Outburst

The sudden, violent ejection of coal, rock and gas from a working face into the workings — hundreds or thousands of tonnes of coal reduced to powder and thrown out with tens of thousands of cubic metres of firedamp, in seconds and without warning.

Historical usage

Outbursts are a hazard of deep, gassy, structurally disturbed coal, and in Britain they belong above all to the anthracite districts of the western South Wales coalfield. Cynheidre, sunk to make deep anthracite mining viable, was the site of the worst coal-and-gas outburst disaster in British history: on 6 April 1971 an outburst there killed six men, pulverising and ejecting some 400 tonnes of coal along with 57,000 cubic metres of firedamp. The word is older than that and did not always mean this. Barrowman’s 1886 glossary of Scotch mining terms gives two senses side by side: "OUTBURST, The outcrop" and "OUTBURST, A sudden accession of water or fire-damp" — so in Scottish usage the same word served for the place a seam reaches the surface and for a sudden inrush.

How it worked

Gas in coal is not only in the cracks; much of it is adsorbed within the coal itself, held there by the pressure of the surrounding strata. Where a seam is gassy, poorly permeable and geologically disturbed, cutting into it can release that pressure faster than the gas can bleed away through the coal. The seam then fails explosively into the opening, shattering as it goes and liberating the gas it held — which is why the coal comes out as dust rather than lumps, and why the volume of gas released tracks the tonnage of coal ejected.

Why it was used

Not a technique but a hazard; the entry exists because outburst-prone seams had to be worked differently. Where outbursts were expected, ground was destressed by firing shots into it in advance, or worked by methods that kept men out of the immediate face area.

Risks & limitations

The severity ranges from barely noticeable to the destruction of an entire district, throwing machinery weighing tens of tonnes several metres. The gas is the second danger after the coal: an outburst fills the district with firedamp in moments, so that men who survive the ejection itself may not survive what follows. The predisposing factors are reasonably well understood — high gas content, low permeability, and geological structures such as faults, dykes and zones of crushed coal — but the specific event has never been reliably predictable.

Regional variation

In Britain the outburst-prone ground is the anthracite belt of west Wales; the deeper and more disturbed the seam, the greater the risk, which is precisely what made Cynheidre’s reserves both valuable and dangerous. The Scottish sense recorded by Barrowman, meaning the outcrop, is a genuine and quite separate usage and is now obsolete.

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.

• Seven Sisters Colliery Explosion, 1907 (contextual relationship)
  Named twice in this record, first in the cause: “A defective safety lamp, in an anthracite district prone to sudden outbursts of gas.”

Sources

1. (primary) Glossary of Scotch Mining Terms — James Barrowman (1886), via Scottish Mining Website
2. (secondary) Cynheidre Colliery — Wikipedia
3. (secondary) Outburst (mining) — Wikipedia

Record created: 8 September 2026 · Last researched: 8 September 2026