British thermal unit (B.t.u.) is the quantity of heat required to raise the tempera-
52 Mine Gases And Ventilation
ture of 1 lb. of pure distilled water at maximum density, 1 deg. of the Fahrenheit scale.
The French Thermal Unit or Calorie. — This is the quantity of heat required to raise the temperature of 1 kg. of pure distilled water at maximum density, 1 deg. of the Centigrade scale.
The Pound Calorie. — This is the quantity of heat required to raise the temperature of 1 lb. of pure distilled water, at maximum density, 1 deg. of the Centigrade scale.
Conversion Formulas —
B.t.u. X 0.252 Calories
B.t.u. X % Pound-calories
Calories X 3 . 968 B.t.u.
Calories X 2 . 2046 Pound-calories
Pound-calories X % B.t.u. . Pound-calories X 0.4536 Calories Note. — Since 1 lb. (avoirdupois) 0.4636 kg.; and
1 B.t.u. 0.4536 XH 0.252 cal. Again, since 1 kilogram 2.2046 lb. (avoir.) ; and
1 deg. (Cent.) % deg. (Fahr.), 1 cal. 2.2046 XH 3.968 B.t.u. These simple calculations show the derivation of the constants used in the above formulas.
Transmission of Heat. — The condition known as "heat" is transmitted in any one of the three following ways: 1. By radiation. 2. By conduction. 3. By convection.
Heat is radiated in straight lines in all directions from its source and is then called "radiant heat." It is transmitted through the vibrations of the ether that fills all space and the radiated heat is imparted in varying degree to all matter in its path. Heat so imparted to a body is said to be " absorbed " by the body.
When heat travels through a body the process of transmission is known as "conduction." Heat thus spreads throughout the mass as a solid.
The spread of heat in any fluid (liquid or gas) is through the circulation caused by the unequal distribution of the heat. This mode of transmission is known as "convection."
Heat 53
Mechanical Equivalent of Heat. — Since heat is assumed to be a form of energy, it must be capable of performing work, which is expressed in foot-pounds. This has given rise to what is properly called the "mechanical equivalent of heat." It is the theoretical amount of work expressed in foot-pounds or kilogram-meters per unit of heat absorbed.
The values of the several heat units are as follows:
Foot-pounds Kilogram-meters
1 British thermal unit 778 107 . 5
1 calorie 3087 426.8
1 pound-calorie 1400 193.5
The reverse of these values is as follows:
B.t.u. Calories Lb.-cal.
1000 foot-pounds 1.285 0.324 0.714
100 kilogram-meters 9 . 297 2 . 343 5 . 168
Atomic Heat. — -An important relation has been found to exist between the atomic weights of the elements and their specific heats. Dulong and Petit (1819) found that the specific heats (relative heat capacity) of most of the solid elements vary inversely as their atomic weights, so that the product of these two factors is a constant quantity (6.4), which has been properly called the ''atomic heat." Thus, taking the specific heats of iron, lead and mercury, respectively, as 0.1190, 0.0305 and 0.0333, gives the value for the atomic heat in each case as follows :
At. wt. Sp. ht. At. ht.
Iron 55.40 X 0.1190 6 . 59 heat units.
Lead 205.44 X 0.0305 6 . 27 heat units. .
Mercury 198 . 40 X . 0333 6.61 heat units.
The average value for the atomic heat of the elements may be taken as 6.4, though it is sometimes given as low as 6.25 (Remsen). Atomic heat may be briefly defined as the heat capacity of matter per unit-weight atom.
A gram-atom of any elementary substance is a weight of that substance, in grams, equal to the atomic weight of the
64 Mine Gases And Ventilation
element. Thus, the atomic weight of iron being 65.4 (H 1), a gram-atom of iron is 55.4 grams of that substance; and its heat capacity is the atomic heat value (6.4 heat units).
This average value of atomic heat often assists the determination of the specific heat from the atomic weight of an elementary substance, or, vice versa, its atomic weight when the specific heat is known. For example, since the heat capacity of 55.4 grm. of iron is 6.4 heat units, the average specific heat of iron is 6.4 -5- 5.5.4 0.1155.
In like manner, a gram-molecule of any compound substance is a weight of that substance, in grams, equal to the molecular weight of the substance.
Specific Heat. — 'Investigation has shown that the same quantity of heat imparted to equal weights of different substances does not produce the same rise of temperature in each substance. Also, equal weights of different substances when cooling give out different quantities of heat for each degree the temperature falls. These facts show that different substances have different capacities for absorbing and holding heat as sensible heat causing a rise of temperature.
The "specific heaf of any substance is its relative heat capacity, or its heat capacity referred to that of an equal weight of pure water. The unit of heat is the amount of heat required to raise the temperature of a unit weight of water one degree. Therefore, the specific heat of a substance being referred to water expresses the heat units required to raise the temperature of a unit weight of the substance one degree.
The specific heat of a solid or liquid always refers to the heat per unit weight. The specific heat of a gas may be referred to the unit weight or unit volume, as desired. The specific heat of air and gases is different according as the air or gas is confined (constant volume) or is allowed to expand (constant pressure). The specific heat of a gas for "equal volumes" is the heat capacity of the gas referred to that of an equal volume of air at the same temperature and pressure.
The following table gives the specific heats of a few of the common solids and liquids of interest in mining:
Heat
Specific Heats
OF Solids and Liquids
Substance
Temperature, deg. Fahr.
Specific heat
Aluminum
Copper
Iron
Lead
Mercury
Platinum
Silver
Tin
Zinc
The following table gives the specific heats of the common mine gases, for equal weights at constant pressure and constant volume, and for equal volumes under constant pressure:
Specific Heats of Air, Mine Gases and Vapors
Equal weights
Equal volumes
Substance
Const, pres. Const, vol.
Const, pres.
Air.
Methane
defiant gas
Carbon monoxide . Carbon dioxide . . . . Hydrogen sulphide
Oxygen
Nitrogen
Hydrogen.
Water vapor
Ammonia
When gas, air or vapor is free to expand (constant pressure)- heat is absorbed and becomes latent. For this reason more heat is required to produce the same rise of temperature when expansion occurs than when the volume remains
56 Mine Gases And Ventila Tion
constant, and the specific heats in the first column are therefore higher than those in the second column of the table given above.
The values given in the first column of this table have been determined by experiment directly, while those in the second column have been derived from the first by dividing the latter by 1.405, the ratio of the specific heat of gases at constant pressure to that at constant volume. Likewise, the values given in the third column have been derived from those in the first by multiplying the latter by the specific gravity of the gas or vapor referred to air.
The specific heat of all substances varies more or less with the temperature as appears in the above table. In thp case of gaseSj the increase per degree (Fahr.) above zero is roughly estimated as follows : Air, nitrogen, carbon monoxide, 0.000012; oxygen, 0.00001; carbon dioxide, 0.00006; hydrogen, 0.0002; and water vapor, 0.0001; etc.
Chemistry Of Gases
The chemistry of all matter treats of the interchange of the atoms constituting molecules, by virtue of which interchange the character and nature of the matter is wholly altered. In other words, the matter is transformed and a. new substance created having properties that vary widely from those of the original substance.
Chemical Reaction. — The change that takes place when matter is thus transformed is a chemical change, and the action is described as a ''chemical reaction." It assumes an intimate contact between two unlike substances, under conditions that favor an interchange of atoms. The reaction that takes place is the direct result of different affinities of the atoms for each other.
Chemical Affinity. — The theory of chemical change supposes that all atoms constituting matter have various affinities or degrees of attraction for each other. By reason of this difference in the affinities of atoms, an interchange may or may not occur when two unlike substances are brought into intimate relation with each other, according as the atoms of the
Heat 57
origlDal substances possess a less or a greater affinity for each other in their present state or grouping. If the atoms of one of these substances possess a greater affinity for atoms of the other substance an interchange of atoms will take place and new substances will be formed that will be wholly different from the original substances.
Influence of Heat to Produce Chemical Change.— <The theory of heat assumes a wider separation of the particles of matter as the amount of heat in a substance is increased. Thus, it naturally follows that a higher temperature invites a more intimate mingling of two different gases in contact with each other. This intermingling of the gaseous molecules greatly assists a chemical reaction that otherwise would not take place.
Examples of Chemical Change. — The most common and familiar examples of chemical change are those due to the strong affinity of the oxygen of the air for most other matter. The resulting reaction is described as oxidation. The more familiar forms of oxidation are the rusting of iron and some other metals in a damp atmosphere. The action results in the "corrosion'' or eating away of the metal and the formation of an oxide, which is quite different in its character and properties from the original metal.
Combustion. — In a general sense, any form of oxidation is combustion, and the latter term does not relate alone to oxidation, but describes generally any chemical reaction in which one substance is consumed either slowly or rapidly by reason of the presence of another substance whose atoms possess an affinity for those of the first that invites reaction.
The substance consumed is termed the combustible and the other the supporter of the combustion, while the substances produced are the products of the combustion. The products of a combustion may be gaseous, vaporous or solid, the last named being the ash of an active combustion.
Slow Combustion. — This term implies a slow but continuous wasting away of the substance consumed, the conditions being unfavorable or the affinities of the atoms being insufficient to support a more rapid reaction. Slow combustion is
58 Mine Gases And Ventilation
characterized by the generation of heat without the production of flame.
Active or Rapid Combustion. — Active combustion is generally accompanied by the production of flame. The same amount of heat is generated in less time, resulting in a higher temperature, which in turn frequently modifies the products of the combustion.
Spontaneous Combustion. — Under certain favorable conditions, combustion may start in a mass of combustible material without the application of flame or other exciting cause. This is due to the natural generation of heat within the mass, owing to chemical reaction taking place between the substances. The action is explained as being chiefly due to the absorption of oxygen from the air by the substance, when the ensuing oxidation generates sufficient heat to ignite both the gas produced by the combustion and the material. The combustion, which is at first slow, may, in time, develop actively and inflame and consume the material.
Chemical Symbols. — A chemical symbol is a letter or letters used to designate an element or simple substance. The symbols of the more common elements together with their atomic or specific weights have been given in a table, previously. The symbol written alone expresses a single atom of the substance; but, since an atom is not conceived to exist alone, the symbol of an element should always be written as a molecule.
Symbol of a Molecule. — A molecule is assumed to be the smallest chemical division of matter that can exist in a free state. A molecule of any simple or elementary substance is assumed to contain two atoms only. Its symbol is expressed by writing the symbol for that element with a subscript (2) to indicate two atoms; thus for the molecule of carbon, write C2; oxygen, O2; etc.
The molecule of a compound substance may contain any number of atoms and is expressed by writing the symbols of its elements each with a subscript figure indicating the number of atoms of that element in the molecule. A single atom of an element is indicated by the sjnnbol only, omitting the subscript figure.
Heat 59
The following examples will serve to illustrate the fact that, while a molecule o.f any simple substance is taken to contain two atoms only, the molecule of a compound may contain any number of atoms:
Substance Composition Symbol
Carbon monoxide. carbon, 1 atom; oxygen, 1 atom 2 atoms; CO
Carbon dioxide, carbon, 1 atom; oxygen, 2 atoms 3 atoms; COs
Ammonia, nitrogen. 1 atom; hydrogen, 3 atoms — 4 atoms; NHi
Methane, carbon, 1 atom; hydrogen, 4 atoms 6 atoms; CHi
Olefiant gas, carbon, 2 atoms; hydrogen, 4 atoms 6 atoms; CtHi
All these gaseous molecules are of equal size, though containing different numbers of atoms.
Molecular Theory of Matter. — Chemical investigations have led to the accepted conclusion that all matter is composed of minute particles called molecules, the molecule being considered the smallest division of which the matter is capable without destroying its identity.
Theory further assumes that the molecule is composed of two or more atoms, like or unlike, but bound together by a force of attraction for each other known as affinity. Each of these combined atoms represents an element or a particular kind of matter and their combination as molecules diversifies matter and creates substances of various nature and kind.
Atomic Weight. — Atomic weight is simply relative. The atom of each element has a weight peculiar to that element, referred to the weight of the hydrogen atom as unity.
Molecular Weight. — The molecular weight of a substance is equal to the sum of the atomic weights of the elements of which it is composed. These elements combine in fixed proportions, which are determined by the number of atoms that saturate each other or the "valences" of the elements.
Valence or Valency. — The valence of an element is a term used to express its combining power in relation to the number of atoms of hydrogen (the assumed unit) or its equivalent required to satisfy the affinity. For example, two atoms of hydrogen are required to saturate a single atom of oxygen, and the valence of hydrogen being one, the valence of oxygen is two. The reaction is expressed by the chemical equation
2H2 + 02 2H2O.
60 Mine Gases And Ventilation
There are many elements, however, that do not unite with hydrogen and to determine their valency it is necessary to compare them with other elements that combine with them and whose valence is known. For this purpose the elements oxygen and chlorine are most convenient. The valence of oxygen, as shown above is two. The valence of chlorine is one, since one atom of hydrogen completely saturates one atom of chlorine.
H2 + Ci2 2Hc1.
The element calcium combines both with oxygen and with chlorine but not with hydrogen alone. Its valence is two as shown by the following equations:
Ca2 + 02= 2CaO Ca2 + 2CI2 2CaCl2.
The valence of most elements is not absolute but changes, often by two and frequently by successive units. For example, calcium has a valence of two and four; gold, one and three; copper, one and two; iron, two, three, four and six; while nitrogen forms the following series of oxides :
N2O, N2O2, NaOs, N2O4, N2O5.
Classification of Elements by Valence. — Owing to the change in valency exhibited by many elements it is not possible to make an unvarying classification in this respect. For the sake of convenience, however, many of the elements are designated as univalent, bivalent, trivalent, quadrivisdent, etc.; or as monads, dyads, triads, tetrads, pentads, hexads, etc., according as they exhibit valencies of one, two, three, four, five, six, etc., in combining with other elements.
A Chemical Compound. — A chemical compound is a substance composed of molecules formed by the chemical union of two or more unlike atoms. In a chemical compound the elements are always combined in fixed proportions and the substance has fixed properties that are always the same.
A Mechanical Mixture. — A mechanical mixture is composed of unlike substances mixed together in any proportion and not chemically Combined. The properties of such a mixture
Heat 61
vary with the kind and proportion of the substances of which it is formed.
The atmosphere is a mechanical mixture of oxygen and nitrogen. Although the proportion of these gases is practically always the same in pure air, the gases are only mixed and do not combine with each other.
Acids, Bases and Salts* — Chemistry considers three general classes or conditions of matter, which make the substance either an acid, a base, or a salt.
Briefly and plainly stated, an acid is a substance that dissociates in aqueous solution yielding hydrogen ions.
A base is a compound capable of reacting with an acid to produce a salt* It is an alkaline metallic oxide.
A salt is a generally neutral compound formed by the union of an acid and a base.
In general the nature of an acid is the direct opposite to that of a base. In combination they neutralize each other, forming a neutral salt and water. The distinguishing charac* teflstics of all acids are: 1. The sour taste. 2. The turning of blue litmus red. 3. The evolution of hydrogen by contact with a metal.
A number of acids are formed by the direct union of hydrogen with another element; as hydrochloric acid (HCl); hydrogen sulphide (H2S). Other acids are formed by the union of two radicals — the hydrogen radical or hydroxyl (HO) and an acid radical; or they may be considered as the result of the addition of water (H2O) to an anhydrous acid (anhydride).
In the first instance, the formation is as follows:
Acid radical SO2
Sulphuric acid H2SO4
Or, again, the formation may be regarded thus:
Water H2O
Sulphuric anhydride '. SOs
Sulphuric acid H2SO
62 Mine Gases And Ventilation
Oxides. — Nearly all the elements unite with oxygen to f onn oxides, but the affinity for oxygen is stronger in some cases than in others. When the affinity of the elements for each other is strong the compound formed is more stable than when the affinity is weak.
A monoxide is formed when the molecule contains but one atom of oxygen; as for example, carbon monoxide (CO).
A dioxide is formed when the molecule contains two atoms of oxygen, as carbon dioxide (CO2).
A trioxide contains three atoms of oxygen.
Chemical Change, Reaction. — Any interchange of atoms between two substances, or a combination of two unlike substances, by which one or more new substances are formed, is a chemical change and the process is called a ''chemical reaction.'*
A Chemical Equation. — It is a natural law that no matter is ever lost or destroyed. Matter is Indestructible. As a result of chemical change both the form and nature of the matter may be altered — a solid may become a liquid or gas, or vice versa; but the weight of the resulting products is the same as that of the original substances that are involved in the reaction.
Since there is no change in the weight of matter before and after chemical reaction takes place, it is possible to express the reaction by an equation showing the equality of matter. This is called a chemical equation. It is formed by writing in the first member the chemical symbols of all the substances entering or involved in the reaction, connecting these together with a plus (+) sign. Likewise, in the second member of the equation, write the chemical symbols of the several products of the reaction, connecting them together, as before, with a plus (+) sign. Then complete the equation by writing the sign ( ) of equality between the two members.
For reasons that ill be better understood when discussing molecular volmne, when writing a chemical equation each substance should be expressed by its molecular formula. This means that any elementary or simple substance as carbon (C),
Heat 63
hydrogen (H) nitrogen (N), etc., should be expressed as a molecule; thus, C2, H2, N2, etc.
Illustration. — When carbon (C) is completely burned in a plentiful supply of oxygen (O) there is produced carbon dioxide (COi). The reaction is expressed by the equation
C2 + 2O2 2Co2
The Cixpression 2CO2 should be interpreted to mean two molecules of CO2, each comprising one atom of carbon and two atoms of oxygen.
Observe there are the same number of atoms of carbon and the same number of oxj'gen on each side ot the equation. Not an atom is lost in the reaction, although these are grouped differently. In this case the solid carbon unites with the oxygen (gas) and carbon dioxide (gas) is produced. Also, the weight of the carbon dioxide is equal to this simi of the weights of the carbon burned and the oxygen consumed. There is no loss in weight.
It is important to note that the atoms involved in any reaction represent the weights of the substances they form, while the molecules or molecular formulas of the several substances represent their respective volumes. Hence, when each substance is expressed by its molecular formula the chemical equation shows both the relative weights of all the substances and the relative volumes of the gases.
In the reaction represented by the above equation each atom of the carbon molecule (C2) takes up two atoms of oxygen to form the molecule of carbon dioxide (CO2), the valence of carbon being, four and that of oxygen two. The reaction in this case is complete, the affinity of the carbon for oxygen being fully satisfied. -
Use of Chemical Equations. — As previously stated, when properly written a chemical equation shows both the relative weights and relative gaseous volumes of each respective substance involved in a chemical reaction. The relative weights .are indicated by the molecular weights of the substances as shown by the completed equation.
In estimating relative gaseous volumes, the volume of a
64 Mine Gases And Ventilation
gaseous atom is taken as unity and since, as previously explained, an elementary molecule is assumed to contain two atoms and all gaseous molecules at the same temperature and pressure are of equal size regardless of the number of atoms they contain, it follows that the relatives volume of all gaseous molecules is two.
Application of the Law of Volumes. — The law of molecular volume as just explaiijed finds important application in calculating the volumes of gases that are involved in a chemical reaction. While there is never any change in the weight or amount of matter due to chemical reaction, there frequently results a change in the volume of the gases concerned in the reaction.
To illustrate such change of gaseous volume, write the chemical equation representing the dissociation of ammonia gas (NHs) by electrolysis, foiming free nitrogen (N) and hydrogen (H) gases, placing below each molecular formula its relative or molecular volume; thus,
2NH3 N2 + 3H2 Mol. vol 2 13
It is evident that two molecules of ammonia gas, in dissociation, yield one molecule of nitrogen and three molecules of hydrogen, making four volumes in all. In other words, two volumes become four. The volume of the gases resulting from the breaking up of the molecule of ammonia is, therefore, double that of the original gas.
There is no chemical change of volume when methane or marsh gas (CH4) is exploded in a plentiful supply of normal air, and the methane is completely burned, forming only carbon dioxide (CO2) and water (H2O). The nitrogen of the air being unchanged it may be omitted in writing the equation expressing this reaction, which is as follows:
CH4 + 2O2 CO2 +2H2O Mol. vol 12 1 2
The equation shows that the complete combustion of methane requires twice its volume of oxygen; and there is
Heat 65
produced an equal volume of carbon dioxide and two volumes of aqueous vapor.
On the other hand, when carbon monoxide (CO) is burned in air, producing carbon dioxide (CO2), there results a reduction in volume, as shown by the following equation:
2C0 + O2 + 4N2 2C0j + 4Nj . Mol. vol 2 1 4 2 4
Normal air consists of practically one-fifth oxygen and four-fifths nitrogen. The equation shows that two volumes of carbon monoxide, in burning, consume five volumes of air, and there remain two volumes of carbon dioxide and four volumes of unchanged nitrogen. The seven volmnes of the original gas and air are thus reduced to six volumes of burned gases.
Thermochemistry
Thermochemistry treats of the heat changes that accompany all chemical reactions. A knowledge of such heat changes is of the greatest importance in the study of explosive phenomena.
Heat Changes. — In .a chemical reaction, when combination takes place, the heat energy of the compound or compounds formed is the heat of formation or combination.
Chemical reaction may also be accompanied by dissociation or decomposition of a compound, its heat of formation being then heat of decomposition, which neutralizes or is neutraUzed by the heats of formation of the products of the reaction. The heat of decomposition of a substance is always equal to its heat of formation.
The heat of elements, in a reaction, is always zero, there being no combination or dissociation in the element.
When the sum of the heats of formation of the products of
a reaction is greater than the total heat of decomposition heat
is liberated and the reaction is "exothermic." When the total
heat of decomposition is the greater, heat is absorbed and the
reaction is then '*endothermic."
Mine Gases And Ventilation
Heat of combustiori
Heat of Combustion. — This term is generally applied to the heat liberated in the oxidation of a combustible. The reaction is exothermic ; and, in general,
Heat of formation Heat of formation of products of combustible
The heat -of combustion of a substance, like combining heat and heats of formation or decomposition, is expressed in heat units, per unit weight of substance. The following table gives the heats of combustion of some of the more important combustibles in mining:
Combustible
Methane, to carbon dioxide and water at 32 deg. F
defiant gas, to carbon dioxide and water at 32 deg. F
Carbon, to carbon dioxide
Carbon, to carbon monoxide
Carbon monoxide, to carbon dioxide
Hydrogen, to water at 32 deg. F
Hydrogen, to steam at 212 deg. F
Sulphur, to sulphur dioxide ,
I per cent.
Anthracite . Bituminous Bituminous Bituminous Bituminous Bituminous Bituminous Bituminous
Pennsylvania . Pennsylvania. West Virginia
Illinois
Ohio
Kentucky. . . .
Alabama
Indiana
Heat of combustion, B.t.u. per lb.
The above are average values for each entire state, as taken from Government analyses and do not represent mining districts.
Heat 67
Heat Calculation.-— The calculation of the heat of combustion from the heats of combination of the combustible and the several products, formed, will be best understood by a practical illustration following the statement of a few fundamental principles that always govern the operation. Briefly stated these are as follows:
1. No heat energy is lost, but the heat of an element, in any reaction, is zero, there being neither combination nor dissociation possible in the element as in a compound.
2. Total heat of formation of products is the positive (+) heat developed in the reaction.
3. Heat of decomposition (same as heat of formation) of the combustible is the negative ( — ) heat or the heat absorbed in the reaction.
4. The heat of combustion is the net heat, or the difference between the total heat in the products and the heat in the combustible.
5. The reaction generates heat, or is exothermic, when there is an excess of positive (+) heat.
6. The reaction absorbs heat, or is endothermic, when there is an excess of negative ( — ) heat.
NoTE.-r-The chemical equation expressing a reaction shows the equivalence of weight of matter before and after reaction, but does not show the thermal effect.
A thermochemical equation is written by adding to the chemical equation a positive or a negative term indicating the heat generated or absorbed in the reaction. This heat may be expressed as gram-calories" "kilogram-calories" or 'pound-calories," according as the weight of the combustible taken is a gram-molecule, a kilogram-molecule or a poundmolecule. Or, the heat of the reaction may be given as B.t.u. per pound, or other denomination. The weight-unit is immaterial, since the heat of the reaction is always that due to the molecular weight of the combustible expressed in the same weight-unit.
The amount of heat corresponding to the molecular weight of the combustible (expressed in any weight-unit) is frequently called the ''molecular heat" of the reaction.
Mine Gases And Ventilation
The molecular heat of a chemical reaction, divided by the molecular weight of the Substance consumed, gives the heat of the reaction per init weight of substance, which is the heat of the combustion expressed in the same denomination as the weight of the substance.
Illustration. — The heat of combustion of methane (CH4), as determined by Favre and Silbermann (See Table), is 23,513 B.t.u. per lb.; or 23,513 X 13,063 Ib.-cal. per lb.; or 13,063 kg.-ca\ per kg. or grm.-cal. per grm of the gas.
The molecular heat of this reaction is therefore
16 X 23,513 376,208 B.t.u. or 16 X 13,063 209,008 cal.
It is observed, thus, that the molecular heat, in the combustion of methane, is the heat (B.t.u.) generated by 16 lb. of the gas; or the heat (Ib.-cal.) generated by the 16 lb.; or the heat (kg.-cal.) due to 16 kg.; or the heat (grm.-cal.) due to 16 grm. of this gas. Different authorities have obtained sUghtly varying heat values of the gases.
Heats of Formation of Substances.-The heats of formation of a few substances that are of interest in mining are given in the following table. The heats are given as molecular heats for convenience of substitution in equations.
Table of Heats op Formation of Substances
Substance
Symbol
Molecular heats of formation
B.t.u.
Cal.
Methane
Acetylene
Ethane
Carbon monoxide . , . .
Carbon dioxide
Hydrogen sulphide . .
Sulphur dioxide
Ch4
C2H2
C2H4
C2He
Co
H2S S02 H20 H20 H20 H20
Heat 69
For the-most part, the heat values in the above table have been determined by experiment, by means of the calorimeter. The values of the heats of combustion, as calculated from these molecular heats of formation, by substitution in the chemical equation expressing the reaction, will not be found to check the earlier determinations of Favre and Silbermann; but the variation is slight.
For example, writing the thermochemical equation for the combustion of methane, indicating the required heat of combustion by Xf we have
Ch4 + 2 O2 Co2 + 2 H2O - X
39,060 + 174,600 + - x X 174,600 + - 39,060 388,116 B,Lu.
Then, the molecular weight of methane being 16, the unit heat of combustion is 388,116 4- 16 24,257, instead of 23,513 B.t.u.
Writing a Thermochemical Equation. — The thermochemical equation expressing the reaction that takes place and the heat that is generated in the combustion of methane (CH4) is written thus :
CH4 + 2O2 =C02 + 2H2O - 388,116 B.t.u.
Or, in the French system,
CH4 + 2O2 CO2 + 2H2O - 215,620 cal.
The reaction is exothermic, or generates heat, which is the excess of the heats of formation of the products of the combustion (carbon dioxide and water), over the heat of formation of the combustible (methane).
Likewise, for the combustion of carbon to carbon dioxide, which generates 14,550 B.t.u. per lb., or 14,500 X H 8083 cal., the molecular heat of the reaction is 12 X 14,550 174,600 B.t.u., or 12 X 8083 say 97,000 cal. The thermochemical equation expressing this combustion is
C + O2 CO2 - 174,600 B,Lu. or C + O2 CO2 - 97,000 cal.
In these equations, the heat of combustion is equal to the heat of formation of the product (carbon dioxide), the heats of the elements (carbon and oxygen) being zero.
70 MINE CfASES AND VENTILATION
Hygrometry
Hygrometry is the measurement of the amount of vapor in the air, at any given time. The capacity of the air for holding moisture varies with the temperature. For example, at 32 deg. F., a cubic? foot of air will hold or has a capacity of only 2.13 grains of water; while at 60 deg. the capacity is 5.77 gr. per cu. ft.; at 100 deg., 19.84 gr. per cu. ft.; and at 212 deg. F., air fully saturated with moisture holds about 258 gr. per cu. ft.
Hygrometric State of Air. — Air absorbs moisture from bodies in contact with it, and thus exerts a drying action, which is of great importance in mining. The absorptive power of the air varies with its degree of saturation. For example, air at 60 deg. F., containing, say 2.9 gr. per cu. ft., is only about half saturated and is then said to contain 50 per cent, of moisture. In this condition, the air will readily absorb more moisture. The degree of saturation of air is called its ''hygrometric state."
Air is said to be "dry" or ''wet," according to the degree of its saturation. It is important to observe that these terms have no reference to the actual amount of vapor present in a given volume of air; but only express how nearly the air is saturated. For example, air fully saturated at 32 deg. F. contains 2.13 gr. of moisture per cubic foot and is "wet" because it is full of water vapor; but if the temperature now rises to, say 60 deg., the vapor capacity of the air is thereby increased to 5.77 gr. per cu. ft., and its degree of saturation or humidity" is then 2.13/5.77 X 100 36.9 per cent. In other words, the air at this temperature contains only 36.9 per cent, of its capacity, and is therefore comparatively speaking, "dry" air. Owing to the rise of temperature, from 32 to 60 deg., the air is capable of absorbing 5.77 — 2.13 3.64 gr. of moisture per cubic foot.
Calculation of Weight of Moisture in Air. — In order to calculate the weight (w), in pounds, of moisture contained in one cubic foot of air, it is necessary to know the degree of saturation of the air (c), its temperature (0, and the vapor pressure (pv) corresponding to that temperature. This last
Heat 71
must be taken from tables known as psychrometric tables. Calling the absolute temperature T 460 + t, the formula is
The constant 0.6235 is the specific gravity of water vapor, and the constant 0.37 is the reciproc8,l of the weight of one cubic foot of dry air, at a temperature of 1 deg. F. (absolute) and a pressure of 1 lb. per sq. in.
E3uunple. — Calculate the weight of water vapor carried in an air current of 100,000 cu. ft. when the saturation is 80 per cent, and the temperature 70 deg. F., if the vapor pressure at the given temperature is U 0.3602 lb. per sq. in. (see Table, p. 77).
Solution. — The absolute temperature, in this case, is 5P 460 + 70 530; and the total weight of vapor is
U.o7 X ooU
How Humidity is Measured. — The humidity of the air is commonly measured by an instrument called the ''hygrometer" or "psychrometer.'* This is the ''wet-and-dry-bulb hygrometer."
Other forms of hygrometer have been employed depending on the absorption of the moisture from the air by certain hygroscopic substances, and dew-point hygrometers; but these are less simple and not as portable as the wet-and-dry-bulb hygrometer, which indicates the humidity by the difference in the reading of the wet-and dry-bulb thermometers.
The Hygrometer or Psychrometer. — A neat and portable form of the wet-and-dry-bulb hygrometer, designed by the Davis Instrument Manufacturing Co., is shown in the Fig. 7. Two delicate thermometers are mounted on springs on the inside of a light cylindrical folding metallic case, the dry bulb on the door and the wet bulb in the case. To the latter bulb is attached a fine silk or muslin sack, which forms a wick that extends downward to the small vessel which holds the water that keeps this bulb wet.
72 . Mine Gases And Ventilation
Still another form of this instrument is that known as the "Swing psychrometer," from the manner of its use. Aa shown in Fig. 8, it consists of two thermometers mounted on a metal support, which is firmly attached to a handle on which it is arranged to swing. The left-hand thermometer has a dry bulb and its reading indicates the actual temperature
of the air; while the bulb of the right-hand glass is covered with a sack that is wet with water when an observation is to be taken.
Holding the handle in a firm grasp, the operator swings the instrument so that the metal support holding the two thermometers rotates rapidly on the handle as an axis. The swift movement accelerates the evaporation from the wet sack and cools the bulb of that thermometer, whose reading enables the calculation of the degree of saturation by difference with the dry-bulb reading.
Heat 73
The swing psychrometer is a popular form of the wet-and dry-buib hygrometer, because of its portability and the reliability of its indications, which are generally assumed to be more representative of the actual state of the air, because of its movement when an observation is being taken.
Principle of Hygrometer.- — Unsaturated vapors, like gases, obey Boyle's law; and, for any given temperature, the ratio of the quantity or volume of vapOr is equal to the pressure ratio, or the relative humidity (H), is expressed by the formula.
„ Actual vapor pressure Saturated vapor pressure
74 Mine Gases And Ventilation
The saturated vapor pressure (dry-bulb temp.) is given in the tables. The actual vapor pressure, at the time of observation, is equal to the saturated vapor pressure of the tables for the dew-point temperature, which, if known, would make the calculation easy by the use the above formula. In the use of the wet-and-dry-bulb hygrometer, however, the relative humidity is calculated by the formula
Vd
in which H relative humidity; and pd the respective saturated vapor pressures of the tables, for the corresponding wet-and-dry-bulb temperatures and td\ and B the barometric pressure, in inches.
What the Wet-and-dry-bulb Hygrometer Indicates. — The wet-and-dry-bulb hygrometer shows the difference between the readings of the two thermometers. The dry-bulb thermometer, of course, indicates the actual temperature of the air. The reading of the wet-bulb thermometer is lowered by the evaporation of the water from the little sack surrounding this bulb, and which is kept moist by the water drawn up through the wick from the vessel below.
The difference of temperature indicated by these two thermometers depends on the rapidity of the evaporation of the water from the wet bulb. The evaporation is more, rapid in dry than in wet air; and the difference of reading is, thus, an index or measure of the degree of saturation of the air. When the air is fully saturated with moisture there is no evaporation from the wet bulb and the readings of the two thermometers are the same. The difference increases with the dryness of the air.
Relative Humidity of Air. — -As previously explained the relative humidity of air is expressed by the ratio of the actual vapor pressure in the air at the time, to the saturated vapor pressure. The following table gives the percentage of saturation or the hygrometric state of air for various differences of readings, at different temperatures.
DlFl'ERENCB BbTEEN Drt AND Wet Bulbb
To use the table, find the observed temperature of the an-, in the left-hand column, and the difference of the observed readings of the wet-and dry-bulb thermometers, at the top of the table; the corresponding number in the table is the percentage of saturation which expresses the degree of humidity of the air. For example, if the dry-bulb temperature is 70 deg. and the wet-bulb 64 deg. F. the difference of readings is 6 deg. and the corresponding humidity as taken from the above table is 72 per cent.
Actual Vapor Pressure. — The pressures given in the table below are the pressures the vapor exerts when the space it occupies is fully saturated; they are called the "saturated vapor pressures," When the weight of vapor in the air is not sufficient for saturation the vapor pressure will be exactly proportional to the degree of saturation. For example, if 50 per cent, of moisture is present or the air only half saturated, at, say 70''F., the "actual vapor pressure," aa it is called, is onehalf of the saturated vapor pressure, in the table given later; or H X 0.3602 0.1801 lb. per sq. in.
To calculate the actual vapor pressure from the difference of the wet-and dry-bulb temperatures (t — t„) and the
76 Mine Gases And Ventilation
barometric pressure (B), in inches of mercury, first find the saturated vapor pressure (p,), in inches of mercury, corresponding to the wet-bulb temperature (tu,)y from the table; and substitute this and the given values in the formula
Actual vapor pressure at temperature td "" on ( qq )
Example. — Find the actual vapor pressure when the dry bulb reads and the wet bulb 54**F., the barometric pressure being 5 30 in., and the saturated vapor pressure for the wet-bulb temperature (54**F.) being 0.4178 in. of mercury.
Solviion, —
Since the saturated vapor pressure (see table) for the dry-bulb temperature (60®F.) is 0.5183 in., the relative humidity in the above example is
Pd 0.5183
The Dew Point. — What is called the "dew point," in hygrometry, is the temperature below which the moisture contained in the air begins to be deposited. For example, the weight of moisture, in grains per cubic foot, contained in the air, in the above example is (1 lb. 7000 grs.)
The temperature at which this weight of moisture will fully saturate a cubic foot of air is the dew point, because the slightest fall of temperature below that point will cause a deposition of moisture from the air.
The dew-point temperature is ascertained, in any given case, by first calculating the actual vapor pressure of the moisture in the air, as in the above example; and then, by referring to the table of saturated vapor pressures, find the temperature corresponding to that vapor pressure. This is true, because, as previously stated, the actual vapor pressure, at any given time, is equal to the saturated vapor pressure for the dew-point temperature. Thus, the actual vapor pressure for dry bulb 60° and wet bulb 54° was found to be 0.3497 in., which corresponds to a saturated vapor pressure or dew point of about 49 deg. F.
Heat
Table Showing SAtuRATED Vapor Pressures for Different
Temperatures
DegreeH, Fahr
Barometric pressure, mercury
Pressure, " Df,„ square inch ;
Barometric
pressure,
mercury
Pressure, pounds per square inch
10
0.J979
78 Mine Gases And Ventilation
Caution. — It is absolutely necessary in the use of such formulas as embrace terms or constants of a given denomination to use only values of that denomination. For example, the formula for finding the weight of moisture that will saturate a cubic foot of air at a temperature of t degrees, is
This is recognized as being derived from the formula previously given (p. 71) to find the weight of a cubic foot of dry air at a pressure p and temperature by substituting for the atmospheric pressure p (lb. per sq. in.), the saturated vapor pressure for pv (lb. per sq. in.); and multiplying the formula by the specific gravity of water vapor (0.6235) referred to air.
In these formulas, the pressure must always be expressed in pounds per square inch, because the constant 0.37 is in that denomination; and the temperature must be given in Fahrenheit degrees, for a like reason. Also, the weight will be found in pounds per cubic foot and, if desired in grains per cubic foot, must be multiplied by 7000, as there are 7000 gr. in a pound (avdp.).
On the other hand, the formulas given for calculating the relative humidity of the air, or the actual vapor pressure contain the constant 88, which is based on barometric pressure (in. of mercury) and Fahrenheit temperatures. The constant 88 is used for all temperatures above 32 deg., and 96 for any temperature below 32 deg.
The table of saturated vapor pressures, on the preceding page, gives the pressure or tension of water vapor for different temperatures (Fahr. scale), from —30 deg. to 212 deg. The pressures are given both in inches of mercury and pounds per square inch.
Example. — Find the actual vapor pressure, the relative humidity, dew point and weight of moisture present, in grains per cubic foot, when the readings of the dry-and wet-bulb thermometers are 62 deg. and 54 deg. F., respectively, and the barometric pressure is 28.2 in.
Solution, — The actual vapor pressure, in this case, as calculated from the saturated vapor pressure corresponding to the wet-bulb reading (P54 0.4178 in.), is
Heat 79
The saturated vapor pressure for the given temperature (see Table) is pt2 0.5561 in. and the relative humidity,
u.ddoi
The dew-point temperature corresponding to a saturated vapor pressure of 0.3323 (see Table) is 47.7 deg. F.
The actual weight of vapor the saturated vapor pressure corresponding to the dry-bulb temperature 62 deg. F. (see Table) being 0.2731 lb. per sq. in., is
Dry and Wet Air Compared. — Strange as it may at first appear, wet air is lighter than dry air, volume for volume. This is because the water vapor in the air is much lighter than the same volume of air which it displaces. The specific gravity of water vapor referred to air as a standard or unity is 0.6235.
The weights, per cubic foot, of water vapor and dry, partlysaturated and fully-saturated air, respectively, are calculated by the following formulas :
Air fully saturated, w -" — q 377
c degree of saturation, expressed as a decimal
It is readily seen, from Formulas 2, 3 and 4, that perfectly dry air is always heavier than air containing water vapor, and that the weight of air decreases as its degree of saturation increases. The weight of moisture in air is usually
80 Mine Gases And Ventilation
estimated in grains instead of pounds, per cubic foot, and it is necessary to multiply the results obtained from the above formulas by 7000 (1 lb. 7000 gr.).
The same formulas expressing the atmospheric pressure and the vapor pressure in inches of barometer instead of pounds per square inch, are as follows:
Air partly saturated, w ' (B - . 3766cp,) (7)
It is evident that when air is fully saturated, c 1, and disappears from the formula. The values of pv are given in a preceding table, in pounds per square inch and inches of mercury.
Formula 3 is obtained by the addition of Formulas 1 and 2, making Pa Pa — cp,,; and Formula 5 is derived from Formula 1, by reducing the pressure (lb. per sq. in.) to pressure (in. barom.), since 1 in. barom. 0.4911 lb. per sq. in. and (0.6235 X 0.4911) 0.37 0.82757. But the value of pvj in Formulas 5, 7, 8, must be given in inches of barometer, instead of pounds per square inch as in Formulas 1, 3, 4. '
Important. — Properly speaking, a vapor does not saturate the air, but the space it occupies; since, for any given temperature, the same weight of vapor serves to fill a given space whether that space is full or void of air. Commonly speaking, vapor is said to be saturated or unsaturated according as the space it occupies is saturated or otherwise.
Laws of Vapors. — The following laws express the chief characteristics of vapors:
1. Vaporization takes place at the siuace of all volatile liquids, at all temperatures, till the space surrounding the liquid is saturated or the critical temperature is reached.
Heat 81
2. Vapor pressure (different for different vapors) depends on the temperature and the degree of saturation.
3. For any given temperature, the weight and pressure of a vapor saturating a given space is the same whether that space is full or void of air or other gas.
4. Saturated vapor pressures increase with the temperature and when equal to the pressure above the liquid vaporizing, the ebullition of the liquid begins, which marks the boQing point of the liquid for that pressure.
n
a
I'
Fro. ft.
5. In a confined space, a further addition of heat to the liquid causes a rise of both temperature and vapor pressure till an equilibrium of densities of the liquid and vapor stop8 further vaporization and marks the so-called "critical temperature" for that liquid.
The diagram, Fig. 9, ia useful in showing at a glance the weight of water vapor that wilt saturate a cubic foot of space at any temperature from 20 to 105 deg. F. and the
degree of humidity for different dry-and wet-bulb readings of the psychrometer.
Steam
Steajn is the vapor of water formed at any temperature at or above the boiling point of the water. It is a certain vaporized or gaseous state of water. Water vaporizing below its boiling point forms vapor but not steam. Thus, while all steam is vapor, correctly speaking, all vapor is not steam.
Steam in its natural state or when saturating a given space, has a. temperature corresponding to the pressure it supports. This will be more clearly understood by taking an example of a given volume of steam in contact with the water from which it was formed. For instance, the steam in a steam boiler, at a pressure of 65 lb. gage (sea level) or, say 80 lb. absolute, has ia temperature of 312 deg. F. But any increase of pressure will be accompanied with a corresponding increase in its temperature, so that, at a pressure of 155 lb. absolute, the temperature of the steam will have increased to 361 deg. F.
Again, assuming a given volume of steam in contact with the water from which it was formed, such steam can neither be compressed nor expanded without a corresponding change taking place in its temperature. For example, for the same temperature, any increase of pressure would cause some of the steam to condense, while a decrease of pressure would cause niore steam to form, as the water would vaporize under the decreased pressure. Thus, the space above the water is always saturated by a weight of steam corresponding to the temperature, which is fixed for any given pressure.
Saturated Steam. — Saturated steam may be defined as steam in contact with water. From the foregoing, it will be understood that saturated steam is in its natural state, having a temperature corresponding to its pressure. Saturated steam may be either dry or wet, according as it does or does not hold any entrained water. The density of dry saturated steam is always the same for the same temperature.
Superheated Steam. — When steam is not in contact with water, any addition of heat causes an increase in both
Heat 83
temperature and pressure, the pressure increasing witli the absolute temperature. The steam is no longer saturated, and is said to be "superheated." Superheated steam is always dry.
Unlike saturated steam, superheated steam follows the laws of a perfect gaa. For a constant volume, its pressure increases with the absolute temperature; and, for a constant temperature, the pressure increases inversely as its volume. Steam is superheated, therefore, whenever its temperature exceeds that of saturated steam, for any given pressure.
I13S I
S I ubbI
I set q 310 S30
TO 80 SO 100 IID 110 130 lU 150 ISO 110 ISO 130 ZOO
Pra. 10.
Steam Tables. — The table, in the following pages, gives the temperature, specific volume, heat of the liquid above 32 deg. F., latent heat of evaporation, and the total heat in the steam, for different absolute pressures, as taken from Maries & Davis Steam Tables, which are the generally accepted values, today. The diagram, Fig. 10, was compiled by J. T, Beard, Jr. from the same source, and will be found convenient for use in connection with the tables.
Mine Gases And Ventilation
Pressure Table for Dry Saturated Steam
(Condensed from Marks and Davis, by Permission)
Absolute
Temp., deg. F.
Sp. vol., cu. ft. per lb.
Heat of
Latent heat
Total heat
pressure, lb. per sq. in.
the liquid B.t.u.
of evap. B.t.u.
of steam B.t.u.
P
t
V Ot 8
A or 9
I or r
h
Id
Heat
Pressure Table for Saturated Steam— -(Continued.)
Absolute
Temp., deg. F.
Sp. vol.,
Heat of
Latent heat
Total heat
pressure, lb. per sq. in.
cu. ft. per lb.
the liquid
of evap.
of steam
P
t
hor q
I or r
h
Section Iii
Mine Gases
Geological Conditions — Common Mine Gaseb — Hydro-
CARBOK GaBKS — PhOPEHTIES AND BeHAVIOR OF MiNE
Gases — Methane — Firedamp — Carbon Monoxide —
CaKBO N D I OXI D E — Bl AC KD AMP — A FTEBDAMP — INFLAM- MABLE AND EbcPLOBIVE MiNE GaSES.
Geological Conditions
Gas, Oil and Water. — The strata of the earth's crust form a great natural reservoir for gas, oil and water. These collect in the formations, in the order of their relative densities. As illustrated in the Fig. 11, which represents an ideal geological
section, the subterraneous water collects in the lower permeable strata, the oil next above, while the gas is found higher on the anticline.
This condition is only true, however, in a general way, depending on the nature of the strata and their power to absorb and hold these elements. Water, and oil to a less extent, find their way by gravity to a "hard-pan" or stratum impervious to them; while gas drains to the surface and escapes, unless confined by an overlying stratum of clay or ( il, from the overlying rocks into the synclinal basins, creates enormous pressures, which are exerted more or less equally on the water, oil and gas.
Mine Gases 87
Water Level. — In every geological section, there is a more or less defined "water level'' or depth at which water is found in quantity. Wells or boreholes sunk to this general level strike a usually abundant supply of water. The same is true, but to a less extent, of oil, in oil regions. The flow of oil, in oil-bearing rocks, however, is not as free as that of water, owing to its viscosity and limited supply.
The water level is not constant, but varies according to the changing supply or surface drainage, being higher in wet seasons and lower in seasons of drought. As the oil floats on the water any change in water level is accompanied by a similar change in the oil supply. It is due to this fact that exhausted oil wells often become productive in a season of flood, and producing wells frequently cease to flow in a prolonged season of drought.
Natural Gas. — All gas formed and contained in the strata is called "natural gas/' in distinction from gas manufactured in the industries. Natural gas commonly occurs in large volume, in coal formations, where it accumulates in cavities or pockets and in crevices in the strata. It is very largely compoised of what are commonly known as the 'hydrocarbon" gases.
Effect of Faults. — Fault lines and other geological disturbances of the strata have opened channels by which the gas confined in certain strata escape to other strata or into the mine workings or to the surface. For this reason, the near approach of the working face to a fauH line or a disturbed condition of the strata is often accompanied by a marked change in the gaseous condition of the mine air. The percentage of gas common to the mine may then either increase or decrease depending on the location of the gas and the nature of the fault.
Gas Feeders, Blowers. — Any continuous flow of gas from a crack or crevice in the strata is called a "gas feeder," or simply a "feeder." The gas flowing from the crevice is known as "feeder gas."
When a gas feeder is under high pressure so that the gas issues with considerable velocity, the feeder is called a "blower" and the gas "blower gas."
88 Mine Gases And Ventilation
Occluded Gases. — The gases commonly occluded in the coal formations are methane, ethane, nitrogen, carbon dioxide and oxygen. They are the result of the chemical changes that took place in the formation of the coal; or are produced by the action of acid waters on certain limestones or other carbonates. Occluded gases are held in the pores of the coal and other Strata, from which they drain into the mine openings, or work upward through such pervious strata as shale and sandstone. The process is called "emission" or "transpiration" of gases.
Pressure of Occluded Gas. — At times, the gas is confined in the coal or other strata by an overlying stratum of clay or impervious limerock that prevents its escape to the surface, and the pressure of the gas is then often very great, varying from 500 and 600 lb. per sq. in. to four or five times that amount. This pressure is manifested in different ways. As the mine workings are extended the flow of gas into the mine increases with the exposure of fresh faces of coal, except where the conditions are such as to allow the gas to drain off and reach the surface.
Effect of Gas Pressure in Mining. — The pressure of gas confined in the coal is often sufficient to splinter the coal in its effort to escape, the fine coal being thrown into the face of the miner at work. At times, the gas escapes from the coal with a peculiar hissing sound known as the "singing of the coal." The pressure of gas in the roof frequently causes heavy roof falls, and gas in the floor causes the bottom to heave. In some instances, the gas pressure assists the extraction of the coal and lessens the work of the miner by helping to break down the coal.
Outbursts of Gas. — In the mining of gaseous seams, it is not uncommon for gas to work in the strata as the coal is extracted. As a result, the gas often accumulates in pockets as shown in the ideal section, Fig. 12. The settlement of the roof incident to the removal of the coal affords opportunity for the gas to expand and work forward toward the opening. The working of the gas in the strata is often accompanied by severe "poundings" or "bumps," due to sudden displacement
Mine Gases 89
of the gas. Such sounds often continue for several days previous to a sudden outburst of the gas into the mine workings. The continuance of these poundings are a sufficient warning to experienced miners to vacate that part of the mine till the strata have become more quiet by the gradual draining off of some of the gas.
In many cases, where the gas works down into the coal, either at the face or in the "ribs," as shown in the figure above, the pressure of the gas becomes distributed over a considerable surface, and is sufficiently great to throw down the coal. This is called an "outburst" of gas, since large volumes of gas escape and often hundreds of tons of coal are thrown violently into the opening.
THE COHHOn MING GASES
The gases of most importance in coal mining, together with their chemical symbols, molecular weights, densities referred to hydrogen and specific gravities referred to air of the same temperature and pressure, are the following:
Pra. 12.
Methane {marsh gas) . . Ethene , Ethylene ( olefiant
Eth&ne
Carbon monoxide. . .
Carbon dioxide
Hydrogen sulphide . .
Oxygen
Nitnen
Hydrcen
Symbol
Ch,
le
C,H.
C,H,
Co
Co,
Bs
0,
N,
H,
Mine Gases And Ventilation
Occurrence of Mine Gases. — Aside from the oxygen and nitrogen of the air, the gases commonly occurring in coal mines are methane, carbon dioxide, carbon, monoxide, and less frequently or in less quantity, hydrogen sulphide and olefiant gas. These gases are produced by the processes of decomposition or combustion constantly going, on in the mine, or they emanate from the coal or other strata, where they exist as natural gases.
Condition of Gas Confined in Coal. — The results of careful experimental study of coal indicate (Chamberlin) that gas may exist in coal in three different ways: 1. The gas is occluded, in a true sense, or absorbed (possibly condensed) by the coal. 2. The gas' is entrapped or held mechanically in the cavities, cracks or pores of the coal. 3. The gas may result from chemical changes going on in the coal.
Escape of Gas from Coal. — -Experiments made by the Bureau of Mines, by crushing weighed samples of different coals in closed vessels of known capacity, show that coal continues to give off gas for a long time after it is mined.
Coal exposed to the atmosphere loses much of its occluded gas, but the gas is liberated more freely by crushing the coal, which would indicate that much of the gas is held mechanically within the mass. It is also shown that the coal continues to absorb oxygen from the air, during the same period.
The following table gives the percentages, by volume, of the
constituents of natural gases obtained from various coals, in
different localities.
Table Showing the Composition of Gas Evolved from Coals at
South Wales
South Wales
South Wales
South Wales
Lancashire
7.
Bituminous Bituminous Steam coal Anthracite Cannel
Lancashire
Cannel
Westphalia..
Westphalia
Gas coal Gas coal
Mine Gases
Composition of Feeder or Blower Gas. — A large number of analyses of gas issuing from coal seams as "feeders" or blowers" have been made. Gas has also been obtained by drilling holes several feet into the face of the coal. These analyses show a wide variation in the composition of the gas in different localities. Moreover, since the rate of emission of gases varies, the composition of feeder gas is only suggestive of the contamination of the mine air.
The following table gives the composition, by volume, of blower gas in different localities, which show in a general way a higher percentage of methane, in comparison with that of nitrogen. This may be due, to a large extent, to the higher rate of transpiration of the methane, as compared with nitrogen, which tends to increase its percentage in blower gas over what actually exists in the pores of the coal:
Table Giving Composition of
Blower Gas
IN Different Localities
Locality
Ch4
Nf
COt
Ot
Co
' C,H4
Austria
Austria
Austria
Germany
Germany
South Wales
Wallsend. Eneland
Jarrow, Eneland
Oakwelltrate, Eneland
Wilkes- Barre, Penn
It is important to remember that the occluded gases of coal are not chemically combined with the constituents of the coal as shown by analysis, and do not form a part of the coal itself, although adding much to its inflammability and heat value.
Hydrocarbon Gases
General Formulas of Hydrocarbon Gases. — Carbon (C) and hydrogen (H) unite in different ways to form groups of compounds, having certain distinct characteristics. Such are
92 Mine Gases And Ventilation
the ''paraffins," represented by the general formula CnH2n-f 2; the **olefines," CnH2n; the acetylenes/' CnH2n-2; and other compounds of less importance in mining, as the "benzenes," naphthalines," etc.
Occurrence and Formation. — Methane or light carbureted hydrogen (CH4) and ethane (C2H6), belong to the paraffin or fatty group, while olefiant gas (C2H4) belongs to the define or oily group. These are all products of the destructive distillation of organic matter. Methane is often seen bubbling up from the bottom of stagnant pools, in marshes, which fact suggested the name "marsh gas." It is the result of the slow decay of the vegetable matter (in the presence of water and absence of air), at the bottom of the pool.
On the other hand, olefiant gas is the result of the dry distillation of gas from organic matter, which takes place less frequently in the strata, owing to the almost invariable presence of moisture. The character of these hydrocarbon gases, moreover, varies, also, with the kind of organic matter that undergoes decomposition.
Of the hydrocarbon gases, the paraffins (methane and ethane) are the ones chiefly occluded in the coal measures; while olefiant gas, belonging to the olefine group is rarely found even in minute quantity. Beside the hydrocarbon gases occluded in coal, as has been stated, varying quantities of nitrogen, oxygen and carbon dioxide have been absorbed.
The Heavy Hydrocarbon Gases. — The heavy hydrocarbons occur in the coal measures as occluded gases, only to a limited extent. Of these, there are but two that are worthy of mention; they are
Olefiant gas, ethene or ethylene, (C2H4); sp. gr., 0.978;
Both of these gases are colorless and odorless; they occur but to a limited extent in association with methane; and their chief importance Ues in the fact that they each have a wider explosive range and a lower temperature of ignition than pure methane. The analyses of the gases exuded from coal rarely show any appreciable quantity of olefiant gas (ethene) ; but ethane (C2H6) occurs more frequently as an occluded gas.
Mine Gases 93
Properties And Behavior Of Mine Gases
The symbols, molecular weights, densities and specific gravities of the common mine gases have been given in another place. The properties and behavior of these gases in the mine will be treated here from a practical, rather than a theoretical standpoint.
Methane
This gas is commonly known as "marsh gas*' or ''light carbureted hydrogen," it being the lightest of the hydrocarbon gases. It is a colorless, odorless and tasteless gas. It is combustible, burning with a. pale-blue flame, in the air or in oxygen. It contains no oxygen and is not, therefore, a supporter of combustion, in the generally accepted meaning of the term. A lamp flame is quickly extinguished by this gas unmixed with air. Mixed with air in certain proportions, the gas becomes explosive, the mixture being known as firedamp. " Marsh gas is not poisonous, but when unmixed with air suJBfocates by excluding oxygen from the lungs. The diluted gas can be breathed for a long time with no ill effects, except a slight dizziness, which quickly passes away on return to fresh air.
Marsh gas is the most common of the occluded gases of the coal formations. It seldom, if ever, occurs pure, but is mixed in varying proportions with other hydrocarbons (olefiant gas and ethane) and often with nitrogen. These mixed gases greatly modify the character and properties of the pure gas.
Marsh gas issues from the strata into the mine workings where it accumulates in quantity, unless removed by a copious air current. The most gaseous seams are those that are overlaid with a compact rock, slate, or shale that is impervious to gas and not traversed by faults, which would allow the gas to escape. Gas is generated most freely from a virgin seam and from a freshly exposed face of coal. Hence, new workings generate more gas than old workings; because, in the old workings, the gas has mostly drained from the strata and escaped.
94 Mine Gases And Ventilation
Marsh gas diJffuses rapidly into the air and other gases, the rate of diffusion depending on the relative densities of the two mediums. The question is often asked, if the diffusion of gas is so rapid how is it possible for a large body of gas to accumulate in a void place in the mine. The reason is that diffusion only takes place at the surface of contact, and is therefore limited, and the gas is being generated faster than it passes away.
Marsh gas being lighter than air tends to accumulate at the roof and at the head of steep pitches and in rise workings. It is found in such places where the air current is not sufficiently strong to sweep away the gas and in other poorly ventilated or abandoned places. Gas can generally be found at the roof or close to the face of the coal in chambers generating gas. It is detected by observing the flame of a safety lamp. If gas is present in sufficient quantity in the air a faint nonluminous cap will appear surmounting the flame of the lamp. The gas also lengthens and enlarges the flame.
Firedamp
All gases were formerly known to the miner as "damps," which is a word of Dutch or German origin meaning vapor or fumes.. Later, as the characters of the different gases became known, they were named according to their several characteristics. The term "firedamp" was applied to any inflammable or explosive mixture of gas and air.
The word firedamp, today, in this country, means any inflammable or explosive mixture of marsh gas and air, with or without other gases. In England, the word is taken. to mean any mixture of marsh gas and air without regard to whether or not the mixture was inflammable or explosive, which, however, is not its logical meaning.
When but a small amount of marsh gas is mixed with pure air the gas is so diluted that the mixture is not inflammable. In contact with flame, this small percentage of gas in the air p,dds to the combustion and lengthens and enlarges the flame; but the fim§ is not propagated throughout the
Mine Gases 95
mixture, as the absorption of the heat by the air is too great to maintain the temperature necessary for combustion.
Lower Inflammable Limit. — As more gas is added to the air, a point is soon reached where the combustion of the gas develops sufficient heat to raise the temperature of the air to that required to maintain the combustion. When this point is reached the flame causing the ignition is extended or propagated through the mixture. In other words, the mixture becomes inflammable, because the combustion is supported in the mixture independent of any other source. The theoretical percentage of gas in the firedamp at this point, as calculated, is slightly above 2 per cent., for dry air or saturated air. The heat absorbed by the water of saturation is so slight in comparison that it can be ignored without appreciable error. There are heat losses, however, that cannot be calculated, which fact raises the lower inflammable limit of pure marsh gas to between 4 and 5 per cent.
