depending on the probable pressure head of the water. Accurate maps should therefore be kept and filed by the company concerned and, when a mine is abandoned, by the State inspection department, so that at any future time knowledge may be obtained by a mining enterprise which proposes to begin development near by in the same or in lower coal beds.

Prevention of rushes of surface material requires care in laying out the mine and proper supervision of work. Another requisite is accurate information as to the thickness and character of the overburden, especially where water may saturate overlying silt or gravel.

There have been many narrow escapes from mine inundations in various coal fields where flooded streams rose suddenly and the mine entrances had been placed too low. Obviously, such accidents can be prevented by filling in around the entrances to a level well above the high-water mark.

OTHER MISCELLANEOUS ACCIDENTS

Falling timber other than that incidental to falls of roof injures a large number of men, especially in the anthracite district. Such accidents occur mainly in pitching beds, where it is most difficult to maintain posts or props. Here, again, care in putting up the props and in subsequent inspection will lessen accidents.

Other kinds of miscellaneous underground accidents, like those caused by machinery, especially coal-cutting machinery, the use of hand tools, and falls of persons add a few deaths to the mortality roll annually and many more to the list of injuries. Some of these accidents, except those due to poor lighting, might occur just as readily on the surface as underground. There is no general remedy but care and close inspection by the company.

Many men are injured and some are killed by the undercutting chains of mining machines. To avoid these accidents the mining company must give special attention to safeguards on the machines and to instruction of the machine men. Permanently installed machines, such as underground hoists, can and should be surrounded with guardrails and fences.

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ACCIDENTS IN SHAFTS AND ALONG SLOPES

Shaft and slope accidents constitute only about 2 per cent of all mine accidents, and the largest number of these are caused by persons falling down shafts. This type of accident, with the rarest exceptions, seems entirely unnecessary and is usually due to not having proper fences and protection gates at the top, at landings, or on cages used for hoisting men, or else to the individual's failure to use them. As many as 27 men were killed by falls in 1920. It is desirable to make the guard gates of an upper shaft landing automatic, operated by the cage or skip. The ground landing gates can be made to lock automaticlly except when the cage is at the landing. Keps or rests should be used at the shaft landing when cages are used in hoisting men.

SAFETY MEASURES

Effective safety catches that will bring a cage to a stop, if the rope or coupling breaks, within 5 or at most 10 feet, should be used on all cages that hoist and lower men. The catches should be tested with a weight heavier than that of the largest number of men permitted to ride, as the State mining authorities may determine. Tests of the safety catches should be made at least once a month or at shorter intervals if the State requires.

Safety catches designed for operating on wooden guides usually are unsuitable for use on steel guides. The latter require special catches, or else special timbers may be necessary for the safety catches. Wooden guides should be made of wood that is not likely to splinter. Maple and oak are best, but carefully selected hard pine will do. Steel guides made from 75-pound rail or heavier make excellent guides where the water which may enter the shaft is not acid. In this case acid-resisting steel might be used.

In slopes where men are hoisted and lowered in mine cars or special man cars the hazard of rope or couplings breaking is usually greater than in shafts; ropes may become twisted and the wear is greater, especially if rollers and sheaves are not carefully aligned and kept in order.

Rubber-covered sheaves have been found effective in the deep inclined shafts of the South African gold mines, as the rope adheres well and does not slip over the periphery as steel rope that runs on iron rollers tends to do, with consequent cutting effect.

There are several designs for safety catches for use in steep slopes; these clamp on the rails but have been brought into general use.

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Safety man cars have been used in slopes less than 45°. These include one car whose wheels are placed on hinged pedestals at such an angle that when the rope or coupling breaks they fold back, and the body of the car drops on the ties, steel spikes in the bottom of the car preventing it from skidding.

In slightly inclined slopes a special drag-point truck is placed at the lower end of the trip, so that the "drags" will jab into the ties or bottom if the rope or coupling gives way.

Injuries to persons struck by cages or skips in shafts or by trips. of cars on slopes constitute another accident item which seems unnecessary, yet 2 to 10 men have been killed in this way each year. The man injured or killed is usually trying to look up or down the shaft or slope as the cage or trip passes him. Deep refuge holes should be provided for men who have to repair or inspect slopes in slope mines. If slopes are regularly used for travel by men there should be a separate compartment for those who walk.

Overwinding has caused serious accidents. Detaching hooks were formerly used, but the present use of automatic control and brake devices on hoisting engines has virtually eliminated casualties from overwinding.

Accidents from the breaking of hoisting ropes in coal mines have become almost absent because of the high quality of rope supplied by makers and the prompt replacement of worn-out material by operators. From 1917 to 1924, inclusive, only five persons were killed in coal mines by reason of the breakage of cables. The safest rule is to replace a rope used for hoisting and lowering men when it shows wear and a number of breaks appear in individual wires. Frequently such a rope can be utilized for hoisting or lowering material.

