Fly ash is the very fine portion or ash residue that results from the combustion of coal. The fly ash portion is usually removed electrostatically from the coal combustion gases before they are released to the atmosphere. About 31 percent of the 57 million metric tons produced annually in the United States are beneficially used; the remainder must be disposed of in ponds or landfills.

In coal mining what is meant by damp?

Damp is a poisonous or explosive gas in a mine. The most common type of damp is firedamp, also known as methane. White damp is carbon monoxide. Blackdamp (or chokedamp) is a mixture of nitrogen and carbon dioxide formed by mine fires and explosions of firedamp in mines. Blackdamp extinguishes fire and suffocates its victims.