1887.] 



A Coal-dust Explosion. 



175 



pieces of broken roof, which completely obscured any small quantity 

 of coal or coal-dust that might have fallen upon it, and been left 

 there in the process of coal-getting. 



The tubs consist of rectangular wooden boxes, mounted on 

 wooden frames, with wheels attached to them. They were filled 

 with coal to a level with the top, and then contained about 10 cwt. 

 Thus, although no coal could fall over the ends or sides, the vibration 

 due to the operation of hauling caused coal-dust and small pieces of 

 .coal to be shaken out through the seams in the sides and bottom on 

 to the roadway beneath. Here it accumulated little by little between 

 the rails, and to a distance of a few inches on each side of them, and 

 the attrition due to the constant trampling of men and horses, 

 together with the occasional dragging of the endless chains on the 

 floor, gradually reduced it to a state of fineness. The quantity of 

 coal-dust which accumulated on any roadway was thus, other things 

 being equal, proportional to the number of full tubs that had passed 

 along it from the first ; so that the oldest roadways would naturalty 

 be the dustiest, were the accumulations not removed from time to 

 time. 



Each return air- way represents the continuation of a stall road all 

 the way from near the bottom of the up- cast shaft to the face, and it 

 must therefore contain in any given section of its length about the 

 same average quantity of coal-dust as any ordinary stall road. But 

 the return air- ways are all used as travelling roads for the men and 

 hoys going to and from the faces, and the constant trampling of 

 feet soon mixes up any little coal-dust there may happen to be on the 

 floor with the dust of the roof-stuff, and reduces the whole to an 

 impalpable powder of a light grey colour. 



The following conditions thus prevailed before the explosion : — 



1. An unusual immunity from fire-damp. 



2. Very excellent ventilation. 



3. Blasting going on at the rate of say 2000 shots a year, involving 

 the consumption of upwards of two tons of powder in the same time, 

 and this within the zone of subsidence where, practically speaking, 

 all the fire-damp was given off, and where there was no coal-dust. 



4. Pure air filling the intake air- ways from the bottom of the 

 down-cast to the faces. 



5. Air containing all the fire-damp in the colliery filling the 

 working, places and the return air-ways from the faces to the 

 up-cast. 



6. Coal-dust in the intake air-ways decreasing rapidly near the 

 faces. 



7. Light grey dust of roof-stone, but no visible coal-dust in the 

 return air-ways. 



The colliery had been carried on under these conditions for seven- 



