Information Circular 6056: Prevention of Accidents With Explosives in the Tri-State Zinc and Lead Ore Producing District
Information Circular 6056: Prevention of Accidents With Explosives in the Tri-State Zinc and Lead Ore Producing District by United States Department of…
Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.
a es m6 7 22S <4i, Circular No. 6006 (¢q7_ sted January, 1928.7 cle Deals das ce L. TOT CIesorITR
DEPARTMENT OF COMMERCE BUNMAU Ch MIND
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PRIVSUTICN OF ACCIDENTS WITH EXPLOSIVES IN THE TRI-STATS ZINC AND LEAD Crs PRODUCING DISTRICT
By Se P. Eewell* introduction
Premature explosions and misfires are responsible for a large majority cf the accidents resulting from the use of exnlosives in the Tri-State' zinc and lead ore producing district. Accident Prevention Bulletin No. 56, issued by the Tri-State Zinc and Lead Cre Producers Association, shows that 6 fatal accidents in 1925 and 7 in 1926 were caused by handling high exnlosives and detonators. Analytical study of these accidents shows that 6 of the fatalities were due to premature explosions, 3 occurred wnile holes were being loaded, 2 were caused by picking into failed shots, ani 1 was the result of a dormant snot. However, accidents that occur while a hole is being loaded are premature-#xolosion accidents in the broader sense, while those classed as "nicked into failed shots" end -"explosion of dormant snot" are really due to misfires; hence 12 of the 15 fatalities may be ascribed to one or the other or these two general types of accident. In view of this preponderance, the following discussion of means cf preventing explosives accidents will be confined chiefly to these caused by premature explosions and misfires.
The observations concerning blasting practice unon which this paper is based were made in March, 1627, during a visit to the Tri-State district while the author was assisting in an accident-prevention campaign. arrangements made by R. V. Ageton, accident-prevention engineer and the courtesy of mine officials enable him to inspect 10 mines in the district with F. H. Nesbit, assistant accident-prevention engineer, and to confer with other accident-prevention engineers, superintendents, ground bosses, powder men and machine men, individually arc in grouse The full cooperation accorded by each of these individuals and ground is gratefully acknowledged. :
CONDITICUS SURROUNDING THS USE Cr EXPLCSIVES IN THE TRI-STATS DISTRICT General Practice The snafts of the mines visited are 220 to 348 feet deen. The principal Ores mined contain galena and sphalerite in a flint gangue. The minerals are
eitner disseminated or occur in veins, veinlets, or vugs.
Sa a a a Explosives Engineer, U. S. Bureau of Mines.
er AD x
Inf,cir. No. 6056. Cre is mined by the underhand-stopins metnod and the ai
ri times of blasting may ve classed as "drift," "pull drift," "slabbin;," st
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ne and "split," holin:.
ane so-called "drifts" are driven at or near the top of the ore body and are the pioneering cuts above tre stones. The "drifts" are not as accessible as tne "pull drifts," Dut holes can often be placed to greater advantage becouse of the wictn of tne free face.
The "null drifts" correspond to the main drifts in otner metal-mining districts. One such "pull drift," 6 feet by 6 feet was blasted witn fourteen 6-1/2-foot holes using the 4-hole pyramid cut. The 3 lifters eacn contained tyre "sots" (primers). One 50-pound case of 69 per cent gelatin dynamite was used in tne 4 cut and 4 reliever holes, and one 50-pound case of 40 per cent gelatin in
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tne S oac'zs holes and @ lifters. The holes were wet.
The usual depth of "drift" holes and "null drift" noles is 9 feet.
Stone rounds are used on cr near the bottom of the stone and normally vary from 1 to 5 holes per round, are up to 16 feet deep, and their placement depends largely on the height and shane of the unbroken rock. Tne lower holes nceint slightly downward. Stope noles are "squibbed" or enlarged by preliminary smaller dynamite cnarses if the burden requires it or if tne rock can not be otnrerwise broken without forming bowlders. Otherwise, holes are loaded "slice," that is, witnout being squibbded.