Effect of Dust and Other Gases. — Owing to the fact that marsh gas is rarely, if ever, found pure, but is generally mixed with dust or other gases or both, it is never safe to work with open lights, in air containing more than 1 per cent, of gas, in bituminous mines; or per cent, in anthracite mines.
Gases are divided into two general classes, in respect to the eJBfect they produce on the inflammability of firedamp. Gases having a lower ignition point than marsh g-s, as for example, carbon monoxide, hydrogen sulphide, ethane and olefiant gas, lower the inflammable limit of firedamp, as given above. Fine coal dust floating in the mine air has a similar effect, in proportion as the dust is highly inflammable. On the other hand, extinctive gases such as nitrogen and carbon dioxide raise the limit given above.
In the working of bituminous mines, coal dust is a most dangerous factor, especially when the coal is highly inflammable. In many cases, the finely divided dust produces an explosive atmosphere even when no gas is present. The presence of such dust in the mine air, acted on by the flame of a blowout shot, is certain to cause trouble.
96 Mine Oases And Ventilation
To Calculate the Lower Inflammable Limit — In order to calculate the proportion of gas (methane) and air when the firedamp mixture first becomes inflammable, it must be assumed that all the heat generated by the combustion of the gas is absorbed by the products of the combustion and the remaining unburned air. Owing, however, to there being a certain amount of heat lost by radiation or otherwise that cannot be estimated or accounted for, the calculated inflammable limit will only approach the actual, to the extent that the conditions are fully realized in the calculation. The process is as follows:
The weight of oxygen necessary to burn 1 lb. of methane or marsh gas (CH4) is shown by the relative weights of these gases in the following reaction :
CH4 -f 2O2 CO2 + 2H,0
Molecular weights 16 64 44 36
Relative weights 1 4 2?i 2K
But oxygen forms 23 per cent., by weight, of the air, the remaining 77 per cent, being practically all nitrogen. The weight of nitrogen concerned in burning 1 lb. of this gas in air is then calculated as follows:
and N 13.39 lb.
The table giving the heats of combustion of different substances (p. 66) shows that methane, burned in air or oxygen, gives out 23,513 heat units (B.t.u.). The temperature of ignition of this gas is 1200° F.
Now, since the specific heat of a substance is the heat (B.t.u.) absorbed by 1 lb. of that substance, during a rise of 1 deg. F. in its temperature, the heat absorbed by the products of combustion of 1 lb. methane, for each degree rise in temperature, is found by multiplying the specific heat of each of the products, including the nitrogen of the air, by the relative weight of each product, respectively. The total heat is then found by multiplying that result by the number of de-
Mine Gases 97
grees rise in temperature; and adding the latent heat in the steam or water vapor, as follows:
The specific heats of the several products of combustion, referred to water as unity (1), are carbon dioxide, 0.2163; nitrogen, 0.2438; water vapor, 0.4805; and air, 0.2374. The latent heat of the water vapor (steam) or the heat absorbed when 1 lb. .water becomes steam at 212°F. is 970.4 B.t.u. The heat absorbed by the products of combustion, for a rise of 1200 - 32 1168''F., is therefore
Carbon dioxide, . 2163 X 2 . 75 X 1 168 694 . 7264
Nitrogen, 0.2438 X 13.39 X 1168= 3812.9360 4507.6624 B.Lu,
Water, 1. 0000 X 2.25 X 180- 405.0000
Latent heat, 970.4000 X 2.25 =2183.4000
Watervapor, 0.4805 X 2.25 X 988 1068.1515 3656.5615 B.Lu,
Total heat absorbed by products 8164.2139 B.Lu.
Having found the heat absorbed by the products, the next step is to find the heat absorbed by the unburned air. Let x weight of air required to make 1 lb. of the gas inflammable; and, since 1 lb. CH4 consumes 4 lb. O + 13.39 lb. N 17.39 lb. air, the unburned air is a: — 17.39 lb. The original temperature of the air being 60°F., the rise is 1200 - 60 1140 deg. and the heat absorbed is - 270.636x — 4706.36 B.t.u., which makes the total heat absorbed
8164.2139+270.636a:-4706.36 270.636x+3457.8539B.w.
Since the heat absorbed is assumed equal to the heat generated,
270.636X + 3457.8539 23,513 B.Lu.
This is the total weight of air required to make 1 lb. of
methane (CH4) inflammable. In other words, the weight
ratio of gas to air, at the lower inflammable limit, is 1 : 74.10.
But since the specific gravity of methane, referred to air as
unity, is 0.559, the volume ratio of gas to air, at this point, is
1 : 0.559 X 74.10; or 1 : 41.42. That is to say, a mixture of
98 Mine Gases And Ventilation
pure methane and air first becomes infiammable when 1 volume of this gas is mixed with 41.42 volumes of air. The percentage of gas in this mixture is
Lower Explosive Limit. — The continued addition of gas to the air causes the firedamp mixture to become more and more inflammable till a point is reached when the combustion of the gas is so rapid that the mixture is explosive. As this condition is approached, in practice, owing to the mixture of the gas and air not being uniform, the ignited gas often snaps and cracks in the combustion chamber of a safety lamp.
In the same manner, an accumulation of firedamp, in the mine, when ignited, may burn with greater or less energy or violence and small explosions may occur here and tliere, followed perhaps by the general explosion of the entire body of the firedamp. The explosion depends not alone on the proportion of gas and air in the mixture, although that is important, but on the intensity and volume of the igniting flame. Thus, it happens that a firedamp mixture ignited in the narrow confines of the mine workings may, after burning for a brief period with more or less energy, suddenly develop a violent explosion.
The lower explosive limit of pure methane has been determined, by experiment, to occur when 1 volume of the gas is mixed with 13 volumes of air; or the percentage of gas in the mixture is
X 100 7.14 per cent.
This limit, however, is considerably modified by any conditions that tend to increase or decrease the amount of heat developed.
Maximum Explosive Point. — The maximum explosive force of a combustible gas is developed when the proportion of gas to air is just sufficient for complete combustion. If the gas in the mixture is in excess of this proportion the full heat energy is not developed, owing to the incomplete combustion of
Mine Gases 99
the gas. On the other hand, if the air is in excess of what is required for complete combustion, the unbiu-ned air absorbs a portion of the heat generated by the combustion, which thus becomes latent.
The maximum explosive force of methane is developed when the proportion of gas to air is 1 : 9.57. It is calculated in the following manner: Write, again, the chemical equation expressing the reaction that takes place when this gas bums in oxygen, forming carbon dioxide and water; thus,
CH4 -f 2O2 CO2 + 2H2O Molecular volumes, 12 12
It should be observed that when the symbol of eacli gas is written as a molecule (oxygen O2) the prefix or number written before the symbol, indicating the number of molecules of that gas taken, shows also the relative volume of the gas concerned in the reaction; because the volume of all gaseous molecules at the same temperature and pressure is the same.
The above equation shows that two volumes of oxygen (2O2) are required to completely burn one volume of methane (CH4); and there are formed one volume of carbon dioxide (CO2) and two volumes of water (2H2O).
But, oxygen forms 20.9 per cent., by volume, of the atmosphere. Therefore, when methane is burned in air, the volume of air required to completely burn two volumes of the gas is
Hence the proportion of gas to air that will develop, in explosion, the maximum force is 1 : 9.57. The percentage of gas in the mixture, at this point, is
X 100 9Ae per cent.
Higher Explosive Limit. — The continued addition of gas after the maximum explosive point is reached, causes the explosion of the firedamp mixture to be less and less violent, till a point is finally reached where the proportion of air is so
100 Mine Gases And Ventilation
reduced that explosion ceases and the mixture becomes simply inflammable.
The point at which explosion ceases is called the ''higher explosive limit." For pure methane, this point is practically reached when the proportion of gas to air is 1 : 5, although the position and character of the igniting flame, may vary this proportion slightly. The percentage of gas in the firedamp, at this point, is practically
X 100 W.Q7 per cent
Higher Inflammable Limit. — By the continued addition of gas, the firedamp having ceased to be explosive, now becomes less and less inflammable. The mixture not only ignites less readily, but when ignited burns less regularly and quietly than did the same firedamp mixture, in the lower inflammable stage when less gas and more air were present.
The higher inflammable stage of the gas is more dangerous, in mining practice, than the lower inflammable stage of the same gas, because the slightest addition of air, which is liable to occur at any moment in the mine, causes the mixture to approach the maximum explosive point. The addition of air to firedamp in the lower explosive or inflammable Stages makes the mixture less explosive or inflammable.
Another important distinction between the lower and higher stages of firedamp mixtures is the relative ease with which the flame cap may be detected in the two stages. While the flame of a safety lamp bums steadily and yields a good cap that is easily detected, in the lower inflammable stage; the lamp flame is unsteady and the flame cap generally hard to discern in the higher inflammable stage. The reason is probably to be found in the uncertain and varying amount of air in the mixture feeding the flame, which makes the gas continually approach the explosive point The gas in this (higher) stage is said to be "sharp."
The following table will make the several stages of firedamp more clear; but it must be remembered the proportions of gas to air and percentages of gas given as marking the
MINE GAfES
dividing line between the different stages or the inflammable and explosive limits are only suggestive and vary with the degree of purity of the gas; the volume, intensity and position of the igniting flame, and the pressure and temperature of the surrounding atmosphere.
Lower inflammable
Explosive stages Higher
Lower stage
Maximum point , Higher stage!
Proportion of Gas to Air
Percentage of Gas
The continued addition of gas thus renders the firedamp extinctive of its own flame and therefore noninfiammable. The proportions and percentages given in the table denote more or less closely the limits of the several stages.
Flashdamp. — This is a mixture composed almost wholly of marsh gas (CH4) and carbon dioxide (CO2), mixed in the proportion in which these gases diffuse into each. It is formed under special conditions, in mines, where carbon dioxide from the old workings of an abandoned seam becomes mixed with the undiluted marsh gas generated in the strata. The mixture is lighter than air and possesses the peculiar and misleading property of extinguishing the lamp at the roof of the 5eam or the face of a steep pitch.
Calculation of Composition of Flashdamp. — According to the law of diffusion, gases diffuse into each other in the inverse ratio of the square roots of their densities or specific gravities. For example, the specific gravities of methane and carbon dioxide are 0.559 and 1.529, respectively; and the ratio of the velocities of diffusion of these two gases into each other is then the inverse ratio of the square roots of these numbers.
Ch4 V 1.529 1.236
CO2 Vo:559 0.747
102 . , . MINK PAiFJi AND VENTILATION
which can be written 1.65 : 1 ; or 1650 : 1000. This ratio shows that when these gases diffuse into each other, directly, before dilution with air takes place, the mixture will contain 1650 volumes of methane for each 1000 volumes of carbon dioxide. The same result is obtained by stating the law thus: The ratio of diffusion is equal to the square root of the inverse ratio of the densities or specific gravities of the gases; or, as follows:
Ch. Co2
A slightly different, though theoretically more correct result is obtained when the calculation is based on the densities of these gases, referred to hydrogen as unity (1). The process is as follows: Methane (CH4) :
C 1 X 12 12 H4 4 X 1 4
Molecular wt. 16; density, 16 2 8 Carbon dioxide (CO2) :
C 1 X 12 12 O2 2 X 16 32
Molecular wt. 44; density, 44 2 22
The ratio of diffusion is then equal to the square root of the inverse ratio of these densities; or
Calctilation of Percentage Composition, by Volume. — The
mixture is estimated to contain
Total. 2658 volumes.
Percentage, by volume,
Methane, — 62.38 per. cent.
Carbon dioxide, tkq 37.62 per cent.
Mine Gases 103
Carbon Monoxide
This gas, formerly known in mining textbooks as "carbonic oxide/' or "whitedamp," is the product of the combustion of carbon in a limited supply of pure air. Because the supply of oxygen is limited the combustion of the carbon is incomplete and the monoxide is formed instead of the dioxide.
Carbon monoxide is a colorless gas. It is extremely' poisonous, owing to its being absorbed very rapidly by the haemoglobin or red coloring matter of the blood, from which it is separated slowly and with difficulty. The effect on the systetn is therefore cumulative when exposed to the smallest percentage of this gas in the atmosphere breathed. The affinity of carbon monoxide for the haemoglobin is from 250 to 400 times as great as that of oxygen, so thit the blood corpuscles are quickly rendered inert and death is the sure result. The gas is not displaced by the oxygen administered in treatment, but is eliminated slowly by natural processes that take place in the system, unless the latter is too weak or the percentage of the gas absorbed is too great for such result to take place.
The treatment for carbon-monoxide poisoning is the enforced inhalation of pure oxygen'n, by the use of the pulmotor. This is a device that consists essentially of a small portable tank containing compressed oxygen, which is pumped into the lungs by a bellows, while another below withdraws the same from the lungs after use. The pressure of the gas in the oxygen tank automatically operates the bellows at a rate of 16 strokes per minute as in normal breathing. A face mask completes the equipment. It is important to draw the tongue forward with tongs provided for that purpose, and to close the gullet leading to the stomach, by a gentle pressure of the thumb on the throat, in order to avoid the gas filling the stomach.
The presence of the smallest percentage of carbon monoxide in the atmosphere breathed is dangerous to health and life because of its cumulative tendency, its possible toxic effect on the nervous system and the impairment of the vital
104 Mine Gases And Ventilation
organs of the body. The fatal percentage of this gas cannot be definitely stated because of numerous other factors that together determine a fatal effect. The more important of these are the following: The depletion of the oxygen of the air breathed; the length of the time of exposure to the poisonous atmosphere; the energy expended in physical work in such atmosphere ; the state of health and the normal physical condition of the person.
Some persons are more sensitive to gas poisoning than others, owing to a less vigorous constitution, a temporarily weakened condition, a more nervous temperament, or previous exposure to gas poisoning, the baneful effects being hard to eradicate from the system. For these reasons, what would prove a fatal percentage in some instances of less purity of atmosphere, longer exposure, more difficult work, or physical ailment of any nature, would not necessarily produce fatal results under better conditions and more robust health of the individual exposed to the gas.
Relative Rate of Absorption by Blood. — The experiments of Dr. J. S. Haldane and others have shown that 0.02 per cent, of carbon monoxide in otherwise pure air produces about 20 per cent, of saturation in a brief period of time (20 min.?). Since pure air contains 20.9 per cent, of oxygen, the ratio of carbon monoxide to oxygen, in the air breathed, is 2 : 2090, or 1 : 1045. But the ratio of absorption, carbon monoxide to oxygen, in this case, is 20 :80, or 1 :4, the blood showing only 20 per cent, carbon monoxide and 80 per cent, oxygen. Hence, the relative rate of absorption by the blood, carbon monoxide to oxygen, is about 260:1, since 1045-4 say 260. In other words, the blood in this experiment absorbed carbon monoxide about 260 times as rapidly as it absorbed oxygen, under the same conditions.
Another experiment showed 50 per cent, saturation in the blood when the air breathed contained 0.08 per cent, of carbon monoxide. In this case, the ratio of carbon monoxide to oxygen in the air breathed is 8 : 2090, or 1 : 260. But the corresponding ratio of absorption is 1:1, the blood showing 50 per cent, of saturation, or equal quantities of these two
Mine Gases 105
gases. Hence, in this case also, the relative rate of absorption of carbon monoxide and oxygen is the same as before, namely, 260:1.
Another experiment showed 50 per cent, saturation in the blood when the air breathed contained 0.05 per cent, of carbon monoxide. Here the ratio of carbon monoxide to oxygen in the air breathed being 5 :2090, or 1 :418, and the ratio of absorption, as before, 1:1, the relative rate of absorption is 418 : 1, showing that the blood absorbed carbon monoxide, in this case, about 400 times as rapidly as it absorbed oxygen, under like conditions, in the two previous experiments.
The experiments suggest not only the variation in the rapidity of the absorption of carbon monoxide by the blood of different individuals, with varying constitutions and degrees of health; but show clearly the great affinity of the haemoglobin of the blood for carbon monoxide as compared with oxygen. These facts demonstrate forcibly the danger of working in a mine atmosphere containing the smallest possible percentage of this gas even when the worker is in robust health.
Production of Carbon Monoxide in Mines. — Carbon monoxide does not occur naturally in mines, but may be and often is produced in dangerous quantities under the practically unavoidable conditions and occurrences incident to coal mining.
This gas is produced in considerable quantities by any combustion, on a large scale, commonly occurring in the limited confines of mine workings. Examples of this are mine fires and explosions of gas or dust. This gas is also produced by the explosion of powder in blasting. It is produced in dangerous quantities by the slow combustion of fine coal and slack thrown in the waste, in poorly ventilated places and abandoned areas void of circulation. Carbon monoxide is the deadly coifiponent of afterdamp, which renders the latter so quickly fatal to life, as shown by the fatal results that follow many mine explosions.
106 Mine Gases And Ventilation
m
Detection of Carbon Monoxide in Mines. — There is no reliable flame test for the detection of carbon monoxide as it occurs in mines. ' The lamp flame is, no doubt, lengthened when fed with air containing the gas, but this effect is imperceptible in a percentage that would be fatal to life..
The lengthening of the flame is plainly noticeable when the fine dust of an inflammable coal is suspended in considerable quantity in the still air of a mine entry or chamber. This is the result of the increased combustion owing to the dust-laden air feeding the flame. It is possible that a barely perceptible cap may be discerned at times under particularly favorable conditions. This, however, would be a dust cap and would not indicate the presence of the gas.
What is known as the "blood test" will reveal the presence of very small percentages (0.01 per cent., Haldane*) in the air. The delicacy of this test, however, is greatly impaired by the difiiculty of correctly judging of the change in the color of the blood solution employed in making the test. The difiiculty is increased by the dim, artificial light of the mine and the impaired eyesight and possible partial colorblindness of the observer. The blood test also requires time and care in its making, which together with the necessary apparatus do not recommend its use in the mine.
The experiments of Dr. J. S. Haldanef to ascertain the extent to which animal life is affected by the presence of carbon monoxide in the atmosphere breathed into the lungs led him, first, to suggest the use of small animals as a plainly visible and thoroughly reliable index of the presence of gas in quantity dangerous to human life. Dr. Haldane observed that mice and small birds, preferably canaries, were prostrated by the gas in a much briefer period than is required to produce the same effect on a man.
Exposed to an atmosphere containing 0.1 per cent, of carbon monoxide, a mouse became giddy in 12 min., while a man experienced a like effect only after breathing the same atmosphere for a period of two hours. Again, three small
♦Trans. I. M. E., Vol, 38, p. 275. tTrans. I. M. E., Vol. 38, pp. 267-280.
Mine Gases 107
mice and a canary were exposed to an atmosphere containing 0.6 per cent, of this gas. In 4 min. the canary fell from its perch and died, and the mice became helpless, but recovered quickly in fresh air. A man continued to breathe the same atmosphere and, at the expiration of 10 min., was unaffected, a test of his blood showing but one-fourth saturation.
Dri Haldane's conclusions, based on his experiments, are briefly as follows:
1. Noticeable symptoms are never produced by less than about 0.02 per cent, of carbon monoxide in otherwise pure air.
2. The poisonous effect is decreased somewhat by a moderate addition of carbon dioxide; but increased by depletion of the oxygen of the air.
3. Small animals recover quickly and do not exhibit the after effects of the poisoning so often fatal to man.
4. The analyses of the blood of victims of the afterdamp of mine explosions usually show 80 per cent, saturation.
A series of experiments made at the Pittsburgh testing station to determine the effect of repeated exposure of mice and canaries corroborates the conclusion of Dr. Haldane in respect to the complete rapid recovery of these small animals from the effects of carbon-monoxide poisoning.
As previously explained, men who have been once overcome by this gas are more sensitive to its effects again. This is not the case, however, with mice and birds, which fact makes them the more useful in mining-practice. A bird or a mouse that has been exposed to the gas and* overcome a great number of times shows no more sensitiveness to its poisonous effects than one never poisoned by the gas.
Following is the record of eight exposures of a canary to an atmosphere containing 0.25 per cent, carbon monoxide, as given on p. 8, Technical Paper 62, of the U. S. Bureau of Mines, each exposure, except the last, being made immediately upon the recovery of the bird from the previous one. The table shows the time, in minutes intervening between the moment of exposure, first signs of distress, collapse of the bird and recovery in fresh air.
Mine Gases And Ventilation
Table 1. — Effect of Repeated Exposure on Canary
No.
of exposures
Time in minutes
Distress
Collapse
Recovery
' 8
The above record shows earlier signs of distress after the first two exposures. This may naturally be attributed to the alarm and expectancy of the bird arising from its previous experience; but the total interval to collapse was uniform (4 min.), except in the fourth andxthe two last exposures, which were 5, 3 and 2 min., respectively.
The following table shows the same data recorded in four successive exposures of a mouse to a 0.3-per cent, mixture of carbon monoxide and pure air:
Table 2. — Effect of Repeated Exposure on Mouse
No. of exposure
Time in minutes
Distress
Collapse
Recovery
not given
A similar series of experiments, performed by exposing a canary at irregular intervals and on different days to atmospheres containing from 0.18 to 0.24 per cent, of carbon monoxide and numbering 14 exposures in all, extending over a period of nine days, showed practically the same results.
Mine Gases 109
Carbon Dioxide
This gas, often called carbonic acid or "chokedamp" is a colorless and odorless gas, having a distinctly acid taste. It is not combustible and will not support combustion in any ordinary form.
How Produced. — Carbon dioxide is the product of the complete combustion of carbon or carbonaceous matter in a plentiful supply of air or oxygen. It is produced, in mines, by the breathing of men and animals; burning of lamps; explosion of powder slow combustion of fine coal and slack in the gob; and other forms of combustion taking place.
Effect on Flame, — Carbon dioxide has a similar effect on flame to that caused by an exces of nitrogen; or, what is the same thing, a dep etion of oxygen in the air. The presence of carbon dioxide in the air tends to reduce the activity of combustion. It dims the flame of a lamp and extinguishes it when present in sufficient quantity.
The percentage of carbon dioxide that will extinguish flame depends on both the nature of the flame and the amotmt oi oxygen in the air feeding the flame. A gas-fed flame, as the hydrogen flame of the Clowes lamp, or the acetylene flame of a carbide lamp, is less susceptible to extinction from this cause than is an oil-fed flame.
The flame of a lamp burning sperm or cottonseed oil is extinguished in an artificial atmosphere (which is the usual condition in a mine) containing 14 per cent, of carbon dioxide. But, in a resddtial atmosphere formed by allowing the lamp to bum in a closed place tiQ extinguished, only 3 per cent. of carbon dioxide is required for extinction of the flame.
Effect on Life. — Carbon dioxide is not classed as one. of the poisonous mine gases, although it exerts a toxic effect on the human system. It is irrespirable when unmixed with air and if breathed produces death by suffocation. In smaller quantities, it causes headache, nausea and pains in the back and limbs.
According to Dr. Haldane, no appreciable effect is produced by breathing air containing carbon dioxide, until there
110 Mine Gases And Ventilation
is about 3 per cent, of this gas present. Breathing then becomes slightly more difficult; 5 or 6 per cent, of the gas causes decided panting; and 18 per cent, suffocation and death. The effect of the gas is much increased if the oxygen content of the air is below the normal.
For example, with 18 per cent, carbon dioxide present, there is 0.209 (100 - 18) 17.14 per cent, oxygen and 0.791 (100 — 18) 64.86 per cent, nitrogen, under normal conditions. This is a fatal atmosphere.
But, if the oxygen of the air has been depleted so that the ratio, oxygen : nitrogen, is less than 20.9 : 79.1; then a less percentage of carbon dioxide than that named above (18%) would be fatal to life.
Treatment when Overcome. — Remove promptly to fresh air; apply alternately cold and lukewarm bandages to the chest; rub the limbs and body briskly to start circulation; and, if necessary, use artificial respiration. When consciousness is restored put the patient to bed and keep him quiet for several days.
Blackdamp
It is a common mistake, in mining practice, to regard carbon dioxide as another name for blackdamp,' which is found in such quantities in many poorly ventilated mines. Carbon dioxide is one constituent only of blackdamp.
The term blackdamp describes a variable mixture of air deficient in oxygen, and carbon dioxide. It consists therefore of carbon dioxide, nitrogen and oxygen, in varying quantities. The percentage of oxygen in the mixture will determine its respirable quality. The nitrogen is wholly inert and acts only to dilute the mixture and thus reduce the percentage of oxygen present. The carbon dioxide not only dilutes the mixture but produces also a toxic effect on the human system, although this effect is not of such a nature as to class carbon dioxide as a poisonous gas.
The production of blackdamp in coal mines is due to two chief causes: 1. The absorption of the oxygen of the air by the coal. 2, The generation of carbon dioxide by the various
Mine Gases 111
#
forms of combustion or oxidation continually taking place in the workings of the mine.
The absorption of oxygen from the mine air by the freshly exposed surfaces of coal is more rapid than what is generally supposed. Experiment has shown that a certain freshly mined bituminous coal absorbed from one-eighth to oneseventh of its volume of oxygen from the siurounding air, in 24 hr.; while only about one-tenth of this oxygen was converted into carbon dioxide. It is suggested that the remaining nine-tenths of the oxygen absorbed unites chemically with certain unsaturated hydrocarbons in the coal.
The effect of this rapid absorption of oxygen, in the still air of badly ventilated places, in coal mines, as can be readily imagined, is to deplete the oxygen content of the air. This is especially the case where tons of coal are shot down at night and left to be loaded out the following day and the ventilation during the night is much diminished in the mine.
On the other hand, where the ventilation is adequate and there is still blackdamp produced in quantity, it is the result of the generation of carbon dioxide from some cause, generally a mine fire or the slow combustion of fine coal.
Afterdamp
The term 'afterdamp,'' as the word implies, is used to describe the variable mixture of noxious gases that remains after any explosion of gas, dust or powder in a mine.
Composition. — It is impossible to give the composition of afterdamp, except in the most general way; because the gases formed depend on so many varying conditions, in respect to the-character of the* gas or dust burned; the relative volume of available oxygen; the size of the workings where the explosion takes place, as determining the temperature and pressure developed; and the condition of the mine with respect to gas, dust and moisture.
Afterdamp may contain variable quantities of nitrogen, carbon dioxide, carbon monoxide, water vapor and, at times, lesser amounts of nitrous oxide gas and possibly some un-
112 Mine Gases And Ventilation
burned methane. The mixture is extremely dangerous, being fatal to life and often highly explosive.
Inflammable And Explosive Mine Gases
The presence of combustible gases in the atmosphere of a mine is always an element of danger for three principal reasons. 1. The percentage of gas in the mine air may be sufficient to form an explosive mixture known as firedamp. 2. The temperature of ignition of most of these gases is lower than that of methane, which is usually the chief constituent of firedamp, and the latter is rendered more readily ignitable by reason of their presence. 3. The presence of the smallest percentage of a combustible gas assists to that extent the ignition of a dust-laden atmosphere and increases the violence of its explosion when ignited.
The Inflammable Gases. — The inflammable or combustible mine gases, in the order of their importance, are methane (CH4), carbon monoxide (CO), ethane (C2H6), ethene or olefiant gas (C2H4), hydrogen (H2) and hydrogen sidphide (HjS). Each of these gases is not only combustible but forms an explosive mixture when mixed with air in certain proportions.
Inflammable Range of Gases. — The combustion of an inflammable gas, under mining conditions, requires the presence of air or available oxygen. The relative proportion of air and gas in the mixture determines the character and completeness of the combustion and the range of inflammability of the gas.
The maintenance of flame throughout a gaseous mixture requires that the heat of combination between the combustible and the atmosphere supporting the combustion shall be equal to that lost by radiation, conduction and absorption by the air and gaseous products formed. Two conditions are possible.
1. The proportion of gas to air may be such as to give a low rate of combination and a correspondingly small generation of heat, which is insufficient to raise the adjacent gaseous molecules to an equal temperature, resulting in a still lower rate of combination and a lesser generation of heat as the action proceeds through the mass till it finally ceases.
Mine Gases 113
2. Again, the proportion of air to gas may be such as to cause an absorption of heat greater than that generated when the condition will likewise be a falling one and there can result no general extension of flame throughout the mass.
The first of these two conditions (excess of gas) determines the higher inflammable limit of the gas, while the second condition mentioned (excess of air) marks the lower inflammable limit. Beyond these two limits the gaseous mixture is not inflammable. In mining practice, mixtures above the higher limit are more dangerous than those below the lower limit, as more air will make them explosive.
Explosive Range of Gases. — A combustible gas is always inflammable in proportions of gas to air outside of the explosive range of the gas. In other words, the range of inflammability is wider than and embraces the range of explosibility. The same principles, however, apply in respect to each of these conditions.
The degree of explosiveness of a gaseous mixture is increased as the rate ©f combination is more rapid and the loss of heat less; or decreased as the rate of combining is slower and the loss of heat greater.
Maximum Explosive Point.— It is quite generally assumed that the maximum explosive force of a gas is developed when the proportion of air or oxygen is just sufiicient for the complete combustion of the gas. While this is sufiiciently close for all practical purposes, it is stated (Emich) that the explosibility is not necessarily greatest at this point.
Inflammable and Explosive Limits. — The following table gives the lower and higher inflammable and explosive limits and the maximum explosive point of the three most important combustible mine gases, except only the higher inflammable limit of carbon monoxide, which has not been determined, but is probably about 80 per cent. The table shows the percentage of gas present in the mixture, at each of the five stages given. The lower inflammable limit and the maximum explosive point have been calculated for each of these gases, while the other data are the results of experiment. A normal condition of the air is assumed :
Mine Gases And Ventilation
Table Giving the Inflammable and Explosive Limits and the Maximum Explosive Point of Methane, Hydrogen and
Carbon Monoxide
Gas
Lower
inflam.
limit
Lower
explo.
limit
Maximum explo. point
Higher
explo.
limit
Higher
inflam.
limit
Methane
Carbon monoxide
Hydrogen
The same data, in reference to olefiant gas (ethene or ethylene), C2H4, are: Lower explosive limit, 4.0 per cent.; maximum explosive point, 6.5 per cent.; and higher explosive limit, 22 per cent. These, however, have only a relative importance in respect to mining, because the percentage of this gas present in mines is very small.
Peculiarities of Explosion.: — A peculiarity in the explosion of a mixture of methane and air is that, at the temperature of ignition (1200°F.), about 10 sec. are required before the gas will ignite (Mallard and Le Chatelier), while both hydrogen and carbon monoxide ignite at once, upon contact with the flame. The time required for the ignition of methane grows rapidly less as the temperature is increased.
The same authorities also claim that mixtures of methane and air in any proportion are explosive at high temperatures, and the same effect has been observed at high pressures. In other words, an increase of temperature or pressure has the effect to widen the explosive range of a gas
A mixture of carbon monoxide and air will not explode in the absence of moisture. The explosion, in this case, seems to require two stages, the carbon monoxide taking the oxygen from the water, which is replaced immediately by the oxygen of the air, as represented by the following equations:
and
Co + H2O Co2 + H2 2H2 + 02 2H2O
It has been argued that, since carbon monoxide, which is distilled from coal dust floating in the mine air, is not ex-
Mine Oases
plosive in dry air, the safest condition is a dry mine atmosphere, which, however, is practically impossible.
Explosive Mine Gases. — The diagram, F. 13, given below combines, in a compact form, most of the important reactions and data, relating to the combustion and explosion of those mine gases that form explosive mixtures with air. In the upper left-hand comer w a graphic illustration of the relative extent
;
5:
Iso
-Si
M
—
t
r
ij.
ir~
ft
M
a r-fbun Is
Aas
""Ss"
S-r-—
S„
aw
Ss!W
-w
„
f"
Wcm
-r
"
"X " J f '
Pio. 13. of the explosive and inflammable zones of each of these gases when mixed with air. The horisontal lines, in each gas column, mark, approximately, the maximum explosive point and the lower and upper explosive and inflammable limits; also the fatal percentage "is indicated by the dotted lines. These marks are explained by the legend in the upper right-hand corner The epeciiic heats are given for equal weights of the gases, for constant volume and constant pressure, referred to water as unity.
Section Iv
Explosions In Mines
Definition, Gas Explosion, Dust Explosion — Inflammation OF Gas — Nature and Temperature of Flame — Explosion of Gas — Coal Dust, Its Inflammability AND Influence, Effect of Stone Dust — Mine Explosion, Development, Causes, Mixed Lights, Electric Mine Lamps, Prevention of Mine Explosions.
Definition. — A mine explosion is understood to be a violent disturbance of the atmosphere within a mine, as manifested by a destructive blast or rush of air accompanied by more or less flame, and is the result of the ignition and combustion with explosive rapidity of gas and dust or either accumulated in the mine.
Gas Explosion. — An explosion produced and maintained chiefly by gas accumulated in the mine workings and passages or mixed with the air current is described as a "gas explosion," although practically every mine explosion involves the combustion of both gas and dust.
Dust Explosion. — An explosion in which the fine coal dust accumulated in the mine or suspended in the air current plays a prominent part is commonly called a "dust explosion," although it may have originated in a local explosion of gas, which is true of most mine explosions.
Few if any mine explosions are wholly due to gas or dust, but combine both of these elements in varying proportions the character of the explosion as "gas" or "dust" being determined by the later evidences.
Inflammation Of Gas
Theory of Inflammation. — The inflammation of a combustible gas involves, at least, two main conditions that are essential to the reaction. They are as follows:
Explosions In Mines
1. The presence of another gas that will support the combustion by reason of the different affinities of the elements of the gases that invite dissociation and recombination to form other compounds.
2. A rise of temperature, at the point of contact of the two gases, sufficient to start the reaction.
The ignition of a combustible gas in some cases (carbon monoxide) requires, besides the above, the presence of water
Temperature of Ignition. — At the same pressure and under the same conditions of ignitiofi, the temperature at which a given gas inflames or the temperature of ignition for that gas is fixed. The following table gives the average temperatures of ignition of the principal mine gases, as determined by experiment :
Average Temperatures op Ignition of the Combustible Mine
Gases in Normal Air
Gas
Carbon monoxide . . .
Methane
Ethane
Hydrogen
Acetylene
Symbol
Temperature
of ignition
Co
Ch4
C.H.
C,H4
H,
C,H,
Nature Anx> Temperature Of Flame
The Nature of Flame. — Flame, as here considered, is burning gas. It may be luminous or nonluminousi according to the presence or absence of carbon either free or combined as hydrocarbons. The incandescence of the carbon particles when present renders the flame Imninous. This is the case with most oil-fed flames and flames burning in a dusty atmosphere. The flame of hydrogen burning in clear, pure air is practically nonluminous. Methane produces an almost non-
118 . Mine Gases And Ventilation
luminous flame, but the flame of the heavy hydrocarbon gases is always more or less luminous. '
The Temperature of Flame. — The temperature of flame is variable, owing to numerous conditions that affect the combustion of the gas both as to its rapidity and completeness. The temperature will vary in different parts of the same flame, because of a, variable supply of air that not only affects the combustion of the gas but absorbs much of the heat developed and lowers the temperature of the flame.
Owing to these varying conditions it is clearly impossible to calculate the actual flame temperature of a burning gas. This is often roughly assumed to be about one-half of the theoretical value as calculated from the heat of combustion per pound of gas and the heat absorbed by the corresponding products of combustion, for each degree rise in temperature*
It is important not to confuse the flame temperature of a combustible gas with its temperature ignition, as they have no connection with each other.
Calculation of the Theoretical Flame Temperature. — The theoretical temperature of the flame of a burning gas is the highest possible temperature that results from its complete combustion, assuming (what is never the case in an openburning flame) that only sufficient air is present for the complete combustion of the gas.
There is always an excess of air in the outer envelope or zone of a flame exposed to the air, and this excess of air beyond what is required for the combustion absorbs heat and lowers the temperature of the flame in the outer zone.
The temperature within or in the body of the flame more nearly approaches the theoretical maximum, which can be calculated. This maximmn temperature is found by dividing the total heat of combustion above 32 deg. F., per pound of combustible, less the heat rendered latent in the water vapor produced, by the heat required to raise the temperature of the products of combustion one degree. The quotient obtained gives the rise of temperature above 32 deg. F., which must therefore be added in order to find the theoretical temperature of the flame.
Explosions In Mines 119
Flame Temperature of Methane Burning in Air. — The first portion of the process is similar to that explained in the calculation of the lower inflammable limit of methane and need not be repeated here. It was found that for every pound of methane burned there was produced carbon dioxide, lb. ; water vapor, 23 lb. ; and nitrogen, 13.39 lb. So far the two operations are the same. (Page 96.)
As before, one pound of methane, burning to carbon dioxide and water at 32 deg. F., develops 23,513 B.t.u. From this must be subtracted the heat required to convert lb. of water at 32 deg. into steam at 212 deg., which is absorbed in the formation of the water vapor; thus,
The result obtained is the net heat available for raising the temperature of the products of combustion, which constitute the larger portion of the body of the flame.
It is necessary now to calculate the heat required to raise the temperature of the respective weights of the products of combustion one degree. The weight of each of these products, as previously given, is multiplied by its specific heat for constant pressure and the sum of these products is the total heat required for each degree of rise in temperature; thus,
Sp. heat Weight B.t.u.
Carbon dioxide 0.2163 X 2. 75 0.5948
Water vapor 0.4805 X 2.25 1.0811
Nitrogen 0.2438 X 13.39 3.2645
Heat absorbed, per degree rise ... 4 . 9404
Finally, the rise of temperature in the body of the flame that is possible, in this case, assuming that all of the heat developed is absorbed by the products of the combustion only, is as follows:
Rise. of temperature, 20,924.6 -f- 4.9404 4235 deg. F.
This rise of temperature, like the heat developed by the combustion, is estimated from 32 deg. F. The theoretical flame temperature is therefore 4235 + 32 4267 deg. F.
120 Mine Gases And Ventilation
Flame Temperature of Carbon Monoxide. — The first step in calculating the flame temperature of this gas is to write the chemical equation expressing the reaction that takes place when carbon monoxide burns to carbon dioxide, ignoring for the present the nitrogen in the air; thus,
2C0 + 02 2CO2 Molecular weights, 56 32 88
Relative weights, 1 ij
Since oxygen forms 23 per cent, of normal air, by weight, and nitrogen 77 per cent., the ratio of nitrogen to oxygen is 77 : 23, and the relative weight of nitrogen involved here is
Hence, for every pound of carbon monoxide burned, there is produced carbon dioxide, ij lb.; and nitrogen, 1.91 lb.
The heat of combustion of carbon monoxide burning to carbon dioxide, as taken from a table giving the heat of combustion of various substances, is 4325 B.t.u. per lb. of gas burned. There being no water vapor formed in this reaction, the above is the actual heat available for raising the temperature of the products of the combustion, which form the body of the flame, disregarding radiation and conduction losses.
Now, calculating, as before, the heat required to raise the temperature of the respective weights of the products of this combustion one degree, by multiplying the weight of each product by its specific heat for constant pressure and finding the sum of those products, we have
Sp. heat Weight B.t.u. Carbon dioxide 0.2163 X 11/7 0.3399
Nitrogen 0.2438 X 1.91 0.4667
Heat absorbed, degree rise . 8066
The resulting rise of temperature above 32 deg. P., in the body of the flame, which determines the theoretical flame temperature, is then 4325 -r- 0.8056 5369 deg. F. and the corresponding temperature, 5369 + 32 say 5400 deg. F.
EXPLOSIONS m MINES 121
Although the presence of moisture (water vapor, H2O) is necessary to the ignition of carbon monoxide, it is not required to take this into account in making the above calculation, for the reason that the heat of dissociation is balanced by the heat of recombination in the molecule of water and no loss of heat is assumed to occur. It has been suggested that the water only serves to start the reaction by effecting the ionization of the elements.
The theoretical flame temperature as calculated above, however, both for methane and carbon monoxide, is considerably modified by the humidity of the air supporting the combustion.
Volume of Flame. — -It is frequently estimated roughly that the volume of a flaming gas is proportional to its absolute temperature. For example, assuming the original temperature of the gas as deg. F., the theoretical flame volumes of methane and carbon monoxide are, respectively,
Methane, 460 + 4267 460 say, 10 volumes.
Carbon monoxide, 460 + 5400 -J- 460 say, 12% volumes.
Explosion Op Gas
Influence of Temperature on Explosion. — A rise of the initial temperature of an explosive mixture slightly extends the lower inflammable limit, but has no appreciable effect on the higher limit, owing to the small relative value of the increase as compared with the high temperature developed in the explosion.
Influence of Pressure on Explosion.— Pressure exerted on an explosive mixture increases its density and temperature and renders it more readily ignitable. In other words, an increase of pressure lowers the lower inflammable limit of an explosive gaseous mixture. An increase of pressure, likewise increases the velocity of propagation of explosion in the mixture, raises the temperature developed and extends the higher inflammable limit. In other words, an increase of pressure widens the explosive range of a combustible gas.
122 Mine Gases And Ventilation
Influence of Relative Humidity on Explosion. — While the presence of moisture (water vapor) in a gaseous mixture is often necessary to secure its explosion, as explained in reference to carbon monoxide, the water vapor absorbs much of the heat and lowers the temperature developed, thereby reducing the rate of combination and the force of the explosion, except where fine coal dust is suspended in the air, when partial dissociation may take place in the water vapor and result in increasing the energy of the reaction.
Influence of Catalysis to Cause Explosion. — Catalysis is the eifect produced by a foreign substance to assist chemical reaction between two other substances, while the substance itself undergoes no change — first, discovered by Berzelius. Much difference of opinion exists as to the suggested catalytic action of fine incombustible dust suspended in mine air, to . assist the explosion of combustible gases. Finely powdered stone dust has been shown to retard the ignition of coal dust by mixing with and diluting the latter. This effect, however, is wholly physical and not related to the possible catalytic action referred to by Sir Frederick Abel and others who have studied the subject closely.
Influence of Character of Initial Impulse. — The manner in which the gas is ignited or the character of the initial impulse determines largely the explosion of gaseous mixtures. . For example, a firedamp mixture ignited by a lamp flame may not explode, while if fired by the flame of a blowout or windy shot, the greater volume and intensity of the flame may cause an explosion.
The volume of the flame is important, because it envelops a larger portion of the gaseous mixture and ignition is thus started generally throughout the mass, causing a greater development of heat and reducing the percentage of loss by radiation, convection and conduction.
The intensity of the initial impulse or the higher temperature of the igniting flame will often cause the explosion of a gaseous mixture that would burn quietly if ignited by a less intense source of heat energy. The dissipation of heat is so rapid and general in a burning gas that the transition
Explosions In Mines 123
from inflammation to explosion requires a conservation of heat or greater local energy than can often be realized in the large open workings of a well-ventilated mine.
Coal Dust
Influence of Coal Dust on Explosion. — The fine dust of an inflammable coal when floating in the mine air may render the air explosive in the entire absence of explosive gas. Under such conditions, however, the ignition and explosion will only take place when the floating dust is acted upon by a flame of considerable volume and intensity.
When a small percentage of methane is present, insufficient of itself to make the air explosive, the presence of the dust floating in the air is more dangerous than when no gas is present. The dust-laden air is more easily ignited and the force of the resulting explosion is increased in proportion to the inflammability of the mixture.
The purity, fineness, humidity and inflammability of the
dust are important factors in determining the character of
. the explosion, since these with oxygen are the chief elements
that promote the rapidity of the combustion, which is the
necessary condition of any explosion.
The suspended dust feeds the flame of an explosion that is started in a mine, and thus serves to propagate the blast and extend what would otherwise have proved only a local explosion. This action is cumulative in a dry and dusty mine. The dust lying on the roads and clinging to the sides and timbers of the passageways is blown into the air by the force of the rushing wind that precedes the explosive wave, producing what has well been called a "pioneering cloud" of dust that is itself highly explosive.
The weight of fine bituminous coal dust required to render normal air explosive has been variously estimated. Tests made at the Pittsburgh Experiment Station* with dust from a 200-mesh sieve showed explosion took place in a density of 32 grm. per cu. m. (0.032 oz. per cu. ft.) or, say 1 lb. of dust in 500 cu. ft. of air. The Taffanel experiments (Livin) gave explosion in 70 grm. per cu. m. (0.07 oz. per cu. ft.) or, say
124 Mine Gases And Ventilation
1 lb. of dust in 230 cu, ft. of air. In one instance only, explosion occurred in 23 grm. per cu. m. (0.023 oz. per cu. ft.), or 1 lb. of dust in about 700 cu. ft. of air.
It is quite evident, as experiments also show, that conditions in respect to the purity, humidity and particularly the inflammAbility of the dust are so variable that the question of the density of the dust cloud has only an experimental value. The size of the workings, as determming the conservation of heat and pressure, will also modify the results in the mine.
Theoretically, since the atomic weights of carbon and oxygen are 12 and 16, respectively, 1 lb. of carbon will yield
But, carbon monoxide measures 13.5 cu. ft. per lb., at normal temperature and pressure. Hence, lb. of this gas produced by 1 lb. of coal dust makes X 13.5 31.5 cu. ft. Then, since the lower inflammable limit is reached when the mixture of gas and air contains 8.4 per cent, of the gas, inflammation might be expected when the dust present was 1 lb. in 31.5 0.084 375 cu. ft. of air. Also, the lower explosive limit of the gas occurring when 116.5 per cent, of gas is present, explosion might be expected to take place when there was 1 lb. of dust in 31.5 -h 0.165 190 cu. ft. of air.
Inflammability of Coal Dust. — The inflammation of a dust cloud in mine workings, under like conditions, depends largely on the inflammable nature of the coal. The experiments at different testing stations have demonstrated that the volatile combustible matter contained in coal is a fair index of its susceptibility to inflammation when held in suspension as fine dust in the air.
Experiments performed with anthracite dust seem to indicate that the fine dust of that coal is not capable of propagating an explosion in a mine, under ordinary mining conditions. This fact points significantly to the conclusion previously stated that the volatile combustible matter in a coal is an important index of its explosibiUty. It is not asserted or
Explosions In Mines 125
claimed that anthracite dust cannot be exploded under favorable conditions. However, the conditions that would cause anthracite dust floating in the air to explode are not liable to occur in ordinary mining practice.
Influence of Shale or Stone Dust. — Shale or other soft rock of the coal formations have been ground to a fine powder for use in mines and, in this form, have been sprinkled on the roads in a manner to form stone-dust zones or distributed on shelves hung across and overhead in the entries to form so-called stone-dust "barriers."
The purpose of these dust zones and barriers is to arrest the progress of an explosion should one occur in the mine. Their use, however, has not been attended with unvarying success, which is due in part to the different conditions of temperature, humidity, air space or volume of mine workings available for expansion, inflammability of the gas-and dust-laden air and the initial intensity of the explosion; also, in part to the limited extent or adequacy of the dust zone or barrier as compared with the strength developed by the explosion.
Notwithstanding the apparent failure of these means for preventing the spread of an explosion in a mine in many observed instances, there is no question but that finely powdered shale or stone dust blown into the path of an explosive wave by the pioneering impulse, or suspended in the air with the inflammable coal dust has a most decided effect and reduces explosive conditions.
The action of incombustible dust, suspended in an otherwise explosive atmosphere, to allay the explosiveness of the mixture or reduce the violence of the blast should ignition and explosion occur, is wholly physical. The in9ombustible particles disseminated through a dust-laden atmosphere separate more widely the inflammable particles of coal dust and dilute the air necessary for combustion. In other words, the percentage of inflammable matter in the mixture is reduced and the liability to inflame diminished in the same proportion. Also, by its absorption of heat, the incombustible matter lessens the heat available for ignition and decreases the heat
126 Mine Gases And Ventilation
energy developed when ignition has taken place. The action is entirely similar to that of the inert nitrogen of air depleted of its oxygen, or to the extinctive effect of carbon dioxide when present in firedamp mixtures, both of which conditions act to diminish the explosibility of gaseous mixtures.
Mine Explosion
Development of a Mine Explosion. — Explosion does not necessarily follow the ignition of gas in mine entries and workings. The firedamp mixture must, of course, be within the explosive range, as determined by the conditions in that, portion of the mine. But even then a mine explosion will only take place when the conservation of heat is sufficient to render the explosive action self-supporting. Otherwise, a local explosion of gas or dust will expend its .energy within a limited area and the disturbance will not be propagated throughout the mine.
The ignition of an inflammable mixture of gas or dust in the mine air may produce a considerable body of flame that, within the narrow confines of the mine, may gather force and generate sufficient heat to cause an explosion. Experiment has shown that an explosive mixture of gas and air placed in a tube and ignited at one end will burn quietly at first, then flutter or vibrate with increasing energy as the combustion penetrates deeper in the tube, the contending forces being the entering air and the escaping products of the combustion. This action, however, quickly develops sufficient energy to produce an explosion, which darts through the entire length of the tube.
This experiment illustrates more or less closely the development of an explosion in a mine entry or chamber. Investigation has shown that the explosion gathers force and probably develops characteristic energy within a few yards of its origin or the point where the ignition of the gas took place. This may vary from 10 to 30 yd. or more, depending on many conditions — chiefly the size or volume of air space available for the expansion of the gases of the explosion, the
Explosions In Mines 127
intensity of the igniting flame and inflammability of the mixture.
All of these factors determine severally the initiation as well as the character of the explosion and its limitations in the mine
Causes of Mine Explosions. — The causes of mine explosions may be generally stated as the ignition of gas or dust by one of the following causes:
1. By the use of open lights or defective safety lamps in mines where the air current is charged with gas or dust, or where gas has accumulated in void or abandoned places in sufficient quantities to be dangerous.
2. By the use of mixed lights in mines generating gas.
3. By the inexperienced or careless use of a safety lamp, or by fooling or tampering with the lamp, or exposing it to gas too long or to a strong gas blower or strong current or blast of air, or carrying too high a flame.
4. By the use of a dirty lamp or one that has been improperly assembled or injured by a fall or other accidental cause.
5. By the explosion of powder in blasting or the accidental explosion of a keg of powder, or the flame of a blowout shot or a windy shot* -
6. By the use of matches or other means of lighting.
7. By the sparking of electric wires, switches or brushes, or the blowing out of an electric fuse, or the breaking of an incandescent lamp*
8. By the spontaneous ignition of oily waste carelessly thrown aside, or of fine coal or slack in the gob.
9. By the fall of certain hard roof rock striking sparks, as claimed in the Bellevue mine explosion (1910), Alberta, Canada.
10. By the possible generation of heat due to concussion of the pine air in contracted workings in thip seams.
Mixed Lights in Mines. — By "mixed lights" is meant the use of open lights in one or more sections of a mine in which gas is generated in other portions of the mine in sufficient quantity to require safety lamps being employed therein.
128 Mine Gases And Ventilation
The expression does not refer, however, to the use of open lights by drivers, triprunners or motormen whose duties are confined to the main intake haulage roads and shaSt or slope bottom of a mine worked on safety lamps, provided there are lamp stations beyond which these men may not pass.
The use of mixed lights is a dangerous practice. The danger does not consist wholly in a man carrying an open light into the safety-lamp section, or to a foreman or fireboss forgetting that he has an open light on his head while carrjdag a 'safety" at his side. These are possibilities that can be prevented by properly safeguarding the entrances to the gaseous section.
The real danger lies in a heavy fall of roof occmring in the safety-lamp section and driving out the gas into other parts of the mine where open lights are in use. Or, a squeeze may develop in any part of the mine and permit the gas to find its way without warning into an open-light section and cause an explosion.
Electric Mine Lamps. — Any installation of electricity in a mine worked on safety lamps is necessarily accompanied with more or less danger. Whether the installation is for the purpose of lighting, hauling, coal cutting or drilling, pumping or ventilation, it should be made by a competent electrician. The entire system of wiring should be closely inspected at frequent intervals and tested to insure freedom from shortcircuiting or grounding of the current, which are not only wasteful of power, but may start combustion and result in an explosion of gas.
The use of incandescent lamps in mines has become so common that the Bureau of Mines has made a careful investigation to determine their safety. Their experiments show that ignition of gas may follow the breaking of the glass bulb of a lamp in an explosive mixture. The experiments also seem to indicate that the liability of ignition increases with the cross-section of the filament of the lamp. In the breaking of an incandescent lamp two conditions may arise that materially affect the possibility of the ignition of the gas. The same
Explosions In Mines 129
blow that breaks the bulb may or may not break the filament. The result in either case may be briefly explained as follows :
1. If the filament is broken and its parts do not shortcircuit the current ignition of the gas is not likely to occur. If the broken parts, however, fall across each other in such manner as to again close the circuit their burning out in the air will generally ignite any gas present.
2. If the filament remains intact when the bulb is broken it will burn out more or less rapidly, according to. the manner of fracture and consequent inrush of air and gas. A small hole due to the breaking of the tip may admit the air so slowly that the gas is consumed without explosive violence. In that case there may occur a slight explosion within the bulb, which is not biioken but only pierced. This feeble explosion, however, may not be communicated to the outside gas.
Prevention of Mine Explosions. — No means has yet been devised that will insure absolute freedom from mine explosions. But the tendency to explosion and the frequency of these occurrences can and has been greatly reduced by studying their causes and adopting measures to remove them.
The following points are of chief importance:
1. Effective mine regulations and discipline.
2. Operation in accordance with the state mining law.
3. Enforcing by suitable penalties all mine regulations.
4. Thorough frequent inspection by competent men.
6. Education and training of all men employed in any capacity in the mine, in respect to the proper performance of their duties, the dangers to which they are exposed and the mining law and mine regtilations in force.
6. Eternal vigilance of mine officials and a regard for safety greater than the desire for increasing the daily output of the mine*
7. Cooperation of employers and employed in increasing the safety of mine work.
8. Cooperation of all coal companies in respect to mining requirements.
Aside from the above general outline there is the necessity for each company to study carefully the conditions existing
130 Mine Gases And Ventilation
in its own mines, and to adopt a system of inspection and methods of ventilating the mine and mining and hauling the coal that will produce the best results and insure the greatest freedom from accumulations of gas and dust on the roads and in the workings. Immunity from explosion can only be secured by removing the cause.
Section V
Mine Rescue Work And Appliances
Pbbuminart, Entering a Mine After Explosion, Firstaid Suggestions — Breathing Apparatus, Principle, Action and Requirements in Respiration, Development, Dbsiqn and Testing op Breathing Apparatus — Types of Breathing Apparatus, Draeger, Fleuss Proto, Gebbs, Paul — Bureau of Mines, Permissible Breathing Apparatus — Specifications bt the Bureau OF Mines — First-aid Work.
preliminary
Entering a Mine after an Explosion. — Prompt action and intelligent and effective measures are necessary for the rescue of any possible survivors of a mine explosion. The nature, of the work and the great risk incurred in its undertaking demand that it shall be performed by the most experienced of the volunteers, of whom there is never any lack. . Immediately fter an explosion in a mine, the following procedure is important:
1. Call for volunteers and from them choose those who are more experienced and familiar with the irvine and the work to be performed.
2. At the same time, observe the mine entrances and judge of the probable effect of the explosion in the. mine; examine the ventilating apparatus and have any necessary repairs made at once.
3. Collect the necessary safety lamps, tools, timber, canvas, brattice boards, nails, etc. Caged canaries or mice should glso be provided, and two or more sets of breathing apparatus should make up the equipment.
4. Divide the rescuers into three parties, as follows: (a) Apparatus men to explore in advance;
132 Mine Gases And Ventilation
(c) Supply gang to render every possible assistance. Organize each party under a competent leader who shall
be in absolute control while underground.
5. Enter the mine at the earliest possible moment — the apparatus men proceeding first and keeping from 100 to 200 yd. in the lead of the others, who must not advance ahead of the air.
6. Each section of the mine should be explored hyi the apparatus men to discover any possible fire therein, before restoring the circulation In that section.
As quickly as any survivors are found they must be promptly removed to fresh air and the proper restoratives applied. At the surface, physicians should be in attendance and ambulances provided for the prompt removal of those brought out of the mine.
Suggestions on First-aid to Explosion Victims. — Those trained in first-aid work are the ones who should assume charge and have absolute control of the care of any smvors as quickly as found, until the arrival of a physician. The following brief suggestions are important:
1. Be calm and quiet; act promptly but not in a hurry; keep cool and observe closely every symptom, and condition.
2. Remove promptly but carefully to fresh air.
3. Do everyiihing possible to stop bleeding.
4. Examine for broken bones before moving far.
5. Use aromatic spirits of ammonia if stimulant is needed.
6. If overcome by gas, give artificial respiration.
7. If unconscious, loosen clothing/ warm and stimulate by rubbing the limbs; give no stimulant if face is flushed and pulse strong, but sprinkle cold water on face and chest. If the body and limbs are cold, use warm applications; keep the patient covered with blanket or other coverings; apply smelling salts or spirits of ammonia cautiously to the nostrils.
Breathing Apparatus
Principle of Breathing Apparatus.-The principle of all breathing apparatus is that the wearer breathes the same air
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over and over again, the carbon dioxide exhaled in the breath being absorbed after each expiration while, at the same time, the requisite amount of oxygen is restored, thus rendering the expired air pure and fit to be again inhaled.
Action in Respiration. — In the act of inhalation, the air enriched with oxygen passes from the breathing bag in the bottom of the cooler, up through the latter and is drawn through the inhalation valve and tube into the lungs.
In exhalations the air, deprived of some of its oxygen and containing from to 4 per cent, of carbon dioxide, depending on the amount of the exertion, is discharged through the exhalation tube and valve into the exhalation side of the cooler where it meets the oxygen supply, as previously stated, and passes into the regenerator where it is to give up its carbon dioxide, by contact with the absorbent caustic soda.
Requirements in Respiration. — The average full capacity of the lungs of an adult person is about 300 cu. in. This volume, however, is never utilized in the act of breathing; that is to say, all of the air contained in the lungs is never exhaled or the lungs would collapse, which would be fatal. There is a certain volume of residual air, about 100 cu. in., that remains in the lungs after a deep expiration. In the ordinary act of breathing, the average person expires only about 20 or 30 cu. in. of air at a single breath. This has been called "tidal air.'* In the performance of work or when undergoing any extra exertion, a larger quantity of air is expelled from the lungs at each breath and a corresponding quantity again mhaled.
The ordinary rate of respiration is 16 breaths per minute when a person is at rest, making the volume inhaled, from 300 to 500 cu. in. per min. When making violent exertion in the performance of work, breathing is more rapid and a much larger volume of air is respired. This quantity will vary with the person and the exertion made or the work performed. When doing strenuous work a man may inhale 200 cu. in. of air at a single breath.
Approximately, the volume of carbon dioxide exhaled is equal to that of the oxygen breathed into the lungs, the ratio of carbon dioxide to oxygen being slightly less when the person
Mine Gases And Ventilation
is at rest, than it is in the performance of work. However, for the purposes of ordinary estimate, it may be assumed that a man, at rest, will inhale from 25 to 30 cu. in. of air at a single breath and this may be increased to 150 or possibly 200 cu. in. when making violent exertion. Practically, one-fifth of this volume of air is oxygen; but, in the act of breathing, only onethird or one-half of this oxygen is consumed.
