Carbon dioxide. This type of extinguisher is a late development in equipment of this kind. It consists of a heavy-duty steel cylinder that serves as a container for the carbon dioxide liquid, a screw-type discharge valve that seals the liquid in the cylinder, an operating handwheel, a locking pin that holds the handwheel disengaged from the valve proper, a safety disk designed to rupture at 2,800 to 2,900 pounds, a flexible reinforced hose, an insulated hose grip, a discharge tube, and a carrying handle.

The extinguishers are received from the manufacturer already charged. The carbon dioxide in the cylinder, due to pressure when charging, takes the form of a liquid, changing to a gas or a solid (carbon dioxide snow) as soon as the discharge valve is opened.

To operate the extinguisher it is either held or set firmly on the ground. The operator then withdraws the locking pin from the hand wheel, thus permitting the hand wheel to snap downward and engage the stem of the discharge valve. The discharge tube is then released and the hose grip held firmly in one hand while the discharge valve is opened with the other hand, releasing a cloud of gas and carbon dioxide snow.

The discharge range of this type of extinguisher is limited to about 5 or 6 feet; consequently, the operator must approach as closely as possible to the fire.

MOUNTED EXTINGUISHERS

Large fire extinguishers (commonly called fire trucks) are used by some mining companies. These extinguishers are mounted on minecar trucks equipped with flanged wheels and designed to be hauled on the mine track by a mine locomotive. Because of their large capacity, extinguishers of this type, if quickly available, are preferable to the hand type for fighting fires of serious proportions.

The extinguishers are stored either on the surface or underground, depending on storage facilities and whether they are to be available for surface as well as underground use.

Large mounted extinguishers generally are of the soda-acid or foam type. However, some of them are designed to use water instead of chemicals.

Chemical. One type of mounted extinguisher (fig. 8) consists of two soda-acid tanks having a capacity of 100 gallons each. The truck is equipped also with 200 feet of chemical hose having a nozzle with a shut-off valve, two 1-quart, carbon tetrachloride, hand extinguishers (or two 212-gallon soda-acid or foam extinguishers), five all-service gas masks, one carbon monoxide detector, two gages for indicating pressure in the tanks, one floodlight, extra chemical charges, tools, etc. This extinguisher and equipment can be obtained also in the two 40-gallon-size tanks designed to use foamite instead of soda acid.

Water-At least one mining company has designed and is using a mounted fire truck equipped to use water. This extinguisher (fig. 9) consists of a tank having a capacity of about 325 gallons of water. A pump and pipe connection to apply pressure to the water being used from the tank furnishes a stream of considerable pressure. The pump and connections can be used also to pick up water from either a water hole or a pipe and force it into the tank. The tank also can be filled through a small opening in the top.

The truck is equipped with 250 feet of 112-inch linen-covered fire hose with nozzle, five all-service gas masks, two 21/2-gallon chemical fire extinguishers, a roll of brattice cloth, a crosscut saw, picks, shovels, slate bars, and other equipment and tools.

Á reel containing a cable and mounted on one side of the tank can be used to obtain electric current for operating the pump in advance of trolley-wire installation.

Other types of mine fire trucks used by some companies are equipped with a number of various types of fire extinguishers, tools, gas masks, and materials for fire-fighting work. One company maintains a fire trip composed of several mine cars equipped with a pump, brattice cloth, tools, gas masks, etc. This trip is stored at a convenient point underground and kept ready for emergency use.

An adequate supply of standard-size fire hose in good condition and with proper fittings, including several nozzles, should be available at all mines for fire fighting. Special types of nozzles, such as perforated pieces of pipe closed on one end and threaded to fit a hose connection on the other end, are often of decided value in fighting underground fires. Various sizes of connections, reducers, and adapters should be available to connect fire hose readily to all sizes and openings of pipe lines.

ROCK DUST

Rock dust can be used efficiently in extinguishing mine fires when it is possible to apply the dust directly on the fire, and numerous instances are on record of the successful use of rock dust in combatting mine fires. A sufficient supply of rock dust in suitable bags should be kept available at all times for fire fighting and general use.

TOOLS

An adequate supply of hammers, axes, saws (hand and crosscut), sledges, hatchets, picks, shovels, bars, bricklayers' hammers and trowels, pipe wrenches, and other necessary tools should be available. To minimize the likelihood of ignition of gas through sparks it is desirable, if not imperative, that hammers, bars, etc., of copper or other relatively nonsparking material be provided for work being done in the presence of explosive gas.

TELEPHONES

Enough telephones always should be available at the base of operations and at such other places as may be necessary to keep contact between those engaged in the recovery work underground and those assisting in various capacities on the surface. After an explosion, as recovery work progresses, the telephone system should be kept in proximity to the fresh-air base at all times.

Under certain conditions the common types of outside and mine telephones can ignite an explosive mixture of gas. Therefore, permissible-type telephones should be used in mines, especially during rescue and recovery operations.

8

The Bureau of Mines, under schedule 9A, approved a mine telephone manufactured by the Western Electric Co. (approval 901) on July 16, 1927.

Portable telephones that operate without batteries have been developed so that they can be used efficiently and satisfactorily for communication between oxygen breathing-apparatus or gas-mask crews and the fresh-air base.

The equipment (fig. 10) consists of a receiver attached to a head set and throat transmitter and provided with a strap and worn by the crew captain, being attached by a jack or plug to one end of about 1,000 feet of light insulated cable. The cable is wound on a light metal reel, which is suspended and encased in a wooden frame. The other end of the cable passes through the core of the reel and is attached to two insulated commutators fastened on the outside of one of the reel flanges. Two bronze springs are in contact with the commutators and connect, by an insulated wire, with a telephone jack attached on the inner side of the frame.

A combination hand set, containing a transmitter and receiver, for use of the man at the fresh-air base is connected ("plugged in") to the jack on the frame. A detachable crank for turning the reel and a short chain with a snap for attaching the cable to a convenient place on the oxygen breathing apparatus or gas mask worn by the crew captain complete the equipment. The transmitters of the telephones are voice-energized and no electric current is used, which makes this type of telephone equipment especially desirable for rescue and recovery work. It is possible with this equipment to conduct an ordinary conversation satisfactorily through 2,500 feet of cable.

The captain of the crew attaches the cable to his apparatus by the chain and snap, places the head attachment over his head with the

8 Bureau of Mines, Procedure for Establishing a List of Permissible Telephones for Use in Coal Mines: Schedule 9A, Dec. 5, 1922, 5 pp.

receiver over one ear, and straps the transmitter loosely around his neck; while talking he holds the transmitter against his throat. As the mouthpiece of an oxygen breathing apparatus offers considerable hindrance to talking, the crew captain should reduce his conversation to a minimum.

A telephone system of this kind should be provided, as it will greatly facilitate the work of oxygen breathing-apparatus and gasmask crews where a life line is required and enable the man in charge of the fresh-air base to keep in communication with the crews working ahead of fresh air much more efficiently than if a life line were used.

Mine maps, with the latest possible extensions of surveys, should be provided as soon as possible after a mine fire or explosion. One of these should be posted in the general headquarters on the surface and additional copies should be available for the men in charge of the underground shifts, captains of oxygen breathing-apparatus crews, State mine inspectors, and others who may require a copy.

Some mining companies maintain a disaster map for emergency use, on which is noted the direction of ventilation in each entry, location of overcasts, doors, pumps, elevations, and other information. A map of this kind may be of much value after a fire or explosion.