A very high stope may require holes called "splitters" between the drift and stope holes. These splitters are drilled, squibbed, ard blasted similar to stope holes. Many stope and splitter holes are wet, altnough certain mines nove few wet holes. Splitter holes are squibbed if the curcen is great or tne rock difficalt to blast.
he time between the preliminary squibcoing shots ard between tne final squibdoing shot and the primar; blast was standardized at 24 hours in one imine visited.
The larger bowlders are broken by blasts in short block holes.
Because of crevices and cavities in the rock the drift holes, splitter holes, and stone holes are frequently ragged, and unless care is taken in cherging, the cartridges may fall into these openings. In drilling, tne rocx often crumoles 6asily, especially at and near the collar of the holes, so that tne collars are mich enlarged. For example, tne collar of one hole was cval in sec-— tion, 5 inches wide, and 12 inches lonz; cther holes were smecoth threugnout and could be easily charged by simply pushing the cartridge "nome." In mest mines the larse percentage of ragged holes necessitates the "leading in" cf? sinsle cartridzes and of the "shot" by placing them on the conner snake of a ccnoer-Terrule: pine taming orr. When thus placed in position the cartridges are jammed firmly witn tne wooden end of the jamming bar.
' InfiGir.s Nol 6056.
At the nines sys tea: eee men.or mache men. charge the holes and spit the: fuse... Se are pee ae Shit: once. in order that a nigh density of loading can be procured.: sh aes ae
7 "The mines of this district generally use Le1/4-Anch hollow drill steel, 'thoush one mine uses 1- 1/8-inch, and -some.mines use some. l-inch as well.as other sizes. In-one mine the steel used for drilling. stone and. "solitter™ holes is 2 to 20 feet long, by 2-foot increments, while the gaze diameter of the drill dit varies from 2-3/4-inches for the started-to l- 5/8 inches for the finisher ty
1 8s inch increments. For shorter holes the finisher has a 6280 of 2-1 1/2 inches. 'Water drills' are used," and wet oeerian pee : aa 38
- Screen Bettas are aaa. 'by. some machine men and their helpers while es and rowan out. nOsESS et RUN ai a uaiaei os ae a.
The Explosives
- Gelatin, extra essnblins and ammonia dyiamives of 33 and 35. per cent grades, and gelatin dynamites of 25, 30, and 40 per cent grades in l- 1/4-inch -diameter are commonly used. However, some 20-60 per cent gelatin dynamite is used, the latter in cut holes and relievers in "pull drifts," and a very small proportion of. the explosive is in 1-1/8~inch diameter cartridges. Explosives are used fresh, deliveries being made at'not more than one-month intervals. The district is particularly fortunate in this: respect, and the practice is a direct result of three of the four manufacturers who supply explosives to. the district having plants nearby. The explosive is delivered 1, 2, 3, or even 6 times a week from manufacturers! or jobbers! distributing magazines to some individual mines. the largest delivery to. one mine.that was noted was sixty 50-pound cases. Gelatir dynamite is commonly used in wet holes, in places where there was inadequate ventilation, for squibbing, and at some mines for"shots' or primers. when the main charge is ammonia dynamite. If deliveries are frequent the explosives are commonly brought by the manufacturer or jobber to the collar of shaft, where they ars promptly taken underground in the cre "cans,". each. accommodating about ten oO-pound cases. They are stored in a dry place as far from the shaft and working place as is feasible. Larger deliveries are made to outside magazines from which daily deliveries are made underground. The district uses aporceximately 8,000,COC ee of mae eeeeos eS mee bg Ph tig oe
The Beton cee
No. 6 detonators are used in"shots' or primers of ammonia dynamite and at some places in"shots"of gelatin dynamite. -Some mines use No. 8 detonatcrs exclumee in aaron eee
The Fuse a th Hep Bal Ghee fe age
Spas with a rated oe speed of 40 se genie per eb is extensively asec but in some mines the: fuse used has a rated burning speed of 30 seconds. Both brands employed 'are designed for use in very wet work.. Fuse was received
3637 oe a ais
Inf.Cir. No. 6056.
standard length of fuse, although a scale cut on a bench wes sometimes used. Fuse used in dependent shots was trimmed about 5 inches. Fuse was spit witha carbide lamp. Blasting during the shift is infrequent and is discouraged.