The standard supply of oxygen, in mine breathing apparatus, ha been fixed, therefore, at 2 liters per min. (122 cu. in,). Compressed to 120 atmospheres, this rate of supply of oxygen, for a 2-hr. period, will require a cylinder capacity of X 60) -5- 120 122 cu. in. Again, assuming that the average amount of carbon dioxide produced in breathing is equal to the volume of oxygen consumed, it appears that the quantity of the former gas required to be absorbed by the caustic soda in the regenerator, in a 2-hr. period, is X 60) 240 liters, or 8.47 cu. ft.
The following table gives carefully compiled data and the results of actual tests regarding the oxygen consumed, carbon dioxide produced, quantity of air breathed and number of respirations per minute, under different conditions of rest and exertion. These data were compiled by James M. Stewart, Instructor at the Brazeau Rescue Station, Alberta, Canada.*
Data Regarding Aib Respired when Walking and at Rest
Condition of subject
Oxygen
consumed
per minute
in liters
COa
expired
per minute
in liters
Air
breathed
per minute
in liters
Average volume of each breath
Number of breaths per minute
At rest in bed
At rest, standing
Walking, 2 mi. per hr. Walking, 3 mi. per hr. Walking,. 4 mi. per hr. Walking, mi. per
hr
Walking, 5 mi. per hr.
BvHetirif November, 1916, Rocky Mountain Branch of the Canadian Mining Institute.
. Mine Rescue Work And Appliances 135
It is evident from the table that more than the standard supply of oxygen allowed in the design of breathing apparatus may be eonsmned by a person imder great physical exertion. Mr. Stewart suggests, therefore, that it is of the utmost importance that the captain of a rescue team observe carefully that his men do not overexert themselves while in the performance of their duties in the mine. He also suggests that, in the use of the nose-clip, greater comfort and security is obtained by inserting a cotton-wool plug in each nostril, before adjusting the clip.
Development of Breathing Apparatus. — 'The development of breathing apparatus, during the past few years, since the Government took up the work of improving mining conditions (1907) has been rapid. In the earlier types of apparatus, a helmet was employed to cover the head and oxygen was supplied through rubber tubes that connected the helmet with a gas cylinder or bag containing the gas. Owing to the danger of these connecting tubes being broken in the rough service to which they are subjected in the mine, the first attempt to improve the apparatus resulted in the adoption of a form that was self-contained, so as to eliminate, as far as practicable, the tube connections.
Mining practice quickly demonstrated that the substitution of a simple mouthpiece, and noseclip to close the nostrils, gave better service underground than the clumsy helmet, although the latter afforded more comfort in breathing and enabled the wearer to talk to his comrades with greater facility than when the mouthpiece was used and a noseclip closed the nostrils. However, these disadvantages were largely outweighed by the greater faciUty offered for work by this form of apparatus.
Design of Breathing Apparatus. — Breathing apparatus is designed to supply the wearer with a perfectly respirable air independent of the atmosphere in which he may be placed. The design of the apparatus is to enable the wearer to work in an irrespirable atmosphere for a limited period of two hours. The principal features of the device consist in maintaining a sufficient supply of oxygen to replace that consumed by the
136 Mine Gases And Ventilation
wearer of the apparatus, and absorbing the carbon dioxide he exhales.
Oxygen, compressed to 120 atmospheres, is contained in a strong steel cylinder. The quantity is sufficient to afford a supply of 2 liters of this gas (122 cu. in., normal temperature and pressure) per minute. A pressure of 120 atmospheres, at sea level, corresponds to about 1800 lb. per sq. in. A reducing valve is employed to control this pressure an( reduce it to the normal pressure of the atmosphere, for breathing. An air-tight breathing bag filled with pure air and equipped with a release valve, forms part of the apparatus and is connected directly with the oxygen supply cylinder and the helmet or mouthpiece.
Another important feature of breathing apparatus is the regenerator, holding a supply of 4 or 5 lb. of caustic soda or caustic potash. This minimum weight of caustic soda (4 lb.) will absorb, if fully utilized, 532 liters of carbon dioxide and is ample for all contingencies. By the absorption of the carbon dioxide, the caustic soda is converted into sodium carbonate and some water is produced according to the equation
2NaOH + CO2 NagCO, + H2O
The molecular weight of the caustic soda or sodium hydroxide is + 16 + 1) 80, while the molecular weight of the carbon dioxide is 12 2 X 16 44. The ratio of the weight of carbon dioxide absorbed to that of the caustic used is, therefore, — aiid the 4 lb. of caustic soda, if completely utilized, would absorb 2.2 lb., or 18.78 cu. ft. of carbon dioxide (532 liters), at normal temperature and pressure.
In the absorption of carbon dioxide, however, the caustic soda becomes encrusted with the sodium carbonate formed, which prevents or at least impedes the action of absorption. The shaking of the regenerator helps to break up this crust and restore the absorptive power of the caustic.
Testing Breathing Apparatus. — All breathing apparatus should be regularly tested to insure its perfect condition. Especially should this be done by the wearer before he enters an irrespirable atmosphere. The apparatus may be defective
Mine Rescue Work And Appliances 137
from any one of a number of such causes as negative pressure; leaks in joints, tubes, breathing bag or other container; obstructed valves or tubes, imperfect regeneration, owing to insufficient absorption of carbon dioxide or inadequate supply of oxygen; etc
Before putting on the apparatus, the wearer should examine and test its various parts to ascertain that it is tight, the valves and tubes free from obstruction and the supply of oxygen and caustic soda adequate. Each tube, the bag and the assembled apparatus should be tested for leaks, by means of the pressure gage and observing the constant water level in the U tube kept for that purpose. The old habit of immersing apparatus in water to show leakage is harmful.
Types Of Breathing Apparatus
The principal types of breathing apparatus now in use in this country are the Draeger breathing apparatus, the Fleuss Proto apparatus, the Paul type of apparatus and the more recent and highly improved Gibbs apparatus, which combines all of the best features of other types and many improvements.
Draeger Breathing Apparatus. — There are two general types of this apparatus, one employing the helmet and the other the nosecUp and mouthpiece. These two types are shown in Fig. 14 together with side and rear views of the apparatus as worn by the rescuer. Owing to its bulkiness the helmet type is not so well adapted to mine work as that equipped with the noseclip and mouthpiece.
Since its introduction in 1903 the Draeger apparatus has undergone various marked improvements and is at present one of the standard types of rescue appliances in. use. The canvas breathing bags, one for inhalation and the other for exhalation, are rubber-lined. The oxygen cylinder is supplied with a perfected high-pressure valve that enables the wearer to shut off the pressure at any moment desired, by a simple thumb pressure. These together with the safety locked couplings securing-all tube conne'ctions, and the time recorder and pressure gage, always ready for inspection by the wearer, insure both safety and comfort.
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Mine Rescue Work And Appliances 139
Essential Parts. — The diagram, Fig. 15, shows the arrangement of the several parts of the apparatus for the purpose of making clear their relation and the circulation of the system. The diagram shows the helmet H, the expiration valve Vs, th exhalation bag La, that receives the exhaled air, the regenerator R, the cooler K, the aspiration pipe C, the inhalation bag Li, holding the purified air and the inspiration valve Vi. The oxygen cylinder and pressure gage also appear, the former has withstood an official test of 225 atmospheres and is coin- ' monly chained to a pressure of 120 atmospheres.
Capacity of the Apparatus.- -This apparatus will purify about 3000 liters (105 cu. ft.) of air per hour, besides supplying 120 liters (4.2 cu. ft.) of oxygen, and absorb 50 liters (lcu.ft.) of carbon dioxide. This is claimed to enable the wearer of the apparatus to perform 260,000 ft.-lb. of work. While an untrained man will generally do less than this, the work done in one instance amounted to 398,000 ft, -lb.
Fleuss Proto Apparatus. — -This apparatus is designed to supply the user with a perfectly respirable air, entirely independent of any communication with the outside atmosphere
140 Mine Gases And Ventila Tion
for at least two hours at a time. It has been designed to withstand the severe conditions to which it must be subjected in mining use and insure the safety of the wearer while engaged in the dangerous work of rescuing men from mine workings filled with poisonous or irrespirable gases.
Front and rear views of the apparatus are sliown in the Fig. 16, in the position in which it is worn, the large, doublecompartment breathing bag being in front and the oxygen cylinder in the rear of the wearer. A diagrammatic view is shown on the opposite page (Fig, 17) explaining the various parts of the apparatus.
Essential Parts.— The principal feats are the oxyiren cylinder B; the reducing valve C; the breathing bag D with
Mine Rescue Work And Appliances 141
inhaling and exhaling divisions; inspiratory and expiratory valves T and S; mouthpiece and noaeelip R and Y.
The wearer exhales through valve S, the air passing down ene aide of the partition of the breathing bag and through the caustic soda, which absorbs the carbon dioxide, and thence up
the other side of the partition to valve T to be again inhaled, after mixing with fresh oxygen, which is being constantly delivered at the rate of two liters per minute from the oxygen cylinder through the reducing valve C. Connected to a flexible tube TT is a pressure gage P indicating the quantity of oxygen in the cylinders and the duration of supply. An
142 Mine Gases And Ventilation
emergency by-pass / is for use in case the reducing valve fails; it enables the wearer to fill his breathing bag direct from the oxygen cylinders. A saliva trap Z prevents the saliva from entering the breathing bag. .
The steel cylinder contains about 10 cu. ft. of oxygen, compressed to 120 atmospheres, which gives a two-hours' supply when the reducing valve is passing two liters per minute. The cylinder can be charged to 150 atmospheres if desired, which will give a hour-supply.
A reducing valve C is fitted to the bottle nipple and is so adjusted as to pass a regular supply of from 2 to 23-liters of oxygen per minute, no matter what the pressure may be in the cyUnder. This valve can be readily adjusted to deliver any flow from one to three liters per minute, as desired. The valve is fitted with a by-pass, having a small wheel valve I so that should it from any cause fail to act properly the wearer of the apparatus can supply himself with what oxygen he requires direct from the cylinder by turning the small valve. Also, by the same means, the automatic supply of two liters per minute can be increased at any time by the wearer if desirable. When working in an excessively hot atmosphere it is possible to cool the hot air by exhausting all the air from the bag through the reUef valve K, and then filling the bag with pure, cool oxygen from the cylinder, by means of this by-pass.
The reducing valve delivers the oxygen through the flexible tube F to the breathing bag D, carried on the wearer's chest. Another connection at F, made through a flexible high pressure tube W with a pressure gage P, carried in a pocket of the canvas cover, enables the wearer to ascertain the available supply and duration of oxygen. Each division of the pressure gage indicates 10 atmospheres of pressure, or 10 minutes of time, assuming the valve to be passing two liters per minute. The connection V is also fitted with a small valve, to enable the wearer to shut off the oxygen should the gage or its flexible tube become damaged.
The breathing bag D is of strong vulcanized India rubber and contained in an outer strong canvas bag. The rubber
Mine Rescue Work And Appliances 143
bag has two compartments, connected, however, at the bottom of the bag. The bag is fitted at the upper left-hand corner with a saliva trap Z and relief valve K to allow the escape of any excess oxygen that might be delivered by the reducing valve. At the upper right-hand corner is a small connection N for the oxygen supply from the cylinder. The mouth of the bag is closed with metal clamps and wing nuts 0.
The mouthpiece is of soft vulcanized India rubber, fitted to a German silver connection R and shaped to fit tjomf ortably between the lips and the . To the connecting piece R are also fitted strong flexible corrugated tubes XX y sometimes called " bellows tubes, " to the opposite ends of which are fitted the exhaling and inhaling valves S and T, respectively. These valves are of mica and extremely sensitive. They are screwed into their respective connections L and M, The noseclip Y is made to fit any nose comfortably. The skull cap has a back apron to which the mouthpiece can be securely buckled, which supports it comfortably.
One feature of the Fleuss Proto apparatus is the fact that the caustic soda is held in a bag instead of a rigid container and the movements of the wearer when walking or at work automatically rubs off the carbonated surface of the soda, and constantly exposes a fresh surface for the absorption of carbon dioxide. The bag is easily emptied after use, and a fresh supply of soda added at once, thus making the apparatus ready for use again in two or three minutes. The bag is so constructed that external pressure on it does not impede the wearer's breathing. In fact, a man may lie flat upon the bag and still be able to breathe freely.
Gibbs Breathing Apparatus. — This form of apparatus was developed by W. E. Gibbs, of the Federal Bureau of Mines, who sought to improve on the older types of English makes of breathing apparatus in mining use. '
The general requirements sought to be fulfilled in this design were: (1) Automatic control of oxygen supply in rest or exertion. (2) Adequate absorption of carbon dioxide. (3) Freedom of respiration under constant positive pressure. (4) Avoiding collapse of breathing bag from any cause. (5)
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Efficient heat radiation and cooling to avoid high temperature. Simplicity, durability and strength and tht joints m every part.
The position of the apparatus when in use is shown by the side and rear views in the Fig. 18. For the better protection of the parts from injury, in the mine, a cover is provided as a
Fig. 18.
shield. The general arrangement of the parta is shown by the Fig. 19 in which the several elements are numbered to correspond to their description in the text.
Circulation in the Apparatus.— -Oxygen from the bottle (1) in which it is compressed to 135 atmospheres, passes through the closing valve (2) to the reducing valve (3) ; thence, under normal pressure, by rubber tube connection, it passes through
MWR REfteUE WORK ANTi APPUANCES 145
a metal tube Burrounded by a cooler; through an admission valve into another metal tube inclosed in cooler, being then discharged into the exhalation side of the cooler where it meets the exhaled air and passes downward with it into the regenerator; then upward into the inhalation side of the cooler, where
Fia. 19.
it enters the breathing bag in the cooler. From the breathing bag the air passes through an inhalation valve and enters the lungs, from which it is discharged through the exhalation tube into the exhalation side of the cooler.
Testing Gibbs paratus. — The following series of tests of the Gibbs breathing apparatus are recommended by its manufacturers:
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1. Oxygen bottle should be charged to 135 atmospheres. The oxygen cylinder being tested under water for leaks, with main valve both open and closed. The cylinder is first tested with valve closed, then cap is placed on cylinder and tested with valve open. Connect oxygen bottle to reducing valve, using wrench in order to make tight connections.
2. Examine seals of regenerators in order to see that they are not broken. Connect regenerator to cooler, being sure that gaskets are in place between the connections. Screw down screws by hand and tighten with screw driver.
3. Hft breathing bag from bumper on admission valve, then turn on main oxygen valve.
Observe fnica inhalation valve — if admission valve leaks the mica inhalation valve will raise and let oxygen escape.
Turn pressure tube valve on and observe the number of atmospheres indicated by the pressure gage. Pressure gage valve should always be left open. Squeeze bellows of reducing valve in order to open seat over orifice; this approximately increases the pressure to five pounds in rubber tube and metal tube. Safety valve will whistle at the above pressure if working properly. Try all connections from oxygen bottle to cooler for leaks by using brush and soap suds. Turn off main oxygen valve.
4. Blow into exhalation valve and observe air returning by way of inhalation valve, showing circulation of air through exhalation side of cooler, regenerator, inhalation side of cooler, and breathing bag. Next, close inhalation valve either by cupping hand over valve or by special connection, then blow into exhalation valve until bag is fully inflated. Exlalation valve seat and mica should make an air tight connection, keeping bag fully inflated. Test all connections for leaks, using brush and soap suds.
5. Connect mouthpiece to cooler, seeing that gaskets are in place. Inflate breathing bag and test mouthpiece connections for leaks, using brush and soap suds. Try release valve and saliva pumps for leaks.
6. After apparatus has been tested and adjusted to wearer, before adjusting noseclip, it is essential that the wearer turn on main oxygen valve, inhale from apparatus, exhale into open air several times before readjusting the clip. In this way a high percentage of oxygen and a low percentage of nitrogen will be contained in breathing apparatus. While inhaling from the apparatus the wearer will observe whether the whole apparatus is functioning properly. After noseclip is adjusted, the wearer is ready for §, preliminary test in room filled with fumes. After remaining in room for five (5) minutes and no leaks being observed, the wearer can feel assured that his apparatus is in good working condition for doing wock in poisonous gases and irrespirable air.
7. Under no. circumstances should grease or oil be used on apparatus parts.
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The Paul Breathing Apparatus. — This type of apparatus was designed by James W. Paul, long in charge of the minerescue work, as engineer of the Federal Bureau of Mines, at Pittsburgh, Penn. The apparatus is manufactured by the old Draeger Company, now known as the American Atmos Corporation, Mr. Paul having disposed of his right and title in the apparatus to that company.
One of the highly essential improvements of the Paul apparatus, which is modeled chiefly after the Gibbs, is the combination of the self-adjusting oxygen-feed valve with a low-pressure oxygen-control valve, at the intake of the circulatory system. This device regulates the supply of oxygen and proportions it to the rate of consumption, which varies with the work performed by the wearer. Also, a pressure slightly in excess of 1 cm. of water column is automatically maintained in the system and minimizes the liability of an outside poisonous atmosphere penetrating within the apparatus.
Bureau Op Mines
The Federal Bureau of Mines recommends that the circulation in breathing apparatus be under positive pressure throughout and that the apparatus be equipped with mouthpiece and noseclip and provided with a by-pass valve. The helmet, for mining use, is objectionable and dangerous, not only because of the diflSculty of obtaining a perfectly airtight joint around the face, but also because it is easily dislodged and greatly cuts down the range of vision. Also, the large dead-air space in the helinet permits an excessive accumulation of carbon dioxide.
The injector used in some types of breathing apparatus is compUcated and Uable to be out of order when needed. Any slight particle is sufficient to choke the orifice and cut off the supply of oxygen. The use of the injector also involves a negative pressure, which would cause an inflow of the surrounding atmosphere into the apparatus should there be any leak in the joints or tube connections.
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Permissible Breathing Apparatus. — Owing to the grave importance of securing safe types of mining appliances manufactured in this country, an act of Congress (37 Stat., 681), approved Feb. 25, 1913, authorized the director of the Bureau of Mines to prescribe rules and regulations for testing such appliances as may be submittedto the bureau for that purpose.
Acting under this authority the Federal Bureau of Mines has prepared and published. Mar. 5, 1919, "Schedule 13," defining the requirements necessary to establish a list of socalled "Permissible'* self-contained, mine-rescue, breathing apparatus. Following are the more important specifications contained in that schedule.
Definition. — The Bureau of Mines considers a self-contained minerescue breathing apparatus to be permissible for use in irrespirable and poisonous gases if all the details of construction and materials are the same in all respects as those of the self-contained mine-rescue breathing apparatus that met the requirements and passed the tests for safety, practicability and efficiency made by the bureau and hereinafter described.
Conditions of Testing. — The conditions under which the Bureau of Mines will examine and test self-contained mine-rescue breathing apparatus to establish their permissibility are as follows:
1. The examination, inspection, and test shall be made at the experiment station of the Bureau of Mines at Pittsburgh, Pa.
2. Applications for inspection, examination, and test shall be made to the Director, Bureau of Mines, Washington, D. C, and shall be accompanied by a complete written description of the self-contained mine-rescue breathing apparatus including the regenerator, and a set of drawings showing full details of construction of both the regenerator and the apparatus.
3. The appUcant submitting the self-contained mine-rescue breathing apparatus for inspection, examination, and test will be required to furnish the apparatus in duplicate, which shall be sent prepaid to the minesafety engineer, Bureau of Mines, 4800 Forbes Street, Pittsburgh, Penn. In the event of the apparatus successfully passing all of the Bureau of Mines tests and requirements hereinafter specified, one set will be retained by the Bureau of Mines as a laboratory exhibit and the other set will be returned to the owner. In the event that an apparatus does not pass all of the bureau's tests or requirements, both sets will be returned to the owner.
4. Each self-contained mine-rescue breathing apparatus shall have marked on it in a distinct manner the name of the manufacturer and the name, letter, or number by which the type is designated for trade pur-
Mine Rescue Work And Appliances 149
y
poseS) and a written statement shall be made whether or not the apparatus is ready to be marketed.
5. The applicant will supply the regenerators or regenerating material for the test. For tests of self-contained mine-rescue, oxygen breathing apparatus dependent on a supply of compressed gaseous oxygen the oxygen will be supplied by the Bureau of Mines and will be of the purity specified by the bureau in contracts for the supply of its safety cars and stations; namely, 98 or more per cent, oxygen and not more than 0.2 of 1 per cent, hydrogen; other impurity to consist of nitrogen only.
6. Upon receipt of the self-contained mine-rescue breathing apparatus for which application has been made for examination, inspection, or test, the mine-safety engineer in charge of breathing-apparatus testing will advise the applicant whether additional spare parts are deemed necessary to facilitate a proper test of the apparatus, and the applicant will be required to furnish such parts as may be necessary.
7. No self-contained mine-rescue breathing apparatus will be tested unless the type submitted is in the complete form in which it is to be placed on the market.
8. Only the Bureau of Mines mine-safety engineer in charge of breathing-apparatus testing, his assistants and one representative of the applicant will be permitted to be present during the conduct of the tests.
9. The conduct of the tests shall be entirely under the direction of the bureau's mine-safety engineer in charge of the testing.
10. As soon as possible after the receipt of the formal application for test, the applicant will be notified of the date on which the test of his .self-contained mine-rescue breathing apparatus will begin and the amount and character of the additional material, if any, it will be necessary for him to submit.
11. The tests will be made in the order of the receipt of the applications for test, provided the necessary apparatus and material are submitted at the proper time.
12. The details of the results of the tests shall be regarded as confidential by all present at the tests, and shall not be made public in any way prior to their official announcement by the Bureau of Mines.
13. The results of tests of the breathing apparatus that fail to pass the requirements shall not be made public but shall be kept confidential, except that the person submitting the apparatus will be informed with a view to possible remedy of defects in future mine-rescue breathing apparatus submitted, but such changes will not be permitted while testing is in progress.
14. Tests will be made for manufacturers or accredited manufacturers' agents and for inventors.
15. A list of permissible self-contained mine-rescue breathing apparatus and the results of their tests will be made public, from time to time, by the Bureau of Mines.
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Character of Tests. — After the self-contained mine-rescue breathing apparatus under test for permissibility has been thoroughly inspected for mechanical principles, a series of fifteen (15) working tests, each of two (2) hours' duration, will be made. At the beginning of the series of tests, if an oxygen bottle is used on thiB apparatus it shall be first charged with oxygen to a pressure of 10 atmospheres and the oxygen permitted to escape into the air. The bottle used in the tests shall be charged for the teats at a pressure prescribed by the manufacturer of the apparatus and shall be fully charged at the beginning of each test. At the beginning of each test the breathing bag or bags shall be deflated to expel any nitrogen contained within.
A single test must be continuous, without removal of the apparatus from the wearer during the test.
Samples of air will be obtained from the apparatus on the inhalation side of the circulatory system and as near to the mouthpiece or the face attachment as possible. The first sample will be taken from the oxygen bottle to be used and just prior to the beginning of the test. The second sample will be taken immediately after the apparatus has been adjusted to the wearer and oxygen has been turned on. Samples will be taken every half-hour thereafter during the test. The physiological effects of the apparatus on the wearer will be noted in each test.
Not more than one test of 2 hours' duration will be made on any one day. The tests will be completed within 60 days from date of beginning, unless prevented by conditions arising which are beyond the control of the mine-safety engineer in charge of the tests.
All tests of apparatus will be conducted in a specially equipped gallery ed with an irrespirable atmosphere, at the Pittsburgh experiment station of the Bureau of Mines.
Before beginning each test the apparatus shall be examined and tested to insure that there is no air leakage under working conditions.
Specifications By The Bureau Of Mines
In order to receive the approval of the Bureau of Mines, self-contained mine-rescue breathing apparatus must pass satisfactorily each of the 15 tests required by the bureau and meet the following requirements:
1. The amount of oxygen supplied, by the apparatus must meet the needs of the wearer at all times during the tests.
2. The regenerating material shall absorb, from the expired air, carbon dioxide to the extent that not more than 2) per cent, shall at any time be present in the inspired air. The average shall not exceed 1 per cent, for any of the two-hour periods of test. This average is to be determined by the analyses of air samples taken as near the point of inspira tion as practicable and at uniform intervals of time.
3. The apparatus shall be free from mechanical obstructions in order that the wearer may breathe freely at all times.
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4. The temperature of the inspired air must not exceed a maximum of 110 deg. F. when that of the external air does not exceed 85 deg. F. A much lower temperature than 110 deg. F. for the inspired air is desirable. Temperature readings will be taken at regular intervals.
5. The apparatus shall be sufficiently rugged in construction and all vital parts so protected as to prevent material damage or wear to the apparatus during the period of tests to which it will be subjected.
Construction
1. The apparatus shall be designed to meet the needs of the wearer for not less than a period of two hours when worn in irrespiable air without recharging. The apparatus shall be of a design using a mouthbreathing device or other face attachment that when properly adjusted to the face of the wearer, has a capacity of not more than 250 c.c. of dead space inside the. face attachment or mouth-breathing device, exclusive of tubes or connections thereto.
Preferably the apparatus shall not weigh more than 36 pounds complete with headpiece and fully charged, and no apparatus weighing more than 40 pounds, complete with headpiece and fully charged, will be accepted for final test.
2. The mechanical construction of the apparatus shall be such that every part can be tested, inspected and repaired by persons skilled in such work, and all parts which require sterilizing shall be readily accessible for this purpose.
3. All parts of the apparatus subject to or liable! to be subjected to pressures in excess of 5 pounds per square inch shall be of such construction or equipped with such safety devices as shall insure the safety of the wearer, as determined by the 15 tests.
4. In apparatus equipped with breathing bag or bags, or their equivalent, the inhalation and exhalation compartments shall have a com bined capacity of at least 8 liters. If a single breathing bag is used it shall have a capacity of at least 5 liters.
5. The apparatus shall not have in its circulating system any zone of constant negative pressure.
6. The apparatus shall be provided with a release valve, operated by hand or automatically, placed at some point in the circulatory system of the apparatus. The function of this valve shall be to permit the escape to the outside air of a part of the air in the circulatory system of the machine.
7. Where apparatus is equipped with high-pressure oxygen cylinders, such cylinders shall be tested in accordance with the Interstate Commerce Commission specifications No. 3-A. Such tests shall be made prior to submitting the apparatus to the Bureau of Mines for test and the applicant submitting the apparatus shall furnish the necessary certificate of test as issued by th Interstate Commerce Commission or submit evi-
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deuce satisfactory to the bureau's mine-safety engineer in charge of the' testing of the apparatus, that such oxygen cylinders have been tested in accordance with Interstate Commerce Commission specifications No. S-A,
8. Where apparatus is equipped with high-pressure oxygen cylinders the safety cap attached to the closing valve shall, in addition to the usual copper disk provided, be filled with a metal (such as Roses metal) fusing at a temperature of approximately 94 deg. C. Such fusible metal shall not extrude from the safety cap under a pressure of 150 atmospheres.
9. The closing valve of such oxygen cylinders shall be provided with the necessary device to prevent the wearer of the apparatus from screwing the stem entirely out of the valve. The closing valve shall also be provided with such a device as will enable the wearer to lock the valve stem when the valve has been opened to the desired point.
10. When apparatus is equipped with gages for recording time or pressures of oxygen supply, such gages will be tested for accuracy of calibration by the Bureau of Mines. A toleration -of three atmospheres will be allowed in comparison with the Bureau of Mines standard pressure gage.
11. The apparatus shall be supplied with a valve that will cut off the oxygen supply from the gage; this valve shall be so placed that it can be readily manipulated by the wearer and at the same time not interfere with the flow of oxygen from the oxygen container to the circulatory system of the apparatus.
12. The gage shall be placed on the apparatus at such a point that it can easily be read by the wearer.
13. Apparatus equipped with a reducing valve giving a constant flow of oxygen shall be provided with a by-pass valve which will permit a free flow of oxygen from the oxygen container to the circulatory system of the apparatus independent of the reducing valve.
14. When the oxygen supply of the apparatus is contrpUed by automatic devices, such devices shall readily adjust themselves to the needs of the wearer.
15. When an apparatus is equipped with mouth-breathing device, such apparatus shall be provided with an adequate saliva trap. The adequacy of the saliva trap will be determined by the tests to which the apparatus will be subjected.
16. When an apparatus is equipped with mouth-breathing attachment, a suitable noseclip shall be provided and properly attached to the apparatus. The suitability of the nose clip will be determined by the tests to which the apparatus will be subjected.
The apparatus under test will be worn during each and all of the 2-hour periods of the 15 tests by the Bureau of Mines safety engineer in charge of the testing or by one or more of his assistants. Immediately before participation in any or all of these tests the prospective wearer of the apparatus under test shall pass, in a satisfactory manner, physical examination by a qualified physician. If it is impossible to carry any
Mine Rescue Work And Appliances 153
one of these tests to completion solely on account of the physical condition of the wearer, where such condition has been brought about through no fault of the apparatus under test, such test shall be disregarded and the apparatus under test shall not be penalized or disqualified thereby.
At the conclusion of each test a note shall be made of the general physical condition of the apparatus and the amount of oxygen, if any, remaining in the container. The schedule of work to be performed by the wearer of the apparatus in each one of the 15 working tests is as follows:
Detail of Procedure in Tests. — Following is an outline of the manner of proceeding in the making of each successive test of breathing apparatus submitted to the bureau.
Test 1. — The wearer of the apparatus shall walk continuously, except for time necessary to take air samples and temperature readings, over a level measured course at the rate of miles per hour. At the end of each 30-minute period, 2 minutes shall be allowed for taking air samples and temperature readings.
Testa 2, 3, and 4 will be repetitions of Test 1.
Test 5. — In Test 5 the wearer of the apparatus shall —
(a) Walk over a level measured course at a rate of 3 miles per hour for a period of 10 minutes.
(b) Carry a sack of bricks weighing 50 pounds over an overcast ten times, making one complete trip in 2 minutes.
(c) Allow two minutes for taking of air samples and temperature readings.
(d) Walk at the rate of 3 miles per hour over a level measured course for a period of 10 minutes.
(e) Carry a 45-pound weight a distance of 1000 feet, consuming 5 minutes while doing this work.
(J) Raise a 45-pound weight through a vertical distance of 5 feet 75 times, consuming 5 minutes while doing this work.
(g) Saw wood for a period of 10 minutes.
(h) Allow two minutes for taking of air samples and temperature readings.
(t) Carry a sack of bricks weighing 50 pounds over an overcast 10 times, making one complete trip in 2 minutes.
0) Walk at the rate of 3 miles per hour over a level measured course until the end of the 2 hours allowed for this test, air and temperature readings to be taken in 2-minute periods at IK and 2 hours after stai of test.
Tests 6, 7, and 8 will be repetitions of Test 5.
Test 9. — In Test 9 the wearer of the apparatus shall —
(a) Walk at the rate of 3 miles per hour over a level measured course for a period of 10 minutes.
154 Mine Gases And Ventila Tion
(h) Crawl for a distance of 100 feet, consuming 5 minutes while doing this work.
(c) Lie down on side for 5 minutes.
(d) lie down on back for 5 minutes.
(e) Allow 2 minutes for taking of air samples and temperature readings. (/) Walk at the rate of 3 miles per hour over a level measured course
for a period of 10 minutes.
(g) Run 600 feet at a rate of 6 to 8 miles per hour over a level measured course, consuming 2 minutes while doing this work.
(A) Walk 1000 feet over a level measured course at the rate of approximately 3 miles per hour, consuming 4 minutes while doing this work.
(t) Walk at the rate of 3 miles per hour over a level measured course until end of the 2 hours allowed for this test. Air and temperature readings to be taken in 2-minute periods at one hour, hours and two hours after the beginning of the test.
T-este 10 and 11 will be repetitions of Test 9.
Test 12. — In Test 12 the wearer of the apparatus shall —
(a) Walk 1000 feet at the rate of approximately 3 miles per hour over a level measured course, consuming 4 minutes while doing this work.
(b) Run 600 feet at a rate of 6 to 8 miles per hour over a level measured course, consuming 2 minutes while doing this work.
(c) Walk 1000 feet at the rate of 3 miles per hour over a level measured course, consuming 4 minutes while doing this work.
(d) Raise a 46-pound weight 75 times through a vertical distance of 5 feet, consuming 5 minutes while doing this work.
(c) Carry a 45-pound weight over a level measured course 1000 feet, consuming 5 minutes while doing this work.
(J) Carry a sack of bricks weighing 50 pounds over an overcast 5 times, making one complete trip in 2 minutes.
(g) Allow 2 minutes for taking of air samples and temperature readings.
(h) Raise a 45-pound weight 75 times through a vertical distance of 5 feet, consuming 5 minutes while doing this work.
(i) Walk over a measured course at rate of 3 'miles per hour for a period of 10 minutes.
(j) Carry a sack of bricks weighing 50 pounds over an overcast 10 times, making one complete trip in IJ minutes.
(k) Allow i minutes for taking of air samples and temperature readings.
(0 Walk 1000 feet at rate of approximately 3 miles per hour over a level measured course, consuming 4 minutes while doing this work.
{m) Raise a 45-pound weight 75 times through a vertical distance of 5 feet consuming 5 minutes while doing this work.
(n) Walk at the rate of 3 miles per hour over a level measured course imtil the end of the two hours allowed for this test. Air and temperature readings are to be taken in 2-minute periods at IH 2 hours after the start of the test.
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Tests 13 and 14 will be repetitions of Test 12.
Test 15. — This test will be made to determine the maximum length of time that the apparatus will supply the needs of the wearer when in a quiescent state. The wearer will remain as far as possible in a sitting posture throughout the test and perform no work. He will be allowed to manipulate the devices controlling the oxygen supply with a view to conserving such oxygen supply to the greatest advantage.
At the end of each 30-minute period, 2 minutes shall be allowed for taking of air samples and temperature readings.
Note. — Self-contained mine-rescue breathing apparatus in course of development may be submitted by manufacturers and inventors for preliminary test or inspection with the view of ascertaining defective construction or the misapplication of safety principles. The nature of such tests or inspection will be determined by the bureau's mine-safety engineer in charge of the testing of such apparatus.
Approval of Apparatus. — The manufacturers of such types of selfcontained mine-rescue breathing apparatus as have passed the tests of the bureau will be required to attach to each apparatus a plate containing the following inscription:
Permissible Mine-Rescue Breathing Apparatus, U. S. Bureau of Mines Approval No. .
The use of the plate will not be required if the same inscription is stamped or cast into the metal of the apparatus.
. Manufacturers shall, before claiming the bureau's approval for any modification of a permissible self-contained mine-rescue breathing apparatus, submit to the Bureau drawings or parts that shall show the extent and nature of such modifications, in order that the bureau may decide whether test of the remodeled apparatus will be necessary for approval. If it is decided by th bureau that testing of the remodeled apparatus is necessary, the word "permissible" shall not be used on the remodelled apparatus until it has again passed the complete schedule of tests or such part of these tests as the bureau's engineer in charge of the tests shall deem necessary.
The bureau will, on application, make separate tests, identical with the foregoing tests, of regenerators manufactured for use in connection with any mine-rescue breathing apparatus that has been approved by the bureau under the provisions of this schedule.
Regenerators that fulfill the requirements of the foregoing tests will be approved for use only in connection with that particular type of apparatus for which they are designed and which has previously received the bureau's approval.
156 Mine Gases And Ventila Tion
The listing by the Bureau of Mines, as "permissible/* any self-contained mine-rescue breathing apparatus shall be construed as applying only to apparatus of that specific type, class, form and rating, made by the same manufacturer, which have the same construction in all detaik directly or indirectly affecting the safety features of the apparatus.
The bureau reserves the right to rescind for cause, at any time, any approval granted under the conditions herein set forth. Cause for rescinding of approval shall be considered to be the use of the bureau's issuance of approval in an unauthorized manner; that is, placing the approval stamp on apparatus that has not been approved by the bureau, or on apparatus certain parts of which have been altered in construction or material without submittal to the bureau for test.
Notificatioii to Bfanufacturer. — As soon as the mine-safety engineer of the Bureau of Mines is satisfied that a self-contained mine-rescue breathing apparatus has passed all the tests herein set forth in a satisfactory manner, the manufacturer or inventor shall be formally notified to that effect.
When two or more applications for tests on different apparatus are received within a period of 10 days, the announcement of approval for each shall not exceed the interval of time between the receipt of the applications.
When a manufacturer or inventor receives this formal notification he shall be free to advertise this type of successfully tested self-contained mine-rescue breathing apparatus as permissible according to the Bureau of Mines standards and may attach approval plates to this type of breathing apparatus.
Fees for Testing. — Careful investigation has been made regarding the necessary expenses involved in testing mine-rescue breathing apparatus, at the Rttsburgh experiment station of the bureau. The following schedule of fees to cover expenses to be charged on and after March 5, 1919 has been established and approved by the Secretary of the Interior, in accordance with the provisions of the statute previously quoted,
Complete mine-rescue breathing apparatus test SlOO
Separate preliminary inspection and test $10
Separate regenerator test $5
Separate inspection and test of reducing valves $10
The fees specified above may be increased to cover the cost of testing an unusually complicated type of mine-rescue breathing apparatus, and are also subject to change upon the recommendation of the Director of the Bureau of Mines and the approval of the Secretary of the Interior.
Application for Test of Apparatus. — 1. Application for tests should be addressed to the director of the Bureau of Mines, Washington, D. C. This application must be accompanied by check or draft made payable to the Secretary of the Interior, and by a complete written description of the mine-rescue breathing apparatus to be tested, and a set of the drawings
Mine Rescue Work And Appliances 157
as specified in the Conditions of Testing, page 148, and marked " Drawings of Approved Mine-Rescue Breathing Apparatus to be Filed." Duplicate copies of the application and drawings should be sent to the mine-safety engineer, Bureau of Mines, Pittsburgh, Penn.
2. As soon as the application is received by the bureau's mine-safety engineer, the applicant will be notified of the date the tests will begin.
3. After the applicant has received this notification, he should send the material required to the minensafety engineer, Bureau of Mines, Pittsburgh, Penn. This material should be delivered not less than one week in advance of the date set for the beginning of the tests.
4. The tests will be begun on the date set and continued until the minerescue breathing apparatus has been approved, rejected or withdrawn.
6. After the bureau's mine-safety engineer has considered the results of the tests, a formal report of the approval of the self-contained minerescue breathing apparatus will be made to the applicant, in writing, by the director of the Bureau of Mines. No verbal report will be made, and the details of the test will be regarded as confidential by all present. Approved March 5, 1919.
.S. G. Hopkins, Van H. Manning,
Assistant Secretary. Director,
First-Aid Work
Practical Use of Breathing Apparatus. — It is of the greatest importance that all breathing apparatus should be carefully examined and tested before the wearer proceeds to enter an irrespirable atmosphere. First, it is necessary to observe the gage or meter to see that the proper supply of oxygen is contained in the oxygen cyUnder. Observe also that the required quantity of oxygen (2 liters) is being deUvered each minute, as indicated by a registering meter. The breathing bag must be carefully tested and all valves examined to see that they are in good working condition and to ascertain that the breathing bag contains no airleaks.
In use, always inflate the bag with pure air when ready to put on the apparatus and before turning on the supply of oxygen. It is well for the wearer, then, to take the precaution of going into a smoke chamber, for a short period before entering the mine. This will enable him to ascertain that there are no leaks in the apparatus and that breathing is normal.
Resuscitation. — To resuscitate is to revive, or to restore animation in an unconscious person or one who is seemingly
1 58 Mine Gases And V En Til A Tion
dead. A person may be apparently lifeless as the result of any one of several causes; (1) Fainting from overexertion. 2. The result of a nervous shock. 3. An electric shock, received by contact with a live wire. 4. Suffocation, by reason of inhaling irrespirable gases, or the lungs being filled with water, as in drowning. 5. A blow on the head. In fact, unconscious ness may result from any accidental occurrence affecting directly or indirectly the nervous system on which respiration and animation depends.
In the work of resuscitation, due regard must always be had to the cause of suspended animation. Where the lungs have filled with water, as in drowning, or with gas inhaled in the mine or elsewhere, immediate steps must be taken to driv the water or gas from the lungs and permit the entry of fresh air through artificial respiration applied vigorously and continued till the person revives, or it is absolutely certain that life is extinct. If the trouble arises from the inhalation of ga!s, the victim must be removed promptly to fresh air before treatment is administered, loosen the clothing about the neck and chest and give artificial respiration, at the same time chafing the limbs, rubbing them toward the body to assist the flow of the venous blood back to the heart.
Smelling salts applied to the nostrils assist to quicken animation. As soon as the victim is able to swallow and on the first signs of returning life, give a stimulant, hot coffee or tea, or half a teaspoonful of aromatic spirits of ammonia in a half-glass of water, administered in small doses at slight intervals. Where shock has resulted from injury and loss of blood, however, stimulants should not be given, as these will assist the action of the heart and increase the flow of blood from the wound. In all other cases, return of animation will be assisted by any means that will assist the circulation of blood and revive the respiratory system. Keep the patient warm with blankets and give plenty of fresh air during treatment for resuscitation.
Artificial Respiration. — -There are two general methods of applying artificial respiration. In the Sylvester method, which is now little used, the patient is laid on his back, while
Mine Rescue Work And Appliances 159
the Operator kneeling at his head grasps the wrists of both arms and proceeds to alternately swing the arms, first forward on the chest and then back to a poeition above the head, at the normal rate of breathing or, say 10 times a minute. In the forward movement, the arms are doubled at the elbow and pressed down firmly against the sides of the chest so as to compress the lungs and force out the gas therefrom. This is followed by the backward movement, which has the effect of expanding the lungs and inducing inhalation. These movements are continued alternately, first compressing the lungs and then expanding them in turn. While doing this, it is
important to secure the tongue and hold it forward in the mouth so that it will not impede the access of air to the lungs. A handkerchief covering the fingers will help to hold the tongue forward, or a clip must be used for that piu-pose.
The common method of resuscitation now most generally employed is that known as the "Schaefer method," or the "prone method" of resuscitation. By this method, the patient b laid prone on his face, except that the head is turned to one side to facilitate breathing. The operator, having made sure that the tongue is drawn forward in the mouth so as to give free access of air to the lungs, straddles the patient's thigh, as shown in Fig. 20, and rests the -palms of his hands
160 Mine Gases And Ventilation
on the person's loins with the two thumbs together and the fingers reaching well down on each side, in a manner to bring pressure on the short ribs and across the small of the back.
In this position, the operator first swings forward so as to throw his weight on the patient's body compressing the lungs to drive out the gas or water they contain. Then, swinging backward, he gives opportunity for the expansion of the lungs, which induces the inhalation of fresh air. As in the Sylvester method, this forward and backward movement must be continued alternately, for a period of an hour or two, until there are signs of returning life or it is absolutely necessary that life is extinct. There are instances on record where the victim has been revived after several hours of hard work. It is often necessary for the operator to be relieved for a time by another, but the process must be continued without cessation, until a doctor gives it as his opinion that life has fled. In every case, send for a doctor while giving first-aid to the patient.
Section Vi
Theory Of Ventilation
Mine Ventilation — Problems — Flow of Air in Airways — Ventilating Pressure How Produced and Measured, The Water Gage — Velocity of air Currents — Quantity of Air, Requirements — Work or Power ON THE Air — Equivalents in Measurement — Examples FOR Practice — Mine Airways — Symbols and Formulas — Mine Potential Methods — Measurement op Air Currents — Examples for Practice — Tandem Circulations — Splitting the Air Current — Natural Division of Air — Examples in Natural Division — Proportionate Division of Air, Regulators — Secondary Splitting — Theoretical Considerations in Splitting — Practical Problem
Mine Ventilation
The ventilation of a mine, as the term implies, involves the supply and maintenance of a sufficient current of air throughout the mine to render the same healthful and safe.
Requirements of Ventilation. — The quantity of air in circulation must be sufficient to comply with the state mining law, and to dilute, render harmless and sweep away the gases that would otherwise accumulate in the mine. The air current must be conducted so as to sweep the entire working face and all void places with a moderate velocity sufficient to remove the gas without danger from the lamps or inconvenience to the workmen.
The Circulating System. — In order to circulate a current of air through a mine, it is necessary to provide two separate openings, one for the air to enter, called the "intake opening," and the other for it to leave the mine, called the "return" or "discharge opening.". Two distinct air passages or airways are also required, leading from these openings into the mine, in order to conduct the air current to and from the working n 161
Mine Gases And Ventilation
face. These are called, respectively, the intake'' and return '' airways. These openings and airways form a part of the circulating system in the mine, similar to the arteries and veins of the human body.
Ednds of Ventilation. — There are three different kinds of ventilation-, in mining practice, known as "natural ventilation," "furnace ventilation'* and mechanical or "fan ventilation," according to the agency employed for its production.
Natural Ventilation. — Ventilation is natural when it is produced by any natural agency, such as surface winds, falling water or the natural heat of the mine. The accompanying Fig. 21 illustrates the manner in. which the natural heat of the mine produces a warm upcast air column, in either a drift mine or a shaft mine. , .
Surface
s
Fig. 21.
'v////Enir://ML
In the drift mine shown on the left, the warmer air column in the shaft only partly balances the cooler outside air. Above the level of the top of the shaft the two air columns are of equal temperature and equal weight, and, therefore, need not be considered since they balance each other. The same is true in the shaft mine shown on the right, whenever the two shafts have the same elevation at the surface.
Natural Ventilation in Slope Mines and Dip Workings. — A similar condition in respect to the natural heat of the mine producing or modifying the circulation of the air, holds in all slope mines and dip workings, the same as in shafts and drifts. Whenever the mine temperature is much below or above that of the outside atmosphere, the difference in temperature makes the retiun air heavier or lighter than the
Theory Of Ventilation 163
intake air; and the difference in weight of these two air columns destroys the equilibrium of the mine air and creates a current in the airways throughout the mine.
A considerable difference of temperature is often observed between the dip and rise air currents in particular sections of a mine. It is this difference in the temperatures of the intake and return currents that often makes dip workings harder to ventilate in summer than in winter. For the same reason, rise workings are frequently found to be more easily ventilated in the summer season.
Air Columns. — The term *'air column/' like water column, always refers to a vertical column. The air column, in ventilation, is an imaginary vertical column of air, of unit section (commonly, 1 sq. ft.) and of such height that its weight, in pounds, is equal to the pressure it measures (lb. per sq. ft.). The density of the air wt. per cu. ft.) is either stated or understood, so that when the height of air column is given the pressure it indicates is readily calculated.
In mining practice, it is common to express ventilating pressure in feet of air column or, as we say, "head of air." Calling the weight of 1 cu. ft. of air w (lb.) and the head of air column h (ft.), the pressure p (lb. per sq. ft.) is calculated by the formula
p wh
Or the air column corresponding to any given pressure is found by transposing this formula; thus,
w
Example. — What is the head of air column corresponding to a ventilating pressure of 10 lb. per sq. ft., assuming a temperature of 60 deg. F. and a barometric pressure of 30 in.?
Solution. — The weight of 1 cu. ft. of air, at the given temperature and
pressure is
The required head of air is then
164 iklNE GASES AND VENTILATION
Example. — Find the ventilating pressure and water gage corresponding to 80 ft. of air column, At the same density. Solution. —
p it;A 0.0766 X 80 6.128 W. per sq. ft. w.g. 6.128 5.2 1.18 in., nearly
Furnace Ventilation. — When the circulation of air throughout a mine is created and maintained by means of a furnace built in the mine the system is known as "Furnace ventilation."
Principle of Furnace Ventilation. — The heat of the furnace imparted to the air in the furnace shaft makes it lighter, volume for volume, which causes it to rise in obedience to the law of the equilibrium of fluids. The cooler and heavier outside air, in obedience to the same law, flows into the mine by way of another opening, to take the place of the air displaced. The action is continuous as long as the furnace is in operation. There is thus created and maintained a constant flow of air into and through the mine.
Location of a Mine Furnace. — The furnace is built in the main-return airway about 20 or 25 yd. back from the foot of the upcast or furnace shaft, so as to reduce the danger of the fire damaging or destroying the shaft.
Construction of Furnace. — The essential details to be considered in the construction of an efficient mine furnace are the following:
1. Beginning, say 50 yd. back from the foot of the shaft, the main-return airway should be gradually widened and its height increased so that the unobstructed sectional area at the furnace will not be less tian 25 per cent, greater than that of the original airway.
2. The roof of the enlarged airway should then be secured by steel rails or I beams supported on posts or concrete walls, as illustrated in Jig. 22, which represents a well built mine furnace.
3. As shown in the figure, both the concrete walls and the brick walls supporting the arch are started on a good firm bottom below the floor line. The thickness of the concrete walls will vary from 10 or 12 in. to 2 ft., depending on depth
THEORY OF VENTILATION lfi5
of cover and other roof conditions. The brick walls and arch will vary in thickness from 8 to 12 in. A good quality of vitrified brick should be used, except where the arch and walls are exposed to the direct action of the flame they should be lined with the best firebrick. All bricks should be first soaked in water before being laid and only the best cement mortar should be used.
4. The brick walls and arch should be started about 2 yd. in front of the furnace proper and extended to the face of the shaft. The clear width between the walls should equal the width of the fire-grate, and should be such as to leave a clear passageway between the brick and concrete waDs.
N Center Line
The arch is semicircular and sprung at such a height above the floor as to leave not less than 12 in. of space between the crown of the arch and the rails that support the roof. The purpose of this air space around the furnace is to isolate the heat, which is thus more completely utilized in heating the air current.
5. The area of the grate or the grate surface must be sufficient to burn the weight of coal per hour required to heat the volume of air passing the furnace in that time, to a temperature that will create the air column, in a given depth and condition of shaft, necessary to circulate such volume of air against a specified mine potential.
The theoretical problem of detennining the weight of ccial burned per hour, per volume of air circulated, is thus seen to depend on many factors. In ordinary mining practice, however, a safe estimate is to assume that each pound of coal burned per hour will cause a rise in temperature of from 10
1 66 Mine Gases And V En Til A Tion
to 15 deg. F., per 1000 cu. ft. of air in circulation. Or, calling the weight of coal burned W (lb. per hr.) ; the volume of air passing Qm, (1000 cu. ft. per min.); the rise in temperature t (deg. F.), and the temperature constant c 10 to 15 deg. F.,
Examikle. — Find the weight of coal required per hour, to produce a rise of temperature of 360 deg. F., in a furnace shaft when a current of 100,000 cu. ft. of air per minute is passing, under fair mining conditions.
Solution. — The weight of coal required is
In very deep or wet shafts or a comparatively small mine resistance, giving a larger air volume and greater loss of heat, the constant 10 deg. should be used; while in dry shafts of less depth, especially if the mine resistance is considerable, a temperature constant of 15 or even 16 may be employed to find the necessary weight of coal.
6. The grate area necessary to burn any required weight of coal W (lb. per hr.) varies with the hardness and the inflammability of the coal. A mine furnace will commonly burn from 15 to 20 lb. of anthracite, or from 20 to 25 lb. of bituminous coal, per square foot of grate, per hour. Hence the weight of coal required, divided by such constant will give the necessary area of grate surface, in square feet.
Example. — What grate area will be required to burn, say 3000 lb. of a very soft, inflammable coal per hour?
Solution. — In this case, the coal being a free-burning, inflammable coal, the constant 25 should be used; and the required area is 3000 25 120 sq.ft.
Estimation of Air Columns in Practice. — In the ventilation of shaft or slope mines or rise and dip workings in inclined seams, the weight of each respective downcast and upcast column is sometimes calculated separately, by multiplying the weight of 1 cu. ft. of air, at a barometric pressure B and a temperature t equal to the average temperature of
Theory Of Ventilation 167
the column, by the height or depth D of the same column, as expressed by the formula
All air columns are of unit crose-section (1 sq. ft.) and the calculated weight of the column, therefore, gives tlie corresponding pressure in pounds per square foot.
Positiye and Negative Air Ctdumns.— An air column that acts to assist the circulation in the mine or airway is called a "positive" column; while one that acts to oppose the circulation is termed a "negative" column. In fan ventilation, a negative air column may exist in the downcast shaft by reason of its temperature being greater than that of the upcast, which frequently happens in the summer reason.
Conditions. — The heht or depth of air colunm, in any particular case, can only be determined by carefully considering the conditions. It is important to remember that, with few exceptions, the temperature of a downcast-shaft column will closely approximate that of the outer air with which this shaft is constantly filled; while the temperature of the upcast column is practically determined by that of the mine or, in furnace ventilation, by the furnace.
When two shafts, upcast and downcast. Fig. 23, (a), are sunk from a level surface or, in other words, have the same surface elevation it is evident that this level marks the upper limit of both columns.
When, however, the two shafts are sunk on a hillside and have different surface elevations, two cases may arise, as illustrated in Fig. 22, (6) and (c), in which, for the sake of clear-
168 Mine Gases And Ventila Tion
ness, the outside temperature is assumed as 32 deg. F. and that of the mine as 60 deg. F.
The two cases are as follows:
1. When the shaft having the higher surface elevation is made the upcast, as is usually done, that elevation marks the upper limit of both shaft colimins; because the do wr. cast shaft has practically the same temperature as the outer air.
2. When the shaft having the lower surface elevation is made the upcast this elevation marks the upper limit of both shaft columns; because the air in the other (downcast) shaft above this level is balanced by the corresponding column of outside air.
These two conditions, therefore, are simply expressed by the statement that, in either case, the upper limit of both shaft columns is the surface level of the upcast shaft.
In the same manner it can be shown that the lower Umit of both shaft colmnns is the bottom of the downcast shaft when the seam has a general inclination. Hence, the length (D) of both shaft columns is measured, in any case, from the top of the upcast to the bottom of the downcast shaft. This rule does not apply to slopes.
Ventilating Iessure and Shaft Columns. — Since the weight of an air column, in pounds, expresses the corresponding pressure, in pounds per square foot; and since ventilating pressure (lb. per sq. ft.) is the difference of pressure between the intake and return; the unit pressure p, in any given case, is found by subtracting the weight of the upcastHshaft column from that of the downcast column; thus,
Downcast-shaft column, Wd .' , D
4o0 + t
Upcast-shaft column, Wu — j. i rp
which can be written
Theory Of Ventilation 169
Calculation oif Air Column. — The air column corresponding to the above unit ventilating pressure can be expressed in terms of either the downcast or upcast air. The air in the downcast being heavier than that in the upcast, gives a shorter air coliunn for the same pressiu*e.
To find the air column (hd) in terms of the downcast air, divide the above expression for unit ventilating pressure by the weight (wd) of 1 cu. ft. of downcast air (temp. Q, which gives
" Wd 400 + T
To find the corresponding air column (hu) in terms of the upcast air, divide the same expression for unit ventilating pressure by the weight of 1 cu. ft. of upcast air (temp. T), which gives
Effective Depth of Air Column. — It has been shown that in all shaft ventilation the effective "head of air column" D is the difference in elevation of the top of the upcast and the bottom of the downcast. This applies equally to all forms of natural, furnace or fan ventilation, in shaft mines, where a positive or negative air column may exist.
Likewise, in drift or slope mines, the same law will apply, except where a long slope causes an appreciable rise in the temperature of the downcast air; and in the furnace ventilation of a slope mine. In either of these two cases, three temperatures may be concerned: (1) average upcast temperature in the shaft; (2) average downcast temperature in the slope; (3) outside temperature.
In fiu*nace ventilation, in inclined seams, also, three temperatures must be considered: (1) average temperature of the furnace (upcast) shaft; (2) mine temperature, rise or dip of seam; (3) average downcast temperature. In a few cases, a fourth (4) outside temperatiu*e may require consideration. In all cases where more than two temperatures are concerned it is necessary to calculate the column for each separate temperatiu and corresponding depth and take their algebraic sum.
170 Mine Oases And Ventilation
In practice, the arrangement of the cbculation in the mine may be such that the rise or dip column is eliminated by a balance of intake and return columns of equal temperature.
Problems
Example. — A shaft mine, in a level seam, is ventilated by a furnace. The furnace shaft is 900 ft. deep and has an average temperature of 300 deg. F. ; the downcast shaft is 600 ft. deep. ' Calculate the air column producing circulation in this mine and the corresponding ventilating pressure and water gage when the temperature of the outside air is 20 deg. F. and the barometer 30 in.
SoltUion, — The effective head of air, in this case, is Z) 900 ft. and, assuming that the temperature of the downcast shaft is practically the .me as that of the outside air, which is commonly true, the air column, expressed in terms of the downcast air, is
Expressed in terms of the upcast air the air column, in this mine, is
The pressure is found by multiplying either of these air columns by the corresponding weight of downcast or upcast air.
Or (upcast), p ' qq X 525 27.5 Ih, per aq, ft.
The corresponding water gage is, then,
w.g. 27.5 -7- 5.2 5.3 in., nearly
Example. — A slope mine is ventilated by means of a blowing or force fan located at the top of an air shaft 800 ft. deep. . The slope is the main return airway and the elevation at its mouth is 275 ft. below that of the top of the air shaft. What natural air column exists, assuming the temperature of the mine is 60 deg. and that of the outside air 10 deg. below zero ( — 10*F.); and is this positive or negative?
Solution. — The effective head of air, in this case, is D 800 — 275 525 ft.; because the downcast fan shaft has the same temperature as the outside air column, which therefore balances 275 ft. of the shaft column. The downcast air in the shaft being colder and heavier than the upcast or return air in the slope, the resulting air column assists the circulation produced by the fan and is, therefore, a positive air column. It is
Theor Y Of V En Til A Tion 171
This air column is in terms of the downcast air, which weighs, assuming a barometric pressure B 30 in.,
The natural pressure due to this air column is then
Pn 70.67 X 0.0886 6.25 lb. per sq, ft.
Qttea. — If the fan, in this example, were to be reversed so as to exhaust air from the mine, thereby making the slope the intake and the fan shaft the upcast, what air column would result, if the avera slope temperature is then F.?
Ana, — In this case, three air columns exist, two assisting and one opposing the circulation induced by the fan. They are as follows:
4oU "T 4U
4oU "T OU
The net air column, expressed in terms of, say the slope air, is now found by dividing the algebraic sum of these positive (+) and negative ( — ) columns by the weight of 1 cu. ft. of the slope air, which gives after simplifying,
The weight of 1 cu. ft. of slope air is
The natural pressure assisting the circulation is then Pn 61.3 X 0.0796 4.88 lb. per aq. ft.
Example, — To show the effect of natural air columns in fan ventilation, assume a shaft mine ventilated by means of a fan; the seam is practically level; the fan shaft is 800 ft. deep and the hoisting shaft 600 ft. deep.
(a) Assume the fan is exhausting and produces a circulation of 200,000 cu. ft. of air against a water gage of 2 in., in the winter when the outside temperature is 30 deg. and that of the mine 60 deg. F., and calculate the resulting water gage and the volume of air that the fan will circulate, running at the same, speed in the summer season when the outside temperature is 70 deg.. and that of the mine, as before, 60 deg. F.
