Afterdamp

[1] The term is etymologically and practically related to other terms for underground mine gases—such as firedamp, white damp, and black damp, with afterdamp being composed, rather, primarily by carbon dioxide, carbon monoxide and nitrogen, with highly toxic stinkdamp-constituent hydrogen sulfide possibly also present.

However, the high content of carbon monoxide is the component that kills, preferentially combining with haemoglobin in the blood and thus depriving victims of oxygen.

[3] Animal sentinels, such as mice or canaries, are more sensitive to carbon monoxide 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.

[4] Gas detectors are available now which detect toxic gases such as carbon monoxide at very low levels.