Generally applied to carbon dioxide. Strictly speaking, a mixture of nitrogen and carbon dioxide. The average blackdamp contains 10% to 15% carbon dioxide and 85% to 90% nitrogen. It is formed by mine fires and the explosion of combustible gases in mines, and hence forms a part of the afterdamp. An atmosphere depleted of oxygen rather than containing an excess of carbon dioxide. Being heavier than air, it is always found in a layer along the floor of a mine. It extinguishes light and suffocates its victims. Hence, it is sometimes known as chokedamp.