SPEED OF HOISTING AND LOWERING MEN IN SHAFTS AND SLOPES

Rapid hoisting is not only dangerous but extremely uncomfortable and affects the morale of men by causing nervous shock. There is little excuse for rapid hoisting or lowering in the comparatively shallow coal mines of the United States.

The speed of hoisting or lowering men is regulated by many of the State laws and ranges from 600 to 900 feet a minute. This rate usually is held to represent the average speed from top to bottom, including acceleration and slowing, so the speed in the middle is much greater; however, the rates of acceleration and of slowing down. are the objectionable features and should be kept under careful control,

In hoisting and lowering men most of the time is taken in getting them on and off the cages. In large collieries double-deck cages,

where permitted by State authorities, greatly increase the speed of handling men, especially if double unloading and loading platforms at top and bottom are provided, as in many deep metal mines and in deep European coal mines; in such mines three or four decks sometimes are used and are loaded and unloaded simultaneously.

The maximum speed of hoisting can be controlled automatically by the hoisting-engine mechanism, but with adequate supervision such control should not be necessary in mines less than 1,000 feet deep; most coal-mine shafts in the United States come within this figure.

Handhold rods or chains on cages are psychologically useful if not strictly necessary when the cages have good gates and the men are lowered carefully and steadily, but the speed should not exceed 1,000 feet per minute. The speed of hoisting or lowering men is more difficult to control in slopes than in shafts. Usually a greater speed is allowed in slopes than in shafts, but there, too, it should not exceed 10 to 12 miles per hour.

SHAFT-HOISTING SIGNAL DEVICES

The modern standard devices for hoisting signals are electric bells and pneumatic gongs; both are good. They should always be supplemented with telephones that afford direct communication from the hoisting engine to the several landings. Another praiseworthy device is the electric flash signal so generally used in German coal mines and in this country in metal mines that have a number of levels from which hoisting is done.

On account of the length of hoist, slope hoisting signals are usually limited to electric bells, and telephone hoisting signals vary so much in different States that no standard set of signals can be formulated at this time, desirable as it would be to have a universal code. Only three signals seem to be universal; these are:

One bell, hoist coal or rock; also for men after man signal has been given from below and answered by the hoister man.

One bell, stop immediately when cage is already in motion going either up or down.

Two bells, lower empty or with material; also for men when man signal has been given from upper landing and after reply is received from hoister man.

Other signals should cover men who want to be hoisted or lowered. Multiplicity of bell signals is undesirable to-day because a direct telephone serves much better for such other signals as fire, start pump, and stop, start, or reverse fan.

In conclusion, it is believed that accidents in shafts and slopes are largely preventable. Daily inspection of all hoisting mechanism is vital, and records of its condition should be kept by designated persons.

SURFACE ACCIDENTS AT COAL MINES

Accidents that happen on the surface in connection with the operation of mines are usually included in the total of mine accidents. In coal mining they represent 6 to 10 per cent of all accidents in and about the mines. This means a considerable hazard, although not nearly so great as that underground, since but 18.3 per cent of the total are employed on the surface. In most years the mortality rate of those employed on the surface is lower than one per thousand. The number of deaths from surface accidents shows a gratifying decrease in recent years. For example, in 1917 there were 261 deaths, whereas in 1924 there were only 138 and in 1925 only 127. The ratio of the number of injuries to the number of deaths is not known.

As will be noted in Tables 1 and 4, mine cars and mine locomotives cause the largest number of accidents. The number of mortalities from such accidents varied from 71 killed in 1919 to 24 in 1925. These deaths evidently occurred chiefly in drift and slope mines, at many of which there is a long haul on the surface from the mine mouth and yard to the tipple. The proper layout of mine yards and adequate safeguards, such as fences and guards, automatic switches, derailing switches, safety blocks to provide against cars and trips running away, and trolley wires and hangers with ample overhead clearance, would lessen such accidents appreciably. Individual care, however, is probably the most important means of prevention, hence educational work in safety should be carried on.

Another class of accidents at mining plants includes those where men are run over or crushed by railway cars or locomotives. The number so killed each year ranges from 16 to 36. Many of the accidents are due to letting cars loose to run down the yard without ample warning being given. Some system of automatic electric bells might be arranged at switches and 200-foot blocks to give warning. Another cause of such accidents is the cramped arrangement of the tracks and lack of enough room between tracks and between the cars and the mine tipple posts and chutes, especially at old mines.

Accidents from machinery form another important item in the classification of surface accidents. The annual number of deaths caused by machinery has ranged from 46 in 1917 to 8 in 1925. The great decrease in accidents of this type is probably due to better guards around machinery as well as to generally better care. It is probable that the injury rate is relatively higher than the mortality rate.