WORK OF THE SAFETY IN MINES RESEARCH BOARD 588 
below the surface of the earth, and perhaps two or three miles from the 
pit-bottom, causes the problems of roof-support and underground transport 
of men and materials to be particularly difficult. It is not surprising, 
therefore, to find that accidents due to falls of roof and accidents incurred 
during underground haulage are by far the most numerous. 
Yet the accidents which cause most concern, both to the miner and to 
the public, are those due to explosions. Partly, perhaps, because of man’s 
inherent dread of fire; and partly because an explosion so often claims 
many victims. 
Explosions may be caused either by gas or by coal dust. During the 
process of formation of coal from decaying vegetable matter, a process of 
bacterial fermentation, the gas methane, the fire-damp of coal mines, was 
evolved. This gas remains to-day pent within the coal substance, or stored 
in the associated strata, whence it may be liberated into the mine workings 
with disastrous results. Coal dust, if fine enough, forms explosive mixtures 
with air as dangerous as or, in some respects, more dangerous than mixtures 
of firedamp and air. 
Efforts to eliminate explosions and, more importantly, the fear of ex- 
plosions from coal-mining, have been fairly successful, more particularly 
as regards coal dust explosions. Little by little the various causes of 
explosions, of the initial ignition of firedamp or coal dust, have been 
recognised and controlled. Our aim is to eliminate them completely. 
The greatest danger, initially, of explosion lies with firedamp, because 
its presence, unlike that of coal dust, may remain unsuspected; and 
because it is so easily ignited. Firedamp is only explosive, however, when 
mixed in certain proportions with air, between the ‘ lower limit’ of about 
5 per cent. and the ‘ upper limit ’ of about 14 per cent. If, therefore, the 
gas, as it issues into the workings, is so diluted with air that it never forms 
more than 5 per cent. of the atmosphere anywhere in the mine, it ceases to 
be dangerous. Good ventilation of the mine is thus the primary safeguard 
against firedamp explosions, and there are, in consequence, stringent 
regulations governing the ventilation. 
Supposing, though, that the ventilation fails to be effective, there are 
many potential means of ignition of firedamp in the pit. Each of these 
potential means of ignition—lights, explosives, electricity, frictional sparks— 
has to be safeguarded. Much of the experimental work on safety in coal 
mines, that is being carried out in this country and abroad, is directed 
towards safeguarding all possible means of ignition of firedamp. 
Coal dust, which during one period in the history of coal-mining, con- 
stituted the more formidable danger, can be rendered harmless as an 
explosive agent. Credit, perhaps for the discovery and certainly for the 
practical application of the remedy, stone dust, is due to a Yorkshire mining 
engineer, the late Sir William Garforth. 
The application of the remedy, the spreading of fine stone dust wherever 
coal dust can accumulate in the mine workings, so that the mixture is 
incapable of propagating flame when raised as a cloud in air, appears at first 
sight to be simple, but the problem is complicated by the fact that there is 
not a dead level of inflammability of coal dusts. Some coal dusts are much 
more inflammable than others, and require to be treated with a proportion- 
ately greater quantity of stone dust before they can be regarded as harmless. 
Wise mine managers treat the roadways of their mines with an excess of 
stone dust considerably above that required by regulations ; and it can be 
said with some confidence that, in this country, the widespread disasters 
due to coal dust extending small firedamp explosions throughout the 
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