The Ignition of Methane and Coal Dust by Air Compression - The Experimental Proof

When a large area of open gob collapses suddenly, a windblast is produced that can cause considerable damage throughout the infrastructure of a mine. In a few cases, the windblast has been accompanied by ignitions of methane and/or coal dust. Analytical and numerical analyses investigated the transient behavior of the air through the small time period during which the roof is falling. This is sufficiently short to allow adiabatic compression of the air, i.e. negligible heat transfer to rock surfaces. Controlled escape of the air via interconnecting entries limits the build-up of air pressure. However, this same phenomenum causes the potential energy of the falling strata to be concentrated into a diminishing mass of air. Computer simulations predicted that the temperature of the air would increase rapidly as the roof descends, reaching values that are capable of igniting either methane or coal dust.

This thesis concentrates on a series of laboratory tests involving the compression of mixtures of air, methane and coal dust under a falling weight and while allowing controlled escape of the mixture. The transient responses on pressure and temperature sensors were recorded. In addition to an analysis of those records, the thesis highlights those conditions in which ignitions occurred.