(6) Assume the same conditions in the mine and the same respective temperatures and calculate the water gage and volume of air this fan will
172 Mine Gases And Ventila Tion
produce when running at the same speed and blowing instead of exhausting the air, for the winter and summer seasons, respectively.
SoliUion. — (a) When the fan is exhausting, the fan shaft being the upcast, the effective depth of air column is D 800 ft. The natural water gage due to this depth (barom., B. 30 in.) is
w 1-3273 X - . , .,. ,
c 1.3273 X - oo- / x
In the circulation of 200,000 cu. ft. of air, under a 2-in. water gage, as stated in the question, therefore, the water gage due to the action of the fan is 2 — 0.72 — 1.28 in., the natural water gage, in this case, assisting circulation, being positive. In the summer season, the fan exhausting at the same speed as before will create the same ventilating pressure and water gage (1.28 in.) ; but, the natural air column now being negative (0.22 in.), the effective water gage producing circulation is 1.28 — 0.22 1.06 in. Then, since the circulation in any given mine or airway varies as the square root of the pressure or water gage, the quantity ratio is equal to the square root of the water-gage ratio.
Voss 0.728
200,000 2 Summer (exhausting), x 200,000 X 0.728 145,600 cu. ft, per min,
(h) When the fan is blowing the hoisting shaft is the upcast and the effective depth of air column is then D 600 ft. The natural water gage is then 600/800 ?i of the value previously found; or ?i X 0.72. 0.54 in. (winter), and X 0.22 0.165 in. (summer). As before, the natural gage is positive in winter and negative in summer, which makes the effective gage 1.28 + 0.54 1.82 in. (wmter) and 1.28 - 0.165 1.115 in. (summer). The circulation is then
/1 go Winter (blowing), x 200,000-1/-- say 190,800 cu. ft. per min.
Summer (blowing), x 200,000 — say 149,400 cu. ft, per min.
Flow Of Air In Airways
The flow of air in a conduit or airway is in obedience to an excess of pressure at one end of the conduit over that at the other end. Air always moves from a point of higher pressure toward a point of lower pressure. The moving air is called the air current.
Theory Of Ventilation 173
Velocity of Air Currents. — The rate of motion or the distance traveled per unit of time is called the velocity of the air current. The velocity is commonly expressed in feet per second or feet per minute, as most convenient.
Relation of Pressure and Velocity. — To double the velocity of air in an airway or conduit requires four times the pressure; and since 2 the velocity v varies as tlie square root of the pressure p; thus
p varies as
For example, if an airway in a mine is of such size and length that the pressure per square foot at the intake is 3 lb. greater than that at the discharge opening, and this difference of pressiu produces a velocity of 5000 ft. per min.; it will require a difference of pressure of 4 X 3 12 lb. per sq. ft. to produce a velocity of 1000 ft. per min. in the same airway.
Solution by Ratios. — 'Expressed as ratios, the solution is always simpler and shorter, because the method admits of ready cancellation, thereby keeping the numbers small and reducing the amount of necessary work. For example, when quantities are proportional their ratios are equal. Or, in this case, the velocity ratio is equal to the square root of the pressure ratio. Calling the first velocity vi, second velocity V2] the first pressure pi and the second pressure p2, we have
or, vice versa,
Example. — What difference of pressure per square foot will be required to produce a velocity of 1200 ft. per min. in an airway where the air is moving at the rate of 500 ft. per min., under a moving pressure of 3.5 lb. per sq. ft.?
Solution, — Let x the required difference of pressure; then
a: 3.5 X 5.76 20.16 lb. per sq. ft.
174 Mine Gases And Ventilation
Example. — If a difiference of pressure between the two ends of an airway, of 8 lb. per sq. ft., produces a velocity of 600 ft. per min., what will be the velocity in the same airway when the difference of pressure is only 2 lb per sq. ft. ?
SoltUion. — In this case, calling the required velocity x,
a: 600 X H 300 per min,
Ventilating Pressure
Pressure Producing Circulation. — In mine ventilation, the term ventilating pressure'' is the pressure exerted to move the air. It is the difference between the intake pressure and the discharge pressure. Since the pressure of the atmosphere is equal at both ends of the airway it may be disregarded, as far as the movement of the air is concerned.
The Blowing System of Ventilation. — To move the air or cause it to circulate in an airway or a mine, an extra pressure must be created at one end of the airway, so as to overcome the resistance of the mine due to friction. This is called the "blowing" system of ventilation, because the air is blown through the airway by the pressure created.
The Exhaust System of Ventilation. — The same difference of pressure may be caused by decreasing the atmospheric pressure at one end of the airway, when the full pressure of the atmosphere at the other end will cause the air to move toward the point where the pressure is less. The principle is that commonly called "suction;" but this system is known as the "exhaust" system of ventilation.
How Pressure is Produced. — Various means have been used to cause a circulation of air in mine airways. The wind cowl, waterfall and steam jet are useful under favorable conditions and where a limited air supply only is needed. The mine furnace, built in the mine near the bottom of the upcast shaft, is often used in nongaseous mines, especially in deep shafts (see Furnace Ventilation). The most reUable means of creating pressure in mine ventilation, however, is the mine fan, which is generally erected at the surface, either at the
Theor Y Of Ven Til A Tion 1 75
top of the downcast shaft, as a blower; or at the top of the
upcast, as an exhaust fan (see Fan Ventilation). The blowing fan creates a pressure above that of the atmosphere, while the exhaust fan reduces the atmospheric pressure.
How Pressure is Estimated. — In mine ventilation, the pressure producing circulation is estimated in height of air column, as in natural ventilation and often in furnace ventilation. The more common method, however, is to state the pressure in pounds per square foot or ounces per square inch. Pressure is also stated in inches of water gage. These all refer to the unit of ventilating pressure or simply "unit pressure.''
Atmospheric pressure is given in pounds per square inch, or, as barometric pressure (which is the same as atmospheric pressure), in inches of mercury.
1 in. water gage 5.2 lb, per sq. ft, 1 in. mercury 0.491 lb, per sq. in. 1 oz. per sq. in. 9 Ih, per sq. ft. 1 in. mercury 13.6 in. water gage
How Pressure is Measured. — In mine ventilation, the pressure producing circulation is commonly measured by means of the water gage; or, in case of high pressures a special form of manometer is sometimes used. The manometer differs from the water gage in having one end of the bent tube closed so that the rise of the water level in that arm of the tube compresses the air above the water, which lessens the rise of water level and gives a greater range of readings.
The Mine Water Gage. — This consists of a glass tube of about -in. bore, bent to the shape of the letta* U and mounted on a soUd base. Three styles of water gage are shown in Fig. 24. These differ only in the kind of scale. The first two on the left have the zero at the center of the scale and read up and down to the respective water levels. The first of these scales is graduated to full-length inches, and to obtain a correct reading it is necessary to add the two readings together, or double either of them, as they are equal. To avoid this necessity the second scale is made of half-length inches, so that either the upper or the lower reading gives the full gage
176 Mine Gases And Ventilation
required, which, in this case, is 3 inches. As shown in the figure, the scale is adjustable by means of the strew rod on which it is mounted.
When the zero of the scale is at the middle and the scale reads up and down, it is evident that the scale must be adjusted so that its zero will correspond with the two water levels, before the pressure acts on the gage. When the pressure acts it depresses the water level in one arm while that in the other arm rises an equal amount. The difference between these two levels ia the actual water column supported by the difference
in the pressures acting on the water in the two arms. As will be explained later, one arm of the gage when in position is open to the intake pressure and the other to the return. The difference between these two pressures is the pressure that circulates the air between these two points.
The scale shown on the right has its zero at the bottom and reads upward. This scale must evidently be set, after the gage is in position, so that the zero will correspond with the lower water level, which is always that in the arm open to the intake pressure, as that pressure is always greater than the return pressure. The reading of the scale at the upper level is then the required g£e.
The reading of each of the three gages shown in the figure is 3 in., which indicates a ventilating pressure of 3 X 5-3 15.6 lb. per sq. ft.
Theory Of Ventilation 177
Reading the Water Gage. — In the common use of the water gage, in mine practice, the scale is not read closer than H in. On the left of Fig. 25, is shown a portion of a water column and scale graduated to eighths of an inch. The scales shown in Fig. 24 are decimal scales, being graduated to tenths of an inch for greater accuracy. In all engineering practice, therefore, and whenever accuracy is desired the decimal scale shown in Fig. 24 is used and the reading taken to tenths or hundredths of an inch.
There are several sources of possible error in reading the mine gage. If the gage is not truly vertical the reading wilt not be correct. Error often occurs from the cupping of the surface of the water in the tube. As shown in Fig. 25, the
reading of the gage should be taken at the bottom of the concave or bowl. This will give greater uniformity in the results obtained.
In fan ventilation, especially when the reading is taken in the fan drift, there is a constant oscillation of the water level, which makes it difficult to decide on the true reading. The oscillation is much reduced when the tube of the gage is contracted at the bend. The best gages are provided with a stop-cock in the bend by which the connection between the two arms can be closed. The gage can then be carried to a more convenient place to be read.
Unit of Ventilating Pressure. — In mine ventilation, the unit of ventilating pressure, or the unit pressure producing the circulation, is estimated in pounds per square foot This
is calculated frotn the reading of the water gage by multiplyii; that reading, in inches, by 5.2.
On the right, in Fig. 25, is shown clearly how the constant 5.2 is derived. The weight of 1 cu. ft. of water is, practically, 62.5 lb. The figure represents a cube that measures 12 in. on each edge; the base of the cube being 1 sq. ft. Since the . weight of 12 in. of water, resting on this square foot, is 62.5 lb., the weight of 1 in. of water covering the same area is 62.5 -i- 12 5.2 lb., which represents the pressure, in pounds per square foot, due to 1 in. of water column. The principle involved is that the unit pressure on a given area of surface depends only on the height of water column the pressure supports.
The Water Gage in the Mine. — As used in the mine, the reading of the water gage shows the difference of pressure
between the intake and return airways, at the point where the reading is taken. The intake pressure is always greater than the return pressure and this excess or difference of pressure is what moves the air or creates the current.
The use of the instrument is clearly illustrated in Fig. 26 where two parallel airways are shown leading into the mine, one of these being the intake and the other the return airway of that section of the mine. It makes no difference on which side of the brattice the instrument is placed; the water will always be depressed in that arm of the gage which is open to the intake, because the pressure on the intake is always greater than that on the return airway.
What the Water Gage Shows. — The water-gage reading indicates the ventilating pressure required to circulate the air,
Theory Of Ventilation 179
and is therefore equal to the resistance of the airways between the two points on the intake and the return; or, in other words, the resistance inby from the point of observation. The nearer this reading is taken to the head of a pair of entries, the closer it will approach zero, while at the next to the last crosscut it would be practically zero.
The use of the water gage in mining practice is of great importance. In connection with the observed velocity of the air, it shows the power on the air" or the power producing the circulation. What is required in the practical ventilation of a mine is the production of the necessary velocity and volume of air, with the smallest expenditure of power. The most economical circulation is obtained when the required air volume is circulated by the least power, which means a comparatively low water gage.
The circulation of a comparatively large quantity of air under a low gage indicates ideal economic conditions, as far as the circulation is concerned. On the other hand, a small air volume and a comparatively high water gage shows a needless waste of power. In practice, an unusual reduction of the quantity of air passing in a mine or entry, accompanied by a similarly uncommon rise of gage pressure would indicate an obstruction of the airways.
Velocity Of Air Currents
The velocity of the air current is one of the most important factors in the practice of mine ventilation. If the velocity of the air current is too low the ventilation of the mine is inefficient, as the air will not sweep away the accumulating gases from their lurking places in the mine. Oh the other hand, if the air moves with too great a velocity, not only do the workmen suflFer inconvenience, but the high velocity of the current is often dangerous.
Danger of High Velocity. — A rapid air current carries a great quantity of dust, and, by suppljdng large quantities of oxygen, maintains an unnecessarily active condition of the mine atmosphere that favors the ignition of the gas and dust. The. high wind creates a draft that greatly intensifies the
180 Mine Gases And Ventilation
flatne of lompe or of a blast of powder and increases the possibility of ignition.
How Velocity is Estimated. — In mine ventilation the velocity of the ventilating current is commonly estimated in feet per minute, or feet per second.
How Velocity is Measured. — A dmple method of ascertaining, with more or less accuracy, the average velocity of the air current passing in an airway is to measure off a distance of, say 300 ft. along a straight portion of the airway; and
note the exact time between the observed flash of powder at one end and the smell of smoke at the other end of this distance. The distance (300 ft.) divided by the time will give the velocity of the air in the center of the entry. The average velocity of the current may then be taken as of this observed velocity. For example, if the observed time is 30 sec, the center velocity is 300 t- 30 10 ft. per sec.; and the average velocity X 10 - 8 ft. per sec. or 8 X 60 480 ft. per min.
The Anemometer. — The common method of measuring the velocity of the air in airways is by the use of the anemometer, one form of, which is shown in Fig, 27. The dial hands record
Theory Of Ventilation 181
the number of revolutions of the vane. The instrument is so calibrated that each revolution of the vane corresponds to 1 ft. of air travel. The reading of the dial, therefore, shows the distance the air traveled during the time that the instrument was exposed to the current. Hence, this reading divided by the time of exposure, in minutes, will give the velocity of the current in feet per minute. A single revolution of the large hand corresponds to 100 revolutions of the vane. The small dials register the total reading.
Quantity Of Air
The term ''quantity,'* in mine ventilation, refers to the volume of air passing in an airway, estimated in cubic feet per minute. This is often spoken of as the "circulation" of the airway or mine.
How Quantity is Estixnated. — As stated above, the quantity of air circulated in an airway or mine, or the "circulation," as it is called, is always estimated, in this country, in cubic feet per minute.
How Quantity is Measured. — To measure the quantity, in ventilation, it is necessary (1) to measure the sectional area of the airway at the point of observation and (2) to carefully measure the average velocity of the air current at the same point. From these measurements, the volume of air passing or the circulation is calculated by-means of the formula,
Quantity area X velocity q — av
Example. — Calculate the circulation in an airway having a sectional area of 50 sq. ft., the average velocity of the air current being 600 ft. per min.
Solution, — Substituting the given values in the formula for quantity in tenns of velocity and area,
g at; 50 X 600 30,000 cu'.ft. p&rmin.
Quantity of Air Required. — In determining the required circulation of a mine, it is necessary to consider (1) the requirements of the mining law of the state in which the mine
182 Mine Gases And Ventilation
is located and (2) the requirements of the mine as determined by the natm-al conditions existing in the seam and the enfolding strata.
Requirements of the Mining Law. — These vary somewhat in different states. Owing to the nmnerous and changing conditions, in mines, mining laws are of necessity arbitrary standards, which must, however, be met, except in-cases where the law specially confers discretionary powers upon the mine inspector or the mine foreman, thereby authorizing them to decrease the circulation in any mine or section of the mine, as conditions may require or their judgment dictate.
The mining law commonly specifies from 100 to 150 cu. ft. per man, per min., for nongaseous, and 200 cu. ft. per min., for gaseous mines. In addition, some of the laws require from 500 to 600 cu. ft. per min., for each animal employed underground.
Natural Requirements. — Gaseous mines naturally require more air than nongaseous mines. The rise workings of seams generating marsh gas or the dip workings of mines giving oflf quantities of blackdamp are often difficult to ventilate and require a circulation greater than what the law specifies, in order to keep the workings free from gas and healthful and safe for work. Slips and faults often give oflF much gas when least expected and require, therefore, a larger circulation of air than would otherwise be necessary in the same mine.
Work Or " Power On The Air "
The terms "work" and power" as used in mine ventilation, are synonymous, because the work performed in moving the air through the mine airways is based on a unit of time, both the velocity and the quantity being rated per minute of time.
Power on the Air.-The air current in an airway or mine is moved by a pressure called the ventilating pressure." The ventilating pressure or the pressure producing the circulation is the total pressure pa exerted on the entire sectional area of the airway, as illustrated in Fig. 28. The small
Theory Of Ventilation 183
arrowheads in the figure represent the unit pressure or the pressure p on each square foot of cross-section. The lai-ge arrow shown at A represents the total pressure P pa.
It is a law of mechanics that when a force pa moves or is exerted through a distance v the work performed is equal to the product pav of the force and the distance. But in this case, the force pa moves through the distance v in one minute. The work (pav) is, therefore, performed in one minute and is the "power on the air," The work performed per minute or the power on the air is expressed in foot-pounds
per minute. Calling this work per minute or power on the air u, the formula for power is
Power unit pres. X area X vel. u pav Again, since g av, the formula for power on the air may be written:
Power quantity X unit pres. u qp The formula for horsepower of the circulation is, therefore, since 1 hp, 33,000 ft. -lb. per min.
H -
gp 33,000
184 Mine Gases And Ventila Tion
The power formulas, in ventilation, make it possible to calculate the power required to produce any given circulation, against any given pressure or water gage when the efficiency of the venilator is known or assumed.
Equivalents In Measurement
Air Column and Water Gage. — Since water is practically 815 times as heavy as air at normal temperature and pressure, 1 ft. of water column measures the same pressure as 815 ft. of ordinary air column; and 1 in. of water gage is therefore equal to .815 h- 12 say 68 ft. of air column, which gives the following:
Rule. — -To reduce feet of air column to inches of water gage, divide by 68.
To reduce inches of water gage to feet of air column, multiply by 68.
Air Column and Unit Ventilating Pressure. — Since air at a normal temperature and pressure weighs, practically, 13 cu. ft. to the pound, every 13 ft. of air column represents, approximately, a ventilating pressure of 1 lb. per sq. ft., which gives the following:
Rule. — To reduce feet of air column to unit pressure, divide by 13.
To reduce unit pressure (lb. per sq. ft.) to feet of air column, multiply by 13.
Air Colunm and Barometric Pressure. — Since 1 cu. in. of mercury weighs 0.491 lb., each inch of mercury column indicates a pressure of 0.491 lb. per sq. in.; 0.491 X 144 70.7 lb. per sq. ft.; and since each pound per square foot of pressure corresponds to 13 ft. of air column, approximately, 1 in. of barometer 70.7 X 13 say 920 ft. of air column, which gives the following:
Rule (Approximate). — To reduce feet of air column to inches of barometer, divide by 920.
To reduce barometric pressure (inches) to feet of air column, multiply by 920.
Barometric and Unit Ventilating Pressure. — Barometric pressure is always expressed in inches of mercury column.
Theory Of Ventilation
Unit ventilating pressure is expressed in pounds per square foot, ounces per square inch, or inches of water gage.
Rule. — To reduce barometric pressure (inches) to ventilating pressure (Ih. per sq. ft.), multiply by 70.7; or to ventilating pressing (oz. per sq. in.), multiply by 0.491 X 16 7.856; or to water gage (in.), multiply by 70.7 5.2 13.6, which is the specific gravity of mercury referred to water as a standard.
Since 13 ft. air column represents a pressure of 1 lb. per sq. ft., a pressure of 1 oz. per sq. in. corresponds to an air column of (13 X 144) -s- 16 117 ft.
EQUIVALENTS IN PRESSITRE voiuHt oit ouantitpor uti in imanunn (cb f "W
Fio. 29.
- 7.86 X barometric pressure (in.); 13.6 X barometric pressure (in.).
Power-Volume-Pressure Diagram. — The diagram shown in Fig. 29 is convenient as showii at a glance the power re-
186 Mine Gases And Ventilation
quired to circulate a given quantity of air against a certain pressure, in pounds per square foot, ounces per square inch, or inches of water gage. In order to find the power required to pass any given volume of air against any given pressure or water gage, follow the diagonal line corresponding to the given water gage to its intersection with the vertical line corresponding to the given volume and read this point of intersection on the power scale at the left of the diagram.
For example, it requires 50 hp. to pass 80,000 cu. ft. of air per minute, under a 4-inch water gage or, reversing the order, 30 hp. will pass about 96,000 cu. ft. per minute under a 2-inch gage. Since the power is proportional to the quantity and pressure alike, in order to deal with higher values than those given in the diagram, it is only necessary to treat these as multiples of the values given in the diagram. Thus, 100 hp would pass 160,000 cu. ft. under a 4-inch gage; or 320,000 cu. ft. under a 2-inch gage. The horsepower in this diagram is the power on the air, which is commonly, in fan practice, 60 per cent, of the horsepower of the engine or the indicated horsepower.
Examples For Practice
1. How many feet of air column is equivalent to a mine water gage of three inches?
Solution. — Under ordinary or normal conditions water weighs 815 times as heavy as the same volume of air ; hence,
1 ft. (12 in.) water column 815 ft. air column 1 in. water gage 815 -i- 12 68 ft. air column 3 in. water gage 3 X 68 204 ft. air column
2. Express the pressure equivalent to 200 ft. of ordinary air column, in pounds per square ft.; ounces per square inch; inches of barometer; inches of water gage.
Solution. —
200 -r- 13 15.39 lb. per sq. ft., nearly 200 -i- 117 1.71 oz. per sq. in., nearly 200 -r- 920 0.22 in. of mercury, nearly 200 68 2.94 in. of water gage.
3. What is the pressure of the atmosphere, in pounds per square inch, corresponding to a barometric pressure of 30 in.?
Solution.-
Theory Of Ventilation 187
30 X 7.86 235.8 oz. per sq, in, 235.8 T- 16 14.74 lb. per sq. in,, nearly
4. Find the pressure in ounces per square inch corresponding to a water gage of 2.5 in.
Solution. —
2.5 X 0.58 1.45 oz. per sq. in.
5. Find the barometric pressure in inches of mercury corresponding to a water gage of 3.4 in.
Solution. —
6. If an aneroid barometer gives a. reading of 29.65 in. on the surface, what should be the reading at the bottom of a downcast shaft 500 ft. deep where the ventilating pressure caused by a blowing fan gives a water gage of 2.85 in., assuming all readings are taken at about the same time?
Solution. — The air column in this shaft will increase the barometric pressure 500 -5- 920 0.54 in. The water gage due to the blower will still further increase the barometric pressure, at the foot of the downcast shaft, 2.85 h- 13.6 0.21 in. The reading of the aneroid, therefore, should be 29.65 -f- 0.54 -f- 0.21 30.4 in., approximately.
7. In a mine ventilated by an exhaust fan, giving a water gage of 2.33 in., if aneroid readings taken on the surface and at the bottom of the upcast shaft show a difference of 0.77 in., what is the calculated depth of the shaft?
Solution. — The action of the exhaust fan makes the aneroid reading at the shaft bottom lower than it would be if the fan were not running, and decreases the difference of the surface and underground readings 2.33 -I- 13.6 0.17 in. of mercury. The difference of reading due to the depth of the shaft only is, therefore, 0.77 -f 0.17 0.94 in. of mercury. Reducing this barometric difference to air column gives for the approximate depth of the shaft 920 X 0.94 say 865 ft. under ordinary conditions.
Mine Airways
Definition of Terms. — The term airway," in mining, generally relates to a passageway for the circulation of the air current, in distinction from a haulage road or travehngway, although these entries may serve also as airways. The entry by which the air current enters the mine is called the main ''intake," and that by which it is carried out, the main "return." In like manner, the two shaft or slope openings in
188 Mine Gases And Ventilation
a mine are called, respectively, the "downcast" and the "upcast."
The "perimeter "of an airway is the distance measmd around the circumference of its cross-section. The "area" or "sectional area" of an airway is the area of its crosssection.
The "rubbing surface" s of an airway is the entire inner surface of the same; and is found by multiplying the perimeter o by the length i, of the airway; thus,
8 lo
Essential Features of Mine Airways.-Airways in mines should be as straight as possible and avoid all sharp bends and other obstructions that increase the resistance of the airway to the flow of air. The shape of the airway is important as affecting the pressure required to pass a given quantity of air.
Shape of Airways. — The cross-section of an airway may be a circle, square, rectangle, elUpse, or any combination of these that best meets the needs or conditions. For the purpose of ventilation, that form of airway is best that has the shortest length of perimeter, for the same area of section.
In this respect, the circular airway is first; the ellipsoidal airway next, until the major axis exceeds 2.73 times the minor axis when, for the same area, the perimeter is equal to that of a square airway. The square airway is then third in the series and the rectangular and trapezoidal forms last.
There are, however, other requirements than those of ventilation. Haulage requires a level bottom for the roadway. Roof conditions or economy of driving entries may put an arched roof out of the question, making it necessary to adopt the square, rectangular, or trapezoidal shape. Again, a weak coal and heavy side pressure may demand an elUpsoidal shape of section or a special type of timbering approaching the same. It is not uncommon to arch the roof of airways for a distance, using either a semicircle or a semiellipse to form the arch, the latter being called a "flat arch."
Theory Of Ventilation 189
The closer the ellipse approaches the circle or the nearer a rectangle comes to being a square, the less is the perimeter of the airway, for the same area of section. For the same length of airway, the perimeter is proportional to the rubbing surf ace of the airway.
Similar Airways. — Two airways are similar to each other when their cross-ections are similar; the term "similar" has no reference to the length of the airway.
The cross-sections of airways are similar when their corresponding dimensions are proportional, each to each, and their perimeters parallel throughout or can be so placed.
Illustration. — All circular or square airways are similar, because they have but one dimension, the diameter of the circle or the side of the square, and these dimensions are, therefore, always proportional.
For example, one circular airway may have a diameter twice or three times as great as that of another circular airway; or the side of a square airway may be two or three times that of another square airway; and their perimeters can always be placed so that their circumferences will be concentric or their sides parallel, each to each.
On the other hand, the rectangle, trapezoid and ellipse each have two dimensions; and while one of these dimensions may be two, three, etc., times as great as the corresponding dimension of another airway of the same form, it does not follow that the other dimensions of the two airways have the same proportion; and unless they do the airways are not similar. Thus, a 6 X 8-ft. airway and a 9 X 12rft. airway are similar, because their corresponding sides have the same ratio, or are proportional and may be written
K joy or6:9::8:12
A 6 X 8-ft. airway and a 3 X 16-f t. airway, however, are not similar airwajfs, though they have equal sectional areas 6 X 8 48 sq. ft., and 3 X 16 48 sq. ft.); because the second airway is twice as wide but only half as high as the first.
190 Mine Gases And Ventilation
It is important to observe that in all similar airways, the ratio of the sectional areas of the airways is equal to the square of the ratio of the corresponding dimensions. For example, in Figs. 30 and 31 showing two similar trapezoidal sections, the top, bottom and sides of the larger airway are each twice those of the smaller, and the area of the larger section is, therefore, 4 times that of the smaller.
Principle of Similar Airways. — Since corresponding dimensions of similar airways have a fixed ratio, which is the same
Y /yirtmefr2AlOfBf24-SeFf.
Fig. 30.
for each dimension (diameter, side, height or width) it is possible to compare similar airways with respect to any of these dimensions.
Application. — Assume, for example, the same pressiure (p) is applied to each of two similar circular airways, and it is required to find how the quantity of air will vary in the two airways. First write the formula for the quantity (5), in terms of the pressure (p) and the dimensions, area (a), perimeter (o) and length if) of the airway, and the coefficient of friction (k); thus.
q'-
klo
Now, if the two airways have the same length, and are under the same pressure, p, I and k are all constant and
varies as —
Theory Of Ventilation. 191
But, the area of a circle varies as the square of its diameter {(P) and the perimeter varies as the diameter (d) ; hence,
— varies as -r* or simply as
Hence,
varies as
In the same manner, it can be shown in respect to all similar airways of any form, that the square of the quantity varies as the fifth power of any corresponding dimension (d), whether diameter, side, height, or width.
Rule. — In comparing similar airways of equal length, for the same unit pressure, the square of the quantity ratio is equal to the fifth power of the dimension ratio; and, for the same power on the air, the cube of the quantity ratio is equal to the fifth power of the dimension ratio.
Example, — If 100,000 cu. ft. of air is passing per minute, in a 6 X 9-ft. airway under a given pressure, what quantity of air will the same pres* sure circulate in an airway 8 X 12 ft. of the same length? What quan* tity will the same power circulate?
Solution. — These airways are similar because their corresponding dimensions are proportional 6 : 8 : : 9 : 12. Therefore, calling the required quantity x,
V4;214 2.0528
X 100,000 X 2.0528 205,280 cu, ft. per min. Assuming a constant power on the air:
100,000 X 100,000 X 1.6152 161,520 cu.ft, per min.
Resistance of Airways.— The resistance that an airway oflFers to the passage of air is of two kinds: frictional resistance due to the rubbing of the air on the inner surface of the airway, and the resistance due to the air striking against obstructions such as timbers, roof falls, sharp bends, etc.
How Resistance Varies, — In mine ventilation, the entire resistance of airways is estimated on a frictional basis, accord-
192 Mine Gases And Ventilation
ing to the extent of rubbing surface and the velocity of the air. It is assumed that when the velocity of the air current is doubled, each resisting particle in the airway is struck twice as often and twice as hard, by the passing air, which makes the resistance offered by each particle 2X2 4 times as great as before. If the velocity is increased three times, the resistance of each particle is increased 3X3 9 times, etc. On this assumption, the resistance of an airway varies as the extent of rubbing surface (s) and the square of the velocity X v v), or as the expression sv for that airway.
Unit Resistance or Coefficient of Friction. — The amount of resistance, per unit of rubbing surface (1 sq. ft.), for a unit velocity (1 ft. per min.) is called the unit of resistance or the coefficient of friction. The values most conamonly adopted for this unit are
k 0.00000002 lb. (Atkinson, revised) k 0.00000001 lb. (Fairley)
Calculation of Resistance of Airways. — To find the resistance of an airway for any given velocity, multiply the unit resistance (fc) by the rubbing surface in square feet (s) , and that product by the square of the velocity in feet per minute (e;); the final product will be the total resistance (ft), in pounds, as expressed by the formula
Example. — Find the resistance of an airway having sq. ft. of rubbing surface, when the velocity of the air current is 800 ft. per min.
SoltUion, — The resistance, in this case, is
R 0.00000002 X 60,000 X 800* 768 lb. SYMBOLS AND FORMULAS
Most of the rules of mine ventilation are expressed by means of formulas, which show at a glance the relation of the several factors to each other, and make possible many transformations and developments.
Symbols. — As far as practicable, the same symbols are used throughout to designate the same factors; and these are, for
Theory Of Ventilation
the most part, those symbols commonly employed in ventilation, as being the initial letter of the word for which they stand. For example, p pressure; v velocity; quantity, etc. The following table gives the more important symbols used :
Table of Common Symbols, Mine
A area of regulator,
a — area of airway,
B height of barometer,
C Centigrade reading,
c constant,
D depth of shaft,
d — diam. or side of airway,
F Fahrenheit reading,
g gravity, H horsepower,
h height of air column, K — Efficiency of fan,
k coefficient of friction,
I length of airway,
n number of revolutions,
o perimeter of airway,
P total pressure,
p unit pressure,
Q total circulation of air,
q single, current,
R resistance of mine or airway,
r any ratio,
8 rubbing surface of airway,
T — absolute or higher temperature,
t actual or lower temperature,
U total power on air,
u power, single current,
V velocity of air, ft
V volume of air or gas, W total weight of body,
w unit weight, X potential of mine or airway, Xp — pressure potential, Xu power potential
X the unknown quantity whose value is w.g. — water gage reading, Sp. gr. - specific gravity.
Ventilation
8q, ft
aq, ft.
in.
deg.
ft.
Si. deg,
ft, per sec.
ft. per cent.
ft. r.p.m.
ft.
lb.
lb. per sq. ft.
cu. ft. per min,
cu, ft. per rrvin.
W,
eq, ft.
deg.
deg,
, ft,-lb. per min.
ft:-lb, per min,
, per sec. J or ft, per min.
cu. ft,
lb.
lb, per cu, ft.
sought
tn.
1 94 Mine Gases A Nd V En Til A Tion
Small subscript letters and figures are frequently written immediately after any symbol to show its reference to a particular kind or thing. For example, gi, q%, qj etc., indicate the quantities of air passing in three or more airways; Qa, Qby Qe, etc., indicate the quantities passing in Splits A, By C, etc. In like manner, the potential values of different airways and splits are indicated by Xi, Xzj X etc. ; or Xa, Xb, Xc, etc., as the case may be.
In some cases, two or more subscript letters or figures are used after a single symbol to indicate its reference; as for example, the pressure potential for Split A is written Xpa or the power potential Xua- The general potential, in a split circulation, is written Xo] or Xpo and Xuo to indicate the general pressure and power potentials, respectively.
It is often necessary to indicate the summation of a number of items of the same kind, for which purpose the character £ is written before the symbol indicating the kind. For example, JXabc indicates the sum of the potential values for the splits A, B and C, instead of writing Xa + Xb + Xc*
In a complex circulation, consisting of a main airway and two or more splits, it is often necessary to indicate the general split potentials by Xo, Xoo, 60, etc., and the mine potential byX (See Fig. 33, p. 236.)
Use of Formulas. — A compar&,tively few formulas form the basis from which practically all the other formulas of mine ventilation are derived. These few basal formulas also show the true relation, one to the other, of the principal factors of ventilation, such as pressure, velocity, quantity, power, rubbing surface and the sectional area of mine airways.
The understanding of these formulas makes it unnecessary to learn and remember a large number of rules of ventilation. A formula is written as an algebraic equation in which each factor is expressed by its proper symbol. The equation shows the equality of certain factors grouped in the form of an expression. For example, the formula
pa= ksv
shows the equality of the total ventilating pressure pa and
Theory Of Ventilation 195
the resistance of the airway when the rubbing surface is s and the velocity of the air ciurent v.
How Factors Vary. — It is evident, from the inspection of a formula, that:
1. Any factoi* in one member of the equation varies directly as any like factor in the other member, provided the other factors remain constant and none of the quantities expressed in the formula are connected by the signs plus (+) or minus
2. Any factor in either member varies inversely as any like factor in the same member, with the provisions just stated (1) above.
For example, the formula previously given shows that:
The total ventilating pressure (pa) for airways varies as the resistance (ksv) of the airway.
For any given airway, a, s and k being constant, the unit pressure (p) varies directly as the square of the velocity (v) of the air current.
For the same total pressure (pa), in an airway, k being constant, the square of the velocity (v*) varies inversely as the rubbing surface (s). Or, in other words, the velocity of the air current varies inversely as the square root of the rubbing surface (\/s
For the same velocity (v) of air and the same rubbing surface (s) in an airway, k being constant, the unit pressiu*e (p) always varies inversely as the sectional area (a) of the airway.
3. Again, transposing the formula for total pressure, the formula for unit pressure producing a given velocity in a
given airway or mine is
V — a
An inspection of this formula shows that:
The other factors remaining constant and none of the quantities being connected by the signs plus (+) or minus (— ), any factor in the denominator of a fractional term forming either member of the equation varies directly as any factor in the numerator of that fraction; and likewise as any similarly placed factor in the other member.
196 Mine Gases And Ventila Tion
Basal Formulas. — There are, in fact, but two truly basal formulas, in mine ventilation; the one expressing the' resistance that an airway offers to the passage of an air current having a certain velocity; the o'her expressing the power on the air producing a certain velocity in an airway, against a certain resistance. These formulas are as follows:
Resistance pf airway, R pa ksv Power on the air, u pav ksv
From these two simple formulas as a basis, with the aid of a few other recognized formulas and principles for determining the quantity, horsepower, water gage, rubbing surface, etc., all ventilation formulas are derived.
Mine Potential Methods
An Important Principle. — One of the most important principles of mine ventilation may be stated briefly as follows:
Every airway or mine possesses a certain definite resisting power, which is determined by the ratio of its area of passage to rubbing surface. For this reason, a given power will produce a certain velocity and develop a certain resistance, in a given airway; the velocity of the air current varying inversely as the resistance. Ventilating pressure is caused by and equal to the resistance developed. Power, then, creates velocity, which in the airway develops resistance; and the resistance produces pressure.
The conclusion is, therefore, evident that it is the resisting power of a mine or airway that determines the velocity and pressure a given power will produce in that airway. The airway, it is clear only possesses this resisting power potentially, its development requiring the passage, of an air current. Hence, . it is proper to term such resisting power, expressed in terms of the airway, the "potential of the airway" or the "mine potential," in respect to a mine.
As has been explained, the equivalent of the mine potential, expressed in terms of the power, quantity or pressure, is properly called the "potential of the circulation."
Theory Of Ventilation 197
Illustration of Formulas. — To illustrate the use of formulas in mine ventilation, and to make clear their application, the following table is given, in which most of the formulas in common use are classified under their proper heads. Many of these formulas, as will be observed, are simple transpositions of another formula or obtained by substitution. The calculations, in the table, all refer to an airway 5 X 10 ft. in cross-section and 4000 ft. long, passing an air current of, say 25,000 cu. ft. per min, against a pressure of 12 lb. per sq. ft.
The Airway .-T-
Length, I 4000 ft.
Rubbing surface, (s fo) s 4000 X 30 120,000 sq. ft 'Sectional area, a 5 X 10 50 sq. ft.
Power potential of airway or mine,
a 50
The Air Current. —
Velocity, v v — 500 ft. per min.
,fu ; j 300,000
Power potential of the circulation,
q 25,000
The square of the pressiu'e potential can always be used instead of the cube of the power potential since these are eqtial as expressed by the formula
198 Mine Gases And Ventilation
Thus, Xp Xu VXu 373.45 \/373.45 7217, nearly Pressure potential,
q 25,000
Quantity, q av q 50 X 500 25,000 cu. ft. per min
u 300,000 onnn /.
flf — o — 77.- 25,000 cu,fi, per mm,
p 12 , "
p 5.2 w.g. p 5.2 X 2.307 12 lb, per sq.ft. Resistance, R pa R 12 X 50 QOO lb.
Ml 2
Pressure, p
P'=
P
-P —
P
R 0.00000002 X 120,000 X 500
Theory Of Ventilation 199
Water gage, w,g, w,g, 2.307 + in.
Power on air, u ksv w 0.00000002 X 120,000 X 500
''" a3 "" 50
u qp u 25,000 X 12
u
per mm.
u=- pav w 12 X 60 X 500
Horsepower, H 33-u 9.09 hp.
Measurement Of Air Currents
The measurement of air currents, in mining practice, involves the careful observation of the velocity and pressure of the current and the accurate measurement of the sectional area of the airway. From these data the volume and power of the air current are determined.
Requirements. — The mining laws of the state, in most cases, require a specified volmne of air per man, per minute, circulated throughout the mine. In order to meet this requirement, it is necessary to estimate the power that will produce such quantity in a given mine.
The Mine Potential. — Every airway and every mine has a certain resisting power, in respect to the circulation of air. For this reason, the same power will circulate different quantities of air through airways that differ in respect to either their size or length.
The formulas of mine ventilation show the following relation of the quantity of air circulated to the power producing
200 Mine Gases And Ventilation
the circulation, and the sectional area to the rubbing surface of the airway.
Quantity sectional area
"V varies as , , . .
S/ Power Sy rubbing surface
Or, say: quantity (cu. ft. per min.) q; power (ft. lb. per min.) u; sectional area (sq. ft.) a; and rubbing surface (sq. ft.) s] the unit resistance being fc, we have
a a
The first of these expressions, being given in terms of the power and quantity of air circulated, may be called, properly, the "potential of the circulation;" while the second expression, being given in terms of the airway, is the ''potential of the airway," or the "mine potential." The significance of the term "potential," in this connection, is apparent since it describes the capacity of an airway or mine in respect to the volume of air it will pass, per unit of power.
Values of the Potential. — Calling the potential factor X, its value for any given mine or airway is calculated by the formula
</l
The value of the potential for the circulation of any quantity (q) , by any power (u) or pressure (p) , is found by the formula
X
u
The value of the potential lies in the fact that it gives to every mine, or air split, a definite value that enables a correct comparison to be made between them, and the proper type of ventilator and system of ventilation to be chosen.
Potential of Airway. — Calculate the potential of an airway 6 X 10 ft., in cross-section, and 2000 ft. long.
Theory Of Ventilation 201
Solution — The sectional area of this airway is 6 X 10 60 sq. ft.; the rubbing surface is + 64,000 sq. ft. The potential of the airway is, therefore,
Potential of Circulation. — What is the value of the potential factor in the circulation of 60,000 cu. ft. of air, by 10 hp.? Solution. — The potential of this circulation is
q 60,000
Find the potential value for the same volume of air when circulated under a pressure of 8 lb. per sq. ft. Solution. — The potential value, in this case, is
,/g2 ,/6o;i
Power, Pressure, Quantity. — -By transposing the formulas for potential, it is possible to calculate the power or pressure required to circulate any given quantity of air against any given mine potential; or to find the air volume a given power or pressure will produce, for any given mine potential.
Example. — Find the (1) power, and (2) pressure required to circulate 24,000 cu. ft. of air through an airway 5 X 14 ft. in section and 3000 ft. long?
Solution, — The area and rubbing surface of the airway are: a — 5 X 14 70 sq. ft.; and s + 114,000 sq. ft. The potential factor of this airway is then
(1) Power, tt ' (Tt) ' 91,900 /f.-H). per min.
(2) Pressure, P goi og 3.83 lb. per aq, ft,
Example. — Find the volume of air circulated in the same mine, by (1) 10 hp.; (2) a pressure of 7.8 lb. per sq. ft.
Mine Gases And Ventilation
q X yfu 531.8 10 X 33,000 36,750 cw. /(. per min,
g X y/Xv 531.8 y/ 531.8 X 7.8 34,250 m. ft per min.
Potential Values of Different Airways. — In order to show the resisting power of airways of different lengths, for those sizes in more common use, the following table has been prepared, showing the potential value of each airway, as calculated by the formula
Potential of airway.
X
yk
Following this is another table giving the potential values of different circulations, by which is meant the circulation of different volumes of air under different pressures or water gages. A comparison of the potential values in these two tables will serve to show what circulation can be obtained in airways of given size and length when properly arranged and unobstructed.
Table. — Potential Values for
Different Airways
Length of Airway, 1
SUe of airway, feet
Potential vi
Eilue of airwi
iy
4 Xio
6 Xio
Potential Values of Different Circulations. — The circulation of a given quantity of air in a certain airway or mine requires
Theory Of Ventilation
a certain pressure or water gage, which determines the "potential of the circulation."
In the following table, the potential of the circiilation is calculated by the formula
Potential of circulation, X — -v/t? —
Table. —
Potential Values for Different Circulations
IVator
gage
Potential value of circulation
2M
13
H
Comparing this table' with that on the preceding page shows that to pass a current of 25,000 cu. ft. per min. through an airway of 5 X 8 ft., 3000 ft. long, including the return will require, practically, a 3-in. water gage. This is ascertained by observing that the potential value of an airway 5X8 ft., 3000 ft. long, as given in the first table, is, say 345. Then find the water gage corresponding as nearly as possible to this value, in the second table, in the vertical column for 25,000 cu. ft. per min. The potential of the circulation of this air volume under a 3-in. gage is, say 342, showing that a 3-in. gage is a little in excess of what is required to circulate 25,000 cu. ft. of air per minute in a 5 X 8-ft. airway, 3000 ft. long, including the return.
Effect of Splitting on Mine Potential. — As a mine is developed and its airways extended, it becomes impracticable to carry the air in a single current throughout the entire length of the airways, as the water gage then increases directly as
204 Mine Gases And Ventilation
the length or distance of air travel. To avoid this difficulty, the air must be divided or split" one ormore times; so that there will be two or more separate currents in the mine. Each of these currents is called a ''split of air/' or simply a ''split'' (see p. 219).
It should be observed that dividing th ciurent does not change the total rubbing surface (s) in the mine; but the area of passage is increased in proportion to the number of splits or currents. Calling the number of equal splits n, the area of passage (p. 211); in splitting an air current is na, and the formula for the potential can be written:
Split potential, X
Since the rubbing surface (s), the sectional area (a) and the coefficient (k) are constant, the potential (X) varies as n, or as the number of equal splits or currents. Therefore, any of the airway potentials of the first table can be multiplied 2, 3, 4, etc. times according to the number of splits or currents employed.
For illustration, suppose the airways of a mine are 5 X 10 ft. and have a total length, including return, say 10,000 ft.; and the required circulation is 100,000 cu. ft, per min. The velocity of the air should not exceed, say 500 ft. per min., in the airways. This will require a total area of passage of 100,000 500 200 sq. ft. But the sectional area of these airways is 5 X 10 50 sq. ft.; and there must, therefore, be 200 50 4 splits or currents to comply with the conditions named. The potential value, as given in the table, for a single current, is, say 275; and the mine potential for four splits is, therefore, 4 X 275 1100. By referring, now, to the second table giving the values of the potential of circulation, it is found that a potential value of 1100, in the circulation of 100,000 cu. ft. per min. shows a water gage between 1 and IJ in. The true value may be found by interpolation, if desired, and is 1.46 in.
The potential value of any desired circulation of air, as compared with the potential value or "potential factor" of the
Theory Of Ventilation 20*5
proposed mine or airway is thus seen to have an important practical value that commends it to all students of mining.
Example, — It is proposed to open a mine in a 6-ft. seam of coal and provide for a capacity of 1000 tons a day, A general estimate is desired of the requirements for the proper ventilation of the mine, under working conditions. In other words, what volume of air will be required and what will be the approximate water gage and horsepower necessary for the circulation of such quantity in this mine?
SohMon. — Assuming an average daily output of 2.5 tons of coal per miner, the number of miners working will be 1000 4- 2.5 400. Then allowing for, say 150 loaders and 50 company men including bosses, the total number of men in the mine will be 600, for whom the quantity of air specified by law must be provided.
Assume that the mine generates considerable gas and to cover all requirements, estimate on supplying 200 cu. ft. of air per man, per minute, which gives a total required air volume of 200 X 600 120,000 cu ft; per min.
In order to estimate approximately what water gage will result in the circulation of this quantity of air, it is necessary to decide on the size of the entries; and make the sectional area such as will allow of a safe maximum velocity of the air current in the cross-headings and find the number of splits required to meet these conditions.
In this case, suppose all entries to be 6 X 10 ft., giving a sectional area of 60 sq. ft.; and the mine being gassy, say the velocity of the air current on all cross-headings or splits must not exceed 360 ft. per min. This condition will require a total area of passage or the sum of the sectional areas of all the splits, 120,000 -f- 360 333 sq. ft. But the area of the entries being each 60 sq. ft., the number of splits required to give this area of passage and thus keep the velocity of the air currents in the splits within the specified limit is 333 -i- 60 5.5, say 6 splits or pairs of cross-headings.
The next step is to decide on the distance each pair of cross-headings will be driven, from which the extent of rubbing surface can be approximately estimated. For example, assume the cross-headings to be driven, say 2000 ft. on each side of the main heading, making 4000 ft. of entry, including the return, in each spUt. The total length of entry for the six splits is then 6 X 4000 24,000 ft. Assume the main headings are driven four abreast, so as to provide two intake haulage roads affording separate tracks for the empty and loaded trips; and two return airways.
If the cross-entries are turned to the right and left of the main headings, every 500 ft., the length of these headings may be taken as 3 X 500 1500 ft., giving a total length for the four headings 4 X 1500 say 6000 ft. The total length of all entries in the mine may thus be assumed as 24,000 + 6000 30,000 ft.
206 Mine Gases And Ventilation
The estimated rubbing surface is then -f- 10) X 30,000 960,000 sq. ft. ; and the mine potential is
i/ks 0.00000002 X 960,000
This is only an approximately correct value for this mine, because the six splits do not start from the shaft bottom.
The water gage required is then calculated from the mine potential and the air volume; thus,
It will be safe to assume, from the above calculation, that the proposed mine can be properly ventilated by the circulation of 120,000 cu. ft. of air per minute under a water gage of say 1.5 in., providing for six main air splits as described, and making due allowance for possible conditions.
The horsepower required to produce this circulation, assuming a general efficiency of if 60 per cent, is
KZS.OOO 0.60X33,000 4+, say ou np.
Example, — Find the unit pressure, water gage and horsepower required to circulate 80,000 cu. ft. of air per minute in a mine in two equal splits. The airways are all 8 X 10 ft., and have a total length of 12,000 ft., including the return airways.
Solution. — The sectional area of the airways, in this case, is a 8 X 10 80 sq. ft.; the perimeter is o + 10) 36 ft. The potential of the airway for two splits is then
The unit pressure is
P jp ygQ3 13.5 lb. per sq. ft.
The corresponding water gage is 13.5 6.2 say 2.6 in. The horsepower on the air, as calculated from the above unit pressure, is
Tf - <?P 80,000 X 13 .5
" " 33,000 " 33,000 "
Theory Of Ventilation 207
Or, the horsepower may be found directly from the mine potential, as follows:-
Example, — Find the quantity of air in circulation in four equal splits in a mine, when the size of the airways is 5 X 14 ft. and the total length of airways in all the splits, including the returns in each case, is 40,000 ft. ; the water gage at the shaft bottom where the air is divided being 3 in.
Solution.— 'The rubbing surface, in this case, is 40,000 X + 14) 1,520,000 sq. ft., and the sectional area of each airway 5 X 14 70 sq. ft. The mine potential for four splits is then
ks V0.00000002 X 1,520,000 The quantity of air in circulation under a 3-in. water gage is then
- 897 \/897 H- 5.2 X 3 say 106,000 cu, ft per min.
Caution. — In the calculation of all problems in mine ventilation, regard must be had to the conditions with respect to the power and the pressure producing or resulting from the circulation of the air in the mine.
Both the power and the pressure are commonly said to produce the circulation; but, as a matter of fact, it is the power that produces the circulation, while the pressure is the result and measured by the resistance of the mine or airway.
Unfortimately, these factors do not vary alike, but the cube root of the power varies as the square root of the pressure; or, more simply, the cube root of the power ratio, in any mine or airway, is equal to the square root of the pressure ratio, for the same circulation; thus,
For example, in what proportion must the power be increased in order to double the pressure (p/pi 2)?
power ratio \/2 1.414 power ratio 1.414 2.828
208 Mine Gases And Ventilation
In other words, if 10 hp. on the air produces a given pressure or water gage in a certain mine or airway, it will require 2.828 X 10 28.28 hp. to double that pressure or gage.
Use of Potential Factors. — Attention has been drawn to the potentiality of an airway or mine, in respect to the resistance it can offer to the passage of air, by virtue of its rubbing surface (s) and its sectional area (a). The potential of an airway or mine is the factor that determines the quantity of air such airway or mine will pass, for any given power or pressure. It is important, in the use of the potential, therefore, to consider whether the pressure or power is in question.
F,OT every airway or mine, therefore, there is a power potential (Xu) and a pressure potential (Xp). The cube of the power potential is equal to the square of the pressure potential, for the same mine or airway, giving the equal values. .
An inspection of these equal values shows that:
1. The quantity of air a given power will circulate varies as the power potential of the airway or mine.
2. The quantity of air a given pressure will circulate Varies as the pressure potential of the airway or mine.
Hence, in comparing the circulations in different airways or mines, a constant power requires the use of the power potential, and a constant pressure, the pressure potential.
Other Potential Formulas. — Transposing the values given above makes it possible to calculate the power or pressure required to circulate a given quantity of air in a certain airway or mine directly from its potential factor.
P-lxj 'X?
It is, likewise, possible to calculate the quantity of air a given power or pressure will circulate against any given potential factor representing a certain airway or mine, by simply multiplying the cube root of the power or the square
Theory Of Ventilation 209
root of the pressure by the corresponding potential of the airway or mine as expressed by the following formulas:
A few examples will serve to make the use of these formulas clear and to show their practical application, in the rapid estimation of what is required in the proposed development of mines, in order to make suitable provision for their proper ventilation.
Examples For Practice
1. If 25 hp. produces a water gage of 1.5 in., in a certain mine, what water gage will 40 hp. produce in the same mine?
Solution. — Since the square root of the pressure or water-gage ratio
is equal to the cube root of the power ratio, calling the required water
fx 3/40 3/8 ,/— ,
X 1.5 X 1.37 2.05 in.
2. It is proposed to provide for the circulation of 75,000 cu. ft. of air, in two generally equal splits, the airways including the return in each split being 6 X 10 ft. in section and about 8000 ft. long, (a) Find the power potential for the entire mine; and (b) calculate from that both the power and the water gage of the circulation.
Solution, — (a) The sectional area of the airways, in this case, isa 6 X 10 60 sq. ft.; the total rubbing surface in the mine, s 2 X + 512,000 sq. ft. Substituting these values and that for the coefficient of resistance k 0.00000002 in the formula for power potential of mine,
The power on the air required to circulate 75,000 cu. ft. of air against this potential is, then,
The water gage, as calculated directly from the power potential, Xu 652.6, is
Or, the water gage may be found thus
mm.
210 Mine Gases And Ventilation
3. (a) Calculate ,ihe value of the pressure potential for the entire mine mentioned in the preceding question, the airways being 6 X 10 ft. in section and about 16,000 ft. long, including the return, assuming as before two equal splits; and (&) calculate from this pressure poljpntial the power that will produce the desired circulation of air; namely 75,000 cu. ft. per min. and the resulting water gage.
Soluiion.—{a) The total rubbing surface is -h 10) 16,000 512,000 sq. ft. For two equal splits, the area of passage in this mine is a X 10) 120 sq. ft. The mine pressure potential is then
(6) The power on the air, calculated from the pressure potential, is then,
The water gage, calculated in the same manner, is
4. What volume of air will 10 hp. circulate in an airway 6X8 ft., in section, and 2500 ft. long?
. Solution. — The sectional area of this airway is a 6 X 8 48 sq. ft. ; the rubbing surface 2500 70,000 sq. ft. The power potential is therefore
Xu -V7= — -. 429.1, nearly,
Vks -0.00000002 X 70,000
For 10 hp. on the air, the quantity of air in circulation in this airway is q Xu 429.1-10 X 33.000 8ay 30,000 cu. /u per min.
5. (o) What quantity of air will be circulated, in the airway, in the last example, under a 3-in. water gage; and what power on the air will be necessary to develop this quantity and gage? (6) What was the original water gage when 10 hp. circulated 30,000 cu. ft. of air, in this mine?
Solution. — (a) Since the square of the pressure potential is equal to the cube of the power potential
Xp y/xu \/429.P 8890, nearly Then, 5 Xp -y/p 8890 \/5.2 X S say 35,000 cu. ft. per min. The power required to produce a 3-in. water gage is
Theory Of Ventilation 211
(6) The previous water gage due to the circulation of 30,000 cu. ft., in this mine, under 10 hp. can be calculated in several ways; but most simply, thus,
The calculation may also be made from the potential ; thus,
Area of Passage. — It is important to notice that the potential value for any mine is determined by its area of passage with respect to the resisting power of its rubbing surface. For a single air current the area of passage is the sectional area (a) of the airway. For 2, 3, etc., equal splits the area of passage is 2a, 3a, etc.; for n equal splits the area of passage, for the mine, is na. .
The unit of resistance being fc, the resisting power of the entire airway or mine is indicated by ks; and the potential values of the mine with respect to power and pressure, respectively, are thus expressed
Mme power potential, — 'kI , yj-
Mine pressure potential, Xp , na
na
It should be observed that the mine power potential varies as the number of equal splits or currents, which is not true of the pressure potential of a mine. This fact has an important application, since, for the same mine, the rubbing surface being constant, the number of splits (n) is equal to the powerpotential ratio. An example will serve to make this clear.
Example. — Suppose it is desired to ascertain quickly how many equal splits would pass the same quantity of air (75,000 cu. ft. per min.), under a 2-in. water gage, in Example 3, previously given where two splits of air gave a water gage of 6.41 in., the power remaining constant.
Solution. — From the equat'ons expressing the potential values previously given (p. 208) , it appears, for the same quantity of air in circulation, the pressure or water gage varies inversely as the cube of the power potential. But, since the power potential varies as the number of splits in a mine, it follows that, for the same quantity of air in circula-
212 Mine Gases And Ventilation
tion, the power remaining constant, the pressure or water gage varies inversely as the cube of the number of splits.
In other words, for the same quantity of air, and constant power, the pressure or water-gage ratio is equal to the cube of the inverse ratio of the number of splits. In this case, calling the required number of splits n, the split ratio is n/2, and the corresponding water-gage ratio 2/6.41, and we write
Mi =3.205 n 2-'a205 2.95, ay 3 spliU.
The reference, thus far, has been to equal division of the air current and the rules and formulas given above applystrictly, only to mines in which the air current is divided at or near the main entrance and passes through the mine in two or more separate and equal splits.
Part Potential Value* — The part potential value is found by omitting k in the calculation, and writing it outside the parenthesis. The relative potential obtained by canceling common factors cannot be used here. The relative potential, so much used in the calculation of the splitting of air currents, can only be employed when the potential appears as a ratio (see p. 221.)
General Potential of a Mine. — An important application of the potential method, in mine ventilation, is the calculation of the potential value for the entire mine when the airways and shafts are of various dimensions.
Example. — Calculate the general mine power potential in the following mine, shafts 1250 ft. deep:
Shafts, upcast and downcast. Main airway seam), Cross-headings ("A" seam). Tunnel to "B" seam. Return air course ("B" seam).
Solution, — The total power producing a given circulation, is clearly equal to the sum of the powers absorbed in the several sections of the mine, as expressed by the. following general formula:
It will be readily observed that this general formula, for a mine of
Area
Rub. Sur.
8 X 10 ft..
6 X 10 ft..
6X8 ft..
5X8 ft.,
5 X 14 ft..
Theory Of Ventilation 213
various sections being the coefficient of efficiency of the ventilator), is derived from the power formula
1
H
But, since 1/Xh* k 8 /a* and being constant, it is much simpler in using the above general formida, to factor and write k outside of the parenthesis, which makes each of the potential values within the parenthesis what may be called a ''part potential" whose value is, omitting kj
Part potential Xu -j7=;andJL i.
Xu' o'
Now, calculating the value of 1/Xu' s/a for each separate section of air passage in the mine given above,
QKf. 1 90,000
Return air course ("B" seam), y, 70 v 70 X 70 "-5522
Potential factor for entire mine - 2.1767
The part power potential for this mine is therefore
Xo - ,. 0.7716 V2.1767
Examyle, — (a) From the part power potential calculated for the mine, in the preceding example, find the horsepower required to circulate 30,000 cu. ft. of air per minute in a single current, assuming the ventilating fan to have a mechanical efficiency /iC 60 per cent. (Jb) What water gage will be produced by the resistance in the mine, for this circulation?
Soiutwn, — (a) The required horsepower of the ventilator is
(6) The mine water gage due to this circulation is
General Mine Potential, Equal Splits. — It is possible to calculate the general mine potential when there are two or more airways of equal dimensions, by simply multiplying the common sectional area by the number of airways, as shown by the following example:
214 Mine Gases And Ventilation
Example. — A drift mine is opened on the triple-entry system. It is proposed to drive the main intake 7X10 ft. in section, a distance of 3000 ft. to the boundary. The cross-entries are to be driven double, 5 X 12 ft. in section and 1500 ft. to the side lines on each side of the main road, making in all 6000 ft. of cross-entries, including the returns. The main-return airways, on each side of the main intake are each 7X12 ft. in section and 3000 ft. long. Calculate (a) the horsepower on the air; and (6) the water gage produced, for a circulation of 50,000 cu. ft. of air in this mine, in two equal parts.
