Chokedamp

An asphyxiating mixture of gases — chiefly nitrogen and carbon dioxide, with the oxygen removed — that can silently accumulate in a mine; also called blackdamp, or stythe in parts of North East England.

Historical usage

The name 'blackdamp' is recorded from 1736 onward, and the closely related term chokedamp is used interchangeably with it in mining sources; both describe the same underlying hazard, distinct from the explosive firedamp and the carbon-monoxide-bearing afterdamp that follows an explosion or fire.

How it worked

Blackdamp typically forms as coal, once exposed to air in a working mine, slowly absorbs oxygen from the surrounding atmosphere while releasing carbon dioxide and water vapour of its own; over time in a poorly ventilated space this steadily depletes breathable oxygen, leaving a mixture — commonly around 10-15% carbon dioxide and 85-90% nitrogen — that cannot support life, though it will not itself burn or explode. It also forms as part of the aftermath of a mine fire or explosion, making it a close relative of afterdamp.

Why it was used

Because chokedamp gives no visible warning and does not burn, it could not be detected the same way as firedamp; miners instead relied on a simple flame test (see this site's own Bad Air term page) — a candle or lamp flame burning low and finally dying well before conditions became lethal to a person.

Risks & limitations

Chokedamp is entirely undetectable by human senses alone and gives no warning until a miner is already dangerously short of oxygen, making good ventilation — rather than any warning system — the only real defence against it.

Regional variation

'Stythe' or 'stithe' was the everyday dialect word for the same hazard in Northumberland and County Durham, while 'blackdamp' and 'chokedamp' were used more widely across British coalfields; all belong to the broader family of 'damp' terms this site's Firedamp and Afterdamp pages also cover.

Sources

1. (primary) Definition of chokedamp — Mindat
2. (secondary) Blackdamp — Wikipedia

Record created: 21 August 2026 · Last researched: 21 August 2026