Afterdamp is the toxic mixture of gases left in a mine following an explosion caused by firedamp

Firedamp

Firedamp is a flammable gas found in coal mines. It is the name given to a number of flammable gases, especially methane. It is particularly commonly found in areas where the coal is bituminous...

, which itself can initiate a much larger explosion of coal dust

Coal dust

Coal dust is a fine powdered form of coal, which is created by the crushing, grinding, or pulverizing of coal. Because of the brittle nature of coal, coal dust can be created during mining, transportation, or by mechanically handling coal.-Explosions:...

. It consists of carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, carbon monoxide

Carbon monoxide

Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 and nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

. Hydrogen sulfide

Hydrogen sulfide

Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

, another highly toxic gas, may also be present. However, it is the high content of carbon monoxide which kills by depriving victims of oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 by combining preferentially with haemoglobin in the blood.

Afterdamp was the deadly gas which caused the majority of casualties in the many pit disasters of the British coalfields, and elsewhere in the world. Such disasters continue to afflict working mines, especially in mainland China.

Detection

Small animals, such as mice

MICE

-Fiction:*Mice , alien species in The Hitchhiker's Guide to the Galaxy*The Mice -Acronyms:* "Meetings, Incentives, Conferencing, Exhibitions", facilities terminology for events...

, or canaries

Domestic Canary

The Domestic Canary, often simply known as the canary, is a domesticated form of the wild Canary, a small songbird in the finch family originating from the Macaronesian Islands ....

 are more sensitive to the gas than humans, so will give a warning to miners. Canaries were introduced into British collieries in the 1890s by John Scott Haldane, the noted physiologist. Gas detectors are available now which detect toxic gases such as carbon monoxide at very low levels. The levels of gas detection depend on the methods used.