Fire, Underground

a fire in an underground mine shaft or in the body of a useful mineral. Underground fires are classified as exogenous and endogenous. The former result from external heat surges caused by careless handling of fire, defective electrical equipment, or mechanical friction; the latter result from spontaneous combustion of coal, carbonaceous rocks, or sulfide ores. Underground fires are especially dangerous if the mine contains methane, coal dust, or sulfide powder.

Various measures are taken to prevent underground fires and to deal with them when they occur. General measures include the use of nonflammable materials for mine supports, fire-resistant conveyor belts, electrical cables in nonflammable sheathing, and water fire-extinguishing systems. Special methods of opening and developing deposits make it possible to isolate part of a mine in case of fire and to draw gases produced by the fire into the general air exhaust current, bypassing parts of the mine where people are working. All underground workers are provided with self-rescue equipment to allow them to exit shafts filled with gases produced by the fire and reach safety.

At the early stage of development, exogenous underground fires are extinguished by direct application of water or fire-extinguishing agents. Heavy exogenous underground fires, as well as endogenous underground fires that have originated in inaccessible places, are extinguished by means of special isolating structures that cut off air to the region of the fire. In some cases, it becomes necessary to flood burning areas with water. When the isolation system of extinction is used in parts of a mine that release dangerous quantities of methane, CO₂ or N₂ is forced into the region of the fire to prevent explosion; a gaseous mixture consisting of the exhaust gases of gas-turbine engines after the gases have been cooled by dispersed water is sometimes used for this purpose. The use of these gases reduces the concentration of oxygen in the region of the fire to below the point at which methane can explode.