Methane gas always a hazard in underground coal mines

Lighter than air and colorless, methane is abundant in nature. It is the main component of natural gas and it is a common accompaniment of coal.

While the gas is typically odorless, the commercial product is dosed with evil smelling compounds to give early warning of pipeline leakage. Both coal and gas were formed contemporaneously from the same decayed vegetable matter. Sometimes the greater part of the gas escaped during geological time; that is, the seams may be close to surface. Elsewhere, the greater part of the gas is retained until tapped by man.

Most often, the release of gas is continuous and unremarkable. If quiet prevails at the coal face (a rare happening), the sound is that of a barely perceptible hiss. The escaping gas is swept away, diluted by the ventilation and made harmless.

Under unusual circumstances, the gas will migrate through the seam and accumulate in a geological trap and remain there until it is broken into by mining. The trap may be a lens of porous rock with the gas stored as water is in a sponge. The lens being sealed in an envelope of impervious shale. Or, the gas accumulation may be within a trashy pocket of the coal seam where there was insufficient fibrous matter to form a continuous seam of hard coal. In either case, the reservoir of gas will be under a pressure up to hundreds of pounds per square inch.

If there is only a thin skin of rock or coal between the gas pocket and the face being mined, this final barrier will burst without warning. On its own, methane burns with pale flame and poses no problems. But if it mixes with the atmosphere, it forms an explosive mixture — the feared “fire damp” of the coal miner.

This critical condition is reached when there is 5-14% methane in the air. An explosion of “fire damp” is followed by another dread of the miner, “after damp.” This asphyxiating atmosphere is a mixture of carbon dioxide and carbon monoxide which replaces oxygen in the air. (Incomplete combustion of the methane created carbon monoxide.)

Methane has been encountered in the crystalline rocks of the Precambrian rocks on occasion. There was, in fact, a regular procedure at the Discovery mine in the Northwest Territories (since closed) to check for methane: all freshly blasted faces at this high-grade gold mine were tested with a flame safety-lamp prior to entry by the regular work crews. This practice was instituted following a fatal methane explosion in the early 1960s.