Damp is any of several dangerous gases found in coal mines. The term probably comes from a German word for vapor. Firedamp is the most common type of damp. It is used to describe methane, a tasteless, odorless, nonpoisonous gas that is lighter than air. Firedamp forms as decaying plant matter changes into coal. It remains trapped within the coal layer until the coal is mined. When miners cut into the coal, the gas is released. Because firedamp is lighter than air, it tends to collect along mine roofs. When enough firedamp is trapped, it becomes explosive. Afterdamp is a mixture of gases resulting from a firedamp explosion. It typically includes carbon dioxide, carbon monoxide, nitrogen, and hydrogen.
Stinkdamp is hydrogen sulfide, a colorless, poisonous gas. It has a strong odor resembling that of rotten eggs. In coal mines, it forms as a mineral called pyrite decomposes. Stinkdamp is flammable, but it occurs in such small quantities that it is not particularly dangerous.
White damp is carbon monoxide, a colorless, odorless, and poisonous gas. It is present in afterdamp and occurs after blasting or fires. Blackdamp, also called chokedamp, is a mixture of nitrogen and carbon dioxide. Blackdamp can be denser than air and will gather along mine floors. Miners can suffocate in the presence of whitedamp or blackdamp.
Miners once carried canaries and safety lamps to test for dangerous accumulations of white damp and blackdamp. The miners knew dangerous conditions were present if the bird collapsed or if the lamp went out. Today, miners use various mechanical, chemical, and electrical gas detectors to test mine air.
See also Coal (Mine safety); Methane.
