TABLE 2.-Accidents from explosives in metal mines at all underground mine operations 1

1 Adams, W. W., and Kennedy, F. J., Metal- and Nonmetal-Mine Accidents in the United States, 1942: Bureau of Mines Bull, 461, 1944, 81 pp.

2 Preliminary totals.

TABLE 3.—Accidents from explosives in metal mines at all open-cut
mine operations 1

1 Adams, W. W., and Kennedy, F. J., Metal- and Nonmetal-Mine Accidents in the United States, 1942: Bureau of Mines Bull. 461, 1944, 81 pp.

2 Preliminary totals.

accidents have a high severity rate. Mining companies of all classes entered in the National Safety Competition from 1925 to 1935, inclusive, reported 819 explosives accidents. Of these, 9.5 percent resulted fatally; 1.1 percent resulted in permanent total injuries; 7.6 percent resulted in permanent partial injuries; and 81.8 percent resulted in temporary injuries. In the metal mines of California, 18 nonfatal accidents from explosives during a 6-year period cost $115,205 in compensation and medical care, or more than 19 percent of the total cost of all accidents.7

6 Fene, W. J., A Study of Explosives Accidents Reported to the National Safety Competition, 1925-35: Bureau of Mines Inf. Circ. 7038, 1938, 23 pp.

7 Ash, S. H., Explosives Accidents in California Metal Mines: Bureau of Mines Inf. Circ. 6725, 1933, p. 5.

FIGURE 1.-Frequency rates, fatalities, and injuries from explosives.
underground and open-cut metal mines, 1931-43.

COMMON CAUSES OF EXPLOSIVES ACCIDENTS

Because accidental detonation of explosives can occur in so many ways and under such unexpected circumstances, constant care and precaution in their handling and use are essential. Men should be selected for blasting crews who are known to be careful and willing to follow instructions; they should be instructed in the safe handling of explosives in accordance with the safety rules established by the explosives-manufacturing companies or the safety codes of industrial organizations. Close supervision of men working with explosives will eliminate much of the common carelessness that has been the greatest cause of accidents.

EXAMPLES OF COMMON ACCIDENTS

The following examples of the most frequent unsafe practices in blasting and misuse of explosives have been taken from the reports of accidents from explosives that were investigated by the Bureau or State mine inspectors.

In a number of accidents that caused permanent disabling injuries, detonators exploded when the fuse was forced into the detonator barrel by pressure and twisting. The detonators had been carried or stored loose, and foreign matter had probably lodged in the barrel. In these cases there was carelessness in the storage and transportation of detonators before use.

A miner attempted to force a primer cartridge to the bottom of a drill hole after it had become wedged in the hole. Pressure with a wooden tamping stick caused the primer to explode. Unless a detonator is well-centered in the cartridge, the end may be forced against the rock in the hole and exploded by hard tamping, even with a wooden stick.

A blaster was springing some drill holes with single sticks of dynamite and detonators with fuse 2 to 3 feet long. A premature shot permanently crippled the blaster, who either had cut the fuse too short or had held the primer too long before dropping it into the hole. Test pieces from the same roll of fuse revealed a uniform burning rate. Using short fuse is dangerous; the fuse should be long enough to extend at least 1 foot outside the hole when the primer is in place.

A yard crew was blasting slag, using mudcapped shots. The man lighting the shot was killed and two others were injured when a premature shot occurred. The fuse lengths used were 10 to 15 inches, and it was said that the blaster had believed this length would give plenty of time to reach a safe place. Use of less than 30 to 36 inches of fuse under any circumstances should be considered dangerous.

Two men were killed in blasting a round in a shaft bottom when they overstayed the burning time of the 6-foot fuse. The round consisted of 19 holes, and on this day the miners had trouble in lighting the fuse and delayed even after an urgent warning from the foreman. The use of fuse in shaft work is inadvisable, and 6-foot lengths are too short in such places. These men also held the belief that fuse burned at the rate of 1 foot a minute.

