Explosions in Coal Mines, 23 



Where the men are at work, this tendency is guarded against 

 by the force of the current sent in, which sweeps the air al- 

 ready there before it; but in the goaf, near which the current 

 is slow, where the roof is a large concavity, where the gas, if 

 present, is likely to be present in greater quantities, and so to 

 make a mixed atmosphere which is lighter than that in the 

 working parts of the mine, there the current probably never 

 ascends to any height, but takes its way sluggishly through 

 the lower parts of the goaf, or moves round the outside of it. 

 We think it probable that the current does not rise much 

 above the level of the highest point in the edge of the goaf 

 basin, and that the top of the goaf is seldom, if ever, reached 

 by it in any sensible degree. 



We have thus far considered the goaf as if in something 

 like a constant state, but there are occasions of sudden and 

 limited disturbance which affect the atmosphere of gas within 

 and about it. The evidence at the inquest states, that a rum- 

 bling was heard on the morning of the accident within the 

 goaf, and this was probably a fall somewhere from its roof. 

 Such falls tend to mix the lighter and heavier strata of gas 

 and air, and so virtually cause the gas to descend. Again, 

 if the atmosphere four or five feet up in the goaf be an ex- 

 plosive mixture, and a fall of this kind take place there or near 

 it, such an event is very likely to throw out a portion of ex- 

 plosive mixture into the workings of the mine, not merely by 

 the agitation, but also by the mixture of upper with lower 

 strata of air, making the lower explosive. 



One cannot but suppose that another source of sudden and 

 partial evolution of gas or explosive mixture from the ^oa^ 

 may be the fall of upper parts of its roofs, and the crushing 

 of the rocks there, by which gas pent up into the seams of 

 coal above and the strata associated with them, has passages 

 open for its escape into the goaf. If a bag of gas (as it is 

 called) were thus opened into the goaf, it would rapidly in- 

 crease the quantity of gas in it, and might soon cause explo- 

 sive mixtures, or the gas, almost pure, to underflow the edge 

 of the concavity into the mine. 



If the goaf cavity were full of gas or explosive mixture to 

 the highest edge level, the mechanical fall of the roof, in 

 drawing a jud close to that edge, would, by mere agitation, 

 drive some portion of the gas or mixture into the workings of 

 the mine. 



When a jud is drawn, and the roof has fallen in, the fall 

 becomes part of the goaf, and the cavity left by it becomes a 

 part of the goaf basin, the edge of the basin extending to, and 

 enclosing the new fall. If this take place at the highest point 



