Sudden Blowout

(of coal and gas), a dynamic phenomenon that occurs as a result of a rapid change in the tension conditions of a gas-saturated coal bed near a mine—usually near the breast of a working or development face. A blowout is accompanied by the partial or total destruction of the coal, the violent expulsion of gas, and the formation of a flow of coal suspended in the gas. The characteristic of a sudden blowout is its intensity, measured by the quantity of coal expelled and by the distance it is thrown. The quantity of coal expelled in a sudden blowout is from several to hundreds of thousands of cubic meters. In a blowout, the mine shafts are blocked with coal for dozens of meters and are filled with gas, and a cavity or cavern forms in the bed. In steep beds the cavern is often pear-shaped.

Sudden blowouts are preceded by warning signs (increased pressure on the timbering, peeling of the coal, and loud crackling in the seam), although a blowout can also occur unexpectedly. As the depth of the coal workings grows, so does the pressure of rocks and gas, which increases the frequency and force of sudden blowouts.

A complex of measures for forecasting and preventing sudden blowouts has been developed. There are several types of forecasting: regional (estimation of the danger of a blowout by data from geological prospecting), local (determination of danger according to data from inspection of mechanical, filtration, sorption, and petrographic properties, the structure of the coal, and the structure of the bed as a whole), and constant (detection of warning signs or precursors of sudden blowouts, including seismic and acoustical methods).

The most reliable methods for preventing sudden blowouts are preventive working of protective layers, boring or degas-sing and moistening shafts from the drifts in order to reduce the gas pressure ahead of time and to moisten the part of the layer intended for removal.