Handbook for Methane Control in Mining - AMMSA

80Figure 6–1.—Gas content of coal versus gas pressure for some U.S. coals[Kissell et al. 1973].THRESHOLDS FOR COAL SEAM DEGASIFICATIONMethane drainage must be performed whenthe ventilation air cannot dilute the methaneemissions in the mine to a level below thestatutory limits.Generally, it is economically feasible to handle specific methane emissions 3 from a mine up to1,000 ft 3 /ton with a well-designed ventilation system. At higher specific emission rates, a stageis reached where ventilation cost becomes excessive or it becomes impossible to stay within3 Specific methane emission is the total amount of gas released from the mine divided by the total amount of coalmined. Specific emission values are much higher than the gas content of the coal because of methane emission fromcoal that is not mined (ribs and pillars) and methane emission from strata adjacent to the mined coalbed.