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A true gas given off from the coal and surrounding strata during the normal working of coal seams. Some seams are much more gassy than others. Generally it is given off at a high rate at the time the coal is being broken down.
It is lighter than air and is usually found near the roof, and at ripping lips in the roof, although ultimately due to diffusion and dispersion it becomes intimately mixed with the general body of the return air. It may occur in high percentages in the unventilated workings, goaves and wastes, and may accumulate to a high percentage in workings that have been sealed off.
Firedamp is a highly flammable gas, it burns with a pale blue non-luminous flame,and is explosive over the range 5.5% to 14.6%, exploding with maximum violence at 9.3%. On exploding it leaves behind a mixture of gases known as afterdamp, a constituent of which is the deadly poisonous gas carbon monoxide. Its presence is detected by means of the flame safety lamp, on the lowered flame of which appears a non-luminous gas cap, the shape and size being indicative of the percentage present. Also by the use of special equipment such as the Ringrose and McCluckie apparatus.
By the standards of ventilation laid down in the Coal Mines Act of 1911, if 1.25% of firedamp is present all electricity must be switched off ; where 2.5% is present workmen must be withdrawn from the place affected, and there must be not more than 0.25% in the general body of the intake air, nor more than 1.25% in the general body of the return air. The lower percentages can only be determined accurately by the laboratory analysis of samples collected in the mine.
Firedamp is not a poisonous gas, but it can cause asphyxia by reducing the normal oxygen content of the mine atmosphere. Asphyxiated persons should be treated by a method of artificial respiration, the administration of oxygen, and for shock by using blankets and hot water bottles. In every case of asphyxia, physical rest, quietness and warmth are essential and Medical Aid should be obtained at once.