Canoed fuse is commonly made up at primer stations either above ground or underground by crimping the detonator on the 6-foot to 10-foot measured fuse with hand crimpers. One bench crimper was observed in use underground.
in coils, each containing two 50-fcot lengths. It was commonly measured by a
Primers "Shots" )
"Shots" are made in a Variet: of ways. Usually the detonator is placed iz cne end of the cartridge so as to be isolated from the copper spike of the tampir: bar, which is inserted in the opposite end of the"snot! Where no "shot tube" is used, the fuse is secured in place by tying the loosened paper of one end of the cartridge around it with cord (see fig. 1) or by lacing the fuse tnrouch the cartridge. Where the McLaughlin & Anderson'shot tube! (see fig. 1) is used the detonator is commonly placed in the end of the cartridge near the wooden plug.
The hole in the center of the plug does not go through the plug by 1/4 inch, thus isolating tne detonator from the copper spike of the tamping bar. When the Chica. type of "shot fic. 1) is used the detonator is commonly placed in the fe: end of the cartridge so that the detonator is at least 4 inches from tne copper spike of the tamping bar. The writer's observation was that the fuse was laced througn less tnan half of the "shots" used in the mines visited. In all instance: noted save one the fuse emerge from the side of the end of the"shot') permitting tne spike to te placed in the opposite side of the end of the"sact'!protecting the fuse from the tamping bar. In all holes of primary blasts the detonator was pointed toward the bottom of the holes. In all -lasts noted in which there were dependent shots the primer was placed near the bottom of the hole, thus preventing tne fuse from being cut by an overbreak. In squibbing and in single stope holes the primer was at or near the tcp of the charge. 7
Many powder men prefer to use gelatin dynamite in"shots' because these are easily made with plastic explosive.
Stemming
Stemming was not used in any holes. One mine reported unfavorably on the use of stemming after a triel. It is noted, however, that two of tne larger mining companies plan to use stemming in all of their mines. Tris is, of course, the best practice.
Sevsnting Mispires
aS previously noted, 3 fatal accidents in two years were caused by misfires. These can not be attributed to aged and therefore insensitive exnlosives because explosives in this district are very generally used in a fresh condition. The fuse is likewise of high quality. The writer believes that when fuse is used misfires can be largely, if not wholly, prevented in any metal mine using hish- . grade explosives and blasting supplies (a) if prover standard primers (shots) are adopted; (b) if care is used in preparing the charge and preparing and charging
cE SFL ee ER Se ee gee
4637 45s
Strong tied firmly
ch ay Z Cartridge a
Detonating composition
etonston
Primer (Shot) without shot tube
Wooden plug cf shot tube glued in place Detonating composition McLaughlin and Anderson shot tube
N
Cartridge
Ye Cardboard tube
!
Bs
_—2e- ais a — Sad wor — a e5wr ste oe EIN - oa — oom
— Detonator Hole in plug to accommodate copper spike of tamping bar
Primer (Shot) made with McLaughlin and Anderson shot tube
Cartridse Cardboard tube
rd
Detonating composition
Cardvoard cup glued in place
Primer (Shot) made with Chicago shot tube
Figure 1. - Primzrs ("Shots")
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the holes; (c) if steaming is used; (a) if Mo. 8 cetonators or electric detonators are used in primers made with gelatin dynamite which is not fresh; and (e) if "snots" in dependent holes are placed near the bottom of the charge.
In this district, wnere a substantial proportion of the noles are raezced or intercept crevices or pockets, the use of "shot tubes" (see fig. 1) seems desirable as a precaution against misfires. Several hundred thousand"shot tubes!' have been successfully used. At a given mine the "shot' should be standardized so that these conditions prevail: A single tyme of tube; fuse not laced through cartridges fuse emerging from side of end of cartridge; "business! end of detonator in center line of cartridge; detonator points toward bottom of hole; at least 4 inches between detonator and copper spike of tamping bar; and the inside diameter cf tube to fit primed cartridsze fimaly but not closely cr tightly. These conditions are fulfilled if"shots' are made as shown in Figure l. 7
The end cf the fuse to be inserted in the detorator should be cut off squarely with a sharp knife and the freshly cut end inserted in the detonator so as to touch the detonating composition gently.
