The New International Encyclopædia/Mine Gas

MINE GAS. An explosive gas encountered in coal mines, also known as fire-damp. It consists principally of marsh gas (CH₄), which is the combustible element, but it contains also small proportions of nitrogen and carbon dioxide. Owing to its light specific gravity—about one-half that of air—it is always found in the upper portions of the workings. The explosive qualities are first shown when the gas is mixed with from four to five volumes of air; when free from air it will not take fire. The danger resulting from the presence of this gas in coal mines has largely been removed, in recent years, by the use of the safety lamp (q.v.) and by improved methods of ventilation. See Coal.