SdiUian. — The first step is to calculate the value 1/X' for each sectional division; thus
Main intake, 7X10 ft., 3000 ft. long: a 70 sq. ft. ; 102,000 sq. ft. Cross-entries 5X12 ft., 6000 ft. long : a 120 sq. f t. ; 204,000 sq. ft. Main returns, 7 X12 ft., 3000 ft. long: a 168 sq. ft.; =228,000 sq. ft.
Substituting these values in the formula for finding the part potential factor for each section,
rv yr 1 204,000 _niifti
Potential factor for entire mine 1/Xo* 0.4635
For the horsepower and water gage, we have
" SpOO X? 33;006 0.4635= say 35 hp.
w.g. yr- r-jr X 0.4635 4.46 tn.
Tandem Circulations
Summation of Potentials. — When an air current passes in succession through two or more airways of different section, the total unit pressure (lb. per sq. ft.) due to the circulation is equal to the sum of the unit pressures of the several sections. The arrangement, in this case, may be described as "tandem.''
Likewise, in a tandem circulation, the total power on the air (ft.-lb. per min.) producing the circulation is equal to the sum of the powers absorbed in the several sections through which the current passes.
Indicating the potentials of the respective sections of the
Theory Of Ventilation 215
air-course in a tandem circulation by Xi, X2, Xt, etc. ; and the corresponding unit pressures and powers on the air by pi, pi, Pj, etc.; and Mi, mj, w,, etc., respectively, remembering that the square of the pressure potential is equal to the cube of the power potential, as expressed by the formula
p — -Am
we can write the following:
For tandem circulations, calling the general mine pressure Po and the total power on the air wo.
These formulas may be written more simply by indicating the summation of the potential factors by the character £; thus.
Mine pressure, po £
or
In like manner, the total power on the air or power producing tandem circulation in a mine is . expressed by the formula.
Power on the air, Uo — h — h etc. )
or
These formulas may be expressed by indicating the summation of the potential factors by S, as before; thus,
In it tandem circulation, if desired, the general mine po-
216 Mine Gases And Ventilation
tentials for power (Xuo) and for pressure (Xpo) can be calculated by the formulas
To illustrate the formulas that apply to a tandem circulation where a single air current is carried continuously through shafts and airways of different size or cross-section, assume the following mine is passing 30,000 cu. ft. of air in a single undivided current:
1. Downcast shaft 8 X 12 ft., 600 ft. deep
2. Main road and return, each. . ... 6 X 10 ft., 1200 ft. long
3. Cross-tunnel and return, each ... 6X8 ft., 200 ft. long
4. Upper seam and return, each. ... 6 X 14 ft., 2000 ft. long
5. Upcast shaft 10 X 10 ft., 225*0 ft. deep
The sectional areas are 96, 60, 48, 70 and 100 sq. ft.; and the rubbing surfaces, 24,000, 76,800, 11,200, 152,000 and 90,000 sq. ft., respectively.
Part potential factors, " 0.0271
Potential factors for entire mine, L0170
Mine part x.„ ,, ,/ =0.9944
potentials, . vl.0170
Xpo , . 0.9916
Tj fcQ* 0.00000002 X 30,000" , „ „ Pressure, 18.3
Theory Of Ventilation 217
Water gage, w.g. p/5.2 18.3 5.2 3.5 in.
Example, — A shaft mine has been opened on the triple-entry system. The downcast and upcast shafts are each 600 ft. deep and 8 X 20 ft. in section. The main headings have been driven a distance of 2000 ft. from the shaft bottom. The center one of these headings is the intake and is 7 X 14 ft. in section, while the two side headings are the return always for the respective sides of the mine and are each 6 X 12 ft. in section. On each side of the main headings, cross-headings, 6 X 10 ft. in section, have been driven 500 ft., including the return in each.
If the intake air divides at the face of the main heading and equal currents ventilate the two sides of the mine, what power on the air will be required to circulate a total of 60,000 cu. ft. per min. in this mine, and what water gage will be produced in the fan drift?
Solution, — The first step is to calculate the potential values of the two shafts, main intake, two cross-headings and two return airways, as follows, remembering that these being equal spUts, it is only necessary to double the potentials of the cross-headings and return airways by taking twice the sectional area, in each case:
Shafto, 8 X 20 ft., 600 ft.; a 160 sq. ft.; - 67.200 sq. ft.
Main intake, 7 X 14 ft., 2000 ft.; a 08" sq. ft.; - 84,000 sq. ft.
Two cross-headings, 6 X 10 ft., 600 ft.; 2a - 120 sq. ft.; 32,000 sq. ft.
Two return airways, 6 X 12 ft., 2000 ft.; 2a 144 sq. ft.; - 144,000 sq. ft
The part potential factors are then as follows, omitting k
Main intake,
Two cross-headings,
Two return airways,
The horsepower on the air in the fan drift, in this case, is found by substituting this general potential factor, in the formula for finding the power in a tandem circulation; thus,
218 Mine Gases And Ventilation
The water gage, in the fan drift, due to this circulation, can be calculated in like manner, independently, from the same general potential . factor, by substituting the same in the formula for finding the unit pressure and water gage in a tandem circulation; thus,
w
The same result is obtained when the water gage is calculated from the power and the quantity of air in circulation.
Splitting The Air Current
Early Practice, Coursing the Air. — In the early practice of mine ventilation, the method commonly adopted was that known as coursing the air.'' In this method the air was conducted throughout the mine in one continuous current, from the intake opening to the point where it was again discharged into the atmosphere.
Single Current Not Adequate.— rExperience has shown, however, that a single air current is not adapted to the ventilation of a large mine, for many reasons. As a mine is ' developed and the workings extended, more men are employed and greater quantities of air are required to ventilate the mine and dilute and carry away the gases generated.
Need of Dividing the Air Current. — The division of the air into two or more ciurents provides separate ventilation districts in the mine and brings the ventilation under better control, since the quantity of air can then be proportioned to the requirements in each district
A larger volume of air can be circulated by the same power, and the velocity of the current is kept low.
The smoke and gases generated in one section of the mine are not carried by the current into another section, but pass directly into the main return airway and are conducted out of the mine.
A local explosion of gas or dust, in one portion of the mine, is not as liable to extend throughout the mine.
Theory Of Ventilation 219
Method of Splitting the Air-cjirrent. — Whenever two or more passages or airways are provided by which the air current can travel in passing through the mine, the air will always divide between them in proportion to their several potential values. Hence, all that is required to spUt an aircurrent is to provide two or more separate routes for its pa*ssage. Each separate current is called an "air split" or simply a "split."
Natural Splitting. — When all the airways are open to the free passage of the air-current through them, the air divides naturally between them, each airway or split taking a quantity of air in proportion to its potential value. In other words, the potential of the airway is an index of the quantity of air that airway will pass, in natural splitting.
Proportionate Splitting. — When any other division of the air is desired than the natural division, it is necessary to introduce regulators in one or more of the airways so as to obstruct the flow in those splits that natiu-ally take more than the desired proportion, and thereby increase the quantity passing in the other airways till the desired proportion is reached.
. Primary and Secondary Splits. — -A branch or split off the main air ciu-rent is called a "primary split." If a primary air split be again divided, the result is a "secondary split." When the air current is equally divided between two or mol*e airways the spUts are said to be "equal;" but when each airway passes a different volume of air the splits are "unequal."
Increase of Quantity Due to Splitting. — The quantity of air in circulation is proportional to the general mine potential. In other words, the quantity ratio is always equal to the mine-potential ratio; the power potential being used for a constant power, and the pressure potential for a constant pressiu-e; always remembering, however, that the cube of the power potential is equal to the square of the pressiu-e potential. Denoting the original quantity of air in circulation, by Qi and the original mine potentials for power and pressure by Xui and Xpi, respectively; and designating
220 Mine Gases And Ventilation
these factors after splitting, by Q2t Xu2 and Xp2, respectively, we have the following formulas:
Power constant, Qa Qi jf; or Qj Qi -v/ ( v)
Pressure constant,Q2 Qi iJ O2 Qi a/ I y)
An illustration of the use of these formulas is to be found in the solution of the example given under Secondary Splitting. In that example (p. 242), the power on the air remained constant before and after splitting the current. The pressure potential was used, which before splitting was Xpi 0.6708, and after splitting Xp2 0.8554:
cu. ft per min.
Natural Division Of Air
In all splitting calculations, it is. assumed that the unit pressure (lb. per sq. ft.) is the same at the mouth of each split starting from the same point. Therefore, writing the formula for unit pressure.
Then, since p and k are both constant, varies as a/lo
and q varies as clxJy
This expression, as previously explained is the pressure potential of the airway. It must be remembered that the square of the pressure potential {Xp) is equal to the cube of the power potential (X); thus,
It IS the pressure potential that is always used in splitting calculations; because, as stated above, the unit pressure is the
Theory Of Ventilation 221
same for all splits at one point. The calculation of the quantity of air passing in any one of two or more splits starting from the same point in a mine, is based on the following simple rule:
Rule. — The ratio of the quantity of air passing in a single split, to the total quantity for all the splits, is equal to the ratio of the pressure potential of that split, to the sum' of the pressure potentials for all the spUts.
Calling the quantities passing in the several splits, qi, Qty etc., and the corresponding split potentials Xi, X, Xt, etc.; the total quantity of air in circulation in all the splits Q, and indicating the sum of the split potentials by XX;
Q - qi + Q2 + qz + etc. and
XX Xi+ X2+ Xa + etc.
Then, according to the rule given above,
Q Sx
The work of calculation is much simplified and shortened by using what may be called the ''relative potential" values, instead of finding the actual pressure potential for each split. This is only possible in splitting calculations, where the potentials are used as ratios, and the value of the ratio is not changed by the cancellation of any like factors in all the potentials.
Relative Potential Values. — Whenever the potential is used as a ratio, as in splitting air currents, the relative values should be used. These are calculated from the lowest relative values for the areas, perimeters and lengths of the several airways or splits. For example, if the areas are 48, 60 and 72 sq. ft., the lowest relative values, canceling the common factor 12, are 4, 5 and 6, respectively Likewise, instead of the perimeters, 28, 32, 34; use the lowest relative perimeters 14, 16, 17, canceling the common factor 2 from each.
The use of the ''relative potential" value, in all calculations to determine the natural division of air between two or more
222 Mine Gases And Ventilation
airways, is one of the most important considerations in the saving of time and labor and avoiding unnecessary mul-. tiplicity of figures, which increases the opportunities for error and yields less accurate results. An example or two will serve to make this fact plain.
Summation of Split Potentials. — The circulation of air in two or more splits or currents, in a mine, differs from a tandem circulation in the fact that the same unit pressure circulates the air in each and all the splits, which are thus separate currents moved by one pressure; while in a tandem circulation one continuous current passes in succession through different airways or sections of the mine.
While in a tandem circulation the mine pressure is equal to the sum of the pressures for the several sections through which the current passes; and, likewise, the total power for the mine is equal to the sum of the powers absorbed in the sections; in a split circulation, the total power for the mine is equal to the sum of the powers absorbed in the splits, but there is but one pressure, which is the same for all the splits starting from the same point in the mine. As before, indicate the several split pressure potentials by Xpi, Xp2j Xpt, 'etc.; the corresponding powers on the air by Mi, wj, u, etc.; and the total power on the air by wo, remembering that it is necessary, in all splitting calculations, to use the pressure potential,which has the value
Xp a
The work is simplified by using the part potential value, as previously stated, omitting k when finding the potential values and multiplying the final result by that coeffi<;ient.
The following shows the development of the formulas for the summation of the potentials in split circulations where the splits all start from one point in the mine:
A pi A p2
Theory Of Ventilation 223
By the principle of splitting air currents,
Combining equations 2 and 3 and simplifying,
Finally, substituting these values (4) in equation 1, and factoring, .
From Equation 5 is obtained the formula for calculating the horsepower on the air at the point of split, by the summation of the part pressure split potentials:
Horsepower on the air. ff
The formula for calculating the water gage, in like manner, is
Equal Splits. — When an air current is divided natiuaJly between two or more equal splits, the calculation of the mine potentials, velocity, pressure, power, etc., is the same as for a single undivided current, except that the sectional area (a) of the airways must be multiplied by the number of splits (n) to obtain the total area of passage (na).
To illustrate the application of the formulas in this case, assume an air current of 60,000 cu. ft. of air is circulated in three equal splits, the size and total length of the airways, including the returns being 5X8 ft. and 10,000 ft. long.
Velocity, -5L — 500 ft. per min.
na X o;
224' Mine Gases And Ventilation
Water gage, w.g. p/5.2 10.83 5.2 2.08 in.
Power on
the air, fcQ 0.00000002 X 60,000*
Unequal Splits. — To illustrate the formulas used in the calculation of the natural division of an air current between two or more airways and the pressure and power on the air, assume a current of 75,000 cu. ft. per min. is passing in the following three splits, starting from the same point of the main airway or at or near the intake opening. The lengths given for the several splits include the return, in each case; and the pressure and power are for the circulation in the splits only.
Split A, 6 X 10ft.; 2000 ft. long; a 60sq. ft.; 32ft.; I 2000ft. Splits, 6 X 8ft.; 1500ft. long; a 488q.ft.; o 28ft.; I 1500ft. Split C, 4 X 12 ft. ; 2500 ft. long; a 48 sq. ft. ; 32 ft. ; Z 2500 ft.
The lowest relative values are as follows: Areas, 5, 4, 4; perimeters, 8, 7, 8; lengths, 4, 3, 5.
Relative split pressure potentials,
Xp6 4VO905 1.746 Xp, 4 4V0.IOOO 1.265
Sum of potentials, SXp 4.987
Natural division of air current,
qt X 75,000 26,260 cu. ft.
g. X 75,000 19,020 cm. ft. Total circulation, Q 75,000 cu. ft.
Theory Of Ventilation 225
To calculate the pressure and power of the cu'culation, it is necessary to employ the part-potential values, instead of the relative values; thus,
Part potential values,
General part potential for splits, SXp. 4.636
Horsepower on the air,
Examples In Natural Division
Example. — An air current of 100,000 cu. ft. per min. is divided at the foot of the downcast shaft, between the following four air-courses or splits, thereby providing two separate ventilation districts on each side of the shaft :
Split A, 8 X 12 ft., 6000 ft. long
Split By 6 X 20 ft., 12,000 ft. long
Split C, 6 X 12 ft., 8000 ft. long
SpUt D, 4X6 ft., 1000 ft. long
All the splits are open to the free passage of the air, no regulators being used, (a) Rnd the natural division of the main air current or the quantity of air passing in each split, (b) What is the pressure due to this circulation? (c) What is the horsepower on the air?
Solution. — (a) The first step is to calculate the relative pressure potential for each of the four air splits. The area, perimeter and length of each airway are as follows:
Split Ay a 96 sq. ft.; o 40 ft.
Split By a 120 sq. ft,; o 52 ft.
Split C, a 72 sq. ft.; o 36 ft.
Split Dy a 24 sq. ft.; o 20 ft.
I 6,000
I 12,000
I 8,000
I 1,000
226 Mine. Gases And Ventilation
Instead of using these full values as when finding the true potential value of an airway, the lowest relative values for the areas, perimeters and lengths are used. These relative values are obtained by canceling the common factors in the areas, perimeters and lengths separately, which gives the following :
Split A, a 4; ' o 10
Split B, a 6; o 13
Split C, a 3; 0=9
Split D, a 1; 0=5
I 6 I 12 I 8 I 1
The relative split potentials are then found as follows:
Sum of relative potentials 2 . 987
Since the quantity of air passing in each split, in natural division is proportional to the corresponding potential, the quantity ratio is equal to the potential ratio, which is true also for the sum of the quantities and the sum of the potentials. Thus, the ratio *of the quantity (q) passing in any split, to the total quantity (Q) in circulation, is equal to the ratio of the corresponding split pressure potential (Xp), to the sum of all the split potentials (SXp).
Therefore, substituting the relative potential values just found in this formula gives the following:
Split A, Qa 100,000 34,670 cu. ft, per min.
Split B, 96 X 100,000 29,960 cu. ft, per min.
Split C, qc X 100,000 20,500 cu. ft, per min.
Split D, qd 2" X 100,000 14,970 ca, ft, per min.
Total quantity 100,000 cu. ft, per min.
Theory Of Ventilation 227
(6) Since the pressure is the same for all the splits, it can be calculated from any one of the given splits, by substituting the values for that split in the formula
Thus, taking split .4,
(c) The horsepower on the air in the main entry, or the horsepower producing this circulation is, then,
w Op 100,000 X 6.48 iQft .
" 33,000 - 33,000 " '
As an illustration of the usefulness of the summation of potential values, we give below the calculation of the horeepower on the air, unit pressure and water gage developed in the circulation of 100,000 cu. ft. of air per minute, in four splits, previously calculated by the usual method in the las.t example, where it was necessary, first, to find the natural division of the air.
Example. — An air current of 100,000 cu. ft. per rnin. is divided, at the foot of the downcast shaft, between the following four splits:
Split A, 8 X 12 ft., 6,000 ft., long; a - 96 sq. ft.; s - 240,000 sq. ft.
Split B, 6 X 20 ft., 12.000 ft., long; a - 120 sq. ft.; s - 624,000 sq. ft.
Split C, 6 X 12 ft, 8,000 ft., long; a - 72 sq. ft.; 8 - 288,000 sq. ft.
Split D, 4 X 6 ft.. 1,000 ft., long; a - 24 sq. ft.; 8 - 20,000 sq. ft.
Calculate the horsepower on the air, unit pressure and water gage concerned in producing this circulation, using the part potential values and employing the method by summation of potentials; no regulators being used in the mine, but the division of air being natural.
SoltUion. — The part potential values for the several splits are as follows :
A,
Xpi —
Split B,
Xp2 —
Split C,
Xpt
72V; -1.138 SpUtD, A-p4 24 -0.831
Sum of part pressure potentials (2Xp) 5.653
228 Mine Oases And Ventilation
Substituting this value for 2Xp, in the formulas for finding the horsepower on the air and water gage, in natural splitting,
In natural splitting or when no regulators are employed the general mine potential is always equal to the sum of the several split potentials, which is true for either power or pressure.
General Mine Potential. — The power potential for the combined splits can be calculated from the total quantity of air in circulation and the resulting pressure; using the formula
Example. — What is the general power potential for all the splits combined, in the example given above, where 100,000 cu. ft. of air was circulated under a pressure of 6.48 lb. per sq. ft. ?
Solution, — The general power potential for these combined splits is
Example, — An air current of 60,000 cu. ft. per min. is passing in an airway 8 X 10 ft. in section, to a point 1500 ft. distant from the foot of the downcast shaft, where it divides naturally between the following four airways or splits:
Split A, 5X6 ft., 900 ft. long
Split B, 6X6 ft., 825 ft. long
Split C, 4X6 ft., 840 ft. long
Split D, 4X5 ft. 720 ft. long
What is the quantity of air passing in each split; and what will be the water-gage reading for the entire mine and power on the air, at the foot of the downcast shaft?-
SolvHon. — Since the water gage is required in this case, the relative potential values cannot be used; but, instead, the part potential value (omitting k) is found for the main airway and for each split separately;
Theory Of Ventilation 229
thus, taking the length of the main airway including the return as 2X 1500 3000 ft.:
The general split potential (Xo) is equal to the sum of the potentials for the four splits; thus,
Xo HXabcd 4.392
The quantity of air that will pass in each of these splits is proportional to the corresponding split potential, assummg thatno regulators are eAiployed but all the airways are free and unobstructed. The natural division of the air between the four splits is therefore calculated in the usual manner, as follows:
Split Ay Qa - 60,000 .' 15,950 cu.ft. per min.
Split By (ft 60,000t=_20,920 cw. ft. per min.
Split C, gc A per mtn.
Split D, qd 60,000 10,740 cu. ft per min.
Total circulation 60,000 cu. ft, per min.
In order to find the water-gage reading at the foot of the downcast shaft, for this circulation, it is necessary to calculate the general mine potential Xp by combining, in tandem, the mam-au'way potential (Xi) and the general split potential (Xo) previously found, using the formula (p. 215).
Substituting the values of the potential factors previously found. .Main airway, -yT o 177 0.2109
Split section, -y . 0092 0.0518
Sum of values, 0.2627
230 Mine Gases And Ventilation
Finally, substituting this value in the above formula for finding the mine water gage,
0.00000002 X 60,000* X 0.2627 „ . w.g. =3.64 tn.
In like manner, the power on the air, at the foot of the shaft is calculated by the formula
Proportionate Division Of Air
Every large and well managed miDe is, now, divided into two or more separate ventilation districts. The natural division of the air current between these several districts is not generally in proportion to their respective needs.
The longer entries, working more men and requiring the most air for their ventilation are the ones that haVe thfe greater resisting power and, as a result, receive a lesser proportion of the air, in natural division; while, on the other hand, the shorter air-courses where fewer men are working and less air is required, have a smaller resisting power and naturally pass the larger quantity of air.
To Regulate the Air. — In order to overcome these natural conditions, in mine ventilation, and divide the main air current so as to give each district of the mine the required proportion of air, it is necessary to employ some means that will produce this result.
Two methods have been used to divide the air proportionately; they are as follows:
1. The flow of air is obstructed in those airways that take naturally more than the desired porportion.
2. The power on the air, at the mouth of each split, is proportioned to the work to be performed in that split.
The former of these two methods has been in common use for many years; the latter was suggested (Mine Ventilation, Beard, 1894, p. 93) as an improvement and has been put in use since in many mines where practical considerations would permit.
Theory Of Ventilation 231
The Box Regulator. — This form of regulator ia ahown in Fig. 32 (o), and consists of a brattice built in the return airway or haulway. As shown in the figure, an openii is provided in the brattice and a sliding shutter is used to regulate the size of the opening so as to control the flow of air ia that airway or split. If more air is needed the shutter. is pushed back so as to enlat the opening ; or the shutter can be partially closed to decrease the quantity of air passing in the split.
The Door Regulator. — Wherever the conditions will permit this form of regulator to be employed it will be found an improvement over the common "box regulator," just described.
As shown in Fig. 32 (b), the door regulator consists of a door hung at the mouth of an entry or split and swung into the
wind. The door should be arranged so that it will fall naturally against a set-stop, and when not in use will assume a position whereby the air current will be divided in the desired proportion, between the two airways or splits.
Effect of Regulator. — Any regulation of the air current in a mine, to accomplish a distribution of air other than what is natural, causes an increase of both the power producing the circulation and the resulting preaaure or water gage. This is true in every case, whatever form of regulator is employed, provided the total quantity of air in circulation is not decreased. The reason -that an increase of power is necessary in proportionate splitting, is that an increase in the circulation in any split causes a corresponding increase in pressure; and this pressure is the same for all splits starting
232 Mine Gases And Ventilation
from the same point in the mine. To circulate the same quantity of air against this higher pressure requires a corresponding increase of power.
lUustraiion. — Let it be required to find the horsepower and the pressure per square foot, in the following distribution of the air current between the following four splits; the natural distribution of air, as previously calculated (p. 225), being repeated here, for sake of comparison:
SoltUion. — The first step is to calculate the natural pressure for each split when passing the required quantity of air per minute, by substituting the following values for the area, perimeter and length of each split, in the formula for finding the unit pressure:
Split il.
long.
Split B,
6 X 20 ft..
long,
Split C.
6 X 12 ft.,
long.
Split D,
6 ft..
long,
Total circulation.
Split A,
a 96 sq. ft.;
o - 40 ft.;
I 6,000 ft.
Split B,
o - 120 sq. ft.;
I 12,000 ft.
Split C,
o - 72 sq. ft.;
o - 36 ft.;
I 8,000 ft.
Split D,
a - 24 sq. ft.;
o - 20 ft.;
I 1,000 ft.
The natural pressure in each split is then calculated as follows:
Q . 0.00000002 X 6000 X 40 X 20,0 00 o it f,. r.
a 0.00000002 X 8000 X 36 X 30,000 .oom,.
Q y. r, 0.00000002 X 1000 X 20 X 10,000 oaa lu u
The highest natural pressure is developed in Split C, in the required distribution of air, and that is, therefore, the "open" or "free" split, regulators being necessary in each of the other splits, to raise the pressure to the same amount.
The horsepower producing this circulation is then
H 3PQQ 42.09 hp.
Pressure Due to Box Regulator. — The primary effect of this regulator is to increase the pressure on its intake side, by
Theory Of Ventilation 233
obstructing the flow of air in the airway or split that it controls. This increase of ventilating pressure is necessary to accomplish the desired increase of circulation in another airway, which remains open or unobstructed and which, for that reason, is called the ''free split."
The increase of pressure is the pressure due to the regulator; and is equal to the difference between the natural pressure of the free split and that of the split in which the regulator is placed, calculated for the required distribution . of air. For example, in the illustration previously given, the natural pressure required to circulate 30,000 cu. ft. of air in Split C was 13.89 lb. per sq. ft., while that required to circulate 20,000 cu. ft. in Split A was only 2.17 lb. per sq. ft. The pressure due to the regulator in Split A is, therefore,
Velocity of Air Passing Regulator. — The velocity of the air flowing through the regulator is determined by the difference of pressure on its two sides or the pressure due to the regulator. This velocity is calculated from the well known formula
In the case of a regulator, the pressure head is equal to the pressure (pr) due to the regulator, divided by the weight of 1 cu. ft. of ak (w 0.0766 lb.) ; and taking 2gf 2 X 32.16 64.32 ft. per sec, the theoretical velocity of the air due to this pressure is
By this formula, the theoretical velocity corresponding to the pressure due to the regulator in Split A is
Quantity Passing Regulator. — Owing to the vena contracta, at the opening in a box regulator, the effective area of the opening is only 0.62 of the actual area A; and the
234 Mine Gases And Ventilation
quantity (Q), in cubic feet per minute, passing through the opening, is
Q S7.2Av Or, substituting the value of v, as given above,
Q 37.2 X 29AVr 10784 Vpr Or, since p 5.2 w.g,
Q 1078i4V5.2i/;.flf.= say 2460A\/m
Area of Opexiiiig, Box Regulator. — The area of the opening required to pass any given quantity of air, in splitting, is found by solving the last formula given above, with respect to -4, as follows:
Q 0.00G4Q
A
Required circulation
Split A,
Split J5,
Split C,
Split D,
Example, — Calculate the size of opening in each of the regulators in Splits Af B and D, in the illustration previously given where the required circulation was as follows:
Natural pressure
13.89 lb. per sq. ft. FVee split
first step is to find the pressure due to the regulator and reduce that to water gage, in each case. The pressure due to the regulator is found by subtracting the natural pressure for the given split from that of the free split, which is always the one having the greatest natural pressure. Thus,
Pressure due to regulator Water gage
Split A, 13.89 - 2.17 11.72 lb. per sq. ft.; 11.72 -f- 5.2 - 2.25 in. Split 5, 13.89 - 11.55 2.34 lb. per sq. ft.; 2.34 h- 5.2 0.45 in. Split Dy 13.89 - 2.98 10.91 lb. per sq. ft.; 10.91 -i- 5.2 2.10 in.
Substituting these values for the water gage due to regulator in the formula for finding the area of opening,
Split A, Aa — T-=-Z 7 5.33 sq.ft.
Vw,g. V2
o D A 0.0004 X 40,000 Q- .. Split B, Ai -. — 23.85 sq. ft.
Vo.45
a r. n a 0.0004 X 10,000 .. D, Ad y 2.76 so. tt.
Theory Of Ventilation 235
Use of the Door Regulator. — In the use of the door regulator, the same general formulas apply, except that in estimating the quantity of air that will pass the regulator, for a given gage or pressure; or the area of opening necessary to pass a given quantity under such gage, no allowance should be made for vena contracta, which gives the following:
Quantity of air passing through an area of opening ii, in a door regulator under a water gage w.gf.,
Area of opening required to pass a quantity of air Q, in a door regulator, under a water gage w,g,y
. 0.00025Q Area, A. — y.=-
Vw,g,
Example. — What must be the width of opening of a regulator door where the height of the entry is 6 ft. in the clear, in order to pass 40,000 cu. ft. per min., if the natural pressure for the required circulation produces a water gage of 1.25 in. for this split and 1.75 in. for the free split?
Soludon. — The difference of pressure, in this case, is equivalent to a water gage of 1.75 — 1.25 0.50 in.; hence,
Width of opening, 14.14 h- 5 2.83 or 2//. 10 in.
Secondary Splitting
Secondary splitting involves the principles of both tandem and split circulations. The tandem portion consists of one airway of the primary split and the two airways branching from this and forming the secondary split section.
It is necessary to first find the general pressure potential for the secondary split section. This is equal to the sum of the pressure potentials of the airways forming that section. This general potential for the secondary split is then combined with the corresponding primary potential, according to the method employed for a tandem circulation, which is then regarded as one branch of the primary split.
Mine Gases And Ventilation
The diagram Fig. 33 shows clearly the method of naming the splits and indicating them by symbols. The primary splits, branching from the point where the air current is first divided, are designated by the letters A, B, C, etc., and the corresponding potentials by Xay Xb, Xe, etc.
Secondary splits are designated Ai, Aa, etc., and Bi, fij, etc., depending on the primary split from which they branch; and the corresponding split potentials by Xai, Xaiy Xm, Xm, etc. The general potential for a primary split is designated Xo, and for a secondary split Xao, Xbo, etc.
In secondary splitting the operation is much simplified by calculating the general potential for each consecutive point or section, beginning always at the inby end of the system and finding first the general potential for the secondary split;
Secondary
SPLIT femur/r
Mum
SPLITAyOOF T.l JhtcfKC
Split & 5000 Ft.
Infakt
CWL.AOb
Fig. 33.
then combining this in tandem with the corresponding primary potential; and using this result to find the general potential for the primary split, in the same manner as for the secondary split. Two formulas only are necessary; the one expressing the simimation of the potential values for a split circulation, and the other a similar smnmation for a tandem circulation. They as as follows:
General split potential, Xpo SXp General tandem potential (see p. 216), Xpi — — -— .
In all splitting calculations it will generally be found more convenient to use the pressure potential, for the reason that the calculation of the distribution of the air is based on equal pressures, for all splits starting from one point.
Illustration, — Primary splits are best indicated by the large letters, as Splits A, B, C, etc. Secondary splits are
Theory Of Ventilation 237
named after the primaries in which they occur; thus Aiy A a, etc., or fii, Bty etc.
The corresponding split potenti9.1s are indicated thus:
Primary potentials, Xaj Xt, Xej etc.
Secondary potentials, Xi, Xaz; JCti Xn; Xci X; etc.
General split potentials, Xaof Xboj Xeo
General mine potentials, Xo
To illustrate the calculation of the effect of making a secondary split in the circulation calculated under Unequal Splits (p. 224), assume the air is again split in C, at a point 500 ft. inby from the main or primary split.
Splits A and B are the same as before, while Split C is now 500 ft. long; Split d, 1200 ft. long; and Split Ca, 800 ft. long. The part potential values for the splits are, then.
Split A, Xp aJ; Xa (as before) =1.837 Split fi, Xft Cas before) 1 . 623
Split C, Xc 48 J
Split Ci, X.i 48 Jj-5H 1 .697
General split potential, SXc 1 . 697 + 2 . 078 3 . 775
Combining this general potential for Splits Ci and C2 with the potential for Split C, in tandem, we have.
General part potential,
Part potential, Split A, Xa 1.837
Part potential, Split fi, Xt 1.623
Mine pressure potential, Xpo 5.617
238 Mine Gases And Ventilation
For a constant power, the quantity ratio is equal to the power-potential ratio; thus,
Qi Xi' 75,000 2.78'
— o~7Q 85,240 cu, ft, per mm.
The natural division of the main air current of 85,240 cu. ft. between the three primary splits, A,B,C\ and the two secondary splits Ci, C2, in the last example, is calculated first for the primary division, and then for the secondary, as follows: Primary splits.
Part pressure Natural Required
X„ 1.837; X 85,240 27,880 29,240
Xfc 1.623; g6 X 85,240 24,630 16,000
Xco 2.157; qc X 85,240 32,730 40,000
SXp 5.617 85,240 85,240
Secondary splits,
Xci 1 .697; Qci X 32,730 14.710 25,000
X,i 2.078; q,, X 32,730 18.020 15,000
XXp 3 . 775 32,730 40,000
Theory Of Ventilation 239
The natural pressures are then calculated for the required circulation of air in each split. The highest pressure of the secondary splits determines the secondary pressure, which must be added to the natural pressure of the tandem airway, to obtain the effective primary pressure for Split C Finally, the highest primary pressure determines the primary pressure, which is the pressure for the entire split circulation. The process is as follows:
Secondary pressures,
YJ l-042lb.per8q.fi
Primary pressures, Pco Spc 8.971 Z6. per sq. fi
Qp .
Horsepower, H
85,240 X 8.971 H - 23. 17 hp.
The secondary pressure, as determined by the highest natural pressure in those spUts, is that in Split Ci, which is 4.341 lb. per sq. ft. Likewise the primary pressure (the highest of those splits) is that of the tandem split Co, which is 8.971 lb. per sq. ft. These pressures are indicated above by the heavy type.
Regulators. — The difference between the secondary pressure and the natm*al pressure in any secondary split is the pressure due to the regulator or the regulator pressure for that split. The same is true for primary splits.
240 Mine Gases And Ventilation
The pressures due to the regulators required in Splits A, B and C2, in order to accomplish the required distribution of air are, therefore, as follows:
Split A, 8.971 - 5.067 3.904 lb. per sq. ft. (0.751 in. w.g.) Split B, 8.971 - 1.944 7.027 lb. per sq. ft. (1.351 in. w.g.) Split C2, 4.341 - 1.042 3.299 lb. per sq. ft. (0.634 in. w.g.)
The necessary area of opening in a regulator to pass the required quantity of air, under the given water gage is calculated as follows:
y/w,g.
, 0.0004 X 29,240 ., Aa I0.5 sq. ft.
. 0.0004 X 16,000 ., Ah 5 . 5 . ft,
\/l.351 . 0.0004 X 15,000 - - .,
If door regulators are used the openings have the following areas:
Door regulator, A — j -;
Vw.g.
. 0.00025 X 29,240 . -, Aa y — 8.4 sq.ft.
Ab =8.3.4 so.
Ac2 / — 4.7 sq.ft.
The results of making the secondary split in Primary C may therefore be summarized as follows:
The above comparison shows: (1) The increase in the quantity of air in circulation and the decrease in the unit pressure and water gage, for the same power on the air, caused by making a small secondary split, in one of the original primaries. (2) The large increase of power on the
Theory Of Ventilation
air and pressure and water gage necessary to make the required distribution of air, in this case.
Distribution of air
Split B
Split C
Split C,
Split C2
Totals
Example, — An air current of 120,000 cu. ft. per min. is passing in a mine in two splits, as follows:
Split A, 6 X 10 ft., 20,000 ft. long; 40,000 cu. ft. per min.
Split B, 5 X 10 ft., 5,000 ft. long; 80,000 cu. ft. per min.
More air being required, a careful investigation shows that Split A can be again divided at a point 2000 ft. inby from the foot of the downcast shaft, thereby forming two secondary air splits, each 5 X 10 ft., 8000 ft. long, mcluding the return. This would make Split A 4000 ft. long including the return. With the same power on the air, what quantity of air will be circulated in this mine after dividing Split A ? '
SoluHan. — The first step is to calculate the potential values of the different sections or splits, both before and after dividing Split A to form ths two secondary Splits* A 1 and As. This being a comparison of two circulations, it is possible to use the Relative potentials, reducing the areas, perimeters and lengths to their lowest relative values, which gives the following :
Before dividing Split A :
Split A, a 50; o 30; I 20,000 a 1; o 1; i 20
Splits, a=50;o=30;i= 6,000 a l;o l;i= 5
After dividing Split A :
Split A, a 50; o
Split -B, a 50;o
Split Ai, o 50; o
Split As, a 50; o
o l;o l;Z= 5
a 1; 1; I 8
a 1;q 1; 2 8
242 Mine Gases And Ventilation
Relative potentials, before division :
Relative potentials, after division :
Xb Same as before — 0.4472
Xi 0.6708
XaO 0.707
X, , 0.4082
X, Xi + Xfc 0.4082 + 0.4472 0,8554
Since the power is the same, before and after division and calling these respective general potentials Xi, Xg, have
Theoretical Considerations In Splitting
Theory assumes that when an air current traveling in an airway divides, at a certain point called the "point of split," into two separate currents or "splits," the unit pressure (p) at the point of split is common to each split. In other words, two splits starting from the same point in a mine have the same unit pressure (p) and, for the same sectional area (a), the resistance (R pa) is the same for each split. The same holds true for any number of splits (n) of equal area.
Whether the unit pressure (p) or the unit work (pv) is the factor common to each of two or more splits starting from the same point will not be discussed here. The law of dynamic
Theory Of Ventilation 243
equilibrium of fluids points to the equality of unit work for each spUt. The comparison of the relation of the quantity of air (g), the rubbing surface (s) and the sectional area (o), on these two bases of reasoning, is as follows :
Unit pressure Unit work
For constant unit pressure: For constant unit work:
a q varies as a q vanes as
3M
Practical Conditions. — 'In considering the practical results of splitting the air current in a mine, it may be assumed that the power on the air ([/) at the mouth (intake) of the mine remains constant. Assuming a number of splits (n), starting from the same point in the mine, at or near the shaft bottom or mine entrance, the total area of passage is na and the formula for power is then
which shows that, since in any case C/, fc, 5 and a are each constant, varies as n', or Q varies as n, which is the number of equal splits, each having an area a.
In other words, the quantity of air circulated in a given mine, by a given power on the air (effective power), is proportional to the number of splits, assuming the splits all start from the minQ entrance or so near to it that the resistance of the main intake entry, slope or shaft may be ignored. Under these conditions, splitting the air has no effect to alter the velocity or the resistance in the mine.
When the point of &plit, however, is some distance inby from the mouth of the mine or "daylight" the effect of splitting the air, in that case, is to cause a disproportion. The quantity of air circulated by a given power no longer varies as the number of splits; but the ratio of increase in volume is less, because the power on the air at the mouth of the splits is decreased by splitting.
244 Mine Gases And Ventilation
Assuming, as before, a constant power on the air at the mouth of the mine, since the quantity has been increased by splitting, both the velocity and resistance have been increased in the main airway, which absorbs more power thus decreasing the power on the splits.
Effect of Splitting on Velocity. — In order to show the general effect of splitting the air current, at any point in a mine on the velocity (vo) in the shaft or main airway and the velocity (vi) in the splits, it is necessary to know the ratio (w) of the rubbing surface {si) in the splits, to that of (so) in the shaft or main airway; also, the ratio (n) of the total area (Ai) of the splits, to that of (Ao) in the shaft or main airway.
and, since for a given quantity the velocity varies inversely as the area,
n
But, the power on the air (u) at the mouth of the mine is equal to the power (uo) absorbed in the shaft or main airway, or both, plus the power (ui) absorbed in the splits.
or, expressed in terms of the mine, since u
Substituting for Si and vi' the values given in Equations 1 and 2, gives after simplifying
Equation 5 shows clearly that, for a constant power on the air at the mouth of a mine, in splitting,
- V + m
and, observing Equation 2,
Theory Of Ventilation 245
It appears from the last two equations that as the ratio of the split area to the shaft or main-intake area, represented by n, is increased the main-intake velocity (vo) is increased, while the split velocity (vi) is decreased, the increase and decrease of velocity, however, being less rapid than the change in the area ratio.
Effect of Splitting on Quantity. — The quantity of air in circulation varies directly as the intake velocity vo; or, for a constant power (u) on the air,
V + w
Effect of Splitting on the Mine Resistance. — The total mine resistance is the sum of the main-intake and split resistances.
and
Finally, from Equations 6 and 10 is derived
Practical Problem
Example. — A current of 25,000 cu. ft. per min. is passing in a shaft mine. The shafts are 8 X 12 ft. in section and 250 ft. deep. The airways are 6 X 10 ft. and 15,000 ft. long, including the return, (o) What is the water gage due to this circulation? (5) Assuming the power applied to the fan shaft remains unchanged and the current is divided into two equal splits, at a point 1500 ft. inby from the foot of the shaft, what volume of air may be expected to be passing? (c) What will be the water-gage reading on the fan drift and at the bottom of the shaft, after splitting
Solution, — The rubbing surface and sectional area of the shafts and airways are, respectively, as follows:
Shafts — Sq. Ft.
.Rubbing surface + X 250 20,000
Sectional area 8 X 12 96
Rubbing surface -h 480,000
Sectional area 6 X 10 60
246 Mine Gases And Ventilation
Main airway —
Rubbing surface + X 1500 96,000
Sectional area 6 X 10 60
Two equal splits —
Rubbing surface 384,000
The relative part potential factors are then :
Before splitting —
General relative mine potential factor ( 2 -2) 2 . 2449
General relative mine potential factor 2 y— 0.6892
1 /ii vx 1 0.00000002 X 25,000 X 2.2449 . , .
(6) For a constant power on the air, the quantity varies directly as the mine power potential; but, for a constant power applied to the fan shaft, owing to the efficiency of the fan varying inversely as the 3/5 power of the potential the quantity varies as the 4/5 power of that potential.
The mine potentials, in this case, are.
Before spUtting— Since 2.2449; Xi ,, 0.7637
Then, for a constant power applied to the fan shaft, the quantity of air in circulation varies as the 4/5 power of the power potential, which gives for the circulation after splitting
mtn.
(c) Water gage (after splitting). — In the fan drift the gage is
O.OOOOOOO2 X 34,250 X 0.6892 , . w.g, 3.1 tn.
Theory Of Ventilation 247
To find the gage at the shaft bottom it is necessary tq deduct the potential factor for the two jshaf ts from the total potential f act.or for the mine after splitting; thus
Then, since the gage is proportional to this potential factor, the gage at the bottom of the shaft is
Relative Variation of Factors. — The following relation of some of the more important factors in the ventilation of mines by means of centrifugal fans is based on the results of many experiments:
Unit pressure, p varies inversely as Q
—
8
Power Applied to Fan Shaft Constant (U)~~-
Efficiency, 1//C varies as Xp oV
Effective power, u varies as TC
Quantity, Q' varies as Xu*
Effective power, u varies as
Quantity, Q' varies as
Section Vii
Practical Ventilation
Conducting Air Currents, Air Bridges — General Plan OF Mine — Distribution op Air in the Mine — Splitting Air Currents — Systems op Ventilation — Systems op Mine Airways.
The first step, in the practical ventilation of a mine, is to determine the volume of air that will be required in order to maintain a pure and wholesome atmosphere in the mine workings. This will depend on conditions, such as the size and depth of the mine; thickness and inclination of the seam; character and quality of the coal; kind and quantity of gas generated; methods of working the seam and mining the coal. Aside from these conditions the volume of air must always be sufficient to meet the requirements of the mine law.
The second question to be determined is the general ventilating pressure or water gage, under which the mine is to be ventilated. This will depend on the possible extent and size of the workings and the power available. The water gage, in mining practice, varies from a fraction of an inch to 3 or 4 in., in this country; and higher gages are in use in the deep mines of Belgium and other countries. The best practice, however, employs such a system of mining that the required volume of air can be circulated under, say 1 or 2 in. of water gage. This can only be accomplished by so planning the mine, in the start, that it can be divided into separate ventilation districts. The number of ventilation districts should increase with the development of the mine. Each district is thus ventilated by separate air split or current, which insures good air, besides reducing the water gage necessary for the ventilation of the mine.
Practical Ventilation 249
Power Required to Produce a Given Circulation.— Having decided on the volume of air required and the water gage, these factors determine the power that will be necessary to produce the circulation. The power on the air may, generally, be safely taken as 60 per cent, of the indicated horsepower of the engine driving the ventilating fan. For example, the circulation of 75,000 cu. ft. of air against a water gage of 2 in. will require, with a safe margin, an engine capable of developing
The above calculation assumes a properly* designed ventilating fan, since a poorly designed fan, or a fan working under conditions for which it is not adapted, may give an efficiency of only 40 or 50 per cent.; or at times this may not exceed 25 per cent., under particularly adverse conditions. An unsuspected negative air column existing in some portion of the mine may be the hidden cause of the low efficiency of a ventilating fan. .5
Conducting Air Currents
Conducting Air Currents in Mines. — To conduct the air on its course through mine, doors stoppings, brattices, aircrossings, or bridges — either overcasts or undercasts — are employed to deflect the air current. When the air is divided and made to travel in two or more splits regulators are used to proportion the quantity of air to the requirements in each spUt.
In Fig. 34 are shown two forms of self-closing doors used in mines. There are many different methods in use to prevent a mine door standing open, but these are as practical as any. The door on the left is shown with canvas flaps to stop the leakage of air. Both doors swing either way, being heavy enough to overcome . the pressure of the ventilating current.
Stoppings, in mine ventilation, are built in entries or in crosscuts for the purpose of closing the passage. When built
Mine Gases And Ventilation
in crosscuts they serve to carry the air current forward to the head of the entry. A common form of stopping consists of two walls of slate or rock built 10 or 12 in. apart and the space between them filled tight with road dirt or sand. More substantial BtoppingB are built of brick laid in cement, or of concrete.
In F. 34 is also shown the right and the wrong way of erecting a line of brattice in a pair of headings. As shown in
each of the figures, a row of posts is set, one at a time, and canvas or brattice boards nailed to them on the intake side. The posts are stood 18 in. or 2 ft. from the right rib if the intake is on the right, or the left rib if on the left. The same order is followed on the return airway or heading. The work of nailing the canvas or boards to the post is done on the fresh-air side and the brattice extended as the current sweeps away the gas accumulated in these headings. The
Practical Ventilation 251
arrows show the course of the air as it circulates around the brattice in each heading.
Air Bridges. — In Fig. 34 are also shown different methods of constructing air bridges in mines, for the piu-pose of conducting one air current across another. First is shown a standard type of overcast built of reinforced concrete. Immediately below this is shown two common types of air bridges, an overcast and an undercast. In the "undercast" shown on the right, the cross-current of air is conducted under the main road or heading, the bridge in that case forming the floor of the roadway. A safer and more serviceable form of air bridge, however, is the "overcast" shown on the left, by which the cross-current is carried over the haulage road. The undercast possesses the disadvantage that it cannot be drained and may become flooded and cut off the air current completely.
Natural Overcast. — Owing to the difficulty of keeping air bridges air-tight, a.nd for the further reason that the possible destruction of an air bridge by an explosion would cut off the circulation of air in the district fed by that means, a natural overcast is frequently referred.
In the lower right-hand corner of Fig. 34 is shown a natural overcast as driven in the upper portion of a thick coal seam, although the same form of overcast is often driven in the rock strata overlying a thinner seam. Such a natural overcast is formed by starting an uprise in the roof of the cross-entry, a short distance on either side of the main heading, and then driving a crosscut in the solid formation above and across the main roadway, thereby forming a wholly separate air passage for the intake and return air currents.
Regulators. — As described previously and illustrated in Fig. 32, regulators are used to divide an air current in any desired proportion between two entries or . The *'box'' regulator is commonly placed on the return airway, where it offers no obstruction to haulage, while the ''door" regulator is always placed on the intake. The use and effect of these two forms of regulators are fully treated under Proportionate Division of Air," page 231, in the section Theory of Ventilation."
252 Mine Gases And Ventilation
General Plan Of Mine
Requirements. — In the planning or la3dng cut of a mine the most careful consideration must be given to the questions of ventilation, drainage and haulage, as these arrangements, to a great degree, determine the successful operation of the mine.
In order to insure the safe and economic extraction of the coal, the same careful consideration must be given to ascertaining the extent and character of the seam, its depth below the surface, inclination and thickness, the character of the roof and floor and the hardness of the coal; its cleavages and faults, impurities, etc.
The information thus gained wiQ be of the first importance in deciding on the most suitable method of mining to adopt, in order to secure the largest retmns on the investment, the most complete extraction of the coal and the greatest safety in mining the same.
Economy and Efficiency. — The economic ventilation of a mine premises the circulation of the required air volume, with the least expenditure of power. Efficient ventilation requires the circulation and proportionate distribution in the mine workings, of such a volume of air as will not only meet the requirements of the law, but, likewise, produce the necessary velocity in all roads and passageways and at the working faces of all headings and chambers, so as to sweep away the smoke and gases that would otherwise accumulate therein; and to so ventilate all waste, void and abandoned places as to prevent them from becoming a menace to the safety of the mine as reservoirs for the accumulation of gas.
Drainage. — Economic mine drainage requires such a disposition of the openings driven in the seam for the extraction of the coal, including all passageways, headings and chambers, that the water coming from the strata wiQ flow by gravity, either to the main sump at the shaft or slope bottom, or to certain gathering centers from which it can be readily siphoned to the main or piunped directly to the surface.
Practical Ventilation 253
In practically level seams or seams having slight inclination, the question of drainage does not materially affect the general mine plan. In this case, good roadside ditches afford the necessary waterways by which the underground water flows to the sumps provided to receive it Such siunps or catch basins are located at one or more convenient low places or "swamps," in the mine, where it is possible to install a pump of sufficient size to handle the water of that section at all times.
The rooms or chambers, in practically level seams, are turned off both entries of a pair, which greatly reduces the expense of entry driving and necessary maintenance of roadways and air-courses.
In inclined seams the direction and amount of pitch are controlling factors in determining the general plan of the mine, in respect to the course of main roads, cross-headings and rooms or chambers. In respect to drainage, it is important to drive all such openings to the rise, in order to avoid the annoyance and expense of providing artificial means of draining the working faces.
Haulage. — Economic mine haulage requires that the coal, like water must gravitate, as far as practicable, from the coal face where it is mined, to the foot of the shaft or slope opening from whence it is hoisted to the surface.
In level seams, the question of haulage does not affect the plan of mine; but, in seams of more or less inclination, it becomes a matter of first consideration.
In inclined seams, it is always possible to drive the main haulage roads in such a direction that the grade of the road will not only favor the movement of the loaded cars, but will be such that the power required to haul the loaded trip out of the mine will be equal to that necessary for hauling the empty trip back into the mine. This. is called the "economical grade."
The grade of any road, or the road grade, in an inclined seam, may be calculated when the angle of inclination of the seam and the angle the road makes with the strike of the seam are known, by the following rule:
254 Mine Gases And Ventilation
Rule.— The tangent of the grade angle is equal to the tangent of the angle of inclination of the seam, multiplied by the sine of the angle the road makes with the strike of the seam.
Or, calling the angle between the road and the strike of
the seam, the "road augle," this anglEi is calculated by the
use of the formula
tan grade angle
sm road angle -. . — p — -. -
' tan tnmnatton
There is shown clearly in Fig, 35, a perspective plan of a pair of entries with rooms turned off the haulage road. The
left-hand entry is the return air-course, while the haulage road is the intake. A canvas or curtain hung on the entry just inside of the mouth of the first room deflects the intake air mostly into the rooms, where it passes through the breakthroughs from room to room. Better results are generally obtained when the breakthroughs are stared Or not driven directly opposite each other, as shown in the figure. The
PRACTICAL VBNTILAriON
256 Mine Gases And Ventilation
croseeuts on the entries are closed by substantial stoppings, except the last crosscut where the intake air passes into the return, as shown by the arrows.
General Plan, Level Seam. — In Fig. 36 is illustrated thc general plan of a mine shaft bottom in a level seam. At times, it may be necessary to drive the shaft bottom at an angle with the main and cross-entries, as shown in Fig. 37, in order to square the hoisting shaft with the loading tracks
on the surface. In each of these figures the intake current is divided, forming two main splits of air near the foot of the downcast or au-shaft and these main splits are ain divided two or more times to ventilate different sections of the mine, as indicated by the arrows.
Ventilation of Longvrall Workings. — Figs. 3S and 39 are two general plans of longwall workings, showing the main air current carried, in two or more , from the bottom
Tractical Ventilation 257
of the downcast shaft directly to the working face, where it is again divided and made to sweep the entire face, returning by the numerous roads to the main-return airway, by which it is conducted to the foot of the upcast shaft. Fig. 30 shows
a more extended development of the mine, on a slightly different plan from that given in the preceding figure.
Distribution of Air
VentUatiiig a Mine. — Small mines are generally or often ventilated by a single current of air passing in one continu-
258 Mine Gases And Ventilation
ous circuit around the mine. In larger mines the main current entering the mine is divided into two or more currents or " air splits," as they are called.
The current flowing into a mine or section of a mine is called the 'intake current" and that passing out from the mine the "return." Likewise, these airways are termed the "intake" and the "retiun" airways respectively.
The figures previously given show clearly the general arrangement of the circulation in a mine, as indicated by the arrows. In a gassy mine, the hoisting shaft is made the downcast and the main-haulage road is then the intake airway. The mine is ventilated by an exhaust fan located at the upcast shaft, because it is impracticable to use a blower fan whenever the main-haulage road is made the intake. A bio wet fan would require doors placed on the haulage road, at the shaft bottom, to prevent the air short-circuiting and passing out through the hoisting shaft. All crosscuts, except those through which the air must pass, are closed by stoppings or doors. By this means, the air current is forced to travel certain airways from the downcast to the upcast shaft.
In Figs. 36 and 37, the hoisting shaft is the upcast and the haulage road the return. The air is first split near the foot of the downcast shaft. One current or split travels north to ventilate that side of the mine, while the other current travels in the opposite direction to ventilate the south side of the mine. Each of these currents is shown returning to the upcast shaft by the main return air-course- Double doors are used in the crosscut at the shaft bottom to prevent the air current from being broken or staggered, when it is necessary to pass through this crosscut. Only one of these doors is open at a time, and the air is thus prevented from short-circuiting at this point.
On the main south (Fig. 37), the air is divided into three separate splits or currents, which ventilate respectively the main south headings, the first and second east and the first and second west. In order to do this, two overcasts are required, one to conduct the main-south intake current over the first-west haulage road, and the other to carry the second-east intake current over the main-south haulway. It should be
Practical Ventilation
observed that the stables, in both Fig, 36 and 37, are ventilated by a separate scale of air, which is then carried directly into the main return and passes out of the mine as indicated by the arrows.
Ventilation of Cross-entries.-— In the illustration (Fig. 40) are shown two ways of ventilating a pair of cross-entries turned off the main headings. As shown on the left, the main-intake current is deflected into the cross-entries by placing a door on the main heading. The total current is thus made to pass down the first cross-entry and, returning through the second by a crosscut at the face, continues on its way up the main heading, thus forming one continuous current.
In the plan shown on the right in the same figure, the mainintake current is divided at the mouth of the first cross-entry. Part of the air enters the first cross-entry and returning by the second passes over the air bridge at its mouth and through the crosscut into the main-return air-course. The remainder of the main intake current contiimes up the main headit, passing under the air bridge on its way. This method furnishes a separate current for each district of the mine and leaves the main haulage road unobstructed by any doors. As shown in the figure, an inclined crosscut, called a "crossover," connects the two cross-entries near their mouth, which permits the coat from the back entry to reach the main haulage road by passing through the door on the crossover. This door divides the intake from the return on these entries.
260 Mine Oasss And Ventilation
Ventilation of tiie Mine Stable. — The mine stable, as previously stated, should be ventilated by a small split commonly caled a "scale" of air, taken from the main intake current. This current, after ventilating the stables, passes directly to the upcast shaft, without contaminating the air of the mine. It is important to locate underground stables so that they can be ventilated (Figs. 86, 37) with a small scale of air that is conducted at once into the main return air-course. To make possible the rescue of the animals in case of accident, and to
facilitate the handling of feed and refuse to and from the surface, the stables should be located near the bottom of the hoisting shaft or other opening.
Splitting Air Currents
Illustration of Air Splitting.— Fig. 41 gives a diagrammatic perspective of a mine ventilated by two primary air splits, A and B, and two secondary spUts, C and D. In this case either the downcast or the upcast may be made the hoisting
Practical Ventilation 261
shaft, as desired. In gassy minea where hauU is performed OQ the intake air, the downcast becomes the hoisting shaft, which avoids the use of doors on the shaft bottom. In that case, the air bridges are constructed to conduct the return air over the intake current, thus leaving the haulage road unobstructed.
Systems or. Ventilation
Exhaust vs. Blowing System at Ve: ilation. — The natural or physical conditions that exist in a mine will generally determine whether it should be ventilated on the exhaust or the 1 blowing system. A mine generating gas in sufficient quantity to make the mainreturn airway imsafe for haulage will require the exhaust system, in order to leave the hoisting shaft, which would then be the downcast, and the shaft bottom unobstructed by doors.
The exhaust system of ventilation is illustrated in Fig. 42, which shows the circulation in a section or district where
the future development of a pair of cross-entries warrants the building of an overcast on the main headings, and haulage must be performed on the intake air.
As indicated by the arrows in the figure, a ciulain hung on the first cross-entry, just inby from the mouth of the first
262 Mine Gases And Ventilationroom
working, deflects the air into the rooms so that the major portion of the cunent sweeps the face of each room. It is necessary also to hang canvas at the mouth of each room except the last to keep the air at the workii face.
The blowing system of ventilation is illustrated in Fig. 43 which shows the general arrangement under conditions similar to those just described, except that here the haulage is performed on the return air, the hoisting shaft being the upcast. As indicated by the arrows, the air is carried directly to the head of the cross-entries and returned through the crosscuts in the rooms.
Systems op Mine Airways
The Main Airways. — While two airways, an intake and a return airway of sufficient size, furnish the necessary means
for conducting the air current to and from the working faces of the mine, there are other considerations of economy and
Practical Ventilation 263
safety of operation that frequently demand a larger number of main airways.
Sine-eiitry System. — In the early days of mining and in some small mines, today, supplying local trade, the plan is adopted of driving a single entry, which serves the double purpose of haulage road and aircourse, the air being returned through the rooms. The single-entry system is unsafe and no longer used in scientific mining.
Double -entry System. — In this system, all entries are driven in pairs, one entry being made the intake and the other the return, in each pair. This system is commonly employed in a large majority of coal mines and is shown on the crossentries in Fig. 44.
Triple-entry System.— In this
system, three parallel entries are driven abreast, as for example the main entries in Fig. 44, and the same in Fig. 45, which illustrates the workings in a slope mine. The main slope haulage road being the intake for the entire mine, and the air-course on either side being the return for that respective side of the mine. In the use of the triple-entry system, the center entry is generally made the intake and haulage road, while the two side entries are the return air-courses for each respective side of the mine.
Mine Gases And Ventilation
In the slope mine illustrated in Fig. 45, the rooms are driven to the rise of each pair of gangway headings. The mine is equipped with two ventilating fans operating on the exhaust
Fig. 46.
system. The air is spUt and overcast at each pair of headings on the right of the slope, except the last; while there are but two air spUts ventilating the levels on the left of the slope
Practical Ventilation 265
headings. Unfortunately for purposes of rescue and handling feed and refuse, the mine stable is located far in the workings, probably to avoid the necessity of driving the mules to and from the working face.
