7 8 8 9 10 11 12 FIGURE 1. Miner resting and smoking in place used as a powder magazine. 2. Crimping a "cap" with the teeth- —a dangerous thing to do........ 7. Detonator and fuse in primer.... 8. Careless miner punching hole in cartridge with candlestick attached 9. Miner taking dynamite cartridges from underneath his shirt where 10. Hot-water device for thawing dynamite... 11. Dynamite thawer made by filling excavation with manure.. 43591°-14 3 IN METAL MINING. By EDWIN HIGGINS. INTRODUCTION. Next to falls of rock or ore the use of explosives causes more deaths in the metal mines of the United States than any other source of accident. A study of the table on page 15, compiled from figures printed in Technical Paper 61 of the Bureau of Mines, will give an idea of the great number of accidents caused by explosives. It may be noted that the number killed by explosives is second only to the number killed by falls of rock or ore; that serious and slight injuries caused by explosives are far less numerous than injuries received in haulage accidents; and that many of the accidents from explosives are fatal. This circular is published by the Bureau of Mines to bring to the attention of the metal miner the chief causes of accidents from explosives and to suggest ways of preventing them, for there is no class of mine accidents that the miner can do more to prevent. If the miner will remember the nature of explosives and will use care in handling them, he and his fellows will be in little danger of accident. Some miners as they gain knowledge of explosives grow more careless. For this reason many records of fatal accidents contain the names of experienced miners. SOME FACTS ABOUT DYNAMITE. The word "dynamite" used in this circular means that class of explosives in which nitroglycerin is absorbed in or is mixed with other materials. Ordinary dynamite consists chiefly of a mixture of nitroglycerin and such materials as wood pulp, sawdust, or some mineral substance. By the use of different materials and of different methods of mixing, different kinds of dynamite are made, such as the ammonia, low-freezing, gelatin, and granular dynamites. Ordinary dynamite of different grades freezes at 40° to 50° F., but the specially prepared low-freezing dynamites may be used in temperatures above 35° F. without freezing. When heated to about 200° dynamite explodes from a shock or blow. Dynamite also explodes from a shock or blow at ordinary temperatures, but the violence of the shock or blow required to explode it becomes less as the temperature increases. When dynamite is heated to 350° or 400° it explodes from heat alone. When not confined, a small quantity of dynamite usually burns without exploding, but if a large quantity of it is burned, even in the open, it is likely to explode. Although dynamite when burned in air does not always become highly heated, the experiment is a dangerous one to try. Frozen dynamite is difficult to detonate with a "blasting cap," but it is very likely to be exploded by friction such as is produced by punching a hole in it with a metal skewer or by cutting it with a hatchet or ax. Dynamite (especially 40 per cent and stronger) may lose strength if repeatedly thawed and frozen. If dynamite is exposed for a long time to a temperature of 90° or higher it becomes more sensitive to shock and may lose strength. Nitroglycerin is readily taken into a man's body through the pores of the skin; it then makes the heart beat faster and usually causes headache in persons not accustomed to it. STORAGE OF DYNAMITE. In large mines the storage of dynamite is a problem for the management; therefore the following remarks apply to small mines or prospects, where the miner himself must take entire charge of explosives. When storing dynamite on the surface, it is often best to use as a magazine an abandoned drift or other opening on a side hill near at hand; if none is available one can easily be made. Brick or stone buildings are suitable, but are not so cool in summer as an underground storage place. Avoid the use of wooden structures of any kind, for they are liable to catch fire and are often used as targets by thoughtless hunters and others. In selecting a storage place remember that exposure to the heat of the summer sun may make dynamite sensitive and will in time cause it to lose its strength. Surface magazines should be well drained and the ground around them cleared of all dry brush and timber. They should be provided with a lock and key and should have an easily seen signboard showing that dynamite is stored there. If no suitable place can be provided on the surface small quantities of dynamite may be stored underground, in a remote or separate part of the mine where an explosion will be least likely to endanger men at work. Such a storage place should be dry and the door should be fastened with a lock and key. Never store large quantities of dynamite underground. Keep nothing but dynamite in the magazine. Caps, fuse, matches, candles, or refuse of any kind in the magazine are sources of danger. Caps and fuse should be kept in a separate place at least 50 feet away from the dynamite. Dynamite boxes should be laid flat, right side up, and so stored. that the old stock will be used first. If different grades are in use, keep them separate. If the magazine is warm, the dynamite boxes should be turned over, say every two weeks, to prevent the nitroglycerin from settling in the ends or sides of the cartridges. Do not smoke nor carry lighted lanterns, candles, carbide lamps, or torches in the magazine. If possible the key to the magazine should be intrusted to only one FIGURE 1.-Miner resting and smoking in place used as a powder magazine. HANDLING OF EXPLOSIVES. BLASTING CAPS." 'Blasting caps" (detonators) are charged with fulminate of mercury, which is one of the quickest and most powerful explosives. It is poisonous and very liable to explode from heat, shock, or friction. The explosion of an ordinary "cap" will tear a hole in a board about an inch thick, or it will blow off a man's jaw, or tear his hand to pieces. Never open a box of "caps" or remove the "caps" with a wire or nail. 'Caps" should not be scraped with any kind of metal or examined near an open flame. They should not be carried loose in the pocket, |