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in mining, any mixture of gases in an underground mine, especially oxygen-deficient or noxious gases. The term damp probably is derived from the German dampf, meaning fog or vapor. Several distinct types of damp are recognized.
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a combustible gas released usually in coal mines, less often in salt, metal-ore, and sulfur mines. Firedamp is colorless, lighter than air (since it consists mainly of methane), and contains nitrogen, neon, argon, hydrogen, and carbon dioxide and traces of ethane, propane, ethylene, and other hydrocarbons. In mineral deposits it results from the decomposition of organic substances caused by microorganisms, heat, pressure, and sometimes radiation. When the content of firedamp in the air is from 5 to 16 percent (as measured by methane content), the mixture produced can be ignited by a flame or sparks and cause explosions and fires.
Permissible firedamp concentrations range from 0.5 to 2 percent. The explosive accumulation of the gas is lowered by mine ventilation. Special safety lighting and electrical equipment is used to prevent firedamp from igniting. Firedamp in a mine atmosphere reduces the concentration of oxygen, which may lead to suffocation.