car body. This can be done without hindering the dumping of coal if tight-end cars and rotary dumps are used.

Standardized switches should be installed. The layout of haulage tracks-including passing tracks, sidings, and switches-is most important in preventing accidents.

Frog openings should have wood block fillers to prevent a man getting his foot caught.

Large mines use on their main roads a block system of electric signal lights that economizes time and increases safety.

Some mines provide for the haulage of loads and the haulage of empties in separate parallel entries, the safest plan where feasible.

The larger proportion of the accidents from haulage is avoidable. Much depends on the individual men, but a great deal depends on the management in laying out the haulage systems, putting in safety devices, and supervising haulage.

Detailed precautions in connection with haulage accidents are given in Mines' Circular 11.67

In large mines it is advisable to have an assistant foreman in charge of haulage, to see that cars and trips are moving regularly to and from the shaft or mine entrance, and that an equitable share of the empties is going to different parts of the mine. He should be capable of seeing how haulage can be improved with respect to safety and economy and constantly work toward that end.

The limiting of electric trolley haulage in gassy mines to pure air intake entries is discussed on page 81, and the necessity of rock-dusting thoroughly all haulage ways in bituminous mines is considered on page 52.

The great advantage for safety that electric haulage by permissible storage-battery locomotives gives, the avoiding of ignition of gas and dust, is stated on page 75. The prevention of fatalities by electric shock is referred to on page 101.

67 Jones, L. M., Accidents from Mine Cars and Locomotives: Miners' Circ. 11, 1912, 16 pp.

ELECTRIC SHOCKS

The extensive use of electrical machinery in mines has caused annually a considerable number of accidents from electric shocks. The fatalities have ranged (see Table 4) during the past eight years from 69 to 88 a year. Safety guards and better installations have kept pace with the increasing use of electricity, but have not gained rapidly enough to reduce the annual number of fatalities.

Half of these accidents are caused by direct contact of the man with the trolley wire and point to the need (cited earlier) of separate manways or of ample clearance along trolley roads, as well as the use of guards at places where the men have to cross under the trolley wire. Bars or tools carried by the men striking a live electric wire contribute an additional small number of deaths, one to four, a year. These could also be prevented by the means just suggested.

The substitution of storage-battery locomotives for trolley locomotives would practically eliminate deaths from contact with trolley wires.

Another specific cause of electric shocks is contact with machine power lines. Authoritative information is not at hand, but it is believed that the majority of these accidents are caused by attaching clips to the power line and to the grounded return, usually the track. If approved junction boxes are used, as in gassy mines, to lessen the danger of igniting gas, as recommended in connection with the use of electrical mining machines on page 75, this cause of accidents would be practically eliminated.

Each year there are a number of accidents from contact with mining machines. Evidently these happen because the machine frame has not been properly grounded or there has been some internal breakdown of the machine. Constant care is needed to keep machines proper repair, and when they have broken down the power should be cut off at once. Approved or permissible machines are much less likely to cause such accidents because of the care with which they have to be constructed to pass the bureau's tests.

in

Other causes of electric shock are diversified, but in the majority of cases they are probably due to handling and making repairs on circuits and machines, such as pumps, without first cutting off the power.

One most important factor in the prevention of shocks is to have electrical machinery and circuits installed by trained and experienced men and under the supervision of a thoroughly competent official,

who before appointment should pass an examination on all problems likely to arise in installing electricity in mines.

If a man receives a shock that disables him or makes him unconscious and he remains in contact with the wires, any near-by switch that will cut off the power should be closed at once; if no switches are close by and there is a steel bar or pipe at hand, it should be stood against the rail on the side on which the power is received and dropped upon the wires to cause a short circuit. Next, one should stand on a board or, if nothing better is at hand, a piece of dry cloth not in contact with metal, grab the man quickly, and pull him off. (See Miners' Circular 5.)9 Methods of resuscitation are described in the First-Aid Manual of the Bureau of Mines; briefly, if the man is unconscious, he should be treated by the Schaefer method.

68

68 Clark, H. H., Roberts, W. D., Ilsley, L. C., and Randolph, H. F., Electrical Accidents in Mines, Their Causes and Prevention: Miners' Circ. 5, Bureau of Mines, 1911, 10 pp. 69 Bureau of Mines, Manual of First-Aid Instruction for Miners (revised by R. R. Sayers): 1922, pp. 28-29, 33-35.