Detonators may be crimped on the fuse with hand crimpers which are in good condition. The greatest uniformity in crimpitg obtains, however, if bench crimpers are used and operated by a trained man esvecially assigned to the jcb.
Fer use in wet work, the frse at, and for a few inches above, the detcnator should be covered with a waterproofing compound, such as P. and 3. paint, Kapseal, and Celakap but not with oil or liquid grease.
In very wet work delay electric detonators with enameled copper legs should be used in dependent shots
Tae greatest assurance against misfires obtains when electric detonators er delay electric detonators are used.
Before being charged the holes should be cleaned cf loose material. This may be done by blowing out the residual cuttings or by scraping sut smooth holes. Locse material in a borehole may promote misfires dy so separating cartridges that the wnole charge is not detonated. high charging density can be attained by firmly tamping the charge with short firm taps with a wooden jamming bar. Several cartridges of moist, fine stemming, such as moist plastic clay, should be used in each hole of primary blasts. This prevents misfires by securing the explosive in place. In another mining district the writer nas ovcerved cartridges on the muck pile which had been pulled cut of a hole by the blast from a previously fired hole of a round, even though two cartridges of poorly tamped stemming were in the hole. In this case the fuse of the dependent hole had not been svit. Had it been spit the ejected cartridges would have been buried in the mick vile. Such blasts would, on occasion, with unstemmed holes, displace or eject the "shot" or primer and cause amisfire. Among its other advantages stemming should be used to reduce misfires.
TNT Gite, 466. 6006.
In general, No. 8 detonators are recommended for use with 'shots! or primers that are made with gelatin dynamite, tut under the specially favorable conditions obtaining in many of the mines of the Tri-State district,.No. 6 detonators anne r to be wholly satisfactory for use with g¢latin'"shots These special conditions are: The use of fresh gelatin dynamites; the storage of the detonators above g¢rcuri in cool, dry places; and the use of 'shot tubes' in holes that are difficult to charg a,
"Shots! should te placed far enough into the charge of a dependent hele so that, snould tha hole be cut off, the powder core of the fuse will be burning beyond the point of cut off.
Provsnting Accidents While Charging And From Pasmature Explosion
Premature explosions may result from improper methods of opening boxes cf explosives. They should te opened with wooden tools, sucn as wooden wedges and wooden mallets.
Assuming that fresh explosives and hish-grade blasting supplies sucn as are used in this district are employed, accidents durins charging and from premature explosion can be prevented by care in charging bjyr a standard metnoc. The use of "shot! tubes makes it possible to place the "shot" in earety. for they not only prevent the "shot! from falling into crevices and chambers or getting crosswise of the hole but hold the detonators in rlace in the cartridge. sAt a given mine a standard "snot! should be adopted and used in all "drift," stope, and "snlitter" holes, In mines free from ragged holes"shot tubes'need not be used. In any event, the fuse should be so secured that the detonator is anchored in place in the center line of the cartridge and at least 4 inches from the copper spike when placed in the cartridge. The "snot"and the cartridges immediately following it siiould be placed in the hole carefully. Other cartridges should be pressed home firmly but never forcibly. The spiked end cf the tamping bar should be used only for leading in the cartridges and the "shots tamping snould be done only with the wooden erd cf the tarmping bar. Explosives should be protected from snarxs and flames; thus, fires, open lights or smoking should not be permitted near explosives. Tue roles should be charged Just before firing time. Stemming snould be used. From the time the charging of holes is begun until they are fired all cther work near the kKcles snould cease. Only those required to charge and tamm the noles should be permitted near the holes, and they cnly while engaged in the work. No matter new remote the probability of a premature explosion, tne minimum number of persons snould be in the danger zone e~-Information Circular, Bureau cf Mines, Department of Cornmmerce.
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