13. Mining and quarrying have types of peculiar hazards such as fall of roof and explosions. The former can largely be elimi nated by proper timbering. Explosions are due to different causes. Float dust containing to per cent. or more of volatile matter is very explosive when brought in contact with a naked flame. It should either be wet down or covered with stone dust. Fire damp and 0) explodes either from a naked flame or a shot. Danger from CO in old workings can be readily de tected by the use of canary birds (Fig. 102). Many explosions of dust or fire damp are due to the flame produced by explosives. Accordingly the so-called permissible explosive only should be employed. These do not produce a big flame. Miners should not tamp down charges of explosives with metal rods, due to the danger of premature explosions. Charges should be fired from a central switch after all men are checked out from the mine. Fire danger can largely be eliminated by the use of safety lamps and the protection of the shaft (Fig. tor). Addi tional dangers encountered are from collisions between cars and lack of clearance between the cars and the wall, and also of electrocution from low overhead trolley wires.
14. Air air pressure is only encountered by the "mud hogs" in caissons, in whom rapid decompression may produce the condition known as the "bends." This can be avoided by their gradual decompression in the air locks. (Fig. io3).
Is. Fire hazards are numerous and varied. They are affected by the inflammability of the building or of raw mate rials stored therein. Fire escapes should be adequate for the number of individuals in the building. In this connection we may call attention to the fact that the stair escapes permit more rapid escape from a building than the ladder type. They should preferably be built along a blank wall and connected to windows by platforms. Regular fire drills at unexpected moments will do much to permit an orderly exit when danger threatens. Lack of judgment in the location of the stair wells and elevator shafts frequently does much to spread a fire and prevent the escape of the inmates. If exit doors open outward
their jamming by a panic stricken crowd will be largely pre vented. Fire risk from inflammable or explosive gases will be much lowered by adequate ventilation. Automatic sprink lers will usually keep blazes from spreading, and extinguish them in their incipiency.
16. Electrical installations offer many opportunities for accidents of a serious character. Danger signs should be freely employed and dangerous parts of ment should be painted red. Only experienced and competent men should be allowed in rooms where dangerous apparatus or wires are installed, and no man should be left alone with a high tension current. Floors that are in dangerous proximity to wires at high tension should be covered with insulating mats. No repairs of mains or wires, or examinations or altera tions should be permitted while they are under a high tension current. Switches should be provided with tell tale lamps, and when a switch is thrown open it should be tagged, and the switch kept open until the completion of the necessary work has been reported. Workmen should take the same precautions with dead apparatus that they do with live apparatus. Rubber gloves should be worn and the sleeves kept down. When working on the primary side of transformers, switchboards etc., only one hand should be used. Plenty of free room should be maintained about the switch boards and their backs should be enclosed. All motors, generators, transformers, etc., should be guarded and also provided with insulated platforms. Termi nals, brushes and connections should be so situated that they will not be accidentally touched.
17. The most important factors in the production of indus trial accidents are the following: (a) Carelessness.
(b) Poor light.
(c) Unsuitable clothing.
(d) Cluttered up factories.
(e) Lack of safeguards.
(I) Fatigue, and (g) Overcrowding of the workmen in the shop.