MINE FIRES

Mine fires, second only to explosions, are the happenings most dreaded in coal mining. During the last eight years the number of lives lost by burning or suffocation is not large, ranging from only 2 to 26 a year, but these small numbers are not a true measure of the hazard of mine fires, as shown by the Cherry mine fire, Illinois, November 13, 1909, which killed 259 men, and the fire at Price-Pancoast anthracite colliery, Pennsylvania, March 22, 1911, which killed 72

men.

Coal-mine fires probably can never be absolutely eliminated. Combustible material is being mined, and combustible equipment, including roof supports, track ties, doors, temporary ventilating stoppings, brattice cloth, electric insulation, and explosives, must be used to some extent. The material brought into the mine, rather than the coal itself, is the most prolific source of mine fires, hence the greater the use of incombustible material (stone, cement, steel, and iron) for all construction the lower will be the fire risk.

There will always be sources of ignition in a mine, and the danger of spontaneous combustion is always present, but these hazards can be minimized by known means.

Methods of illumination by incandescent lamps at shaft bottoms and improvement in portable miners' lamps have decreased the liability to those fires that start at entrances or junction points and cause the trapping of men. Another important measure in the prevention of fire has been the use of permissible explosives. The bureau recommends the use of these explosives for all coal mines (see p. 61); black blasting powder and dynamite shots will ignite gas readily, and many fires at the face were and still are caused by nonpermissible explosives.

A mine fire, especially in any gassy mine, is liable to cause a disastrous explosion. A number of such explosions have happened. In the mine at Delagua, Colo., November 8, 1910, an explosion attributed to a fire killed 72 men. A recent instance is that of the Horning mine, Pennsylvania, in which 20 men were killed by an explosion resulting from a fire. At the inquest witnesses testified that had it not been for rock-dusting the 400 men in the mine might have been killed. A synopsis of the principal coal-mine fires is now in press and will be issued as Bulletin 229, Bureau of Mines, Fifty-Nine Coal Mine Fires. The lessons derived from these disasters are of great value to mining men.

Fires in nongassy mines (class 1 coal mines, see p. 29) rarely cause explosions, but these have occurred. A fire caused an explosion in a mine in the Sheridan subbituminous district of Wyoming some years ago, and in 1910 a similar occurrence in a Colorado bituminous mine rated as nongassy killed 79 men.

There is no inherent reason why fires may not occur under conditions approximating those prevailing in a gas producer. If there is a fire in a passageway and it is fanned by a current of air, there will be a long stretch of glowing coals. Mine air in the inner workings is usually saturated or nearly saturated with water, and the heat of the fire distills more water from the coal and timbering. Oxygen in the air current would be consumed rapidly in passing through the fire zone, and the breaking up of the water in the air in the presence of hot carbon would cause production of large amounts of carbon monoxide. The heat of the fire would also distill hydrocarbons from the coal. Thus, a large amount of inflammable gas is produced. Whether or not the gas would be explosive when mixed with fresh air would depend upon the amount of carbon dioxide displacing oxygen in the mixture.

Obviously, however, under certain conditions an explosive mixture might be formed and an explosion result if there was a source of ignition, such as an open light or the fire itself. Ignition by the latter might result if the direction of the current of air and gas reversed for one reason or another; for example, if a fall of roof backed up the explosive mixture so it made contact with the live coals.

Although there have not been many such explosions in nongassy mines, their occurrence should be forestalled if possible.

CLASSIFICATION OF MINE FIRES

All mine fires threaten danger to personnel, but in varying degree, according to location.

1. Fires starting in and about shafts threaten the entire working force below ground. The most notable example of such a fire was that at the Cherry mine, Illinois. (See p. 73.)

2. Fires starting at or near the point where ventilating splits turn off, at doors, overcasts, and combustible stoppings between the intake and return of a ventilating split immediately threaten the safety of all the men on the split.

3. Fires starting in working places are rarely of immediate danger to personnel, but in a place producing much gas become a serious menace if not extinguished promptly, because of the possibility of explosions.