Multiplg-entries.— In Pig. 46 is shown a mine opened on the five-€ntry system for the main headings, thus providing three intake airways and two separate return airways, one for each side of the mine.
The number of main airways required, in any case, is determined by their size and the necessary volimie of air that must pass through them. The limitmg factor in this calculation is the safe and economic velocity of the air current traveling the main airways.
While too low a velocity of the air is dangerous because of its failure to remove the accmnulating gases, too high a velocity, on the other hand, is dangerous by reason of its increasing explosive conditions in the mine air, by raising and carrying in suspension fine dust, and by furnishing an excessive supply of oxygen that invites active and explosive combustion.
The velocity of main air currents in mines can safely vary between 250 and 1200 ft. per min.: and for short distances a velocity of 2000 ft. per min. may be permitted, although high velocities rapidly increase the power producing the circulation. Where the main intake airways are used for haulage roads, it will not be possible or advisable to employ a velocity much exceeding 400 or 500 ft. per min., owing to the annoyance and danger of drivers losing their lights.
Economy of Multiple Main Airways. — The economy of driving a multiple system of main airways will not be questioned in the planning of large operations. The same plan should be applied to the opening of mines on a smaller scale, the objective point being to keep the velocity of the main air cmrent so that it will not exceed 1200 ft. per min., fof any considerable distance.
The saving in power (fuel consumption, equipment and attendance) will pay for the increased expense of upkeep of entries; and the system affords a large increase in safety
266 Mine Gases And Ventilation
by reducing explosive conditions and providing additional avenues of escape in case of accident. There is afforded, besides, room for a double-track haulage sysjbem, which will prove a great advantage in the operation of the mine.
Assuming that one-half the power on the air is consumed in the main airways, which more or less closely approximates the fact, and taking the general efficiency of the fan and engine as 60 per cent., a double-entry system, for the main intake and return airways, would effect a saving in fuel of 11.25 per cent.; a triple-entry system, 13.32 per cent., and a4-entry system, 14.10 per cent.
Illustration. — -In the planning of a mine for an output of, say 2000 tons of coal per working day, in a 6-ft. seam of more or less inflammable bituminous coal (shaft, slope or drift openings), the following data may be assumed as approximating possible conditions, but must be modified to suit known facts that have been determined, in special cases:
Number of loaders or helpers 400
Number of drivers, trackmen, timbermen, etc 60
Foreman, assistant foremen and firebosses 20
Total number of men and boys 1280
Number of mules 25
Assuming a gaseous mine requiring, by law, say 150 cu. ft. of air per man, and 600 cu. ft. per mule, per minute, the necessary circulation based on these data would be (1280 X 150) + (25 X 600) 207,000 cu. ft. per min.; or, to allow for certain leakage, say the necessary air volume Ls, in this case, 225,000 cu. ft. per min.
Driving 10-ft. openings in a 6-ft. seam and allowing for necessary timbering would leave an unobstructed effective area of, say 50 sq. ft. In this case adopting a 4-entry system for the intake and the same for the return, would give for the total effective intake and return areas, each 4 X 50 200 sq. ft., which would make the velocity of the intake air
Practical Ventilation 267
current 225,000 -r- 200 1125 ft. per min., which is a safe and economical velocity, provided these airways are not used as haulage roads.
To provide for the expansion of the return air, owing to rise of temperature and addition of mine gases, which may altogether amount to 6 or 8 per cent., the return airways should be driven, say 8 or 10 in. wider than the intake airways.
Section Viii
Mine Lamps And Lighting
Principles op Construction, Classification op Safety Lamps, Requirements — Characteristic Types of Lamps — Special Types of Safety Lamps — Permissible Mine Safety Lamps — Use and Care of Safety Lamps — Testing FOR Gas by Indicators — The Flame Test — Illuminants FOR Safety Lamps, Oils, etc. — Miners' Carbide Lamps — Electric Mine Lamps— Permissible Portable Electric Mine Lamps.
A volume could be written on the development of the socalled **safety lamp.'' It is not proposed to give, here, the history of that development further than to say that it began with the discovery of the two most important and essential principles of all mine safety lamps. Strange to say, these two principles were discovered at practically the same time and by two men of different education and calling.
Principles Of Construction
Principle of Protecting Shield. — George Stephenson was a practical miner of considerable mechanical ability, which led him into the practice of cleaning and repairing watches and clocks, running engines and performing other similar services. It was at the Killingworth colliery, Oct. 21, 1815, that he made the first trial of a lamp he had devised for use in mines generating gas.
The principle of the Stephenson lamp consisted in confining the burnt air and products of combustion in the upper portion of the lamp chimney or bonnet, the idea being that this would furnish an extinctive atmosphere at the top of the lamp and prevent the flame of the burning gases passing' out of the chimney and igQiting the gas-charged air surrounding the lamp. This, today, is one of the important principles of all
Mine Lamps And Lighting
mine safety lamps, though the method of its appUcation differs from that employed by Stephenson.
Principle of Wire Gauze. — The principle of the isolation of a lamp flame, by means of a wire gauze envelope or chimney, was discovered by Sir Humphry Davy, an eminent chemist. As the result of a series of experiments, Davy was able, Dec. 15, 1815, to announce to the world the fact, that an ordinary lamp flame will not pass through the mesh of cool wire gauze. The idea was suggested to the mind of Davy by observing that a flame, as shown in Fig. 47, never comes in direct contact with cool metal. The reason is that the temperature of the burning gas is reduced, in close proximity to the metal, below the point of ignition. He showed that the burning gas, on passing through the mesh of a wire gauze, is broken up into tiny streamlets, which are so cooled by contact with the metal of the gauze that the flame is extinguished. As the gauze becomes heated by the close proximity of the flame, however, it loses its cooling effect and the flame then passes through the mesh.
The effect of cool wire gauze to prevent the passage of flame through its mesh is shown in the lower half of Fig. 48. In the upper half, appears the later passage ot the flame through the mesh of the gauze when the wire has become heated so that it is unable to absorb sufficient heat from the burning gas to extinguish the flame. This isolation of the flame of a safety lamp by means of a wire gauze chimney found its earliest application in the Davy lamp. A careful study of the problem and the experiments performed showed that the greatest safety was secured by the adoption of a standard mesh formed by 28 steel wires, No. 28 B.w.g., making 784 openings per square inch. This standard mesh is still used in England and in this coimtry, today. It was also found that the volume of the chimney, including the combustion chamber of the lamp, should bear a certain relation to the surface of the gauze in order to produce the best results
Fig. 47.
Mine Gases And Ventilation
and insure the greatest security of the lamp when burning in the presence of gas. There is, however, no fixed value for this ratio, which controls the circulation of the air and gas passing in and out of the lamp and varies with the type of construction.
Classification of Safety Lamps. — Mine safety lamps are divided into two general classes, according to their use in the mine, as follows: (a) Lamps for testing for gas. (6) Lamps
for general use at the working face. A good working lamp does not make a good lamp for testing for gas, neither does a good testing lamp answer for work at the face. Each of these lamps is designed for the particular service or work to be performed and the requirements of each are widely different. Requirements of a Good Testing Lamp. — A good lamp for testing for gas must be sensitive to small percentages of gas present in the mine air and must possess, as nearly as practicable, the same conditions with respect to gasintheycombustion chamber as exist in the air surrounding the lamp. Otherwise, the test for gas observed within the lamp will not correctly represent the gaseous condition of the outer air.
The sensitiveness of a lamp to gas depends on both the character of the oil burned and the freedom of circulation within the combustion chamber. A lamp burning hydrogen gas (Clowes* hydrogen lamp) is more sensitive than a lamp
Coot Wire Oauz€
Fig. 48.
Mine Lamps And Lighting 271
burning oil, which is true in general of a gas-fed flame. The Clowes lamp is the only safety lamp burning gas, however, and has but a limited use in testing for gas in mines. There are two general types of oil-burning lamps, according as the illuminant is a non-volatile or a volatile oil, the former being derived from animal or vegetable sources, while the latter are chiefly derivatives of mineral oil or petroleum distilled below 300 deg. P., such as naphtha, benzine, etc. Coal oil (kerosene) is a distillate of petrolemn between 300 and 500 deg. P., and is not classed as a volatile oil.. It is frequently mixed with twice its volume or more of a vegetable oil to improve the illuminating power of the latter.
The volatile oils, while more sensitive to the fJresence of gas, possess the disadvantage of giving a more pronounced oil or fuel cap that is frequently mistaken for a gas cap. Moreover, the height of the flame cap, for any given percentage of gas, is always greater in a lamp burning a volatile oil and allowance must be made for this fact, in estimating the percentage of gas present when making the test with such a lamp.
In order that a lamp shall present the same condition with respect to gas, within as exists without the lamp, two conditions must be fulfilled: (1) The air must enter the combustion chamber at a point below the flame. (2) There must be a free circulation within the lamp and it must always be ascensional so as to avoid the contamination of the atmosphere in the combustion chamber with the products of combustion in the chimney, which are apt to descend from the upper portion of the lamp if the chimney is too closely bonneted and the circulation in the lamp is not wholly ascensional.
Other requirements of a good testing lamp are some means of accurately measuring the height of the flame cap formed in the lamp and, if possible, making the cap more plainly discernible by means of a good background and the absence of a reflection that would interfere with the observation. A good testing lamp should also be provided with a shield or suitable bonnet to protect the lamp against strong air currents and as an added protection against slight explosions that may occur within the lamp, owing to a body of strong gas.
272 Mine Gases And Ventilation
Requirements of a Good Working Lamp. — -Unlike the testing lamp, a lamp designed for general work in the mine must not be too sensitive to gas. Its chief requirements are the following:
1. The lamp must give a good light that will enable the miner to perform his work readily and discover any dangers that may exist in the roof or about him.
2. The lamp should be simple in construction, portable and light and, at the same time, capable of resisting rough usage that is liable to break the glass, injure the gauze or otherwise damage the lamp. There should be as few parts as practicable, and these should be assembled in such a manner that no single part can be accidentally omitted when putting the lamp together in the lamproom.
3. A good working lamp must be secure against strong air currents. It should be suitably protected by a shield or bonnet of such construction as will not unduly obstruct the circulation within the lamp. The best type of lamp admits the air to the combustion chamber, at a point below the flame, and allows the products of combustion to pass out through tangential openings in the bonnet. A shield protects the top of the bonnet from dust and falling fragments of the roof.
4. It is important that every working lamp should be provided with a lock fastening that will betray any attempt on the part of the miner to tamper with the lock. Magnetic locks, it is claimed can only be opened by means of a strong magnet in the lamproom, but the claim has been questioned in numerous instances, especially where a mine is equipped with electrical installation. The fastening that has given, perhaps, the greatest amount of satisfaction because of its simplicity and security is the old lead lock that is fastened in the lamproom with a steel die of special design.
Working lamps are supplied with both round and flat burners, as desired. When a flat burner is used the illumination is much improved by the simple device illustrated in Fig. 49, consistiijg of a semi-circular cut made in the center of the top of the burner. This simple artifice has the effect of producing a rounder and less smoky flame, besides giving a hotter flame when the latter is reduced, in testing for gas.
Mine Lamps And Lighting
The illuminating power of a safety lamp is greatly influenced by the way in which the air supply is brought into contact with the flame and the voliune of air supplied to the combustion chamber of the lamp. The light-giving power of the flame is also increased by the use of duplex flat-wick tubes, or triplex round-wick tubes. Tin or aluminum tubes produce a better light than either brass or copper and porcelain is far better than any metal, in this respect.
Increased light does not mean an increased cost in oil. Petroleum having a high flashing point, such as mineral colza oil, is probably best adapted for use in high-powered lamps. The illuminating power of vegetable oils is greatly increased by the admixture of one-third part of pretroleum (coal oil) having a flashing point of 80 deg. F., although the lamp flame will then have a greater tendency to smoke and will require a better circulation of air in the lamp.
The safety of gauze-protected lamps is much increased by a suitable restriction of both the inlet and the outlet openings, which is a prominent feature of many lamps of high illuminating power. Another important feature of these lamps and one that affords increased protection at the top of the chimney is the inner metal bonnet surmounted by a truncated cone. Still another feature that adds to the protection of the lamp and increases its illuminating power, by the concentration of the heat in the combustion chamber, is the conical glass. All of these features originated in the Ash worth-Gray lamp, a type of which was later styled the Ashworth-Hepplewhite-Gray lamp.
A working lamp must be of a design that will make it most convenient for the use of the miner. The base of the lamp should be sufficiently broad to enable the lamp to be set on the mine bottom, in a position to throw a good light where the coal is being undercut or mined. It is often necessary for the miner to hang his lamp on a timber or post. For that reason, some lamps are furnished with a short hook instead of the usual ring forming the handle. The hook is not commonly
Fig. 49.
274 Mine Gases And Ventilation
used in this country, the miner preferring to hang his lamp on a nail driven in the timber.
An important feature of a working lamp is a good pricker, which will enable the miner to remove the crust that forms on the top of the wick of an oil-burning lamp. The pricker must be of such a form that the wick can be cleaned without danger of extinguishing the light.
A lamp burning a volatile oil, the most common form being those of the Wolf type, requires some kind of igniter, in the combustion chamber, to enable the lamp to be relit when accidentally extinguished. Lamps burning a volatile oil are more subject to extinction, either from a sudden jar or from gas, than those burning a non-volatile oil. The chief objection to lamp igniters is the opportunity that they afford the curious miner of fooling with his lamp.
The old form of igniter consisted of a narrow ribbon of waxed paper containing Uttle nubs of fulminate, which were ignited by a rod-scraper that extended up through the oil vessel of the lamp. This form of igniter has now largely given place to one in which ignition is caused by the sparks from a cerium compound. The objection to the wax-taper igniter is the flame of the burning taper and the charred remains that often proves an annoyance in the lamp, especially when one or more of the nubs fail to ignite, which is frequently the case.
Specifications by the Bureau of Mines. — 'In January, 1915, the Federal Bureau of Mines, acting under the authorization of an act of Congress (37 Stat., 681), approved Feb. 25, 1913, issued "Schedule 7, entitled "Procediu-e for Establishing a List of Permissible Miners' Safety Lamps." Following are the more important announcements and specifications contained in that schedule, which is still in force in relation to socalled "Permissible ''safety lamps for mining use.
The Bureau of Mines is prepared, at its Pittsburgh experiment station, to conduct tests of miners' flame safety lamps for the purpose of establishing a Ust of permissible safety lamps for use in mines in which explosive gas is liberated. This schedule of tests is submitted for the information of those
Mine Lamps And Lighting 275
who may desire to submit a type of lamp for test, which must fulfill the following general requirements. (See also, p. 288.)
1. The lamp must be provided with double gauzes or with some other adequate arrangement serving the same purpose. Every gauze must be of steel or best charcoal-annealed iron wire, not larger than 27 Brown & Sharpe gage (0.014 in. in diameter), with 28 meshes to the lineal inch (784 to the square inch), nor less than 29 Brown & Sharpe gage (0.01125 in. in diameter) with 29 meshes to the lineal inch (841 to the square inch).
2. If lamp standards are used, the standards must be so arranged that a straight line touching the exterior part of any two consecutive standards will not touch the glass.
3. The lamp must be so constructed that it will not be possible without easy detection to assemble the component parts of the lamp without the gauze.
4. The lamp must be provided with an efficient locking device to prevent the fuel vessel, glass, or bonnet from being removed by unauthorized persons, or being loosened to such an extent that the safety of the lamp is impaired. Provision shall also be made for taking up the play due to wear of the screw threads. ,
5. The glass globes shall have their two ends as nearly parallel as it is practicable to make them.
6. The lamp will be examined in respect to its general design, strength, and general character of construction.
Characteristic Types Of Lamps
The purpose, in this volume, is to show the general development of the safety lamp, by explaining those characteristic features that form the most essential elements of all safety lamps. It would be useless to attempt to describe in detail the construction of the many different lamps now on the market, as such a description would not be instructive in the way of demonstrating what features are essential in securing the highest efficiency and a maximum degree of security in the lamp. While the number of different safety lamps in use are legion, there are a comparatively few that are characteristic of the essential features that promote safety in the use of the lamp.
The Davy Lamp. — This is one of the early types of safety lamps that still survives. The common, unbonneted Davy is shown in the illustration. Fig. 50 and consists of a brass
Mine Gasss And Ventilation
or aluminum oil vessel surmounted by a wire-gauze chimney of standard meah. Three round iron or brass rods, called the "standards" of the lamp, are attached to the oil vessel and carry a brass ring that furnishes the upper support of the gauze chimney. Above the ring is a cap or shield of brass to which is attached the handle for holding the lamp.
There are several forms of the Davy lamp known, respectively, as the "fireboss Davy," "pocket Davy," etc. The common Davy has a single, gauze chimney, in the form of a straight cylinder le io-diameter and varying to '6 in. in height. The type known as the ' ' pocket Davy " is somewhat smaller and the height of its gauze is reduced to 4 in. One form of the Davy lamp that was much used in England had a glass cylinder surrounding the lower portion of the gauze chimney, while a steel bonnet enclosed the top of the chimney. Openings were provided in the top of the bonnet for the escape of the gases and burnt air formed in the lamp. Other forma used in England were the "tin-can Davy," having a metal shield covering the entire gauze chimney. This shield was provided Fig. 50. With Openings for the circulation of
the air and a glass window for observing the indications of the lamp. In the "Davy with glass shield" the metal shield was replaced with a glass cylinder that extended the full height of the gauze chimney. The "jack Davy" was a small sized lamp corresponding to the pocket Davy used in this country.
The Davy lamp is desned to bum sperm, cottonseed, or lard oil. Owing to the free circulation of air passing in and out of the lamp, the unbonneted Davy is a favorite among &bosses in this country. It is extremely sensitive to gas,
Mine Lamps And Liohtinq 277
and, on thifl account, flames readily when exposed to a considerable body of gas. Owii to its sensitiveness to gas and the dim light afforded, the Davy is not a safe or suitable working lamp. Its use for that purpose is prohibited by the mining laws of some states. The unbonneted Davy lamp is unsafe in a current having a velocity exceeding 6ft. per second. The Clonny Lamp.— The illustration, Fig. 51, shows the common form of Clamiy lamp, unbonneted and bonneted.
In this lamp the brass oil vessel is surmounted by a glass cylinder above which is the wirejauze chimney. The glass of the Clanny lamp enables it to give a better light than the Davy. The lamp is less sensitive to gas and more or less liable to smoke, however, because the air must enter the lamp above the glass, through the lower portion of the gauze chimney and descend to the flame, which causes a conflict of the descending and ascending currents of air, in the combustion chamber of the lamp.
278 Mine Oases And Ventilation
Owing to the simplicity of its conetniction, the bonneted Clanny lamp is largely used as a working lamp, in many mining districts. Improved types of the Clanny lamp have been introduced, from time to time, by different manufacturers. Some of these have adopted the principle of the early Eloin lamp, by which the air entered the combustion chamber of the lamp at a point below the fiame. This construction is known as the "Eloin principle" of safety lamps. By this means, the tendency of the lamp to smoke is reduced to a minimum.
The Clanny lamp is designed to burn sperm, cottonseed, or lard oil. It is equipped either with the round or the flatwick burner and the usual pricker for cleaning and raising or lowering the wick in the wick tube. The illuminati power of different types of Clanny lamps varies from 0.25 to 0.50 cp. While the imbonneted Clannylamp becomes unsafe in a current velocity exceeding 8 ft. per sec, different types of this lamp when bonneted have been able to withstand current velocities varying from 1200 to 1500 ft. per min., and, in a few cases, certain lamps of this type have not failed when the velocity has been increased to 2000 ft. per min., but this must be regarded as exceptional.
The Marsaut Lamp. — This lamp differs in no respect from the Clanny lamp just described, with the one exception that the single-gauze chimney of the Clanny lamp is here replaced by two or three concentric conical gauzes forming the chimney of the lamp. This feature is clearly seen in the illustration, Fig. 52, which shows an unbonneted Marsaut lamp having a conical gaiize within the cyUndrical gauze forming the chimney of the lamp. The double-gauze chimney is the characteristic feature of the Marsaut type.
The multiple gauzes give protection to the upper portion of
Mine Lamps And Lighting 270
the lamp. The top of a lamp chimney, where the heat is concentrated, always presents the greatest danger of the transmission of the flame through the gauze. This fact is recognized in the construction of both the Davy and Clanny lamps by providing a gauze cap, which serves as a means for the better protection of that point.
The lamp shown here is a modified type of Marsaut, designed on the "Eloin" principle of admitting the air below the glass, which improves the circulation and the illuminating power of the lamp. This type is known as the "Beard Deputy" and contains the Beard-Mackie Sight Indicator, described later (see p. 297).
The Marsaut principle of multiple wire-gauze chimneys has been found particularly applicable to lamps designed on the Eloin principle, where the air is admitted to the combustion chamber of the lamp at a point below the flame, which increases the air column or the upward draft in the lamp.
One type of double-gauze Marsaut lamp, bonneted, when tested, was found to be safe in an explosive mixture having a velocity of 2600 ft. per min., while a triple-gauze lamp of this type withstood a current velocity of 3100 ft. per min.
The illmninating power of the double-gauze lamp, burning sperm oil, was found to be 0.70 cp.; but, in the triple-gauze Marsaut this was reduced to 0.50 cp.
The Mueseler Lamp. — The special featiu-e of this lamp that is characteristic is the central conical sheet-iron chimney, supported with its mouth a short distance above the tip of the flame of the lamp and concentric within the wire-gauze chimney, as shown in the illustration, Fig. 63. The other features of the Mueseler lamp are similar to those of the Clanny lamp, except that the height of the glass cylinder is somewhat reduced and the lamp is provided with a deflector surrounding and supporting the metal chimney and directing the air as it enters the lower portion of the wire-gauze chimney.
The chief effect of the metal chimney of the Mueseler lamp is the increased protection afforded against explosion within the lamp, by separating the descending and ascending air currents. Although the inner chimney improves the circulation, the illuminating power of the lamp is decreased.
280 MINE OASBf; AND VENTILATION
The Muuscler principle, liowevcr, presents the advantage of increasing the security of the lamp against internal explosions. The shape of the central chimney is conical, corresponding to that of the gauze chimney above it. When the lamp is exposed to a body of sharp gas, and slight explosions occur in the combustion chamber of the lamp, the force of these explosions is broken by the solid metal chimney, and the danger of flame being transmitted through the wire gauze is much less than where the gauze chimney must withstand the full force of the explosion within the lamp. This has always been considered
as an important principle in safety lamp construction. For some reason, however, the Mueseler principle has not been generally adopted in the manufacture of safety lamps in this country:
There are two types of the Mueseler lamp, known as the English Mueseler, shown on the right in Fig. 53, and the Belgian Mueseler, grown on the left. These types differ only in the dimensions of the central sheet-iron chimney. The Belgian chimney is taller and narrower than that of the English type. The tests of these two types of Mueseler have
Mine Lamps And Lighting 281
shown that the Belgian lamp is superior to the English type. The former successfully withstood a current velocity of over 2800 ft. per min., while the English lamp failed at a velocity of 1000 ft per min., the explosive condition of the current being the same in each case.
The original Mueseler type of safety lamp has a horizontal wire-gauze diaphragm, at the base of the gauze chimney. This diaphragm separates the air in the combustion chamber from that within the gauze chimney above, except for the opening provided through the central metal chimney. The failure of the English Mueseler at a comparatively low velocity was probably due to the short and broad metal chimney of that lamp, which provided an ample passage between the combustion chamber and the gauze chimney above. The effect of this was to counterbalance the protection afforded by the gauze diaphragm separating these two compartments of the lamp.
The Mueseler chimney, -as stated, in spite of its advantage in increasing the security of the lamp, possesses the disadvantage of decreasing its illuminating power, which is only from 0.20 to OAO cp. This type of lamp also possesses the disadvantage that it must be held in an erect position, as only a slight deviation from the vertical interferes so seriously with the circulation through the central chimney as to give opportunity for gas that accumulates between the gauze chimney and the central tube, to enter the combustion chamber. From this cause, explosions have resulted within the lamp and caused its failure. Owing to the same conditions requiring the lamp to be held in a vertical position, its flame is easily extinguished by the burnt air and gases drawn into the combustion chamber from the gauze-chimney above.
Special Types Of Safety Lamps
Under the head of Special Lamps . may be classed those designed for a special purpose only, such as testing for gas for example, the Pieler, the Chesneau, the Ashworth, Stokes, and the Clowes hydrogen lamps, besides lamps of the Wolf
Mine Gases And Ventilation
type designed to bum a volatile oil and the Beard-Deputy, with the B-M sight indicator attachment for measuring small percentages of gas with accuracy. These lamps will be treated briefly, being modifications of the original types of safety lamp described previously.
The Pieler Lamp. — This is a special Davy lamp designed to bum alcohol and used for the purpose of testing for gas. The alcohol flame, as is well known, is sensitive to gas to a high
degree The presence of of 1 per cent, of gas in the air entering the lamp elongates the alcohol flame to a height of 3.2 in., while per cent, of gas lengthens the flame in the Pieler lamp to a height close to 7 in. Larger percentages of gas than this cause the lamp to flame and makes its use very dangerous in coal-mining practice. In making a test for gas with this lamp the flame is first adjusted so that its tip reaches the top of the conical shield that surrounds the flame. The height of this flame is 2 in.
Owing to the free circulation of air in the Pieler lamp, as in the original Davy, and the lengthening of the alcohol flame, the gauzechimney of the Pieler lamp, as shown in the illustration. Fig. 54, is increased to a height of 7.5 in. and made slightly conical. The lamp'has four standards and is provided with a screen having horizontal slots through which the height of the flame cap is observed and measured. This screen is attached to two of the standards of the lamp in a fixed position.
A slightly conical metal hood surrounds the flame of the lamp and is of such height that the tip of the ordinary alcohol flame just reaches the top of this hood. At times, the Pieler lamp is bonneted, in which case a glass window is provided
Fig. 54.
Mine Lamps And Lighting 283
extending the full height of the bonnet and marked with a scale for meaBuring the observed height of the flame in gas.
The Chesneau Lamp. — This lamp ia very similar to the Pieler lamp just described, except in a few details of construction. The lamp is bonneted and the air enters the lamp through double-gauze openings at the bottom of the chimney. A hollow eheet-metal cylinder surrounds the flame and supports the small gauze chimney, its purpose being similar to that of the metal one in the Fieler lamp. Like the Pieler, the Chesneau lamp is designed to bum alcohol. In both of these lamps cotton is inserted in the oil vessel for the purpose of absorbing the alcohol and preventing leakage in case the lamp is overturned. However, the absorptive power of the cotton is sufficiently strong to modify the height of the flame and affect the accuracy of the determination of percentage.
Ashworth-Hepplewhite-Gray Lamp. — This is a special form of lamp designed to be used both as a working and a testing lamp and which, at one time, attained a considerable popularity in this country. It is designed after the Gray lamp, so widely used in England. As appears in the illustration. Fig. 55, its principal features are: The hollow brass tubes that serve as standards for the support of the cylindrical brass bonnet surrounding the gauze chimney. These standards are arranged to draw the air from the top of the lamp when testing for a thin stratum of air at the roof of a mine airway or room. There are openings at the bottom of these hollow standards that can be closed by sUding muffs when it is desired to test for gas Otherwise, these openings are exposed to the free admission of the air to the bottom of the lamp. At thet op of the lamp, the standards are affixed to a brass plate to which the bale or handle of the lamp is
Mine Gases And Ventilation
attached. Another sliding plate fits cloeely over the firet and is arranged to close the open ends of the standards when the lamp is used m a working lamp.
The A.-H,-G. lamp is designed to burn ordinary sperm,
cottonseed or lard oil. The conical glass chimney has the
advfuitage of throwing the lht upward on the roof. The
illuminating power of the lamp is 0.79 ep. When tested,
this lamp has withstood a cmrent velocity of 6000 ft. per min.,
which is one of the features that
T[ strongly recommended its use in this
I country.
H Stokes Alcohol Lamp. — This lamp
Jl is designed by an English mine in-
" m spector, whose purpose was to supply
an alcohol flameinanoil biung lamp, ' the oil fiametobeused when the miner
was working at the face, and the alcohol flame to be used for testing for gas. The lamp is an Ashworth- Hepplewhite-Gray lamp having a small vessel for holding the alcohol when the lamp is to be used for testing for gas. As shown in the illustration, Fig. 56, this alcohol vessel is screwed into the bottom of the regular oil vessel of the lamp, its long slim wick tube passing up through a hollow tube fixed in the oil vessel of the lamp. In no other respect does the lamp differ from an A.-H.-G. lamp. When the Stokes, lamp is to be used for testing for gas, the alcohol vessel is screwed in place beneath the oil vessel. The oil flame is drawn down and the lamp tilted slightly to ignite the wick of the alcohol lamp, after which the oil flame is extinguished. The lamp is then ready for testing for gas.
The Clowes Hydrogen Lamp. — 'This lamp is also a modified Ashworth-Hepplewhite-Gray lamp. Like the Stokes lamp, it is provided with an oil vessel and burner and a second burner
0/L VESSEL ALCOHOL VESSEL inserfwt from below
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to which hydrogen gas is supplied from the strong brass cylinder shown in the illustration, Fig. 57, and which can be attached to or detached from the lamp, aadesired. There are but few of this type of lamp in the country where it has seldom been used, as it is heavy and cumbersome. The hydrten Same, though extremely sensitive to gas, is easily extinguished when testing and the use of the lamp for that purpose requires extreme care and caution. A small scale with crossbars is atto
the
oil ves-no. 67.— Oil VesBel and Hydrogen Sel for Cylinder Removed from lamp.
the purpose, of observing and estimating more accurately the height of the Eame in testing.
Hydrogen gas is compressed to 120 atmospheres or a pressure of 1800 lb. per sq. in. at sea level. This furnishes an ample supply for making a large number of tests in the mine. The gas cylinder is attached to the side of the oil vessel by a screw joint or union. A valve controls the flow of gas into the lamp when it is desired to make a test in the mine. The oil Same is then drawn down and extinguished after the hydrogen has been turned ou and 58 ignited in the lamp.
Hie Wolf Lamp.— The original Wolf lamp shown in the illustration, Fig. 58, is a German product that was widely introduced into this country and
Mine Oases And Ventilation
Mine Lamps And Lighting 287
288 Mine Gases And Ventilation
became very popular as a working lamp. At the present time, there are a nimiber of lamps of this type in use and manufactured in this country, among which may be mentioned the Koehler, the American deputy, the Hughes acetylene lamp, and many others. All of these, Uke the Wolf lamp, are designed to burn a volatile oil contained in a strong oil vessel of pressed steel, in which absorbent cotton is placed to retain the oil and minimize the danger of leaking should the lamp be overturned.
The volatile oil flame is particularly sensitive to gas, which enables this lamp to show gas when less than 1 per cent, is present in the mine air. A volatile oil, however, cannot be recommended for the purpose of testing for gas, owing to the fuel cap that is often mistaken for a gas cap when no gas is present. Owing to the ease with which a volatile oil flame is extinguished in the mine, all such lamps are provided with igniters. The original Wolf lamp is claimed to have an illuminating power of 1.45 cp., while the average of this type of lamp will but slightly exceed a single candlepower.
On the two pages preceding will be found most of the important types of mine safety lamps grouped in a historical setting that cannot fail to be of interest in connection with the subject. These appear as Figs. 59 and 60.
Permissible Mine Safety Lamps
In "Schedule 7, issued by the Federal Bureau of Mines, the engineers of the bureau have defined what is to be understood as a "permissible" miners' safety lamp in the following words:
Definition. — The Bureau of Mines considers a miners' safety lamp to be permissible for use in gaseous mines if the details of the construction of the lamp are the same as those of the type of lamp that has passed the tests made by the bureau and hereinafter described.
Conditions of Testing. — The conditions under which the Bureau of Mines will examine, inspect, and conduct tests on miners* safety lamps are as follows:
1. The examination, inspection and tests will be made at the experiment station of the Bureau of Mines, at Pittsburgh, Pa.
2. Applications for inspection, examination and test shall be made to the Director, Bureau of Mines, Washington, D. C, and shall be accompanied by a complete description of the lamp and a set of drawings showing all the details of the lamp's construction.
Mine Lamps And Lighting 289
3. The applicant for the inspection, examination and test will be required to furnish two lamps of each type, which shall be sent prepaid to the Engineer in Charge of Lamp Testing, Bureau of Mines, Fortieth and Butler Streets, Pittsburgh, Pa., and will be retained by the bureau as a laboratory exhibit.
Each lamp shall have marked on it in a distinct manner the name of the manufacturer and the name, letter or number by which the type is designated for trade purposes, and a statement shall be made whether or not the lamp is ready to be marketed; also a statement describing the fuel used, its trade name and properties. The applicant may supply the fuel for the test if he so desires.
4. Upon the receipt of a lamp for which application has been made for examination, inspection or test, the engineer in charge of lamp testing will advise the applicant whether additional spare parts are deemed necessary to facilitate a proper test of the lamp, and the applicant will be required to furnish such parts as may be requested.
5. No lamp will be tested unless the type submitted is in the completed form in which it is to be placed on the market.
6. Only the engineer in charge of lamp testing, his assistants and one represent*ative of the applicant will be permitted tk> be present during the conduct of the tests.
7. The conduct of the tests shall be entirely under the direction of the bureau's engineer in charge of the investigation. The tests will be made in accordance with a predetermined schedule, which is outlined herein.
8. As soon as possible after the receipt of the formal application for test, the applicant will be notified of the date on which his lamp will be tested and the amount and character of additional material it will be necessary for him to submit.
9. The tests will be made in the order of the receipt of applications for test, provided the necessary lamps and material are submitted at the proper time.
10. The details of the results of the tests shall be regarded as confidential by all present at the tests and shall not be made public in any way prior to their official announcement by the Bureau of Mines.
11. The results of tests made on lamps that fail to pass the requirements shall not be made public but shall be kept confidential, except that the person submitting the lamp will be informed with a view of possible remedy of defects in future lamps submitted; but such changes other than changing the glass globe or chimney, will not be permitted while the testing is in progress.
12. Tests will be made for manufacturers, manufacturers' agents, state mine inspectors and mine operators.
13. A list of permissible lamps and the results of their tests will be made public, from time to time, by the Bureau of Mines.
14. The glass globe or chimney shall be marked in a distinct manner by a name or design by which its type is designated for trade purposes.
29Q Mine Gases And Ventilation
Mechanical Tests. — The following mechanical tests will be applied to every lamp submitted to the bm*eau to ascertain its strength and resistance under the rough usage common to mining work.
1. The lamp is dropped, by means of a mechanical arrangement, onto a wooden floor, from a height of 6 ft. measured from the floor to the bottom of the lamp, which has been fitted together complete with the glass, a component part of the lamp.
Five successive trials are made, the lamp being fitted with a different glass each time. The lamp passes the test if the glass is broken in not more than one of the five trials. Should the glass be broken in two but not more than two of the five trials, the lamp is submitted to five more trials with fresh glasses and if the glass breaks in two of them the lamp will be considered as having failed to pass the test.
2. A weight of 5 lb. is dropped, from a height of 6 ft., onto the lamp standing vertically on a wooden platform beneath the weighii.
The height of 6 ft. is measured between the bottom of the weight and the top of the lamp. The weight is a lead disk 3 in. in diameter and in. thick and is dropped mechanically.
Should the glass of the lamp break, two more trials are made, each with a diflferent glass, and if the glass breaks in either the second or third trial the lamp will be considered as having failed to pass the test.
3. A weight of 10 lb., attached to a cord the other end of which is secured to the bottom of the lamp, is dropped a distance of 6 ft., the lamp being suspended at a height of 7 ft., from the ground.
The lamp is gripped by means of claws, or slung by means of straps fastened around its upper part, above the standards protecting the glass. A plate is fastened to the bottom of the lamp and the cord is attached to the center of this plate. The weight is a lead disk in. in diameter and IJ in. thick. It is dropped mechanically.
This test is repeated three times. If, as the result of any one of these three trials, the security of the lamp is found to be defective in aay way the lamp will be considered as having failed to pass the test.
Tests 1, 2, and 3 are to be made in succession on one lamp. Cracking of the glass will be regarded as a breakage.
Photometric Test. — The lamp is required to give & minimum candlepower of 0.30, as compared with a pentane standard, during a period of 10 hours.
Explosion Test. — After a lamp has passed the mechanical tests, it will be tested by placing the lighted lamp in an explosive mixture of gas and air, as follows:
1. In currents of air and gas containing per cent, of natural gas drawn from the Pittsburgh gas mains. In a gallery (lamp gallery No. 1) a lamp which has passed the mechanical tests is tested, with a
Mine Lamps And Lighting 291
fresh glass if necessary', in horizontal, inclined and vertical currents of the explosive mixture of gas and air :
a. In a horizontal current, velocity 600 to 2500 ft. per min.
h. In a 45 deg. descending current, velocity 600 to 2500 ft. per min.
c. In a 45 deg. ascending current, velocity 600 to 2500 ft. per min.
d. In a vertical descending current, velocity 600 to 2500 ft. per min.
e. In a vertical ascending current, velocity 600 to 2600 ft. per min. Trials will be made at velocities of 600, 800, 1000, 1200, 1500, 2000,
and 2500 ft. per min. Into the horizontal current moving at 1500 ft. per min., the lamp will be suddenly thrust from below.
The duration of each trial is two minutes and each trial is repeated three times. An ignition exterior to the lamp will cause the lamp to be rejected.
2. In a still atmosphere (lamp gallery No. 3) containing per cent, of natural gas. The lamp is placed, with a fresh glass if necessary, in this inflammable atmosphere for three minutes. Five separate determinations will be made. An ignition exterior to the lamp will cause the lamp to be rejected.
Tests of Glasses. — 1. A weight of 1.1b. is dropped by means of a mechanical arrangement, from a height of 4 ft., upon the glass placed in a vertical position on a wooden floor. The weight is a lead disk in. in diameter in. thick. Twenty glasses of any one kind will be tested. Two failures in the twenty will cause the glasses to be rejected.
2. Ten glasses are healed in an air balh to a temperature of 212 deg. F. and when at that temperature are removed from the bath and plunged into water at a temperature of 60 deg. to 65 deg. F. One failure in ten will cause the glasses to be rejected.
If the lamp has two glasses the outer glass will be tested by mechanical means only and the inner glass by heating onlv.
Igniter Tests. — Lamps having internal igniters will be tested to determine the safety and permissibility of the igniter device: fhc permissibility of the lamp will be dependent in part on the result of the tests of the igniter device.
These tests will be made to determine the liability of external ignition when the igniter device is (jperated in the presence of inflammable mixtures of gas and air under such conditions as may be determined by the engineer in charge of lamp testing, for each type of igniting device. Tests will be made to determine :
1. If external ignition is possible when the igniter is operated in still and moving currents of gas and air mixtures.
2. To determine if the residue left in the lamp after working the igniter device is a source of danger in subsequent use of the lamp in inflammable mixtures of gas and air.
3. To determine the nature of the material used in .the igniter device. The igniter will have passed the tests if no external ignition is caused
by manipulating the igniter when in position within a double-gauze
292 Mine Gases And Ventilation
safety lamp, or if no external ignition is caused by the use of the lamp in inflammable mixtures of gas and air after the igniter has been in service.
Applicants for tests will be required to furnish two complete igniter devices and 5 dozen igniter refills, which shall be shipped in sealed boxes or packages with the trsAe name written on the outside and addressed to the Engineer in Charge of Lamp Testing, Bureau of Mines, Pittsburgh, Pa. When known by the applicant, the proximate chemical composition of the igniter tape or point should be furnished and the place of its manufacture.
Note. — The inflammable gas used in these series of tests will be the natural gas supplied to the city of Pittsburgh The composition of this gas is approximately: Methane, 83.1 per cent. ; ethane, 16 per cent. ; nitrogen, 0.9 per cent. ; carbon dioxide, a trace.
Lamps in the course of development may be submitted by manufacturers for inspection and preliminary tells, with a view to ascertaining defective construction or the misapplication of safety principles. The nature of such inspection and tests will be determined by the engineer in charge of lamp testing.
Approval of Safety Lamps. — The manufacturers of such types of lamps as have passed the tests of the bureau may attach a plate containing, or stamp into the metal of the lamp, the following inscription :
PERMISSIBLE MINERS SAFETY LAMP. U. S. BUREAU OP MINES APPROVAL NO. — .
Before claiming the bureau's approval of any modification of any approved type of lamp, the manufacturer shall submit to the bureau drawings that show the extent and nature of such modifications. Each approval of a permissible lamp will be given a serial number, and approvals of modified types will bear the same serial number as the original, with the addition of the letters a, b, c, etc.
The bureau will, on application, make separate tests of glasses manufactured for use in connection with any lamp that has been approved by the bureau under the provisions of this schedule. Glass globes that fulfill the requirements of the tests will be approved for types manufactured in every particular like those submitted that passed the test.
The bureau will, on application, make separate tests of internal igniter devices for use with any type of lamp that has been approved by the bureau under the provisions of this schedule. Igniters that fulfill the requirements of the tests will be approved for types manufactured in every particular like those submitted that passed the tesl.
The bureau's approval of any lamp shall be construed as applying to all lamps of the' same type as tested, made by the same manufacturer and having the same construction in detail, but to no other lamp. The
Mine Lamps And Lighting 293
bureau reserves the right to rescind, for cause, at any time, any approval granted under the conditions herein set forth.
Notification to Manufacturer. — As soon as the bureau's engineers are satisfied that a lamp is permissible the manufacturer, agent or applicant and the mine inspection departments of the several states shall be notified to that effect. As soon as a manufacturer receives formal notification that his lamp has passed the tests prescribed by the Bureau of Mines, he shall be free to advertise such lamp as permissible.
Fees for Testing. — Careful investigation has been made regarding the necessary expenses involved in testing miners' safety lamps at the Pittsburgh experiment station, and the following schedule of fees to be charged on and after February 15, 1915, has been established and approved by the Secretary of the Interior, in accordance with the provisions of the statute previously quoted:
Preliminary inspection and test $10. 00
C!omplete lamp test 50,. 00
Candlepower test 5 . 00
Separate glass globe tests 5 . 00
' Separate igniter tests 10 . 00
The fees specified above may be increased to cover the cost of testing an unusually complicated type of lamp, .and are also subject to change upon the recommendation of the Director of the Bureau of Mines and the approval of the Secretary of the Interior.
Use And Care Of Safety Lamps
No safety lamp, however perfect, is safe when improperly used; nor has the safety lamp yet been devised that is foolproof. For these reasons, a safety lamp should never be entrusted to an incompetent or an unreliable person. With the single exception of the lamps used by the mine examiners or firebosses, all lamps used in a mine should be the property and care of the operator.
The Lamphouse or Station. — A lamphouse or lampstation should be established convenient to the mine entrance, where the miners can secure their lamps when entering the mine and return the same on coming to the surface. Each lamp should be stamped with a number and, as far as practicable, the same lamp should be given to the same man, each day, and he be made responsible for its use and condition.
The lamphouse should be in charge of a competent man and one or more assistants, whose duties would be to receive and
294 Mine Gases And Ventilation
deliver all lamps in return for checks bearing the lamp number. No lamp must be given out, except in return for this check, which should be placed in the pigeonhole from which the lamp is taken or hung on its hook ready to be given back to the man when his lamp is returned at the close of the shift.
A properly organized and arranged lamphouse will have one or more lampracks with holes or hooks for the lamps. Each hole or hook has a number corresponding to that on the lamp. Tables ar6 provided where the lamps can be taken apart, cleaned, filled and trimmed, after which they are carefully assembled, inspected and returned to their respective places in the rack.
The oil for filling the lamps should be drawn from a tank or reservoir outside of the building. No oil container other than the lamp vessels should be permitted in the lamphouse or station, which should be of fireproof construction and kept free from all accumulations of oily waste or other material liable to spontaneous combustion. The presence of a man's lamp or check on the lamprack will indicate whether he has come out or is still in the mine and will thus serve the same purpose as a checking board, in that respect.
No one must be permitted in the lamphouse other than those in charge. All lamps should be delivered through one or more windows opening on a passageway. The work of delivering and receiving lamps, where a large number of men are employed, will be greatly expedited if there are several windows, each corresponding to a division in the numbering of the lamps. A further advantage in such an arrangement is that each division can be in charge of a man who is responsible for the lamps in that division.
Handling of Safety Lamps.— A safety lamp must never be given to a man who has not been instructed and drilled in respect to its use. Before being entrusted with a safety lamp, a man must show his ability to determine the presence of gas, by observing the flame cap formed in his lamp. He should be taught how to proceed when he has observed a cap in his lamp, and cautioned to carefully lower his lamp and withdraw quietly but promptly from the place.
Mine Lamps And Lighting 295
The man should be shown how his lamp may flame should a larger proportion of gas be present in the air. He should be instructed, in that case, as to the necessity of maintaining his presence of mind and making no quick movement with the lamp, which must be withdrawn promptly but cautiously from the gas, by lowering the lamp toward the floor. The man should be further cautioned in regard to the danger of disturbing a body of gas, which may then surround him and make it difficult for him to escape with safety.
A safety lamp must always be held in an upright position and protected against a rush of air such as follows a blast in the mine. It is necessary to protect the lamp when walking against a strong air current. A lamp should never be swung, but should be held quietly at one's side when going from place to place in the mine. Care must be taken not to drop the lamp or permit it to fall. Under no circumstances must a man tamper with his lamp or attempt any experiment. If the lamp is accidentally extinguished, the man's duty is to proceed at once to the nearest relighting station, which should be provided at a convenient point in the mine.
Testing For Gas By Indicators
The work of testing for gas is the most important work to be performed in the operation of a gaseous mine and can only be safely entrusted to a mine examiner, fireboss or deputy who has had experience both in the testing and the handling of gas. The examination of a for gas and other dangers must be performed conscientiously and faithfully. The work will not permit of the taking of chances, as the life of every worker in the mine depends on the thoroughness and capability of the examiner.
From time to time, different means have been employed in making the test for gas in mine workings. These consist in various forms of indicators and detectors especially designed to reveal the presence of gas in mine air and ascertain its percentage. Besides these appliances, a few of which will be described briefly, there is the old-established flame test, made by the use of the Davy or other safety lamp, and which is
296 Mine Gases And Ventilation
still the most largely employed by mine examiners and firebosses.
Numerous Gas Indicators.— Perhaps the earliest attempt to devise a means of indicating the percentage of gas present in air consisted of a glass tube into which had been fused a platinum wire that could be rendered incandescent by an electric current. A sample of the air to be tested was drawn into the tube where the gas contained in the air was consumed by the incandescent wire. The volume of the remaining gases was then measured. Comparing this with the original volume of gas and air gave the percentage of gas present in the air. Devices of this nature, however, were never of practical value, until the recent design of such a gas detector by George A. Burrell, of the Federal Bureau of Mines, which will be described later (see p. 299).
Another device depended on the increase of pressure in an air container that was separated from a similar container of gas and air by a porous partition through which diffusion of the gas into the air took place. The resulting increase of pressure in the first container was an index of the percentage of gas present in the sample tested, but the device had no practical value for use in mines. Still another device depended on the rise in temperature caused by the absorption of gas by platinum black, which coated the bulb of one of two thermometers. ' The rise in temperature thus indicated furnished the means of determining approximately the percentage of gas present. Again, another device depended on the compression of a sample of gas-charged air contained in a strong glass tube into which was fitted a piston. The rapid compression of the air in the tube would ignite the gas and cause a flash when not less than 5 per cent, of gas was present.
The Liveing indicator was a more accurate means of determining percentages of gas, but this also never came largely into use. Two platinum wires of equal resistance were rendered incandescent by an electric current. One of these wires was inclosed in a tube containing a sample of the air to be tested, while the other wire was in pure air. An ingenious sliding arrangement of the two tubes containing the wires
Mine Lamps And Lighting 297
provided a means of comparing their relative brilliancy, which fm-nished a suggestion of the percentage of gas present in the air tested. None of these devices, however, can be considered of any practical importance in coal mining.
The Shaw Gas Machine. — This machine, though not of portable form, on which account it could not be takn into the mine but samples of air to be tested must be brought to the surface, furnished a means of correctly determining the explesibility of samples of air collected id the mine workings. For this purpose, it was formerly used at many large collieries. The disadvantage in its use lay in the fact that a test could not be made on the spot and time must elapse between the taking of the sample of air and knowing the results of the test. In that time, conditions in the mine might materially change, which rendered the test valueless for the purpose intended.
The Shaw machine consists of two cylinders whose volume ratio is known. Both cylinders are fitted with air-tight pistons operated by a single lever arm. By this means exact proportions of gas and air can be pumped into a combustion chamber where they are ignited when the mixture becomes explosive. A graduated scale indicates the volume percentage of air and gas present when explosion occurs.
In the operation of this machine, it is first necessary to standardize an artificial gas supply to ascertain the lower explosive limit of the gas. To do this the machine was arranged so that the larger cylinder would pump pure air while the smaller one pumped gas, and the point noted when explosion occurred. This having been done, the tube that formerly supplied pure air to the larger cylinder is now connected with the bag containing the sample of mine air to be tested, while the smaller cylinder continues to pump its proportion of the standard gas. Evidently, a less ratio of the supply from the two cylinders will now be required to produce an explosion, should the air pumped by the larger cylinder contain some gas. The difference shown on the graduated scale gives the percentage of gas present in the air tested.
The Beard-Mackie Sight Indicator. — This is a simple and extremely practical device designed to be attached to the
Mine Gases And Ventilation
biinier of a safety lamp burnii sperm, cottonseed or lard oil but' not a volatile oil. As shown on the right, in the illustration, Fig, 61, the device consists of a U-shaped support mounted on a small brass disk that fits over the burner and is held in place by the screw nipple of the lamp. On this support are arranged fine platinum wires at fixed heights above the lamp flame. The lower straight standard wire is for the purpose of standardiziitheflame, which is raised to a height just sufiicient to incandesce that wire. This must be done in pure air, although a ght alteration in the height of the flame produces no practical effect in determining the percentage of gas by the incandescence of the successive percentage wires when the lamp is taken into the mine. Indeed, the standardizing of the flame is generally done after entering the mine when the examiner has once become acquainted with the use of this indicator. The percentage wires are each looped at the cents, the purpose being to make their incandescence more perceptible when observed through the gauze of the Davy lamp, as shown on the left of the figure. The incandescence mounts higher in the percentage wires as the proportion of gas in the mine air increases and the uppermost wire incandesced determines the percentage of explosibility of the mine air.
The use of the aght indicator furnishes the means of determining with considerable-accuracy the explosibility of mme
Oaw Lamp
With
SIOHT INDKATOfi
BEAftD-HACKTE SIOHT INDICATOR
Km DTTEfimm 8AS
Mine Lamps And Lighting 299
air, at the point and at the moment the test is made. Its use eliminates the necessity of the fireboss guessing the percentage from the height of the flame cap observed in his lamp. It enables a just comparison to be made between the reports of different flrebosses whose judgment may differ, or who may not be equally capable of discerning the caps formed in their lamps.
With proper care, the sight indicator can be used, for a year or more, by a fireboss when making his morning examination of the mine. Its construction is naturally somewhat delicate, which requires it to be carefully handled when beii inserted or taken out of the lamp. A careless fireboss will often permit his lamp to smoke and carbonize the wires, which interferes with their delicacy. The same effect is caused by burning a poor quality of oil or oil mixed with kerosene, which increases the smokiness of the flame.
The advantages derived by the use of the indicator are that it standardizes all tests for gas, making them comparable. It eliminates the guessing of the height of a flame cap and the percentage of gas indicated thereby. It indicates the presence of gas as low as one-half of 1 per cent. The
indications are plainly visible by the incandescence of the looped wires. The presence of an indicator in a lamp has often avoided the extinction of the lamp in gas and reduces the tendency to internal explosion in the lamp. Finally, all indications are made with a normal flame, which not only saves time but avoids the necessity of lowering the flame and possibly extinguishing it when making a test.
The Burrell Gas Detector. — This device, which is shown in section in the illustration, Fig. 62, consists of a brass tube A
300 Mine Gases And Ventilation
surmounted by a screw cap P equipped with a valve F, a little cup K and two binding posts M and N. Connected with and supported by the latter is a fine platinum-wire bridge F, which can be rendered incandescent by the current from an electric battery. A stout gage-glass C is surmounted by a brass reservoir or cap H to which a rubber tube R is attached. Both the gage-glass C and the brass tube A are set into an aluminimi base X, by which they are connected, forming a U-tube after the manner of a water gage. A graduated scale provides the means of measuring the height of water column in the gage-glass.
In the use of this instrument for the detection of mine gas in the workings, the brass cap P is unscrewed and water poured into Ay until it rises in the gage-glass to a level indicated by the zero of the scale at S. This level corresponds to the level Q in the brass tube A, just below the platinum wire F.
When a test is to be made in the mine the valve V is first opened and the operator blows gently into the rubber tube R, depressing the water level in the gage-glass and causing it to rise in the brass tube, until it appears in the little cup K, or until a slight cUck of the valve V tells that the water has completely filled the combustion space T, in the top of the brass tube. The rubber tube attached at R is now pinched with the fingers and the instrument raised to the roof or into the cavity where it is desired to test the air for gas. In that position, the rubber tube is released and the water level at once falls in A and rises ill C to where it originally stood at zero of the scale. By this action, the air to be tested is drawn in through the open valve V and fills the combustion space Y above the water level Q,
When equilibrium is established, the valve V is closed and the battery current switched on, causing the incandescence of the wire bridge which is plainly observed through the small glass window E, About 13-min. is required to consume all the gas present in the air contained in the combustion space above the water. The current is now turned off and the instrument shaken, for the purpose of cooling the air and gaseous products of the combustion, and permit of their volume being
Mine Lamps And Lighting
measured at the original temperature. As cooling takes place, the water rises in A and falls in the gage-glass, until it becomes stationary at a certain level. The graduation at that point will show the percentage of gas that was present in the air tested. The aluminum scale is easily removable and is graduated for the detection of any combustible gas or vapor. The two scales that appear in the figure are for hydrogen (H) and carbon monoxide (CO).
This instrument has proved quite effective for the purpose intended in its design. There is no doubt but that some of the carbon dioxide produced by the combustion of the gas is absorbed in the water when the instrument is shaken; but this is probably largely compensated by the slightly higher water level in A above that in the gage-glass C, at the time the measurement is taken. This difference of level is, moreover, rendered extremely slight by reason of the relatively larger diameter of the tube A, as compared with the bore of the gage-glass C. Actual tests of the results obtained in the mine, by comparison with the analysis of the same air, in the laboratory, show the following percentages which are not exceptional.
By detector . By analysis.
For all practical purposes, the slight differences shown by these figures between the tests made in the mine and the analyses made in the laboratory are immaterial.
The Flame Test
From the earliest time, the most universal method of testing for gas in mines has been that of observing the effect of the gas on the flame of a safety lamp. As is well known, in every candle, or lamp flame burning oil, there are three zones as indicated in the illustration, Fig. 63. The inner zone A is dark, being filled with the hydrocarbon vapors formed by the' vaporization of the oil. There is no combustion taking place in this zone. The heat of the flame dissociates the hydrogen and carbon of these vapors, and the second zone B is rendered
302 Mine Gases And Ventilation
lunimoiis by the incandescent carbon particles, which there undergo combustion. The remaining hydrogen and the carbon monoxide resulting from this combustion pass into the outer zone C where they bimi with a non-luminous flame, supported by the surrounding air which here has free access to the Same. Owing to the brightness of the second zone B, caused by the incandescence of the carbon particles, it ia difficult to discern the non-luminous envelope surrounding it and forming the third zone C.
Flame Caps.— When a lamp flame is lowered, almost to its point of extinction, the surrounding air so closely approaches the wick that the hydrocarbon vapors are consumed without the incandescence of the carbon. The dark zone is here greatly reduced, whUe the second luminous zone is practically eliminated, leaving a small aon-luminous flame covering the wick, as shown in the lower rightband corner of the figure.
h
*ssa
Just above, in the upper
jg right-hand corner, the 'fm flme is shown as slightly p,g 83 increased in size by raisin
the wick a trifle. There now appears a small luminous zone siirmounted by a nonluminous cap, which can be readily discerned. This cap is known as a "fuel cap," being due solely to the combustion of the vaporized oil. This fuel cap is often mistaken for a gas cap when testing for gas with a reduced flame.
The description given thus far refers to a Same burning in pure air. Now, when a lamp flame b burning in air charged with a small percentage of a combustible gas, as methane for example, the gas in contact with the flame is consumed. At the same time, the outer zone of the flame is lengthened and rendered more luminous than before because of its increased size, and there now appears what is known as the "gas cap" or more commonly "flame cap."
Mine Lamps And Lighting 303
The height of the flame cap varies with the percentage of gas present in the air, the kind of lamp employed and the oil or luminant burned therein. The visibility of the cap is greatly assisted by the free access of air to the combustion chamber of the lamp. The air should enter the lamp at a point below the flame; in other words, the ventilation in the combustion chamber should be ascensional. Any other arrangement interferes decidedly with the clear observance of the cap.
A dark background in the lamp also renders a cap more plainly visible.
The effect of the form of the lamp and the illuminant burned, to produce a given heht of cap, for a given percentage of gas, is clearly shown in the lamp diagram, Fig. 64. The tall gauze chimney, free access of air and the alcohol burned in the Pieler lamp very greatly increase the height of the flame, in the use of that lamp, for the same percentage of gas present. On the other hand, the bonnet of the Clowes lamp burning hydrogen, or the Wolf lamp burning naphtha, materially reduce the
height of flame cap formed in these lamps, notwithstanding the volatile nature of the illuminants burned. The effect of the bonnet in the Davy lamp burning sperm, lard or cottonseed oil is clearly shown to reduce the height of the cap, for the same percentage of gas, as compared with that obtained in the unbonneted Davy.
The preceding diagram is of interest in connection with the use of different types of safety lamps burning hydrogen, alcohol, naphtha, or a non-volatile oil, as sperm, lard or cottonseed oil, in testing for gas. The height of flame cap, or the elongation of the flame, produced by different percentages of gas, in the use of different lamps is tabulated, in the upper right-hand corner of the diagram.
The heights of flame cap given in the diagram, for the Davy and Wolf lamps, are the minimmn caps produced by drawing down the flame to its lowest point. The heights given for the Clowes (hydrogen) lamp and the Pieler (alcohol) lamp are for the elongation of the flame due to the gas. The original flame of the Clowes lamp is 0.3 in., while the flame of the Pieler lamp is adjusted so that its tip just reaches the top of the shield, at a height of 2 in., as shown in Fig. 64. (See ' description of Pieler lamp, p. 282.)
The presence of other gases or dust will, of course, modify the results shown in this diagram. The effect of carbon dioxide is to diminish the length of the flame and obstruct the formation of the cap. On the other hand, carbon monoxide and dust when present in the air lengthen the flame and assist the formation of a cap.
