Gas Balance

the quantity of gas being generated in a mine shaft and the distribution of gassing either by sources or throughout the system of workings. A distinction is made among the gas balances for individual workings, cutting sections, and shafts or for the mine as a whole. Knowledge of the gas balance is a basic prerequisite for selecting gassing control methods, shaft ventilation systems, and the methods of working the mineral.

One of the methods for determining the gas balance is the gas survey. The gas balance of a shaft is determined mainly by natural conditions and the mining-engineering factors of the working. The gas balance according to methane sources is composed of gassing from the coal seam or seams being worked, from adjacent gas-bearing coal seams; and from enclosing (surrounding) rock. Methane-rich shafts can be divided into two groups according to the makeup of the gas balance: the first group includes shafts working a single seam; the second, shafts working a series of seams. For the first group, gassing in the face area of more than 75 percent (less than 25 percent in the worked-out area) of the total methane discharge in the cutting section is typical during the cutting of a seam with small losses. The distinguishing feature of the second group is that the gassing in the face area is 50-60 percent and less (40-50 percent and more in the worked-out area) of the total methane discharge within the cutting field.