Underground, air is not a comfort — it is a control. Coal seams hold gas, and the single most important gas in a coal mine is methane, known to miners for centuries as "firedamp". Methane is colourless, odourless and lighter than air, and in the right mixture with air it is explosive. Roughly between 5 and 15 percent methane in air, a spark or hot surface can ignite it, with about 9 percent being the most dangerous. Managing that gas — diluting it, monitoring it and where necessary draining it away before it ever reaches a working face — is the discipline that keeps an underground coal mine safe.
Methane is generated as part of the same natural process that forms coal, and it stays adsorbed on the internal surfaces of the coal, held there by pressure. When mining cuts into the seam, the pressure drops and the gas is released into the mine air. How much gas a mine gives off depends on the coal, the depth and the rate of extraction, which is why Indian regulation classifies mines by how gassy they are.
Under the Coal Mines Regulations 2017 (CMR 2017), enforced by the Directorate General of Mines Safety, gassy seams are graded by degree. In broad terms the classification rises with the rate of methane emission and with the presence of methane in the general body of the mine air: the first degree covers the least gassy conditions, and higher degrees trigger progressively stricter requirements for equipment, ventilation and monitoring. The degree of gassiness determines much of how a mine must be worked — from the type of electrical apparatus permitted to the frequency of gas testing.
The primary defence is ventilation: pushing enough fresh air through the mine to dilute methane far below its explosive range and to sweep it out. Large surface fans drive air down one shaft, through a planned circuit of intake and return airways (the "air courses"), across every working place, and back to the surface. The design target is quantity — a sufficient volume of air per person and per working face — because dilution is what keeps the gas concentration harmless. Air courses are laid out so that fresh air always reaches the face and gas-laden return air is carried away without short-circuiting.
Ventilation is backed by continuous monitoring. Methane is measured both by hand-held and fixed instruments, and modern mines use environmental telemetry that reads gas levels in real time and automatically cuts electrical power if methane climbs toward a set threshold. Statutory limits require work to stop and people to be withdrawn when concentrations exceed defined values, well below the explosive range, so there is a wide safety margin between "action" and "danger".
Where ventilation alone cannot cope, or where gas emission is high, mines add degasification — draining methane out of the coal and surrounding strata through boreholes before or during mining, so less gas ever enters the ventilating air. Captured methane can be piped to the surface and, rather than being wasted, used as fuel; this overlaps with coal mine methane (CMM) recovery.
None of this is optional. CMR 2017 mandates adequate ventilation, systematic methane monitoring and, where required, degasification, and DGMS issues technical circulars on ventilation practice. The science is old and well understood — dilute it, watch it, drain it — and it is why, underground, air really is everything.
Canonical source: https://www.dgms.gov.in