145 



COAL-DUST AND EXPLOSIONS IN 

 COAL-MINES. 



Rev. ARTHUR WATTS, F.G.S., F.R.G.S, 



Vice-PrviciJ>al, Bede College, DicrJinvi. 



An explosion in a coal-mine, whatever the cause, is a sudden, and for 

 a short time a continuous, demand for more space in certain or all 

 passages of a mine. It must be borne in mind that space is, in 

 mines, limited in all directions save one, viz, that towards the shafts. 

 This demand for more space is consequent on the presence and 

 propagation of such heat as will produce incandescence in certain 

 materials present ; for example, that developed in the firing of a shot 

 or of a local accumulation of gas. The demand arises from expan- 

 sion of the air already filling the passages, and wherever dust 

 participates, from the generation of new gases by the act of combus- 

 tion, which thus increases the pressure by making an addition 

 through the conversion of what was solid, into a gas. When some 

 or most of these thus-formed gases are themselves fiercely com- 

 bustible, the character of the combustion is so intensified that it is 

 called an explosion. Hence the varying nature of coal-mine 

 explosions, and hence initial causes, at one time operative, are at 

 another time inoperative, not from lack of cause, but from lack of 

 proper material on which the cause can act. Hence too, frequently, 

 not the whole mine, but certain passages only are invaded, because 

 combustion can only go where inflammable material is found. The 

 inflammable materials in coal-mines are, firsts fire-damj^, usually 

 spoken of as gas, found, more or less, in all such mines ; and second^ 

 coal-dust, found chiefly in dry mines, which are mostly the deep 

 mines. This second must be in considerable quantities to become 

 an effective agent. Now, these two materials do not ignite with 

 equal ease or under precisely the same conditions. Gas fires much 

 more readily than dust, and under different conditions. The conditions 

 under which fire-damp can produce an explosion may be considered 

 settled ; not so those under which coal-dust may. Indeed, until 

 lately the latter was not considered capable of i^roducing an explosion, 

 and there' are still some who do not think it is, in spite of apparently 

 irresistible facts. Yet the gas which is the cause of explosion in the 

 one case, is the cause in the other too, for the main difterence will 

 be found to be one of time— of /rz.v/ and of present release of the 

 same substance. The gas in the one case is already free, whilst it is 



iM.iy 1888. 



