Spontaneous Combustion

Coal catching fire underground with nothing to light it. Broken coal left in the waste reacts slowly with oxygen in the air, giving out heat; where the ventilation is too weak to carry that heat away but strong enough to keep feeding oxygen in, the temperature climbs until the coal ignites itself.

Historical usage

Some coals are far more liable to it than others, and a colliery that had the problem had it for its whole working life. Brora, on the Sutherland coast, worked a Jurassic seam contaminated with iron pyrites and suffered fires repeatedly across four centuries of working — the last of them closing the Ross Pit for good in May 1969. Argyll Colliery at Machrihanish lost its Slope Dook to a heating in September 1958, and the pit at Trodigal that preceded it had been abandoned in 1925 after a fire in the seam. Daw Mill in Warwickshire, the last deep mine in the Midlands, was destroyed by an underground fire in 2013.

How it worked

The reaction is slow oxidation: coal at ordinary temperatures takes up oxygen and releases heat. Ordinarily the ventilation carries that heat away and nothing happens. The danger comes where air leaks slowly into broken coal left behind in the goaf, or into a crushed pillar or a spoil heap — enough oxygen to sustain the reaction, not enough movement to cool it. The mass self-heats over a period known in the industry as the incubation period, which is why panels were sized so that the coal could be got out before a heating could develop. Iron pyrites in the coal makes it markedly worse. The first sign is usually not flame but smell and gas — the characteristic 'gob stink' and rising carbon monoxide readings — and the standard remedy is to shut off the air: build seals around the district and, if necessary, flood it.

Risks & limitations

The response is what makes it so costly: sealing a district means abandoning the coal in it, and the seals may have to stay in for months. Brora's 1969 fire and Machrihanish's 1958 heating both ended in flooding the affected ground, and at Machrihanish the fire lay higher than the working places, so four seals had to be built before water could be put in at all. A heating can also fill workings with carbon monoxide long before anything is visibly alight, which is what makes it dangerous to people rather than merely expensive.

Regional variation

Called a 'heating' or a 'gob fire' in the British coalfields, the latter after the goaf where it usually starts; 'spontaneous heating' is the technical term for the stage before ignition.

Related terminology

Barricading, Coal, Goaf / Gob, Pyrite, Spoil Heap, Whitedamp

Mines associated with this term

Included only where MineArchive's own research gives a reasonable evidential basis — not every mine where this might plausibly apply.

• Brora Colliery — Highland (well documented example)
  Automatically linked by scripts/link_terms.py: exact-phrase match in the record's own recorded text.
• Daw Mill Colliery — Warwickshire (well documented example)
  Automatically linked by scripts/link_terms.py: exact-phrase match in the record's own recorded text.

Disasters associated with this term

Included only where MineArchive's own research gives a reasonable evidential basis, with the nature of the relationship stated — not every disaster where this term might plausibly apply.

• Michael Colliery fire, 1967 (contextual relationship)
  Automatically linked by scripts/link_terms.py: exact-phrase match in the record's own recorded text.
• Daw Mill Colliery fire, 2013 (contextual relationship)
  Automatically linked by scripts/link_terms.py: exact-phrase match in the record's own recorded text.

Sources

1. (primary) Assessing and managing spontaneous combustion of coal (CCC/259) — L. L. Sloss, IEA Clean Coal Centre
2. (primary) Brora Coalfield — Northern Mine Research Society — Northern Mine Research Society

Record created: 25 August 2026 · Last researched: 25 August 2026