Calculation of Height of Flame Cap. — For a Davy lamp, burning sperm or cottonseed oil of good quality, in an atmosphere charged with pure methane or marsh gas, experiments have shown that the height of flame cap varies as the cube of the percentage of gas present. Using a bonneted Davy burning colza oil, William Galloway has estimated the height of flame cap to be Ko of cube of the percentage of gas present in the air surrounding the lamp
In a long series of experiments under favorable conditions, the author found when using an unbonneted Davy lamp
Uine Lamps And Lighting
Ijuniing spernii oil the height of flaiiie cap was of the cubi of the percentage of gas preseat iu the feed air entering the lamp. The height of cap was accurately measured by a scale in the lamp, and the percentage of gas in the air was obtained by the use of a Shaw gas machine, which drew the air from the testing chamber in which the lamp was placed and which was ventilated by a continuous current of air charged with the gas. The arrangement eliminated the effects that would otherwise have been produced by accumulation of the products of combustion in the lamp chamber.
IbdKa/ Flame
?t
' ? 5
centoge of
Fio. 65.
The results are expressed by the following formulas, giving the height of flame cap h for any percentage of gas J:
The appearance of the dame and the height of cap, for different pcentages of gas, as derived from the author's experiments, are shown in the illustration, Fig. 65. These tests were made with the game reduced to a height of Ke in. It will be observed that, as the height of the flame increases, its volume is enlarged. At about 3.5 per cent. c& gas, the Same
306 Mine Gases And Ventilation ,
became unsteady and, as the percentage of gas was increased above that point, the flame became more voluminous, rotating in a wierd manner about the gauze, then expanding at the top into a fan-shape and finally filling the gauze chimney with flame.
Beyond this point, the flame has been frequently seen to leave the lampwick, while the gas continued to burn in the upper portion of the chimney. When this occurred with a sight indicator in the lamp, the flame would relight the wick as the percentage of gas was reduced, all of the percentage wires of the indicator being then brightly incandescent. The same action has been observed by the author when holding an unbonneted Davy, equipped with sight indicator, exposed to a strong gas feeder. At that time, slight explosions occurred within the gauze, but the lamp was not extinguished when carefully withdrawn from the gas.
Making a Test for Gas in the Mine. — When approaching a place where gas is suspected, one must move quietly so as not to unnecessarily disturb the gas from its lodgment at the roof or in a cavity. Having lowered the flame, the lamp is cautiously raised into the gas and watched for the fiirst appearance of a cap or the lengthening of. the flame. As quickly as this is observed the lamp should be promptly but cautiously withdrawn from the gas.
On finding a body of sharp gas that has caused the lamp to flame, danger occurs when, in withdrawing the lamp, fresh air enters the combustion chamber, creating a highly explosive mixture within the lamp. For this reason, the lamp must be withdrawn from such a mixture slowly and with great caution, which often requires much presence of mind. One should never trifle with gas he has found in a cavity of the roof or on the falls.
Gas issuing from the coal, at the face of a chamber, will often pass out in a thin film or layer at the roof, and may be unobserved by a fireboss until he is well within the chamber. His movement beneath the layer of gas may cause it to descend as he passes and he finds, too late, that he is enveloped in gas from which he is able to escape with difficulty. Under
Mine Lamps And Lighting 307
such circumstances, a fireboss will frequently smother his lamp beneath his coat, while he retraces his steps cautiously. A thin layer of gas at the roof of a chamber can often be detected by holding the lamp erect toward the roof and blowing a slight piiflf against the roof, so as to cause the gas to descend on the lamp. This is a practice followed by many experienced firebosses. Without doing so, it is possible for a fireboss to miss the gas and report the place safe for work when it is quite unsafe.
Illuminants For Safety Lamps
The principal illuminants used in safety lamps are the various kinds of vegetable, animal and mineral oils. Hydrogen gas is used in the Clowes hydrogen lamp, but this is the only lamp burning gas. For practical purposes, the oils burned in mine safety lamps can be designated as volatile and non-volatile oils. A few testing lamps are designed to burn alcohol (spirits of wine), which is also a highly volatile illuminant.
Nonvolatile Oils Used in Safety Lamps. — These are mostly derived from the vegetable and animal kingdom. Among the vegetable oils largely used in mining practice may be mentioned cottonseed and colza or rapeseed oil. The principal animal oils, which are also non-volatile, are the sperm, lard, seal and whale oils. Of these, sperm and lard oils are most commonly used in safety lamps today.
Both vegetable and animal oils possess less illuminating power than mineral oils, and have a greater tendency to incrust the wick of the lamp. They are more stable, however, and the flame is not as readily extinguished in the mine as when mineral oil is burned in the lamp. The addition of about one-half of their volume of coal oil (kerosene) greatly improves the illiuninating power of these oils but increases their tendency to smoke. The rate of burning is slightly increased and the mixture does not incrust the wick as rapidly as when a vegetable or animal oil is burned.
Mineral Oils, — -All mineral oils are classed under the general term, "petroleinn,'' which is derived in a crude state from the oil-bearing strata. When the crude petroleum or **rock oil,"
308 Mine Gases And Ventilation
as it is sometimes called, is distilled, the more readily vaporized hydrocarbon vapors condense on cooling to what are termed light . or volatile oils. These are distilled at temperatures below 300 deg. P. Coal oil, or kerosene, is the product distilled between 300 and 570 deg. F., while the heavy lubricating oils are distilled at still higher temperatures. These last products contain paraflSn, which is separated from the heavy oils by its solidifying at 130 deg. F., in cooling. Of the light oils, gasoline is distilled below 140 deg., naphtha, below 230 deg., and benzine, below 300 deg. P.
Light, Volatile Oils, — The danger in the use of light volatile oils, as illuminants in safety lamps, arises from their low flashing points. The ready vaporization of the oil, as the lamp heats in gas, renders the test for gas unreliable in the use of a lamp burning such an oil. The storing of a highly volatile oil at a mine and the filling of the lamps in the lamphouse requires extra precautions to be taken to avoid accident. In order to reduce the danger of its use in the lamp, the oil vessel is filled with absorbent or filling cotton. A light volatile oil is not as stable as a vegetable or animal oil, and its flame is more easily extinguished when such an oil is used in the mine. A volatile oil flame, however, is more sensitive to gas and has a higher illuminating power than other oils, which has favored its use in many mining districts.
Miners' Carbide Lamps
The acetylene or carbide lamp that has come into such extensive use in coal mining, within the past few years, is an open-flame lamp constructed to burn acetylene gas, generated within the lamp by the slow feeding of water onto the carbide. The water and the carbide are contained in two separate compartments of the lamp.
The supply of water to the carbide is regulated by a valve having a screw adjustment at the top of the lamp. The water is contained in the upper half of the lamp and the carbide in the compartment below. The latter should not be more than half filled with the carbide, which swells when moistened with
MINE LAMPS AND LIGHtlNO 309
the water. A charge oif oz. of carbide will supply gas sufficient tQ maintain a flame length during a half-shift or more but then it will be necessary to rechai the lamp.
Owing to the brightness of the acetylene flame, the carbide lamp has very largely replaced the old open-flame torch so commonly used in mines generating no gas. The general form of carbide lamp in common use is shown in Fig. 66, although there are different styles of this lamp manufactured, some having no reflectors behind the flame and differii in other details. The lamp shown in the figure is a type very largelyused in the anthracite district. Most of these lamps in use differ only in details.
Generation of Acetylene Gas. — Carbide (CaCj) is a product of the action of coke on quicklime, calcium oxide (CaO). The lime and coke are finely ground, thoroughly mixed and heated to a white heat in an electric fumftce. Under the high heat of this furnace a portion of the cartyjn unites with the calcium
remainder of the carbon taking up the oxygen and passing off as carbon dioxide (CO2), according tothe reaction,
4CaO + 5C, 4CaC3 + 2CO2
When water comes in contact with calcium carbide, calcium hydroxide, is formed and acetylene gas (CjHi) is set free according to the equation.
CaC, + 2HjO + CHj
The acetylene gas is highly infiammable and when ignited in the air burns, producing carbon dioxide and water vapor. Ignoring the inert nitrogen of the air, this reaction is expressed by the following equation:
2C,H2 + 50j 4C0, + 2HsO
310 Mine Gases And Ventilation
One ounce of pure crystallized calcium carbide will generate 622 cu. in. of acetylene gas, measured at a normal temperature of 60 deg. F., barometer 30 in. Commercial carbide, however, will commonly yield only from 400 to 500 cu. in. per ounce of carbide used, depending on the completeness of its consumption in the lamp.
Burning Acetylene Gas. — Por the purpose of estimate, it may be assiuned that an average miners carbide lamp consumes oz. of carbide per hour and generates 250 cu. in. of acetylene gas. Then, since one volume of this gas, in burning, consumes volumes of oxygen or, say 123-volimies of air and produces 2 volumes of carbon dioxide and 1 volume water vapor, the burning of a carbide lamp may be estimated as producing 500 cu. in. of carbon dioxide and half that volume of water vapor, per hour. In the same time, the lamp takes from the air 625 cu. in. of oxygen, leaving practically 2500 cu. in. of excess nitrogen.
The effect of the burning of a carbide lamp to vitiate the mine air is thus seen to be inappreciable and far less than the breathing of a man, who consumes little short ol 1000 cu. in. of oxygen, per hour, when at rest, and over 8000 cu. in. per lir., in violent exercise, and exhales an equal volume of air containing from to 63-per cent, of carbon dioxide.
Calculation. — The molecular weight of calcium carbide (CaCa) being 40 + =64; and that of acetylene (C2II2), + 1) =26; and the specific gravity of this gas referred to air being 0.92, we have the following:
Weight of 1 cu. ft. air (60 deg. F., bar. 30 in.) . . 0.0766 lb.
Weight of 1 cu. ft. acetylene, 0.07047 lb.
Volume of 1 lb. acetylene
Volume of 1 oz. acetylene . . . . 1532.5 cu. in.
Then, since 64 parts, by weight, of calcium carbide yield 26 parts, by weight, of acetylene gas, one ounce of the pure crystallized carbide will generate
measiu-ed at 60 deg. F., bar. 30 in.
Mine Lamps And Lighting 311
Properties of Acetylene Gas. — The gas is colorless and has a strong pungent odor, due to the presence of some sulphureted and phosphureted hydrogen, as generated in the carbide lamp, by the action of water on the carbide. It has a specific gravity of 0.92, referred to air at the same temperature and pressure. Under atmospheric pressure, the gas liquefies at — 115 deg. F., the volume of the liquid being lioo that of the original gas.
Acetylene gas is combustible, igniting, in contact with air, at a temperature of 900 deg. F. When the gas is largely in excess and the supply of air limited the acetylene is smoky and deposits soot, but when a fine stream of the gas is spurted into the air, as in the carbide lamp, a fiame of exceeding brilliancy is the result. , Owing to its low temperature of ignition, the gas can be ignited by a lighted cigar.
Mixed with air the gas becomes highly explosive its explosive range being wider than that of any other gas. While the inflammable range of hydrogen extends from 5 to 72 per cent., that of acetylene ranges from 3 to 82 per cent., as determined by Clowes. This high value for the upper explosive limit has not been obtained by other investigators, whose results vary from 50 per cent. (Federal Bureau of Mines) to 65 per cent. (LeChatelier).
The Carbide Lamp in Blackdamp. — What is known as "blackdamp'' in mining is a variable mixture of carbon dioxide and air deficient in oxygen; in other words, an atmosphere of blackdamp consists of nitrogen, oxygen and carbon dioxide in varying proportions. When carbon dioxide is generated in a mine ventilated by an ample air current containing a normal percentage (20.9 %) of oxygen the addition of any considerable amount of carbon dioxide to this normal air reduces the oxygen content by the dilution of the air with the gas. The air is then said to be '' deficient in oxygen,'' which is due solely to its dilution with the carbon dioxide.
On the other hand a much greater reduction of the oxygen content often occurs when a portion of the oxygen has been consumed by the various forms of combustion that are con-
312 Mine Gases And Ventilation
stantly taking place in the mine. It is this reduction of the oxygen content, or the 'depletion of oxygen" in the mine air that is most harmful to life and affects the burning of the lamps.
It is a well known fact that the carbide lamp will continue to burn in air deficient in oxygen when oil-fed flames and the hydrogen flame are quickly extinguished. The acetylene gas burned in the carbide lamp is generated, in the lamp, by the action of water on the carbide of calcium, the calcium taking the oxygen and some of the hydrogen, while the carbon takes the remaining portion of the hydrogen.
We cannot say but that, in the dissociation of the hydrogen and oxygen of the water (H2O) , some oxygen may go to support the combustion of the acetylene gas (C2H2), instead of the flame being wholly dependent on the oxygen of the air for support. However, it is safe to say that an atmosphere in which a carbide continues to bum may be dangerous to life and therefore unsafe for work.
In an atmosphere containing no carbon dioxide, the oxygen content may fall as low as 14 per cent, before much difiiculty is experienced in breathing; but air containing but 10 per cent, is no longer breathable and will cause death quickly by suffocation."
The toxic effect of carbon dioxide is clearly shown by the fact that the depletion of the oxygen content of air, by the addition of carbon dioxide, produces a fatal atmosphere when the oxygen is reduced to but 17 per cent.; while, if no carbon dioxide is present, a fatal atmosphere is produced only when the depletion of the oxygen reaches 10 per cent.
In the former of these two cases, there is but 83 per cent, of noxious gases present — carbon dioxide, 18 per cent, and nitrogen, 65 per cent.; while, in the latter case, there is 90 per cent, of nitrogen present. In the former case a depletion of oxygen to 17 per cent, marks a fatal atmosphere; while in the latter case, a depletion of oxygen to 10 per cent, is necessary to produce the same result.
It is quite doubtful if a carbide lamp is extinguished when the oxygen of the atmosphere is reduced to 14 per cent., as is frequently assumed.
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Precautions to be Taken.; — In the use of carbide lamps in mines, suitable rules and regulations should be made and enforced limiting the supply of carbide that a miner may carry into the mine to what is ample for his purpose in a single shift and prohibiting its careless use. A supply of carbide should never be permitted to be stored in a miner's box or elsewhere in a mine. With proper care and precautions there need be little fear of trouble. The carbide light being an openflame lamp should not be used in a mine generating gas.
Electric Mine Lamps
The electric mine lamp is now almost universally used in all up-to-date mines in the states and Canada, there being at present 150,000 of these lamps installed by the Edison Storage Battery Co. alone. Of this number, 80,000 of the lamps are in daily use in the mines of Western Pennsylvania.
Selecting a Suitaible Battery .--In the endeavor to provide a portable electric mine lamp that would meet the requirements of mine service, the chief difficulty was to find a battery that would be sufficiently light and have the necessary watt-hour capacity to furnish a good light a full 8-hr. shift.
All forms of primary batteries that depend on the chemical reaction set up between certain elements immersed in a solution, as well as the lead-sulphuric acid storage battery, proved unsuited to service in the mine. The lead-lead battery was too heavy, besides failing in other ways to meet the requirements of mining use. Even the substitution of a gelatinous electrolyte proved ineffectual, owing to the hardened jelly not absorbing the water when once dried and the crack becoming filled with sediment short-circuiting the cells and weakening the battery.
The Edison Storage Battery. — The difficulties just mentioned have been practically overcome in the Edison storage battery designed for mine use. This battery employs as elements nickel hydroxide and iron oxide immersed in a potash solution. The battery cells are incased in a strong nickelplated steel container, which is tightly sealed except for one
314 Mine Gases And Ventilation
small vciit being left for the escape of the liarinlesti gaeea that result in the chaining of the battery.
The illustration, Fig. 67, shows th two cells of the Edison mine-lamp battery removed from the nickeled-steel case. The steel container of one cell is cut away to show the interior arrangement. The positive plates (steel tubes of nickel hydrate) and the negative plates {steel pockets of iron oxide) are assembled on steel poles and intermeshed, which gives an exceptionally stroi and compact construction entirely of steel, there being no acid to cause corrosion.
The construction of this battery is such that it is practically impossible for the solution to find its way out, even should the battery be turned upsidedown ; and no injury can result from a possible-over chaining, or from leaving the cell in a charged, semi-charged or discharged condition, for an indefinite period. While the cell must be charged in the right direction to be fit for service, no injury can result from accidentally reversing this direction. The steel container is proof against rough usage, and no insulation troubles can occm-. Specific gravity tests are not required as the potash solution is renewed after 9 or 10 months of use in continuous daily service.
Cap Lamp and Connecting Cable. — The illustration, Fig. G8, shows the electric cap lamp and the nickeled-steel carrying ca.se holding two cells. The cover of the case is removed to show the steel contact plates affixed to but insulated from the cover. These plates connect with the contact springs shown mounted on the two terminals of the battery. The cover is secured to the case by a strong hasp and padlock. To this
Mine Lamps And Lighting 315
cover is attached a twin-conductor, rubber-covered cable, armored at both ends to prevent injury where sharp bending is Uable to occur. If injured the cable is easily replaced.
The supporting base of the lamp is a nickel-plated reflector having a highly finished surface and provided with a hook to fit into the regulation miner's cap. The angle of distribution is considerably greater than the 130 deg. specified by the government, (see p. 322). A tungsten lamp is forced into a spring socket by means of a clip at its tip in such a way that if the lamp should be broken the base is immediately disconnected and the lamp extinguished. This safety feature has been thoroughly tested by the Bureau of Mines and unqualifiedly
approved under Schedule 6A. In place of a lens is a plain glass that iB easily replaced if broken. The entire design is. such as to afford the greatest possible headroom clearance.
Charging Miners' Lamp Batteries. — The rechargir of a large number of lamp batteries, between shifts, calls for a special design of equipment that will provide at once for the charging of the batteries and enumeratii them so that any individual battery can be found without delay.
A convenient form of charging rack that meets these requirements is one built up on the unit system, corresponding to the sectional bookcase idea. The illustration. Fig. 69, is a view of such a rack, designed and built by the Cutler-Hammer Mfg.
316 Mine Oases And Ventilation
Co., Milwaukee, Wis. The figure shows four units, but the systein can plainly be extended inclefinilely to accommodate an increasing nimiber of lamps as the development of the mine proceeds. The rechargii room must be well ventilated and open lights should not be permitted.
Fro. 70. On the right of the figure are shown two rheostat panels and a meter panel above. These panels are shown in greater detail in the Fig. 70, together with front and top views of a single unit capable of holding ten lamp batteries for chaining.
Mine Lamps And Lighting 317
The contact parts supported by the upper slab are pressed down in contact with the battery by the coil springs above the slab. The batteries are charged in series and provision is made for interpolating resistances to take the place of one or more absent batteries.
Pipe columns to which are clamped supporting brackets, as shown in this figure> form the framework of the rack on which are hung the several battery imits and panels by means of the strong hooks shown attached to each.
Each rheostat panel is designed to control the current in the corresponding line of units, and is equipped with a sliding arm for adjusting the charging rate to any desired value. The double-pole knife switch shown on this panel is so arranged that when partly closed the ammeter on the meter panel is thrown into circuit; but when closed completely the ammeter is cut out and the current passed through the charging racks.
The meter panel not only holds the ammeter for measuring the strength of the current and regulating it in accordance with the number of units to be charged; but is also provided with a magnetic switch and compound relay, which prevents a reversal of current from the partially charged batteries taking place should the charging current be interrupted for a time. This device automatically opens and closes the circuit as the current is broken and again restored. The breaking of the current is immediately announced by the signal bell on each rheostat panel.
Edison mine-lamp batteries require a pressure of 40 volts, which makes it possible to. charge six 10-battery units, on a 250-volt circuit. However, it is generally advisable to install but five such units on this circuit, which would allow the pressure to drop to 200 volts without interrupting the charging.
Use of the Electric Cap Lamp. — The need of a reliable source of iUumination in mining work has long been sought but with limited success. Open-flame lamps or torches are necessarily restricted to non-gaseous mines, or where the conditions are such as not to require the exclusive use of safety lamps. On the other hand, the relatively dim light of a safety lamp and its lack of adaptation to the requirements of mining work make
318 Mine Gases And Ventilation
it always desirable to find a suitable substitute that will be both convenient and safe for general work.
The electric cap lamp with storage battery equipment similar to that shown in the illustration, Fig, 71, has apparently solved the problem, and furnished the miner with a good light that is convenient and safe. The principal objections that have been med against the miners' electric lamp are the slightly increased cost of the equipment, and the fact that an
electric lamp affords no indication of the presence of gas, either methane or blackdamp, and gives the miner no warning of danger in that respect.
Notwithstanding these disadvantages, the electric lamp has steadily grown in favor among miners, as shown by its general adoption and successful use. In daily practice, the miner straps the battery case to his back, by his ordinary belt. The lamp is attached to the leather support in his cap, leaving his
Mine Lamps And Lighting 319
arms entirely free of lamp, cord and battery case. When the case is locked and the equipment handed to the miner charged and ready for use there can be no safer or surer means of illumination.
Permissible Portable Electric Mine Lamps
Schedule 6A, issued by the Federal Bureau of Mines, defines what is to be understood as included under the appellation "Permissible/' in reference to portable electric inine lamps, in the following words:
The Bureau of Mines considers a portable electric lamp to be permissible for use in mines if all the details of the lamp's construction are the same, in all respects, as those of the lamp that passed the inspection and the tests for safety, practicability, and efficiency made by the bureau and hereinafter described.
Conditions of Testinii;. — The conditions under which the Bureau of Mines will examine and test portable electric lamps to establish their perm issibility are as follows :
1. The tests will be made at the experiment station of the Bureau of Mines at Pittsburgh, Pa.
2. Applications for tests shall be addressed to the Director, Bureau of Mines, Washington, D. C, and shall be accompanied by a complete description of the lamp to be tested and a full set of the drawings mentioned below.
A drawing or drawings clearly showing the size and general appearance of the lamp mounting.
A drawing or drawings clearly showing the character, size and relative arrangement of the parts of the lamp mounting and the principle of operation of the safety devices.
Any other drawings that may be necessary to identify the safety devices or to explain how they accomplish their purpose.
A copy of the description, a duplicate of the drawings and one complete lamp shall be sent to the Electrical Engineer, Bureau of Mines, Fortieth and Butler Streets, Pittsburgh, Pa.
3. As soon as possible, after the receipt of his application for test, the lamp manufacturer will be notified of the date on which his lamps will be tested and the amount of material that it will be necessary for him to submit.
4. All material for test shall be delivered by the manufacturer to the Electrical Engineer, Bureau of Mines, Fortieth and Butler Streets, Pittsburgh, Pa., not less than one week prior to the date set for the test.
320 Mine Gases And Ventilation
5, No lamp equipment will be tested, unless it is in the completed form in which it is to be put on the market.
6. Lamps so constructed that they can be used both as cap lamps and as hand lamps must pass the tests for both cap lamps and hand lamps or they will not be approved for either class of service.
7. No one is to be present at these tests, except the necessary government officers, their assistants, and one representative of the manufacturer of the lamp to be tested, who shall be present in the capacity of an observer only.
The conduct of the tests shall be entirely in the hands of the bureau's engineer in charge of the investigation. While the tests are in progress the manufacturer's representative shall not make unsolicited suggestions or criticismsof the method of conducting the test.
8. The tests will be made in the order of the receipt of application for test, provided that the necessary lamp equipment is submitted at the proper time.
9. The details of the results of the tests shall be regarded as confidential by all present at the tests, and shall not be made public, in any way, prior to their official publication by the Bureau of Mines.
Requirements for Approval. — The requirements that a portable electriclamp equipment must have, to pass successfully the inspection and tests required by the bureau, are stated below :
I. he lamp equipment must comply with the following requirements for mechanical and electrical construction :
The construction of permissible portable electric-lamp equipment shall be especially durable. All parts shall be constructed of suitable material of the best quality and shall be assembled in a thorough. workmanlike manner. Current-carrying parts shall be well insulated from parts of opposite polarity and from parts not intended to carry current.
The battery shall be inclosed in a locked or sealed box so constructed as to preclude the possibility . of anyone meddling with the electrical contacts or making an electrical connection with them while the box cover is closed.
The leads connecting the battery with the headpiece shall be made up in a single cable efficiently insulated and provided, where it leaves the battery casing and enters the headpiece, with a reinforcement of flexible metallic tubing. The flexible metallic tubing will not be required if other equally durable means of reinforcement are provided.
It is recommended, but not required, that the headpiece be so designed that it can be sealed or locked. The battery terminals and leads connecting thereto, and the gas vent of the battery shall be so designed and constructed as to prevent corrosion of the battery terminals or of the essential metallic parts mounted in the cover of the battery casing.
The following qualities will be considered in determining the excel-
Mine Lamps And Lighting 321
lenoe of the mechanical and electrical construction of lamps covered by these specifications:
Simplicity of design; mechanical strength of parts and fastenings; suitability of material used; design of moving and removable parts; design and construction of terminals and contacts, for permanence and electrical efficiency ; and ease of repair.
2. The lamp equipment must be provided with a safety device or devices as follows:
Permissible portable electric lamps shall be so designed and constructed that whenever the bulb of a completely assembled lamp equipment is broken the lamp filament shall, at once and under all circumstances, cease to glow at a temperature that will ignite explosive mixtures of mine gas and air.
The mounting of the bulb may be designed so that a blow sufficient to break the bulb will short-circuit it, open the electric circuit of the lamp or otherwise insure that the filament will be wholly or practically extinguished. Ail safety devices with which the lamps are provided shall be so completely protected from injury or disturbance as to insure that the devices will always be in condition to perform their functions.
The design of the safety features shall be such that their action can not readily be hindered or prevented. The design of the safety devices shall be such that they will not act to extinguish the lamp unnecessarily.
3. The lamp equipment must be provided with a battery having a short-circuit current not in excess of the values here specified.
The bureau's engineers have made tests (reported in Technical Paper 47 of the bureau), which have satisfied them that mine gas can not be ignited by the sparks from portable electric-lamp equipments if the batteries used with such equipments are made so that their maximum short-circuit current can not exceed bhe following values: For batteries giving 2.5 volts or less, 125 amperes; for batteries giving more than 2.5 volts but not more than 4 bolts, 85 amperes; for batteries giving more than 4 volts but not more than 5 volts, 65 amperes; for batteries giving more than 5 volts but not more than 6 volts, 45 amperes. Therefore, lamps whose short-circuit current does not exceed these values will be considered satisfactory in that respect.
4. The lamp equipment must meet the following requirements for time of burning, flux of light, intensity of light and distribution of light:
All portable electric lamps offered for test under the provisions of this schedule shall produce, for 12 consecutive hours, on one charge of battery, a light stream having ah averge intensity of light not less than four-tenths of a candlepower. The to'al flux of light produced by cap lamps shall not fall below IK lumens during the 12 hours, and the total flux of light produced by hand lamps shall not fall below 3 lumens diuring the 12
The distribution of light, by lamps that use reflectors, shall be determined both by observation and by photometric measurement. The
322 Mine Oases And Ventilation
lamp& shall be placed so that the filaments are 20 in. away from a plane surface thai is perpendicular to the axis of the light stream of the lamp. When so placed the lamp shall illuminate a circular area not less than 7 ft. in diameter.* All observations and measurements of distribution shall be referred to this 7-ft. circle regardless of how large an area the lamp may illuminate. As observed with the eye, there shall be no black spots" within the 7-ft. circle, nor any sharply contrasting areas of bright and faint illumination anywhere. As measured with a photometer, the distribution of light diametrically across the circle shall fulfill the following requirements:
The curve of light distribution along the diameter of the circle shall be obtained by rotating the lamp and thus obtaining the average distribution curve.
The average illumination in foot-candles, on the best illuminated one-tenth of the diameter, shall be not more than three times the average illumination throughout the diameter; and, for at least 40 per cent, of the diameter, the illumination shall be not less than the average.
5. The lamp equipment must be provided with lamp bulbs that meet the following requirements, for variation in current consumption, variation in candlepower and length of life:
The bulbs submitted for test shall be identified by the name of the manufacturer and by a number or symbol with reference to which approval will be granted.
The current consumption of at least 95 per cent, of the bulbs tested shall not exceed, by more than 6 per cent., the average current consumption of all the bulbs examined.
The candlepower of at least 90 per cent, of the bulbs tested shall not fall short of the average candlepower, by more than 30 per cent.
The life of a lamp bulb will be considered as the number of hours that the bulb can be burned, under normal conditions of voltage, before it becomes so depreciated that when used with an average, standard, freshly charged equipment it fails to produce, for 12 consecutive hours, the flux and intensity of light specified in paragraph 4.
The average life of lamp bulbs shall be not less than 300 hours, for acid storage batteries, and not less than 200 hours, for primary batteries and for alkaline storage batteries. Not more than 5 per cent, of the bulbs examined shall give less than 250 hours' life, with acid batteries, nor less than 150 hours' life, with primary batteries and alkaline batteries.
6. The lamp equipment must comply with the following requirements as to leakage of electrolyte :
Lamps shall be so designed and constructed that they will not spill nor leak electrolyte throughout an 8-hour test, during which they will be placed In any position or sequence of positions that, in the opinion of the bureau's engineers, will be most likely to prove whether or not the electrolyte can be spilled.
This requirement will be met by lamps that have an angle of light stream of 130° or more. ,
Mine Lamps And Lighting . 323
Tests of Design and Construction. — The excellence of the mechanical and electrical features of the design and construction of the lamps will be carefully determined.
The following tests will also be made: Hand lamps and the headpieces of cap lamps will be dropped 10 times, upon a concrete floor from a point 6 ft. above it. As the result of these dropping tests, there must be no breakage of the battery jar or material distortion of the casing of the battery or of the shell of the headpiece. The engineers in charge of the investigation shall be the sole judges of whether or not material distortion occurs. The dropping tests of the headpiece must demonstrate that the safety devices will not operate unnecessarily.
Cap lamps will be dropped 10 times, upon a wooden floor, from a point 3 ft. above it. There must be no breakage of the battery jar or material distortion of the casing.
Tests of Safety Devices. — In making tests of the safety devices, it will be assumed that if the short-circuit current of the battery does not exceed a certain value, stated previously, the glowing filament of the lamp is the only source of danger.
It will also be assumed (based on tests reported in Technical Paper 23) that the glowing filament presents an element of danger, in the presence of mine gas, if the bulb of the lamp can be broken without causing the filament to become wholly or practically extinguished as the result of the action of the safety devices with which the lamp is provided.
The tests wUl therefore be made with a view to determining whether or not the lamp bulb may be broken without causing the safety device of the lamp to extinguish the lamp or cause the filament to glow at a temperature that is not high enough to ignite explosive mixtures of mine £as and air.
If the safety devices are designed to extinguish the lamp before the bulb is broken it will not be necessary to make the tests in gas, unless the safety devices do not completely extinguish the lamp. It will then be necessary to determine whether or not the filament is glowing at a temperature sufficient to ignite gas.
If the safety devices are designed to extinguish the lamp at the same time that the bulb is broken it will be desirable to make the tests in explosive mixtures of gas and air.
Gas, if used, will be the natural gas supplied to the city of Pittsburgh. The composition of this gas, as determined from recent analyses, is approximately 83.1 per cent, methane, 16 per cent, ethane, 0.9 per cent, nitrogen and a trace of carbon dioxide.
The details of conducting the tests will, manifestly, not be the same for all lamps submitted, because different lamps will no doubt have safety devices differing in design, construction and basic principles. The bureau proposes to determine, for each lamp separately, a schedule of tests that, after due examination of the lamp and its safety devices.
324 Mine Gases And Ventilation
seem best adapted to ascertaining the merits of the equipment submitted. This schedule may be examined and discussed by the manufacturer's representative before the tests are begun.
In general, the tests will consist of, striking the mounting or holder of the lamp bulb, in an attempt to break the bulb without extinguishing the lamp.
If the safety devices are designed to extinguish the lamp (as, by disconnecting the bulb from circuit, or by opening the circuit at some other point) the devices will be considered to have acted:
1. If, after the blow has been delivered, the lamp bulb, whether broken or not, is clearly disconnected from circuit.
2. If, after the blow has been delivered :
(a) When the lamp filament is not broken by the blow and does not glow;
(6) When the lamp filament is broken by the blow a sound filament, replacing the broken filament, does not glow.
If the safety devices are designed to decrease the temperature of the filament (by short-circuiting the filament or by other means), the devices will be considered to have acted if, after the blow has been delivered:
(a) When the lamp filament is not broken by the blow it does not glow at a temperature sufficient to ignite gas;
(b) When the lamp filament is broken by the blow a sound filament, replacing the broken filament, does not glow at a teniperature sufficient to ignite gas.
If there is any question as to whether or not a filament is glowing at a dangerous temperature the point will be settled by surrounding the filament with an explosive mixture of gas and air.
If, after the blow has been delivered, the bulb has not been broken and the safety devices have not acted the test will be repeated with the same equipment, or with a different equipment, at the discretion of the bureau's engineers.
. The bureau believes that approximately 60 tests will be necessary to determine whether or not the safety devices of a lamp are permissible for use in gaseous mines; but more or fewer tests may be made at the discretion of the engineer in charge of the tests.
To Determine Maximum Short-circuit Current.— The short-circuit current of the battery will be measured under conditions that will give the same current that would flow through a short-circuit between the conductors of the flexible cord, at the point in the cord nearest to the battery casing.
Tests of Lighting. — The tests to determine the time of burning, flux, intensity and distribution of light will be made, for not less than 20 batteries, 6 reflectors or lamp mountings, and 100 lamp bulbs.
The average performance of the various equipments will be taken as the average performance of the lamp. The measurements of flux
Mine Lamps And Lighting 325
and intensity of light will be made after the bulbs have been burned for about 10 hours in order to season them somewhat.
Tests of CiuTent Consumption, Candlepower, Life of Bulb. — Mea> surements of current consumption and candlepower will be made with bulbs that have been burned about 10 hours.
Measurements of current consumption will be made at approximately 'the average potential given by the lamp battery, after having been used for one. hour.
Measurements of bulb candlepower will be made in one direction only. Usually the direction that gives the largest exposure of filament will be selected.
Determination of bulb-life will be made with batteries that have the same voltage characteristics as those used with the lamp. Tests will be made with the bulbs in a fixed position.
Although, as stated in Technical Paper 75, Bureau of Mines, the bureau considers that the batteries of portable electric mine lamps should give 3600 hours of service (300 12-hour shifts) without requiring repairs or replacements of any part, it is manifestly impracticable for the bureau to carry out the 3600-hour test upon each battery submitted for approval. Therefore, the requirements of the bureau, with respect to the durability of batteries, will be considered as satisfied if the batteries shall perform their functions without repair while being used by the bureau, in accordance with the written instructions of the lamp manufacturer, to conduct the bulb-life tests; and, at the completion of these tests, the condition of the batteries shall give no evidence of weakness that indicates the early failure of any part of the battery.
Test of Leakage of Electrolyte. — The lamps will be tested for leakage and spilling of electroljrte, by placing the batteries for various lengths of time, totaling eight hours, in various positions that seem most likely to cause the cells to leak or spill. If a battery does not leak or spill more than one full drop of electrolyte during the eight-hour test the battery casing will be regarded as non-spiUing.
Approval of Blectric Mine Lamps. — The manufacturers will bo required to attach to the battery casing of each permissible lamp equipment a plate bearing the seal of the Bureau of Mines and inscribed as follows:
Pbrmissiblb Portable Electric Mine Lamp. Approval No. — .
Issued for safety and for practicability and efficiency in general
service to the Co.
The use of the plate will not be required if the same inscription is stamped or cast into the casing of the battery.
Manufacturers shall, before claiming the bureau's approval for any modification of any approved lamp, submit to the drawings
326 Mine Gases And Ventilation
that shall show the extent and nature of such modifications, in order that the bureau may decide whether or not it should test the remodeled lamp before approving it. Each approval of a permissible lamp will be given a serial number. Approvals of modified forms of a previously approved lamp will bear the same number as the original approval with the addition of the letters a, &, c, etc.
The bureau will, upon request, make tests of lamp bulbs to determine whether or not they will comply with the bureau's requirements when used in connection with any lamp that has been approved by the bureau under the provisions of this schedule. Lamp bulbs that fulfill the requirements will be specifically approved for use with stated lamps. Applications for tests of bulbs should be made in a manner similar to application for tests of lamps.
The bureau's approval of any lamp shall be construed as applying to all lamps made by the same manufacturer that have the same construction in the details considered by the bureau, but to no other lamps. The bureau reserves the right to rescind, for cause, at any time, any approval granted under the conditions herein set forth.
Notification of Manufacturer. — As soon as the bureau's engineers are satisfied that a lamp is permissible, the manufacturer of the lamp and the mine-inspection departments of the several states shall be notified to that effect. As soon as a manufacturer receives formal notification that his lamp has passed the tests prescribed by the bureau, he shall be free to advertise such lamp as permissible. t
Fees for Testing. — The necessary expenses involved in testing portable electric mine lamps have been determined, and the following schedule of fees to be charged, on and after the date of issue of this schedule, has been established and approved by the Secretary of the Interior:
1. For a complete official investigation leading to the formal approval
of a portable electric mine lamp, the investigation to include tests of the' safety devices and the determination of the time of burning, flux of light, intensity of light, distribution of light, bulb characteristics, leakage of electrolyte, and durability S150.00
2. For tests of the safety devices only $30 . 00
For additional necessary tests, under the same investigation
(for each five tests or fraction thereof) $2 . 50
3. For tests to determine only the time of burning, flux of light,
intensity of light, distribution of light, bulb characteristics,
and leakage of electrolyte $120. 00
4. For tests to determine only bulb life, variation in bulb candle-power
and variation in bulb current consumption : If such tests involve making discharge-voltage determinations $75.00
If such tests do not involve making discharge-voltage determinations $50.00
Mine Lamps And Lighting 327
5. The following charges will be made for individual tests
included under item 3:
Discharge-voltage tests $25 . 00
Reflector tests $20.00
Time-of-buming tests $10 . 00
Light-distribution tests $5 . 00
Electrolyte-spilling tests $3 . 00
Short-circuit tests of battery $1 . 00
Mechanical tests of cord $6. 00
Bulb-life tests $35.00
Bulb-uniformity tests $15 . 00
6. Special tests that circumstances shall render necessary, during the
course of the investigation, will be made at the request of the lamp manufacturer and will be charged for in accordance with the amount of work involved.
Addenda
Logarithms — Circular Functions, Sines and Cosines, Tangents and Cotangents— Squares, Cubes, Roots and Reciprocals op Numbers — Circumferences and Areas — Denominate Numbers — Weights and Measures — United States and British Systems — Metric Systems OP Weights and Measures — Conversion Tables — Conversion OP Compound Units.
Logarithms
The treatment of logarithms here will be simple and practical and such as to enable their use to be clearly understood. Much time and labor are saved when multiplying and dividing, or when extracting the roots of numbers, or raising a number to a given power by the use of logarithms.
Definition. — The logarithm of a number is the exponent of the power to which it is necessary to raise a fixed number called the "base" to produce the given number.
Systems of Logarithms. — There are two systems of logarithms in use: 1. The Briggs or common system employs 10 as a base. 2. The Naperian or hyperbolic or natural system is derived from 2.71828+ as a base. The common logarithms (log) are those generally used, while the natural logarithms (nat. log) are often employed in theoretical analyses.
The Naperian or natural logarithm of a number can always be found by multiplying the common logarithm of the number by 2.302585, which is expressed thus:
Nat. log. 2.302585 com. log.
In any system of logarithms, the logarithm of 1 is zero, and the logarithm of the base of the system is always 1.
The Logarithm. — Every logarithm is composed of two distinct parts separated by a decimal point The number preceding the decimal point, or the integer of the logarithm is called the characteristic ," while the decimal portion of the logarithm is the "mantissa." These two parts of a logarithm must be regarded separately. The mantissa is always positive, but the characteristic may be either positive or negative, according as the given number is greater or less than 1, in a system whose base is greater than 1.
The characteristic is always 1 less than the number of figures in the integral portion of the given number; or 1 greater than the number of ciphers following the decimal point when the given number is wholly
Addenda 329
decimal. In the former case the characteristic is positive; in the latter case it is negative. The following examples will make this clear:
log 326.00 2.61188 log 0.326 1.51188
log 32.60 1.51188 log 0.0326 =2.51188
log 3.25 0.51188 log 0.00326 3.61188
The mantissa, as is readily observed from the above examples, is determined by the sensible figures of a number, without regard to the decimal point. Also, the mantissa of the logarithm of a number is unchanged when the number is multiplied or divided by ,10, 100, 1,000, etc. For example, the mantissa of the logarithm of 3, which is 0.47712, is the same for 30, 300, 3,000 or for 0.3, 0.03, 0,003, etc.
A table of the common logarithms of numbers from to 10,000 follows and will be found useful. In this table the mantissas only are given and, to avoid unnecessary repetition, the first two figures are not repeated. An asterisk appearing before the remaining three figures of the mantissa indicates that the first two figures must be taken from the line below. Bars are employed to mark the division by tens, which facilitates the finding of the mantissa of any desired number given in the left-hand column. In this table, the differences are given as proportion parts and placed in the right-hand column marked "P. P.,'* which avoids the necessity of multiplying by the decimal as will be explained.
To Find the Logarithm of a Number. — From the table of logarithms, find the mantissa corresponding to the give'h number, ignoring the decimal point. To do this, the first three figures on the left of the given number are found in the left-hand column of the table, and the fourth figure in the line at the top. The required mantissa is then taken from the line and column thus indicated.
' But if the given number contains five or more figures, write the excess figures as a decimal and multiply the difference between the mantissa found and the one next following by this decimal; point off and add the integral portion of the result to the mantissa already found. If desired this logarithm can be extended by annexing the decimal portion of the same result, but this is not commonly necessary. When there is but one excess figure, as when finding the mantissa of a number halving five figures, the difference to be added to complete the mantissa is taken from the corresponding proportional part, in the right-hand column without multiplying.
Having found the mantissa, prefix a decimal point preceded by a characteristic one less than the number of integral figures in the given number. If there is but one integral figure the characteristic of the logarithm will be zero.
If the given number is a decimal, having no integral figures, the characteristic will be negative and numerically one greater than the number of ciphers that follow the decimal point.
330 Mine Gases And Ventilation
Illustratioiis. — The following examples will illustrate the method of finding the logarithms of numbers under different conditions and make clear the use of the table.
1. Suppose it is required to find the logarithm of the number 4,657. Opposite 465, in the column under 7, is found 811, and this annexed to 66 found at the left gives for the mantissa of this number the decimal 0.66811. The characteristic, in this case, is 3, since there are four integral figures in the given number. Hence, log 4,657 3.66811.
2. To find the logarithm of 32.567, ignoring the decimal point, opposite 325 in the column under 6, is found the mantissa, 0.51268; but there is still another figure 7 in the given number. Therefore, to complete this mantissa subtract it from the one following, giving the difference 14 found in the right-hand column. The proportional part of this difference corresponding to the fifth figure 7 is 9.8 or, say 10. Then 51,268 -f 10 61,278 and the complete mantissa is therefore 0.51278. In this case, the given number contains but two integral figures, which makes the characteristic 1; hence, log 32.567 1.51278.
3. To find the logarithm of 0.509065, ignoring the decimal point, opposite 509, in the column under 0, is found the mantissa 0.70672. To complete this mantissa subtract it from the one next following, thus, 680 — 672 8, and multiply the remaining figures of the given number written as a decimal, by the difference 8 and add the integral of the result to the mantissa already found.
Thus, 70,672 + 0.65 X 8 70,672 + 5 70,677.
Now, since the given number is a decimal, the characteristic of its logarithm is negative; and its numerical value is 1, as there are no ciphers immediately following the decimal point. The complete logarithm is, therefore, log 0.509065 1.70677, the minus sign being written over the characteristic, since the characteristic only is negative.
Use of Logarithms. — By the use of logarithms the processes of multiplication, division, involution and evolution are greatly shortened and simplified. The two latter processes are in fact a repetition of the two former; while division and evolution are the reverse operations of multiplication and involution, respectively.
It is important to observe that the use of logarithms enables the finding of decimal powers and decimal roots of numbers, which is impossible by other means. When the index of a power or root of a number can be expressed as a fraction the numerator and denominator of such fraction express, respectively, the indices of the power and root or the root and power, as the case may be. A decimal index, therefore, expresses in one operation the extraction of any given root of any given power of a number, which will be better understood later.
The application of this principle is shown in numerous instances where quantities vary in their relation to each other according to different powers. For example, in fan ventilation, the fourth power of the speed
Addenda 331
(n*) of the fan varies as the fifth power of the quantity (q) of air in circulation ; which is expressed as follows :
varies as
and q varies as n; or w"-®
The expression or the fourth-fifths power of n is identical with or the fifth root of the fourth power of n. Hence, to extract the root of a power, divide the exponent of the power by the index of the desired root and the quotient will be the new exponent, which combines the two operations in a single transaction.
Rules for the Use of Logarithms. — The following four simple rules cover all the operations of logarithms:
1. Multiplication: To find the product of two or more numbers, add their logarithms; the number corresponding to this logarithmic sum is the desired product.
In other words, the logarithm of the product of two or more numbers is equal to the sum of the logarithms of the numbers.
2. Division : To divide one number by another, subtract the logarithm of the divisor from that of the dividend; the number corresponding to this logarithmic remainder is the required quotient.
In other words, the logarithm of the quotient is equal to the logarithm of the dividend minus that of the divisor.
3. Involution: To find any given power of a number, multiply the logarithm of the number by the exponent of the power; the number corresponding to the resulting logarithm is the required power of the given number.
4. Evolution : To find any given root of a number, divide the logarithm of the number by the index of the root; the number corresponding to the resulting logarithm is the required root of the given number.
Arithmetical Complement. — The arithmetical complement of a logarithm is the remainder found by subtracting the log from 10; the logarithm of 3 is 0.47712, and its arithmetical complement is, therefore, 10 — 0.47712 9.52288. Its use involves subtracting from the final result as many tens as have thus entered the solution. The antilog is more convenient for use.
The Antilog. — The solution of problems frequently involves the multiplication and division of many quantities. In the use of logarithms, the sum of the logs of the divisors would be subtracted from the sum of the logs of the multipliers, to obtain the log of the final result. By the use of what is called the antilog" of each divisor, it is possible to complete such a solution in a single operation, by adding together the logs of the multipliers and the antilogs of the divisors.
The antilog of a number is obtained as follows: Subtract the mantissa of its log from 1, for the mantissa of the antilog. Then, add 1 to the characteristic of the log and change its sign, the addition being always algebraic. The following examples will make the process understood:
332 Mine Gases And Ventilation
1. To find the antilog of 800: Log 800 2.90309 Mantissa of antilog, 1 - 0.90309 0.09691 Characteristic of antilog, 2 1 =3; and changing sign — 3 Hence Antilog 800 3.09691
2. To find the antilog of 2: log 2 0.30103 Mantissa of antilog, 1 - 0.30103 0.69897 Characteristic of antilog, -f 1 1 ; giving — 1
Hence Antilog 2 T. 69897
3. To find the antilog of 0.4 : Log 0.4 . T . 60206 Mantissa of antilog, 1 — . 60206 . 39794 Characteristic of antilog, — 1 -f- 1 — (zero has no sign)
Hence Antilog 0.4 0.39794
4. To find the antilog of 0.00125: Log 0.00126 3.09691 Mantissa of antilog, 1 - 0.09691 0.90309 Characteristic of antilog, — 3 -f- 1 — 2; giving + 2
Hence Antilog 0.00125 -2.90309
Note. — The use of the antilog accomplishes the same purpose as the arithmetical complement and requires no correction of the final result as explained in reference to the latter. It should be observed that the antilog of a number is always the log of the reciprocal of that number.
Thus, Log 800 antilog 1/800 or 0.00125
As shown above, log 800 2.90309; antilog 0.00125 2.90309. Example, — Solve the following by the use of logarithms:
Solution.— log-0.00000002 , 8 .30103
log 40,000 4.60206
antilog 50S (log 50 1.69897 X 3 5.09691) 6.90309
Log p. 1.20412
Hence p 16 lb. per sq. ft.
Logarithmic Tables
Common Logarithms Of Numbers
Ko.
Log.
No.
Log.
No.
Log.
No.
Log.
No.
Log.
eo
Mine Oases And Ventilation
N.
P.P.
4S
R.8
4 B
A 9
18J
16Jb
2SJ SO.l
S9
A t
Bfi
2U.0
i:
8 T
T.G
t.4
S
&
Itf.U
25J
zi.B
ss
S4
Ss
8B
t.O
1S.6
S2
Si
'So
S 9
Ua
28J
N.
P.P.
Logarithmic Tables
N.
p.p.
S.9
S.8
8.T
as8
ac.i
Is
1S.0
1R B
ifi 1°
2S.4
1T7
S I
8
O
6
6.S
A
1A A
Is.2
16J
"
N.
G
P.P.
Mine Gases And Ventilation
N.
p.p.
.6
8G9
i.O
1 B
Iss
4W
1 A
a
Hi
G
N.
Logarithmic Tables
N.
P.P.
It
T.2
lA Q
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Denominate Numbers
A denominate number is one expressed in units of a certain kind; as, for example, 5 days, 8 men, etc.
A compound denominate number is one expressed in two or more units; as 3 hr. 20 min., 8-ton mi., 4-acre-ft., etc. The terms ft. per sec, mi. per hr., rev. per min., etc., are all compound units.
An abstract number is any number not expressed in units of a kind; as 3, 5, 8, etc.
Kinds of Units. — The principal kinds of units may be classed as follows:
1. Units of weight; as tons, pounds, oimces, grains, etc.
2. Units of length or distance; as miles, feet, inches, etc.
3. Units of volume ; as cubic yards, cubic feet, etc.
4. Units of capacity ; as gallons, quarts, pints, etc.
5. Units of surface or area; as square miles, square feet, etc.
6. Units of time ; as years, months, days, hours, etc.
7. Units of circular measure ; as degrees, minutes, etc.
8. Units of currency ; as dollars, dimes, cents, etc.
Weights And Measures
Systems in Use. — There are two systems of weights and measures in general use, known as the English, United States or British,'' and the " French or metric" systems.
The basis of comparison of the English and French systems is expressed by the following established values:
Weight. — The pound (7,000 grs.) is the same in the United States and Great Britain. The pound avoirdupois is equal to 453.5924277 grams in the French system.
Length. — (United States) The length of the meter, by act of Congress, is 39.37 in. (Great Britain) The length of the meter, by act of Parliament, is 39.37079 in.
The difference in the length of the meter, as established by law in the United States and in Great Britain, makes the English inch and yard proportionally shorter than the same units in the United States.
Capacity. — The gallon and liter are the accepted units of comparison in the English and French systems, respectively. The United States or "Winchester gallon," however, is quite different from the "Imperial gallon" of Great Britain, which was made the volume of 10 lb. of distilled water, at maximum density (4 deg. C), weighed with brass weights in air at 62 deg. F., barometer 30 in.
Since 1 cu. in. pure water, under the same conditions, weighs 252.458
398 Mine Gases And Ventilation
grs. and 1 lb. 7,000 grs., the volume of the imperial gallon of Great
Britain is
The volume of the Winchester gaDon of the United States is 231 cu. in. The French liter is the volume of 1 kg. of distilled water, at 4 deg. C, weighed in a vacuum, or 1,000 c.c, which gives
Winchester gallon (United States), 231 cu. in. 3.78543 liters.
Imperial gallon (Great Britain), 277.274 cu. in. 4.54346 liters.
United States And British Systems
Following are the more useful of the tables of weights and measures in the English system :
Avoirdupois Weight
16 drams 1 ounce 437 . 5 pounds
16 ounces 1 pound 7,000 grains
25 pounds 1 quarter 400 ounces
4 quarters 1 hundredweight 100 pounds
20 hundredweight 1 short ton . 2,000 pounds
28 pounds 1 quarter 448 ounces
4 quarters 1 hundredweight 112 pounds
20 hundredweight 1 long ton 2,240 pounds
The short ton (2,000 lb.) is more generally used in the United States, although the long ton (2240 lb.) is used at times. ,
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Troy Weight
20 pennyweights 1 ounce. 480 grains
12 ounces 1 pound 5,760 grains
Apothecaries Weight
3 scruples 1 dram 60 grains
8 drams 1 ounce 480 grains
12 ounces 1 pound 5,760 grains
The grain (troy) is the same as the grain (apothecaries) and is the basis of comparison of these and avoirdupois weights. Thus,
1 lb. avoirdupois 7,000/5,760 1.21528 lb. troy. 1 lb. troy 6,760/7,000 0.822857 lb. avoirdupois. 1 oz. avoirdupois 437.5/480 0.911458 oz. troy. 1 oz. troy 480/437.5 1.097143 oz. avoirdupois.
Denominate Numbers 399
Long Measure
3 feet 1 yard 36 inches
6M yards 1 rod, perch, or pole 16? feet
8 furlongs 1 mile 5,280 feet
3 miles 1 league
The old surveyor's chain of 100 links (1 link 7.92 in.) was 66 ft. long, making 80 chains — 1 mi. Chains now in common use are 50, 100 and 300 ft. long, made up of 1-ft. links.
A fathom is 6 ft. or 2 yd., used in estimating depth.
Square Measure
9 .square feet 1 square yard 1296 square inches
30K square yards 1 square rod 272K square feet
40 square rods 1 rood 10,890 square feet
4 roods 1 acre 43,560 square feet
640 acres 1 square mile 102,400 square rods
An acre contains 43,560 sq. ft. and measures 208.7 ft. on each side; \/43560 208.7 ft.
Cubic Measure
27 cubic feet 1 cubic yard 46,656 cubic inches
16 cubic feet 1 cord foot 27,648 cubic inches
8 cord feet — 1 cord 128 cubic feet
A cord of wood is a pile 8 ft. long, 4 ft. wide and 4 ft. high, and contains 8 X 4 X 4 128 cu. ft.
, A cord foot is one foot of the length of the pile that makes a cord, and contains 1 X 4 X 4 16 cu. ft.
A ton of squared timber (green) is 40 cu. ft., it being assumed that hewed or squared timber has lost one-fifth of its original volume in squaring.
A long ton (2,240 lb.) of anthracite or a short ton (2,000 lb.) of bituminous coal broken (mine-run) occupies about 40 cu. ft.
There are two measures of capacity, known as "Liquid" and "Dry" measures, having like denominations but of different values. The old English wine gallon (231 cu. in.) was replaced in England, in 1824, by the imperial gallon (277.274 cu. in.), but is still the standard "Winchester" gallon in the United States. The "Dry " gallon, now practically obsolete, contained 268.8 cu. in.
400 Mine Gases And Ventilation
4 gills 1 pint 28 . 876 cubic inches
2 pints 1 quart 57.76 cubic inches
4 quarts 1 gallon 231 cubic inches
Slji gallons 1 barrel 4. 21 cubic feet
2 barrels 1 hogshead 63 gallons
2 hogsheads — 1 pipe 126 gallons
2 pipes 1 tun 8 barrels
2 pints 1 quart 67. 2 cubic inches
8 quarts 1 peck 537. 6 cubic inches
4 pecks 1 bushel 2150. 4 cubic inches
36 bushels 1 chaldron 44 . 8 cubic feet
Or, 4 quarts 1 gallon 268.8 cubic inches
8 gallons 1 bushel 2150. 4 cubic inches
The standard bushel, in the United States, is the old Winchester bushel, which is a circular measure diameter and 8 in. deep, containing 8 (0.7854 X 18.5*) =2150.4 cu. in. This was replaced in England, in 1826, by the imperial bushel (2218.192 cu. in.), which was then made the legal bushel.
4 gills 1 pint 34. 659 cubic inches
2 pints 1 quart 69 . 318 cubic inches
4 quarts 1 gallon 277.274 cubic inches
2 gallons 1 peck 554 . 548 cubic inches
4 pecks 1 bushel 2218. 192 cubic inches
There is no separate standard for liquid and dry measures in Great Britain, both being referred to the same unit or standard, which is the imperial gallon (277.274 cu. in.).
Measure of Time
7 days 1 week
12 calendar months 1 calendar year 100 years 1 century
Commonly speaking, a day is marked by one complete revolution of the earth on its axis, and a year by one revolution of the earth in its orbit about the sun. Unfortunately, however, the earth does not make an even number of turns on its axis, while making one complete revo-
Denominate Numbers 401
lution in its orbit. There are approximately. 3G5K revolutions on the axis to a single revolution in the orbit.
In order to compensate for this eccentricity and make the calendar year conform as closely as possible to the solar year, so as to preserve uniformity in the return of the seasons, it was necessary to add one day to the calendar every fourth year, except the closing year of the century. Thus, the common year of 365 days was supplemented by a leap year containing 366 days.
The "Gregorian" calendar, established by Pope Gregory XIII (1682) and generally adopted in Great Britain and elsewhere (1752), replaced the ''Julian" calendar and, in dropping 10 days by making Get. 5, Oct. 15, 1582, restored the equinoxes to their proper date. To obtain closer* correspondence of the calendar and solar years, the closing year of each century, 1600, 1700, etc., was made a common year, although these would be leap years in the regular course.
The Day. — A day is the interval of time marked by two successive transits of a heavenly body across a given meridian, caused by the revolution of the earth on its axis.
The solar day (24 hr., min.) is the time interval marked by two successive transits of the sun across the meridian.
The sidereal day (23 hr., 56 min.) is the time interval marked by two successive transits of a fixed star across a given meridian.
The Month. — The calendar year has been arbitrarily divided into 12 months, in correspondence to the "number of moons" or the revolutions of the moon about the earth in a solar year. But, since 365 days are not equally divisible by 12, it was necessary to make an unequal division, as follows:
January 31 days May 31 days September 30 days
February 28 days June 30 days October 31 days
March 31 days July 31 days . November 30 days
April 30 days August 31 days December 31 days
The extra day required in a leap year is added to the month of February, making 29 days in that month every leap year, instead of 28 as in the common year.
The Year. — A year is the period of time in which the earth completes one revolution in its orbit.
The solar year (365 d., 5 hr., 48 min., 45.51 sec.) marks a complete revolution about the sun.
The sidereal year (365 d., 6 hr., 9 min., 8.97 sec.) marks a complete revolution with respect to a fixed star.
60 minutes — 1 degree 3,600 seconds
15 degrees 1 hour angle 900 minutes
30 degrees 1 sign 1,800 minutes
12 signs 1 great circle or circumference 360 degrees
402 Mine Gases And Ventilation
The "sign** is one of the twelve divisions of the zodiac, which correspond to the twelve calendar months of the year. The sign has no practical value technically.
It is often convenient to express the length of an arc, or the angle it subtends, in terms of the radius of the circle. In that case, the unit of length is called a "radian.'' A radian is a length of arc equal to the describing radius. Its value expressed in degrees is -h t 180/3.14159 67.2958 deg., or 57 17' 44.88". Since the length of the circumference of a circle is 2irr, there arc 2ir radians in a circumference or 360 deg.