A miner was killed and another permanently disabled when they remained too long in lighting a round of 29 holes in a drift. Four men were available, but one man lit the fuse while another spit them. The original length of the fuse was 7 feet, and 2 to 18 inches were trimmed to time the holes. The place was wet, and 2 fuse lighters were used in succession. The holes started to go off as the spitting was completed. This was unsafe blasting practice by experienced miners who were not given necessary instructions or supervision to cope with abnormal conditions.

Two instances of disastrous explosions in well-drill holes occurred during loading. In one case, 60-percent gelatin dynamite had coated the ragged sides of the hole when cut-up cartridges were dropped in to fill the cavity made by springing. Detonation occurred when a metal weight was lowered into the hole to measure the height of the charge. In the other case, a large cartridge of 75-percent gelatin dynamite stuck in a ragged hole and was detonated by pounding with a wooden tamping block.

Two miners were permanently disabled when they drilled into a "bootleg" containing explosives. In this case the hole was started near but not in the "bootleg.' In another mine a miner was killed and his helper partly blinded and disfigured when they started a hole in a "bootleg" which proved to contain unexploded dynamite. These instances could be multiplied at length from the accidents due to this cause that are reported in 2 or 3 years' time. Failure to find and detonate explosives in missed holes or "bootlegs" is a prolific source of fatal and serious accidents.

A miner was fatally injured when he returned to a crosscut face in which two holes were being blasted. Some other holes were being blasted nearby, and although this man had helped prepare the shots, he confused the reports and returned through smoke to the face just as those shots went off. In this case company rules against returning before a safe interval were violated.

A bomb on a blasting pole was placed in a raise over a grizzly to blast down the hung-up muck. The bomb and pole fell through the grizzly to an empty chute below, where the bomb exploded, killing a miner stationed there to guard the chute during the blast. This man did not stand in a safe place, as he should not have been in front of the chute from which an open raise led directly to the blast.

Three miners were killed by the explosion of 140 sticks of dynamite in a sack from which a round of 24 holes was to be loaded. One of the three men was preparing primers, and the explosion occurred when one of the capped fuse lengths was accidentally ignited by a carbide light. Similar accidents have occurred so frequently that there is serious doubt as to the safety of preparing primers in the close vicinity of other explosives, especially when carbide cap lamps

are worn.

While reopening some old workings, a shift boss connected the leg wires of a loaded slabbing hole to a firing line and caused an explosion which killed him and injured another miner. A battery which the foreman had attached to the wire circuit in order to use it for signaling had not been removed. The foreman failed to follow the usual precautions in connecting electric blasting circuits.

A grizzly man returned to a grizzly chamber where he had prepared some shots to break large boulders and had connected them to the section firing line. He was killed when others put in the switch to shoot the blasts prepared in the section. The victim had failed to notify others of his return after having told them he was leaving, and the others failed to make sure that no men were in the places to be blasted.

EXPLOSIVES ACCIDENTS REPORTED TO NATIONAL SAFETY COMPETITION, 1925–35 The following classification shows the prevalence of different kinds of explosives accidents reported to the National Safety Competition by metal and nonmetal mines in an 11-year period:

TABLE 4.-Explosives accidents reported to National Safety Competition, classified by type and location of accident; 1925–35 1

1 Fene, W. J., A Study of Explosives Accidents Reported to the National Safety Competition, 1925-35: Bureau of Mines Inf. Circ. 7038, 1938, pp. 16 and 17.

The pertinent facts of 106 explosives accidents on which reports were received by the Bureau of Mines from 1940 to 1944 are summarized in table 5. This table includes the reported explosives accidents from all types of mines, except coal mines, from quarries, and from related construction and other miscellaneous activities. The reports received were from all parts of the country and should be representative of explosives accidents in metal mining and related activities.

360

32

482