Circular measure is used in the measurement of angles and in the estimation of latitude, longitude and solar or sun time, which varies from standard time according to the location of the observer.
Measurement of Time. — The passing of time is measured I y the revolution of the earth on its axis, as determined by the observation of the sun or one of the fixed stars when crossing the meridian of a place. A single revolution of the earth marks a period of 24 hr. or one day.
Sun Time. — Owing to the inclination of the earth's axis to the plane of its orbit and the eccentricity of the orbit, the sun's apparent motion in the celestial sphere is not wholly uniform, on which account solar time is referred to a '' mean sun" having an assumed uniform motion.
Equation of Time. — The difference between the mean sun and the true or observed sun, expressed in hours, minutes and seconds, is called the " equation of time." This is found for any date in the " Ephemeris " or Nautical Almanac.
Sidereal Time. — The apparent movement of the fixed stars, unlike that of the sun, is uniform, which makes the sidereal day correspond precisely with one complete revolution of the earth on its axis. About Mar. 21, or at the vernal equinox, sidereal time agrees with mean sun or solar time.
Local Time. — When the 24-hr. cycle is referred to the local meridian as zero (noon or midnight) the indicated hour is the local time, or the time for that place only. Since there are 360 deg. in a circle, which marks 1 day or 24 hr. of the celestial equator, 1 hr. corresponds to 360 t- 24 15 deg. Hence, a difference of 15 deg. marks a difference of 1 hr. in local time.
Longitude, Latitude. — Longitude is the distance either east or west of the meridian of Greenwich, which is marked by the Royal Observatory, and measured in degrees, minutes and seconds, on the equator. There are thus 180 deg. of east longitude and 180 deg. of west longitude.
Latitude is likewise distance north or south of the equator, measured in degrees, minutes and seconds, on any meridian or great circle passing through the poles. There are thus 90 deg. of north latitude and 90 deg. of south latitude.
Standard Time. — To obviate the confusion caused by the difference in local time, a system of "standard time" has been adopted. Starting
Denominate Numbers 403
from the meridian of Greenwich, standard time is 1 hr. later for each 15 deg. of east longitude, and 1 hr. earlier for each 15 deg. of west longitude. Calling the equatorial circumference of the earth 25,000 mi., a degree of longitude represents a distance on the equator of 25,000 360 60.4 mi. One hour (15 deg.) corresponds to a distance of practically lyOOO mi. at the equator.
In the United States and Canada, there are four divisions of standard time, known as Eastern, Central, Mountain and Pacific time, which are exactly 1 hr. apart. These are all referred to the observatory at Greenwich, which marks the zero of longitude.
Eastern time is the solar time of the meridian 75 deg. west longitude, and is the standard time for all places within 7H deg. on either side of that meridian. Eastern time is therefore 75 -5- 15 5 hr. earlier, than Greenwich.time.
Central time is solar time for the meridian 90 deg. west longitude, and is likewise standard for all places within 7M deg. east or west of that meridian. Central time is 1 hr. earlier than Eastern time.
Mountain time is solar time for the meridian 105 deg. west longitude and standard for all places within deg. east or west of that meridian. Mountain time is 1 hr. earlier than Central time.
Pacific time is solar time for the meridian 120 deg. west longitude and standard for all places within deg. east or west of that meridian. Pacific time is 1 hr. earlier than Mountain time.
When it is noon at the observatory at Greenwich it is 7 a.m. at New York, 6 a.m. at Chicago, 5. a.m. at Denver and 4 a.m. at San Francisco. At the same time it is 1 p.m. at Berlin and Rome, 2 p.m. at Petrograd and 8 p.m. in the Philippines.
Civil Time. — The day, for all common purposes of reckoning, begins and ends at midnight. The 24 hr. are divided into two periods of 12 hr. each. The hours from midnight to noon are designated by the letters a.m. (ante meridian), and those from noon to midnight by the letters p.m. (post meridian).
Astronomical Time. — The astronomical day is reckoned from noon to noon, the hours being counted from 1 to 24. The astronomical day begins 12 hr. later than the civil day, as the following comparisons will show:
Civil time, Nov. 6, 3 a.m.; Nov. 6, 3 p.m.; Nov. 7, 3 a.m.
Astronomical time, Nov. 5, 15 hr.; Nov. 6, 3 hr.; Nov. 6, 15 hr
BfETRIC SYSTEM OF WEIGHTS AND MEASURES
The units of the metric system are the gram, meter and liter. The system, unlike that of the United States and Great Britain is wholly a decimal system and, for that reason, is more convenient for use.
Denominations. — The higher denominations of weight, length and capacity are obtained by multiplying each respective unfit by 10, 100,
404 Mine Oases And Ventilation
1000, etc:, while lower denominations than the unit are likewise obtained by dividing the same by 10, 100 or 1000.
The denominations of the metric system are expressed by the Latin and Greek prefixes, the former being used to indicate divisions of the unit, while the latter are employed to express multiples of the same unit. These prefixes and their respective values are as follows:
Unit of Weight 1 gram
Deca, 10 1 decagram =10 grams
Hecto, 100 1 hectogram 100 grams
Myria, 10,000 1 myriagram 10,000 grams
The same prefixes are used to express similar divisions and multiples of the units of length and capacity. Area and volume are expressed by the words square and cubic preceding the same denominations of length. Following are the tables of the metric system and equivalents:
Metric Weight
10 milligrams — 1 centigram 0. 15432356 gr. (troy)
10 centigrams 1 decigram 1 . 54323564 gr.
10 decigrams 1 gram 15.43235639 gr.
10 grams 1 decagram 0. 35273957 oz.
10 decagrams 1 hectogram 3 . 52739575 oz.
10 hectograms 1 kilogram 35.27395746 oz.
2.20462234 lb. 10 kilograms 1 myriagram 22.04622341 lb.
10 myriagrams 1 quintal 2.20462234 cwt.
10 quintab 1 tonne 1 . 10231117 tons
The French tonne (2204.6 lb.) dififers but slightly from the British long ton (2240 lb.)
Metric Length
10 millimeters 1 centimeter 0.3937 inches
10 centimeters 1 decimeter 3 .937 inches
10 decimeters 1 meter 39 . 37 inches
10 meters 1 decameter 32.8083 feet
10 decameters 1 hectometer 328.0833 feet
10 hectometers 1 kilometer . 6214 miles
The Austrian, Prussian, Danish and Norwegian mile is equal to about 4.7 American miles; the Swedish, to about Qi American miles; while the Russian "verst" is 3500 ft.
Denominate Numbers 406
Metric Area
100 sq. millimeters 1 sq. centimeter 0. 155 sq. in.
100 sq. centimeters 1 sq. decimeter 15.500 sq. in.
100 sq. decimeters 1 sq. meter (centare) 1549.997 sq. in.
0.025 acres 100 ares 1 sq. hectometer (hectare) ... 2 . 471 acres
100 hectares 1 sq. kilometer 247 . 104 acres
0.3S6 sq. mi. 100 sq. kilometers 1 sq. myriameter 38 . 610 sq. mi.
The unit of area is the square meter or centare.
Metric Volume
1000 cu. millimeters 1 cu. centimeter 0.061 cu. in.
1000 cu. centimeters 1 cu. decimeter 61 . 023 cu. in.
1000 cu. decimeters 1 cu. meter 35. 314 cu. ft.
The weight of 1 cu. centimeter of distilled water at maximum density (4°C.), weighed in a vacuum, is 1 gram; or 1 cu. decimeter of same under like conditions is 1 kilogram.
Metric Capacity
10 milliliters 1 centiliter 0. 610 cu. in.
10 centiliters 1 deciliter 6. 102 cu. in.
10 deciliters 1 liter 61.023 cu. m.
The liter is the unit of capacity in the metric system. Its volume is 1000 cu. centimeters or 1 cu. decimeter. It contains 61.02338189 cu. in., or 0.26417 gal. (Winchester). Or a single Winchester gallon contains 3.785434 Uters.
The Fluid Ounce. — What is known as the "fluid ounce'' is a quantity of any liquid equal to that of pure water at maximum density (4''C.) and weighing exactly 1 oz. avoirdupois. The volume of the fluid ounce is calculated as follows:
1 ounce avoirdupois 437.5 grains.
1 gram 15.43236 grains.
Hence, since the volume of 1 gram (water) is 1 C.c. and the fluid ounce
406 Mine Gases And Ventilation
has a volume based similarly on the avoirdupois ounce, the value of the fluid ounce is
The minim (a drop), the smallest liquid measure, is Ho of a fluid dram or the equivalent in volume of 1 grain, which is 1 -s- 16 . 43236 0.0648 c.c; or 28.3495 437.5 0.0648 c.c.
Metric Abbreviations. — The following are the common abbreviations used in the metric system:
Milligram, mg.; millimeter, mm.; milliliter, ml. Centigram, eg.; centimeter, cm. ; centiliter, cl. Decigram, dg.; decimeter, dm.; deciliter, dl. Gram, g. ; meter, m. ; liter, 1.
Kilogram, kg. ; kilometer, km. ; kiloliter, kl. Square millimeter, mm*; cubic millimeter, mm*. Square centimeter, cm*; cubic centimeter, cm*. Square decimeter, dm*; cubic decimeter, dm*. Square meter, m*; cubic meter, m".
Square kilometer, km*.
Compound Units. — It is often convenient to express values involving two or more denominations in terms of a single compound unit. The following are examples of such compound units:
Work is expressed as a force (pounds) exerted through a distance (feet) and its unit, therefore, combines both of these denominations, giving foot-pounds (ft.-lb.), or inch-pounds (in.-lb.), as the case may be.
Power is expressed as work performed per unit of time, as foot-pounds per minute (ft.-lb. p.m.), or per second (ft.-lb. p.s.).
In like manner, the speed of rotation is given in revolutions per minute (r.p.m.); or the speed of a train as miles per hour (mi. p. hr.); or the velocity of an air current as cubic feet per minute (cu. ft. p. m.).
It is common to estimate the value of coal lands in tons per acre, or acre-tons; or to express the amount of underlying coal in acre-feet, which combines in a single unit both the acreage of the seam and the average thickness of the coal in feet.
Conversion Tables
Numerous forms of tables are in use for converting denominations of the United States system into the corresponding denominations of the metric system and vice versa, but the following are believed to best serve the purpose. For the sake of more ready reference, the denominations of weight, length, area, volume and capacity are here given in separate tables, and the values given in the tables are simple multipliers:
Denominate Numbers
Drams Ounoee Pounds
Tons
1 milligram
1 centigram
1 decigram
1 gram
1 decagram
1 hectogram
1 kilogram
1 myriagram
1 quintal
1 tonne
as
When closer determinations are desired the values given in the metric tables should be employed.
Milligrams
Grams Kilograms Tonne
1 ounce
1 pound
I 0.453€
1 ton
0.W718
Penny
Grains
weights
Ounces
Pounds
1 milligram
sr
1 centigram
1 decigram
a
1 gram
ss
1 decagram
;
1 hectogram
s
:
1 kilogram
s
:
1 myriagram
as
TROt Milligrams/
Grams
Kilograms
1 grain
1 pennyweight
1 ounce
s:
1 pound
Grains
Scruples
Drams
Ounces
Pounds
1 milligram
s
1 centigram
s
1 decigram
1 gram
1 decagram
1 hectogram
1 kilogram
Mine Gases And Ventilation
1 grain
1 scruple
1 dram
1 ounce
1 pound
MilligramB Grams
Kilograms
Inches
Feet
Yards
Rods
Miles
1 millimeter
1 centimeter
s
1 decimeter
1 meter
S
1 decameter
a
1 hectometer
B
1 kilometer
1 myriameter
The old surveyor's chain (66 ft.) contains 20.1168 meters, and one kUometer (3280.83 ft.) is 49.71 of such chains.
Millimeters
Centimeters
Meters
Kilometers
1 inch
s
1 foot
a
1 yard
1 rod
a
1 furlong
1 mile
B
Sq. in. Sq. ft. Sq. rods
Acres Sq. mi.
1 sq. millimeter
1 sq. centimeter
s
1 sq. decimeter
1 sq. meter
:9
,
1 sq. decameter '
1 sq. hectometer
1 sq. kilometer
B
1 sq. myriameter
s
Denominate Numbers
1 sq. inch 1 sq. foot 1 sq. yard 1 sq. rod 1 acre 1 sq. mile
Sq. mm.
bq. om.
CentareB Arefl
1 cu. millimeter
1 cu. centimeter
1 cu. decimeter —
1 cu. meter
Cu. inches Cu. feet
Cu. yardB
Cu. mm. Cu. cm. Cu. dm.
Cu. m.
1 cu. inch
le
k387
1 cu. foot
s
1 cu. yard
Gilln
Pints
Quarts
Gallons
Barrek Hhd.
1 milliliter
1 centiliter
1 deciliter
1 liter
1 decaliter
1 hectoliter
s
1 kiloliter
1 myrialiter
One myrialiter contains 10.48295 tuns.
u. s., :
Pints
Quarts
Gallons
Pecks
Bushels
1 centiliter
1 deciliter
1 Uter
1 centistere
1 decistere
1 stere
1 decastere
The decastere is equal to 7.88269 chaldrons.
MINE GASES AND VENTILATION Capacity (U. S. to Metric)
Ml.
Cl. Dl. L.
Kl
1 gill
1 pint
1 quart
1 gallon
1 barrel
s
1 hogshead
1 pipe
1 tun
1 pint
1 quart
1 gallon
1 peck
ss
1 bushel
1 chaldron
GUIs
Pints Quarts Gallons Pecks
Bushels
1 milliliter
1 centiliter
ss
f
1 deciliter
1 Uter
1 decaliter
1 hectoliter
1 kiloliter
1 myrialiter
Ml.
Cl. Dl. L.
K1.
1 gill
1 pint
1 quart
1 gallon
1 peck
1 bushel
The conversion factors in these tables have been derived independently from the following standards :
1 meter (U. S.) 39.37 in. (1 in. 25.4 mm.); 1 sq. meter 39.37 144 10.76386736 sq. ft. ; 1 cu. meter 39.373 1728 35.31445447 cu. ft.; 1 Uter 61.02338189 cu. in.; 1 U. S. (Winchester) bushel 2150.4 cu. in.; 1 British (Imperial) bushel 2218.192 pu. in.
Denominate Numbers 411
a
Conversion Of Compound Units
In the conversion of compound units from the United States to the metric system, and vice versa, it. is more convenient and saves much
ime and frequently avoids error arising from confusion of terms to employ a single factor. The following are the more common conversion
actors:
Weight per Unit Length
long ton per mi (1.016 X 0.6214) 0.6313 tonnes pr km.
Weight per Unit Area
ton per sq. ft (0.9072 X 10.764) 9.765 tonnes per
long ton per acre (1.016 X 2.471) 2.5105 tonnes per hectare
Weight per Unit Volume
oz. per cu. in ... (28.35 X 0.06102) 1.73 g. per cm*
lb. per cu. ft (0.4536 X 35.3145) 16.0184 kg. per
ton per cu. yd . . (0.9072 X 1.308) 1.1866 tonnes per
ton per acre-ft. . . (0.9072 X 8.106) 7.3538 tonnes per hectare-m.
long ton per acre-ft (1.016 X 8.106) 8.2357 tonnes per.hectare-m.
It is worthy of note that ounces per cubic foot are equivalent to kilograms per cubic meter, or grams per liter, since 1 m' — 1000 liters.
Weight per Unit Capacity — Liquid
1 gr. per gal.-— U. S ( 64.8 X 0.264) 17.107 mg. per 1.
Weight per Unit Capacity — Dry
1 lb. per bu.— U. S (0.4536 X 28.378) 12.872 kg. per stere
1 lb. per bu.— Gt. Bt (0.4536 X 27.51) 12.479 kg. per stere
Pressure
1 oz. per sq. in (28.35 X 0.155) 4.394 g. per cm*
1 lb. per sq. in (453.59 X 0.155) 70.306 g. per cm
412 Mine Gases And Ventilation
Work
Work in Heat Units
C ALORinc OR Heating Value
1 B.t.u. per lb (0.252 X 2.2046) 0.55556 cal. per kg.
1 B.t.u. per cu. ft (0.252 X 36.3145) 8.89925 cal. per
1 Ib.-cal. per lb (0.4536 X 2.2046) 1.00000 cal. per kg,
1 Ib.-cal. per lb 2.20462 Ib.-cal. per kg.
1 Ib.-cal. per cu. ft (0.4536 X 35.3145) 16.01866 cal. per
Power
The metric horsepower (force de cheval), which for convenience may be abbreviated "cheval," is the power capable of performing 75 kg.-m. of work per second, or 75 X 60 4500 kg.-m. per min.
Power Factors
1 cu. ft. per hp (0.028 X 0.986) 0. 0276 per cheval
Fuel OR Water Consumption
1 ton per hp.-hr (0 . 9072 X . 986) . 8945 tonnes per cheval-hr.
1 gal. (U. S.) per hp.-hr. . (3.785X0.986) ==3.7320 liters per cheval-hr. 1 gal. (Gt. Bt.) per hp.-hr. (4 . 644 X . 986) 4 . 4804 liters per cheval-hr.
Evaporation Factors
1 gal. per sq. ft.— U. S (3 . 785 X 10 . 764) 40 . 7417 1. per m.
1 gal. per lb. fuel (3.785 X 2.2046)= 8 . 3444 i. per kg.
1 gal. per B.t.u (3.785 X 3.968) 15.0189 1. per cal.
1 gal. per sq. ft.— Gt. Bt (4. 544 X 10. 764) 48. 9116 1. per
1 gal. per lb. fuel (4.544 X 2.2046) 10.0177 1. per kg.
1 gal. per B.t.u (4.544 X 3.968) 18.0306 1. per cal.
Denominate Numbers
Equivalents in Air Measurements
Atmospheric pressure, sea, level, normal, 14.696 lb. per sq. in.
(14 . 696 X . 0703) 1 . 033 kg. per cm* (29'. 925 X 25 . 4) =760 mm. mercury /29.925 X 13.
(33.915 X 0.3048 10.34 m. water column
The specific gravity of mercury (32 deg. F.) being 13.593, 1 in. barometer (standard reading) corresponds to 13.6 in. water gage and, roughly, to (13.6 X 815) t- 12 say 900 ft. air-column.
Pressure, in fan ventilation is frequently expressed in ounces per square inch, instead of in pounds per square inch. The following table giving the equivalent values in these denominations and inches of water gage.
Water
Lb. per
' Oe. per
Water
Lb. per
' Oa.per
gage
sq. ft.
sq. in.
Gage
sq. in.
sq. in.
%
K
H
%
H
H
K
y4.
%
K
H
K
K
M
M
H .
M
y4.
The table on the following page will be found convenient in comparing short and long tons. It expresses the decimal equivalent of the short and long ton, per hundredweight, to 20,000 lb. or 10 short tons.
Mine Gases And Ventilation
Table of Comparative Values of the Short and Long Ton
Index
Note. — Numbers refer to pages. Letters are used to abbreviate words in the same line or in the heading in which they stand. Other abbreviations are those in common
use.
Absolute pressure, ld2
A. temperature; A, zero, 18 Rel. of a. p. to a. temp., 20 AcceleratioiL, 26 . Acetylene gas, Generation of.
Burning a. g.; Oxygen consumed; Calculation, 310 Chem. reactions, 309 Properties of a. g., 311 Acetylene lamp (See L., Miners*
Carbide) Acids, Bases, Salts : Nature of a. ; Distinguishing characteristics, 61 Affinity of atoms, 59 Afterdamp: Composition, etc., Ill Air, 1 (See Respiration)
Composition of a., 4; Percentage c. calculated, 30 Density of a. calculated, 30 Dry a., 4, 70; Formulas, 4,
Hygrometry) Early theories of a., 1 Mechanical mixture, 2, 61 Moisture in a. (See Hygrometry) Normal a., 4, 5; Exhaled a., 3; Free a., 19; Residual a., Tidal a., 133 Weight of a.: Formulas 4,
Weight of a.: Dif. altitudes
Air bridges: Overcasts; Under-casts
; Natural o., 251
Air crossings, 249
Average temp, (atmos. a. c.) Calc. of, 14; Observed temp. Table of, 15 Air columns, in mines:
Estimation of, 166; Conditions affecting; Positive and negative a.c., 167; Downcast, Upcast c. 168; Calculation of a. c; Effective depth, 169; Problems, 170; Relation of a. c. to imit ventilating press., 184; Wwater gage, 184; Barom, pres., 185 Air currents, Conducting, 249 (See Mine Ventilation)
Appliances used: Air bridges (overcasts undercasts), brattices, doors, stoppings, regulators, 249-251
Circulating system : Intake and discharge openings, 161; Intake and return airways, 258; Coursing the a. ; Single current not adequate, 218
Distribution of a., 257; A. splits, 258 Measurement of a. c, 199 Splitting the a. c. (See S. the A.C.)
Velocity of a. c, 173, Danger of high v., 179; How v. is estimated and measured, 180; Rel. of pres. and v., 173
Index
Definition of a., 187; Essential features; Shape, 188 Intake and return a., 258 Potential of a., 200; Table, 202 Similar a., 189, Principle of 8. a., 191; Rule, 192 Systems of mine a., 262 Resistance of a.; How r. varies, 191; Unit of r.; of fric; Calculation of r. of an a., 192; Formulas for r. 196, 198 Anemometer, The, 180 Artificial respiration (See R.)
Sylvester method, 158; Schaefer method, 159 Ashworth-Hepplewhite-Gray safety lamp, 283 Atmosphere, The, 5 (See Air) Constant composition, 61 Pressure expressed in a's, 19 Atmospheric pressure, 5
A. p. at dif. altitudes, Table of,
altitude, temp., etc., Table
of, 16
. method), 15 Measurement of (See Barometric Pressure) Variation of. Daily and yearly, Atoms, corpuscles, electrons, molecules, 22 Atomic heat, re a. wt., 53 Atomic volume, imit of gaseous
v., 29, 63 Atomic weight, reL w., 69; A. w. of elements (table), 28 Attraction, Law of, 22, Terrestrial
a., 23 Authorises: Abel, 122; Atkinson, 191; Avogadro, 29;
Beard, 305; Berzelius, 122; Boyle, 19; Burrell, 296; Cavendish, 1; Chamberlin, 90; Charles, 18; Clowes, 311; Dalton, 22; Davy, 269; Dulong, 63; Emich, 113; Fairley, 191; Favre, 66, 68; Galloway, 304, 305; Gay Lussac, 18; Gibbs, 143; Graham, 37; Haldane, 106, 107, 109; Hopkins, 157; Lavoisier, l;LeChatelier, 114, 311; Mallard, 114; Manning, 157; Mariotte, 19; Paul, 147; Petit, 53; Priestley, 1; Remsen, 5S; Schaefer, 159; Silbermann, 66, 68; Stephenson, 268; Stewart, 134; Stoney, 22; Sylvester, 158; Taflfanel, 123; Thomson, Avogadro law of gaseous volume, 29
B
Barometer, The, 6 Aneroid b., 9
Mercurial b., 6; Description 8; Principle of b., 7 Barometric pressure, 6 (See Atmospheric P.) Calculation of p. from b. reading 6; Calculation for any altitude, 12; Formula, 13 Standard, b. readings, 8 Table of b. p. at dif. altitudes, Bases, in chemistry, 61 Battery, Edison storage, 313 Beard-Mackie sight indicator! for gas, 297
Index
Birds, Effect of carbon monoxide on, 106; Table showing length of exposure and recovery, 108 Blackdamp, 110 (See Carbon Dioxide) Carbide lamps in b., 311 Definition; Production in mines; Effect on human system, 110 Blood, Circulation of, 3 (See Respiration) Absorption of carbon monooxide by the b., 103; Rate of a., 104 B. test for carbon monoxide,
Percentage of saturation in b. re p. c. in air breathed, 106; P. of carbon monoxide fatal to life, 107 Blowers, Gas, 87 (See Geological
Conditions) Blownout shot, cause of mine explosion, 127 Boiling, Evaporation, Vapoiization, 50 B. points of dif . liquids. Table, 51; Effect of pres. on b. p. and v., 60 Bonnet, Lamp (See L. Mine
Safety) Box regulator, The, 231 (See Regulators) Area of opening, Example,
234, 240 Pres. due to b. r., 232 Brattices, 249; How built, 250 Breathing Apparatus, 132 (See Respiration) Design; Development, 135 Permissible b. a.; Definition, . Principle of b. a., 132 Regenerator, 136 Specifications by the Bureau
of Mines: Conditions of testing, 148; Character of tests, 150; Construction of b. a., 151; Detail of procedure in tests, 163; Approval of a., 155 Notification to manufacturer; Fees for testing; Application for test of a., Testing b. a., 136 Types of b. a., 137:
Braeger b.a., 137; Essential parts; Capacity, 139 Fleus Proto b. a., 139; Essential parts, 140; Capacity, 142
Gibbs b. a., 143; Circulation, 144; Testing 146 Paul b. a., 147 British thermal unit, 51 Bturell gas detector, The, 299 Bureau of Mines, 147
Requirements in breathing apparatus, 147; Specifications b. a, 148; Electric mine lamps, 319; Mine safety lamps, 288
Calorie, 62
Pound, c, 62; Equivalent B.t.u., etc., 63 Canary, (See Birds etc.) Cap, Flame, ( See F. C.) Cap lamp, Electric, (See E. Mine
L.) Carbide lamps (See L. Acetylene C.) Carbon Heat of combustion of, Thermochemical equation, 69 Carbon dioxide, 109
Absorption of, in breathing
apparatus, 136 Amount produced in breathing, 134
Index
Carbon dioxide, Effect on flame;
on life; on respiration;
Production in mines, 109
Reduces poisonous effect of
m
carbon monoxide, 107 Toxic effect, 2, 109, 312 Treatment of victims, 110 Carbonic acid gas (See Carbon
Absorption by blood 103; Rate of a.; Fatal percentage, 1G4 Combustion in air (chem.
Detection in air; Blood test,
Effect on birds and mice; on flame, 106; on life, 103; Haldane's conclusions,
Explosive and inflammable range (table); Effect of high press, and temp., 114; Moisture necessary, 114, 121
Flame temp., Calculation of,
Production in mines, 105
Properties, 103
Treatment for c. m. poisoning, Catalysis, 122
Centigrade re Fahrenheit scale (table), 44
Conversion formulas; Examples, 45 Charts: Explosive mine gases; E. range; Max. e. point; Inflammable limits; Symbols; Molecular wts., Densities; Wt. per cu. ft. ; Vol. per pound; Specific heats; Heat of combustion in oxygen ; Chem. equation showing reaction, 115
Flame caps in safety lamps; Height of f . cap or elongation of f. for dif . illuminants and dif. percentages of gas; Inflammable and explosive zones, 303 Humidity of air for dif. dry-and-wet bulb readings; Percentage and weight of water vapor in air, 81; Table, 75 Pressure (atmospheric) at dif. altitudes; Corresponding water column and barometer; Man observed temp, of atmosphere, 15 Pressure, power, volume: Lb. p. sq. ft.; Oz. p. sq. in.; water gage, inches, 184 Temperature : Expansion
curve for air and gases; Relation of jEtbsolute t. and volume, 19 Chemical affinity, 46, 56
C. change; C. reaction, 56, 62 ; Examples of c.r. ; Effect of heat 57; C. compound, 60; C. equation; How written, 62; What it shows, 67; Use of c. e., 63; C. symbols, 58 Chemistry of gases, 56 Chesneau safety lamp, 283 Chokedamp, 109 (See Carbon
Dioxide) Circulation in mines (See M. Ventilation) Flow of air in airways, 172; Potential of c, 201; P. values for dif. c, 202; Table, 203; Pres. producing c, 174; Power required to produce a given c, 249 Tandem c; Summation of potentials, 214; Formulas,
Index
215; Examples in t. c, 216, 237; T. vs. split c, 222
Clanny safety lamp, 277
Clowes hydrogen safety lamp, 2S4
Coal: Condition of gas in c; Escape of g. from c; Gas evolved from o. in vacuum, 90; Heat value of some coals (table), 66; Inflammability of c, 124
Coefficient of friction of air: Atkinson c; Fairley c,
Cohesion, 22
Combustion : A form of oxidation ; Products of C; Slow c; Supporter of c, 57 Heat of c. (exothermic); Formula; Table of h, of d., 66; Calculation of h. of c, 67 Rapid (active) c. ; Spontaneous c, 58
Composition, Percentage : By volume, 40; By weight, 39
Conduction of heat, 52
Convection, 52
Conversion formulas: Degrees of temp., 45; Heat units, 52
Corpuscles, 22
Critical temp, of a liquid, 81
D Damps, 94
Davy safety lamp. The, 275 Deliquescent, 48 Denominate numbers, 397 Density defined; Formula, 29 Calculation of d. from relative
Dew point, 5, 76 D. p. temp., 76 Diffusion of air and gases 34, 36 Law of d., 36; Graham's 1.; Illustration; Experiment, 37.; Calculation of density based on 1. of diffusion; Formula, 41 Dip workings. Ventilation of, 162 Distribution of air in mines, 257 Division of air: (See Splitting the A. Current) Natural d. 220; Proportionate d. 230 Door regulator. The, 231 ;
Area of opening; Use of the d. r., 235; Example, 240 Doors, Mine, 249 Double-entry system, 263 Draeger breathing apparatus, 137 Drainage, Bftine 252 Dust, Coal, 123 (See D. Explosion) Anthracite d., 124 Efifect of c. d. on. flame, 123 Inflammability of c. d., 124 Dust, Shale or Stone,
Barrier to propagation of
explosion, 125 Catalytic action of s. d., 122 Dust explosion, 116 (See E., D.) Djmamic force, 25
E
Edison storage battery for mine
lamps, 313 Electric mine lamps, 128, 313 (See Incandescent L.)
Battery, Selecting a suitable; Edison storage b., 313; Charging the b., 315; Cap 1. and cable, 314
Permissible e. m. 1.; Definition, 319
Specifications (Bureau of Mines) ; Conditions of testing, 319; Require-
Index
ments for approval, 320; Tests of design.
and construction;
safety devices, 323;
short circuit;
— fighting 324; current consumption, candle
power, life of bulb;
— leakage of electrolyte; Approval, 325; Notification of manufacturer; Fees for testing, 326 Use of e.m.l., 317 Electric wires, switches, fuses, brushes, sparking of, 127 Electrons, 22 Elements, The, 28
Classification of the e., 60 Combining power; Valence,
Heat of e. ; in reaction, always zero, 65 Emission of gases, 34 (See Transpiration of G.) Endothermic reaction, 65, 67 Energy: Definition; Forms of e; Kinetic e.; Potential e., 27; Heat e. never lost, Equations: Chemical e., 62; Thermochemical e., 67; E. of time, 402 Ethane, 89; Occurrence and
properties, 92 Ethene (ethylene), 89 (See defiant Gas) Equivalents in measurement, 184 Air column re water gage; re unit of vent, pres., 184; re barometric pres., Atmospheric pressure e., 413 Barometric pressure re air column; re imit of vent, pres., 185 Power, volume (diagram), 185 Pressure e. (table), 185
etc.) Exothermic reaction, 65, 67 Expansion of air and gas ; 17
Adiabatic e.; Formidas, 21; Isothermal e., 22
Coefficient of e. or contraction,
Effect of press, and temp., 17; Addition of heat, 20
Pressure re abs. temp., 20; re volume (Boyle's or Mariotte's law), 19
Temperature (absolute) re volume (Charles* or Gay Lussac's law), 18
Voliune, press., abs. temp., Rel. of; Formulas, 20
Work of e., calculated in two ways, 20j 21 Explosion, Dust, 116:
Absence of gas; Character of d.; Influence of d. on e.; Pioneering cloud of d.; Weight of d. per cu. ft. of air to render air explosive, 123; Inflammability of coal d., 124
Anthracite d. not explosive; Volatile combustible matter in coal an index of its explosibility, 124
Incombustible d, Influence of, 125 (See D., Shale or Stone) Explosion, Gas (See Mine Gases; E., Mine)
Definition of g. e., 116
E. of g.; Influence of pres. and temp, on e., 121 ; I. of catalysis, initial impulse, moisture, volume and intensity of flame, 122; I. of coal dust on e., 123; I. of rock dust to arrest e., 125
Peculiarities of e. of methane,
Index
Dust; E., Gas) Causes of m. e., 127 De&iition of a m. e., 116 Development of the e., 126 Propagation of an e. in a m.;
Pioneering cloud, 123 Prevention of m. e., 129; Shale
S. or S.) Rescue and first-aid work; Entering a. m. after an e.,
F-A. W.; Breathing Apparatus) Explosive Mine Gases, 112, 115
of m. g., 115 Effect of high pres. and temp.
one. range, 114 E. and inflammable limits;
E. range of g. ; Maximum
e. point ; Lower and higher
limits; Degree of explosiveness
, how affected,
113; Table, 114 Inflammation of gas; Theory
Fahrenheit scale, 43
F. re centigrade, s. (table), 44; Conversion formulas; Examples, 45
Feeders, Gas; Blowers, 87; Composition of f. g., 91; Occurrence, 87
Firedamp, 94
Definition, 94
Firedamp, Effect of dust and other gases, 95
F. is a mechanical mixture, 38
Infiammable and explosive range, Table of, 101; Lower i. limit, 95; Calculating the 1. i. 1., 96; Percentage of gas, 98; L. e. Hmit; Max. e. point, 98; Percentage of gas, 99; Higher e. limit, 99; Percentage of gas, 100; Higher i. limit, 100 -aid work, 157 (See Artificial Respiration; Breathing Apparatus)
Resuscitation, 157
Suggestions on f.-a. to explosion victims, 132 Flame, Nature and temperature of,
Effect of coal dust on f ., 123; E. of carbon dioxide on f . , 109 ; E. of c. monoxide on f ., 106
Extinction of lamp f . in car bon dioxide, 109; E. of carbide f . by depletion of oxygen, 312
Kinds of f. : Gaa-fed f.; Oil-fed f., 109, 312
Lamp f.. Chart of, 303
Temp, of f., Theoretical; Calculation of f. t., 118; Methane in air, 119; Carbon monoxide in air, 120; Temp, of f. re temp, of ignition of gas, 118
Volatile-oil f . sensitive to gas,
Volume of f., Estimated, 121
Zonesinf., 118, 301 Flame caps: Fuel c; Gas c, 302
Calculation of height of f. c. 304; Formulas, 305
Chart of f. c, 303
Index
Flame caps: Height of L c. re percentage of gas, 303,
Flashdamp: Definition; Calculation of composition of 1, 101; Percentage composition, 102
Fleuss Proto Breathing Apparatus,
Flow of air in airways, 172 (See Air Currents, ; Conducting; Airways). Appliances for conducting the
a., 249 Coefficients of friction: Atkinson; Fairley, 192 Pressure producing circulation, 174; Power required to produce c, 249 Resistance of a.; How r. varies, 191; Unit of r.,
Fluid ounce, The, 405
Fluid state, 23
Force: Measurement of f.; Static f.; Dynamic f., 25
Formulas and symbols, 192
Basal f . ; Important principles,
How factors vary, 195 Use of f., 194; Illustration of f., 197
Free air, 19
Free split, 233
Difference bet, melting and
f. p.; Effect of pres., 49
French thermal unit, 52
Friction, Coefficient of; Atkinson c. ; Fairley c, 192
Fuel cap in testing for gas, 302
Furnace ventilation; Principle of f. v.; Location of a mine furnace; Construction of
f., 164; Area of grate; Wt. of coal burned per hr., 165; Formula; Example, 166 Fusion, Heat of, 48; Table of h. of f., 50 Effect of pressure on f ., 49-
G
Gas cap, in testing for g., 302 (See
Flame C.) Gases, 23 (See Mine G.; Geological conditions)
Composition of g.; Simple or elementary; Compound,
Density, Standard for g., 31
Expansion and contraction of g.; Coef. of e. or c.
Gaseous state, 23; Distribution of heat by convection in, g., 52
Natural g., 87; Gases, defines; Paraffins, 92 (See Hydrocarbon Gases)
Vapors and g.. Difference, 24 Gas explosion, 116 (See E., G.) Gas feeders, 87 (See F., G.; Geological conditions) Gas indicators, 296; Beard-Mackie, 297; Burrell, 299; Liveing, 296 Geological conditions, 86
Condition of gas in coal; Escape of g.; Composition of g. evolved, 90
Effect of faults, 87
Gas feeders. Blowers, 87; Composition of f. g. (table), 91
Gas, oil and water in the strata, 86
Index
Geological conditions, Natural gas, 87 Occluded gases; Pressure of
o. g., 35, 88 Outbursts of gas, 88 Water level in strata, 87 Gibbs breathing apparatus, 143 Gram-atom, 53; G.-calorie, 67;
G.-molecule, 47, 54 Gravitation : Gravity, 23
H
Haemoglobin or red corpuscles of the blood, 3; Affinity of h. for carbon monoxide, Haulage, as affecting plan of mine,
Direction of road for given grade inclined seam ; Rule and formula, 254 Heat, 42
Definition; Theory of h.; H. in bodies, 42; Absorption of h., 47; Disappearance of h.; Total h. in a body, 48; H. calculation, 67; H. changes; H. of decomposition ; H. of elements, H. of formation or combination, 66; H. of fusion; h, of vaporization; H. of condensation, 48; H. of reaction, positive h., negative h., 67
H. energy, 20; No h.e. lost, 67; Transformation of h, e., 47
H. re temp., 43; Sensible h.; Latent h., 46
Kinds of h.: Atomic h., 63; Chemical h. ; Molecular h., 46;
Combining h. ; H. due to friction, impact, pressure, 47;
Heat, H. of combustion, 66; Specific h. or relative h. capacity, 54
Mechanical equivalent of .h,
Sources of h., 46
Tables: H. of combustion, 66; H. of formation or combination, 68; H. of fusion, - Specific h., solids and liquids; S. h., gases and vapors, 55
Transmission of h.; Radiation; conduction; convection. 52
Units of h., 51; Conversion formulas, 52; Definition of a u. of h., 54 Horsepower in mine ventilation:
Calculation of h. from mine potential, 207, 212, 213; C. of h. in natural division of air, 227; Proportionate div. of air, 232; secondary splitting, 230 Humidity (Relative) of air, 74; How measured 71; Tables, 75,81 Hydrocarbon gases, 91; Acetylenes; Olefines; Paraffins,
General formulas for h. g.,
Heavy h. g.; Ethane; Ethene, ethylene or olefiant g.
light carbureted hydrogen, methane, 92
Occurrence and formation, 92
Hydrogen: Symbol, mol. wt.,
Explosive range, Inflammable limits (table) 114
Index
Indicates degree of saturation of air, 74
Principle of the h., 73
Swing p., 73
Wet-and-dry-bulb h., 72 Hygrometry, 70
Calculation of wt. of moisture in air, 70; Formulas, 79, 80; Caution, 78
Dew point, The, 76
Dry vs. wet air, Deg. of saturation, 70 D. and w. a compared, 79; Formulas, 79, 80
Tables, 75, 81
Vapor pressure. Actual; How calculated, 75; Saturated (table), 77
Vapors, Laws of, 80
niuminants for safety lamps, 307
Light volatile oils: Benzine,
gasoline, naphtha, 308
Mineral oils: Crude petroleum
Incandescent lamps :
Cause of mine explosions,
Conditions of breaking, 128 Indicators, Gas (See G. 1.) Inertia, a property of matter, 23 Inflammable and Explosive Mine Gases, 112, (See £. M. G.) 1. gases, The, 112; I. limits of gases (table) 114; range, Inflammation of gases; Theory of, 116
Lamp flames (chart), 303 Lamphouse or station, 293 Lamps, Acetjdene (Carbide), 308 (See A. Gas) C. 1. in blackdamp, 311 Extinction of c. 1., 312 Precautions in use of c. L, Lamps, Electric Mine, 313 (See
Bonnet or shield, 271; Effect
on flame cap, 303 Chart of 1. flames, 303 Classification of s. L, 270 Defective s. 1., cause of explosion, 127 Historical grouping of s. 1.,
286, 287 Illuminating power, 273 Lock fastenings. Lead 1.;
Magnetic 1., 272 Oil-burning 1. ; Non-volatile
o.; Volatile o., 271 Permissible m. s. 1.; Definition, 288 Principle of construction ; Protecting shield ; Stephenson L, 268; Wire gauze, Requirements of a good testing L; Sensitive to gas, 270; R, of working 1., Specifications by the Bureau of Mines, 274; Conditions of testing, 288; Mechanical tests; Photometric t. Explosion t., 290; Tests of glasses; Igniter t., 291; Approval of s. 1., 292; Notification to manufacturer; Fees for testing,
Index
Lamps, Mine safety:
Types of L, Characteristic, 276: Davy, 275; Clanny, 277; Marsaut, 278; Mueseler, 279 Types of 1., Special, 281: Pieler, 282; Chesneau; Ashworth - Hepplewhite- Gray, 283; Stokes alcohol; Clowes hydrogen, 284, Wolf, 285; MisceUa neousl., 286, 287 Use and care of s. 1., 293; Handling of s. 1., 294 Volume of L chimney, 269 Latitude etc., 402 Laws of gases:
Avogadro, law of gaseous
volume, 29; Application, 64
Boyle-Mariotte, law of vol.
re pres., 19 Charles-Gay Lussac law of
vol. re temp., 18 Graham, law of diffusion of air and g., 36, 37 Liquid state, 23; Liquefaction, 48; Distribution of heat by convection, in hquids, 52 Logarithms :
Definition; Systems; Characteristic, Mantissa, 328; How to find L of a number, 329; Use of L, 330; Rules; Arithmetical complement, Antilog. 331; Examples, 332; Table of 1. Lighting, Mine lamps and, 268 Liveing gas indicator, 296 Longwall plans, 256, 257
Ventilation of 1. workings, 256 Longtiude etc. 402
M
Marsant safety lamp, 278 Marsh gas (See Methane)
Mass, property of matter, 22
M., volume, density; Unit of m., 24; Measure of force, 25 Matter, 22
Definition; Divisions of m.;
Properties of m., 22 Heat a condition of m., 51 M. is indestructible, 62 Molecular theory of m., 59 Measurement, 25
Distance; Force; Static f., Dynamic f.; Formulas, 25; Tine; Special units of m.; Compound units, Energy; Forms of e.; Kinetic e.; Potential e. 27 Measurement of air currents, 199
Standards of h. m.; Thermal
units; British t. u., 51;
French t. u. or calorie; Pound
c; Conversion formulas,
Measurement of time, 402
Sun t.; Equation of t.; Sidereal t.; Local t.; Standard t., 402; Eastern t.; Central t.. Mountain t.. Pacific t.; Civil t.; Astronomical t., 403 Measurement of humidity (See
H. of Air) Measurement, Relative (See Specific M.) Measures, Weights and (tables), U. S. and British system, 398; Metric system, 403; Me- , trie abbreviations; Conversion tables 406; Compound units, 411 Mechanical equivalent of heat,
Index
Melting points of substances, 49
Difiference bet. m. p. and freezing p. ; 49
Table of m. p. of substances, Mercuri barometer, The, 6 Methane (Marsh gas), 93 (See Firedamp)
Combustion of m. in air or oxygen, 64; wt. of o. per lb. of m., 96; Vol. of .o. per unit vol. of m., 64; Effect of other gas and dust, 95; Heat of c. of m. in air (table), 66; Heat of formation of m. (table), 68; Heat calculation, 67
Flame temp, of m. burning in air, calculation, 119
Occurrence and properties, 93, Occluded in coal formations, 88
Percentage composition of m., Mine air, 5 (See A.)
Concussion of a. in mines, Mine gases, 86 (See Geological Conditions)
Chart of m. g., 115
Properties and behavior of m. g., 93 Mine potential. The, 199 (See P.)
Effect of splitting on m. p., 203, Illustration, 204; Practical example, 205 ; Examples, 209; Formulas: M. power p.; M. pressure p. 211
Mine potential:
Formulas: Power p., 197; Pressure p., 198
General m. p., 212; G. m. p., equal splits, 213; G.m.p., natural division of air. Example, 228
P. of airway, 200; Table of values, dif. a., 202; P. of circulation, 201 ; Table of values, dif. c, 203 Mineral oil, 307
Mine-rescue work and appliances, 131 (See Explosion, M.) Mine Ventilation, 161 (See Furnace v.; v.. Practical)
Conducting air currents in mines (See A. C, C.)
Formulas, 197-199; Basal f.,
Kinds of v.; Natural v.; Slope and dip workings,
Power on the air; Work and p. synonymous, 182; P.- pr?ss.-vol. chart, 185; P. formulas, 199; P., press., quantity, 201
Pressure, Ventilating, 174: P. producing circulation; P. how produced, 174; P. how estimated; P. how measured, 175; P. formulas, 198; unit of v. p., 177; P. calculated from m. potential, 206; P. due to regulator, 232; P. re velocity; 173; Equivalents in v. p. (table) 175, 185
Quantity of air, 181: Q. of a. required; Q. how estimated ; Q. how measured, 181; Q. formulas, 198; Q. calculated from m. potential, 207
Index
Mine Ventilation:
Resistance of airways, 191
(See A.) Requirements in v., 161; R. of the m. law, 182, Spitting air currents (See S. A.
C; Symbols and formulas, 192 Systems of v;, 261: Blowing s., 174, 262; Exhaust s., 174, 261; E. vs. B. s. of v., 261 Variation of factors, 247 Mixed lights in mines, 127 Molecular state, 23
M. forces: M. attraction; M. repulsion, 23; M. heat, 46; M. h. of reaction, 67; M. theory, 59; M. volume, 29; M. weight, 69 Molecule, The, — Definition, Symbol; Atoms in a m., 58 Mueseler safety lamp, 279
English and Belgian types,
N
Natural gas, 87
Natural overcast, 251
Nitrogen in air: Percentage by vol., by wt, (table), 4; Rel. veloc, of transpiration from coal (table), 35; N. in blackdamp, 110; N. in afterdamp. 111; Symbol, mol. wt., density, sp. gr. (table), 89
Non-volatile oils used in safety lamps, 307
O
Occlusion of Gases :
Examples of o,; Pressure of o. g., 35, 88 Oil -burning lamps, 271 Oils : Non-volatile o. used in safety lamps; Animal o.; Vegetable o., 307 Mineral o. (rock o.), 307; Coal
o. or kerosene, 308 Volatile o., 271; Benzine, naphtha, gasoline, 308 Water, gas and o. in strata, Olefiant gas (ethene, ethylene), 92 Composition, 59 Density, sp. gr., mol. wt., symbol, 89; Chart, 115 Inflammable, 112 Occurrence and properties, 92 Rel. rate of transpiration, 35 Olefines, 92
Open lights cause of explosion, 127 Open-flame lamp, (carbide 1.), 308 Ounce, The fluid, 405 Outbursts of gas, 88 Overcasts, 249, 250, 251 Oxides: Monoxide; Dioxide; Trioxide, 62 O. of nitrogen, 60 Oxygen:
Absorption of o. in spontaneous combustion, 58; A. by coal. 111 Consumed in breathing, 3
(See B. Apparatus) Density, sp. gr., mol. wt., symbol, 89 Depletion of o. in air, 4; Caused by absorption of o. Ill; Effect on flame, 312; Effect on life, 4; Increases poisonous action of carbon monoxide, Normal percentage of o. in air, 4
Index
Paul breathing apparatus, 147 Percentage composition: By volume, 40; By wt., 39 Caloulation of p. c. of air, 30 Percentage of gas re height of fame cap; Chart; 303 Calculation of h. of f. c, 304; Diagram; Formulas, 305 Permissible breathing apparatus,
148 (See B. A.) Permissible electric mine lamps,
319 (See E. M. L.) Permissible mine safety lamps,
Expansion of A. and G.;
Pieler safety lamp, 282; Chart of
L flame, 303 Plan of mine, General, 252
Requirements re drainage, haulage and ventilation; Economy and efficiency; Drainage, 252; Haulage, 253; Road angle re grade in inclined seam; Formulas, 254; Distribution of air, 257 System of mining: Room-andpillar, 254, 255; Longwall, 256, 267; Single, Double, Triple-entry systems, 263; Multiple-entry system; Economy of m. main airways, 265 Output, Estimation for given, Ventilation of longwall workings, 256
Explanation of potential principle, 196
Formulas: P. of airway, 200; , Values,dif.a. (table), 202; P. of circulation, 201 ; Values, dif. c. (table), 203 Pressure p.; Power p. — Caution, 207; Equivalent p. f.;- Power; Pressure, 208; Quantity, 209; Illustration 197, 198
Part p. values, 212; Illustration, 213, 216
Relative p. values, 221; Illustration, 224
Split p. formula, 204; Examples, 205-207, 209; Split power p. and press, p. f. 211; Ex.; General 8. p., 229
Summation of split p., 232
Tandem circulations, 214: Summation of p., 214, 215; General t. p. formulas, 216
Use of p. factors, 208 Pound : Unit of mass, 25 Pound -calorie, 52; Value of, 53;
Pound-molecule, 67 Power on the air, 182 (See Mine
Ventilation) Power, volume, pressure diagram,
ventilation (See V. ,P.) Pressure (See Mine Ventilation)
Effect of p. on air and gas, 17; E. on freezing, fusion, melting points, 49; E. on boiling point and vaporization, 50 Heat due to p., 47
Power, volume, p. diagram,
P. re absolute temp. 20
P. of occluded gas, 35
Index
Pressure:
Primary and secondary splits, 219; P. and s. pressures,
Proportionate division of air, 230 (See Splitting the A. Current) Regulators required, 219, 230 (SeeR.)
Pulmotor, 103
Q
R
Radiation of heat, 52 Ratios, Solution by (in mine ventilation), 173 Reaction, Chemical, 56
Endothermic; Exothermic, 65,
Interchange of atoms, 62 Molecular heat of the r., 67 Regulate the air, To, 230 Regulators (in mine ventilation), 239, 251 Effect of r., 231 Kind: Box r.; Door r,, 321 Pressure due to box r., 232; Area of opening in b. r., 234; Example, 240; Velocity and quantity of air passing, 233 Use of the door r.; Area of opening; Example, 240; Quantity of air passing, 235 Rescue work in mines (See Explosion, M.) Resistance of airways, 191 (See
A.) Respiration (See Artificial R.) Action in r. wearing breathing apparatus, 133
Respiration :
Capacity of lungs; Rate of breathing; Quantity of air exhaled each breath; Quantity of air inhaled per min. depending on exertion; Volume of carbon dioxide exhaled about equal to vol, of oxygen inhaled, 133
Effect of carbon dioxide on r., 109, 110
Quantity of oxygen consumed in breathing, 3 Respiratory action, 3
Origin and regulation at nerve center; Transmitted to r. muscles produces breathing; Oxygen absorbed by the blood and carried in the circulation oxidizes the impurities, which are expelled largely in the carbon dioxide of the exhaled breath containing 2 or 3 per cent, of that gas, 3 Respiratory system, 2
Purpose to oxidize the organic matter of the body and accomplish its removal in form of carbon dioxide in the exhaled breath.
S
S.) Salts, in chemistry, 61 Saturation of air (See Hygrometry) Scale of air, in ventilation, 260 Secondary splitting, 235
Diagram of s. s.; Formulas,
general spUt potential and
gen. tandem potential;
Illustration of s. s., 236;
Index
Examples, 237-239; Primary and s. pressure, 239; Symbols, 236
Secondary splits, Primary and, 219
Shaft columns, in ventilation, 168 (See Air C.)
Slope mines, Natural ventilation in, 162
Shaw gas machine, 297
Single-entry system, in ventilation, 263
Solids, 23; Conduction of heat in 8., 52; Standard for s.,
Solution, Solvent, 48
Specific, Meaning of the term: S. gravity; S. heat; S. volume; S. weight; Relative measurements referred to adopted standards, 28
Specific gravity, 30
Definition; General formula, 30; S. g. of substances (table), 32; Finding s. g. of gases, liquids; solids — formulas, 31; Use of s. g., 33; S. g. of mixed gases; Calculation, 40; S. g. caluclated by law of diffusion; Formula, 41; S.g. of mine gases (table), 89
Specific heat, 54
S. h. per gram-molecule is molecular h., 47; S. h. of a substance is its relative h. capacity, 54; S. h. of solids, liquids,. gases (tables), 55; S. h. varies with temp., 56
Specific measurement: Elements the basis of relative m., 30; Relative m. shown by chemical equation giving mol. wts. and vol's., 63; Rel. vol. of a gaseous
atom the unit of vol.,
of air expressed by ratio
of actual vapor pressure
to the saturated v. p., 74
Specifications, by Bureau of
Mines:
Permissible breathing apparatus, 148 (SeeB. A.); P. electric mine lamps, 319 (See E. M. L.); P. mine safety lamps, 288 (See L., M. S.) Splitting the air current, 218, 260
A. splits, 258
Effect of s. on mine potential, 203; E. on mine resistance, 245; E. on quantity, 245; E. on velocity,
Equal splits; Illustration, 223; General mine potential, 213; Ex., 214
Formulas Split potential, 204; S. power and s press, pot., 211; General tandem power and press, poi's. 216; Summation of split pot., 222; Sum. of pot's in secondary s., 237; Advantage in sum. of pot. values, 227
Natural division of a., 220 Ex., 224, 225-230; N. s.; Proportionate s., 219
Need of s. the a. c, 218; Method of s., 219
Practical conditions, result of s., 243; Ex., 245
Primary and secondary ,
Proportionate division of a., 230 (See Regulators) ; Ex., 232
Index
Splitting the air current :
Quantity y Increase of, 219; Q. proportional to number of splits, 243 Theoretical considerations in
s., 242 Unequal splits, illustrated, 224 Spontaneous combustion, 58 Cause of explosion, 127 Standards, Comparison of, 30
Air, hydrogen, water 30, 31 S. for gases; S. for liquids and solids, 31 Static force, 25 Steam, 82
Definition; Saturated s.; Superheated s., 82 Diagram of heat and temp.
curves, 83 Steam tables (Marks and Davis), by permission of publishers, Longmans, Green & Co., 84, 86 Stone Dust (See D., Shale or s!) Stoppings, in mine ventilation, 249 Stokes alcohol lamp, 284 Sulphuric acid, 61 Symbol, Chemical, 58 S. of a molecule, 58 S's in mine ventilation, 192
Tables:
Circumferences and arecus of
circles, 391 Conversion of compound imits,
Weights and measures,
U. S. and metric, 407 Logarithms of numbers, 333 Sines and coins, 353 Squares, cubes, s. roots, c.
roots and reciprocals of
numbers, 373 Tangents and cotangents, 363
Temperature, 43
Absolute t. Bel. to vol. of air and gas, 18; Rel. to press, of air and gas; T., press., vol. of air and gas, 20; Abs. ssero, 18; How t. is measured-two scales, 43; Table, Fahr. and centigrade scales, 44 Mean observed t. dif. altitudes (table), 11; Drop in t. as altitude increases above sea level (table), 12; Rel. of drop in t. to alt. (formula), 13; Averiage t. of atmos. air column (formula,) 14 Volume of air and gas, Effect of t., 17
Temperature of ignition, 117
Table of t. of i. of gases,
Testing for gas, 295 (See Flame Caps) Making a test for gas in the mine, 306; Use of gas indicators (See G. 1.); Use of lamps in t. for g, (See L., Mine Safety)
Thermochemistry, 65
Writing a therm chemical equation, 67, 69
Thermometer scales, 43
Comparison of Fahr. and centigrade s. (table) 44
Time in estimation of velocity and power, 26 Calendar t. — Day: Solar d., Sidereal d.; Month; Year:Index
Solar y. ; Sidereal y. ; Common y. ; Leap y,, 401 Measurement of t.: Sun t.; Sidereal t. ; Equation of t.. Local t.y Standard t., 402; Eastern t., Central t.. Mountain t.; Pacific t.; Civil t., Astronomical t., Transmission of heat, 52 (See H.) Transpiration of Gases from Coal, Relative velocity of t. (table), Triple-entry system, 263
U
Undercast, in mine ventilation, 249, 251
Units of measurement: Special u.; Compound u.; U. velocity; U, work; U. power, 26, 406; Heat u., 51; Kinds of u., 397; U. of ventilating press., 177; U. resistance, 192
Valence, valency, 59 Vaporization, Evaporation, Boiling, 50
Effect of press, on v., 50; B. points of liquids (table) 51; V. takes place at all temp., 24, 80 Vapors and Gases, 24 (See Hygrometry)
Definition of a v., 24
Laws of v., 80
V. saturates space it occupies,
Wt. of water v.; formulas, 79, 80; Diagram, 81
Velocity (See Air Currents, Conducting) Constant v., 25; Acceleration, Ventilating pressure, 174 (See
Mine Ventilation) Ventilation, Mine (See M. V.) Ventilation, Practical, 248 (See Air Currents, Conducting) Distribution of air, 257 (See Splitting the Air Current) Entry systems : Single, Double, Triple, 263; Multiple, e. s., 265; V. of cross*entries, 259; V. of mine stables, 260; V. of longwall workings, 256 Natural v. in slope and dip
workings, 162 Plan of mine (See P. of M.) Systems of V. (see Mine V.) ; S. of mine airways, 262 Volume: Atomic or specific v; Molecular v. ; Avogadro's law of v., 29; Application of L of v., 64; V. of atom, unity, 64 Density and v., 29 Mass, v., density, 24 V. re abs. press., 19; re
abs. temp., 18 v., press., temp., 20 Power, v., press, diagram, 185 Volatile oil flame, sensitive to gas,
Volatile oils, in safety lamps, (See niuminants for S. L.) Give fuel cap in testing for
gas, 271 Light V. o., 308
W
Water: Density referred to air, 31; Unit wt. dif. temp, (table), 34
Index
Water column, Calculation of, 6 Water gage, The Mine, 175
Calculation from m. potential,
Equivalents in measurement,
175, 1S5; Diagram, 184 Reading the w. g., 177 Scales, Dif., 176 Use of w. g. in the mine; What it shows, 178 Water vapor (See Vapors and
A property of matter, 22 Atomic w., molecular w., 59 W; of air: Formulas, 4, 79, 80; Dif. altitudes and temp. . (tables), 11, 16; W. of elements (table), 28; W. of substances (table), 32; W. of water, dif. temp., 31, 33; W.of oils (table), 33; W. of woods (table) 34 Weights and measures, 397
Systems in use; Standards of weight, length, capacity,
Weights and measures:
U. S. and British systems, 398 Calendar time, 401 Measurement of time, 402 Metric system of w. and m., 403; Metric abbreviations, 406; Conversion tables, 406; Compound units, 411 Wet-and-dry bulb hygrometer, 72
(See H.) Whitedamp (See Carbon Monoxide) Wire gauze: Cooling effect; Principle of w. g., Standard mesh, 269 Windy shot, in blasting, cause of explosion, 127 Wolf safety lamp, 285; Flamecap diagram, 303 Wood, Wt, of dif., (table), 34 Work:
Internal w. due to expansion of air or gas, calculated in two ways, 20, 21 W., in mine ventilation, synonymous with **power on the air/' 182
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