316 RESPIRATION 



Colliery explosions were formerly attributed simply to ex- 

 plosions of fire damp. About 40 years ago it was first clearly 

 pointed out by Mr. Galloway that this explanation is unsatis- 

 factory, and that the spread of an explosion must be due to coal 

 dust. Further evidence of the predominant part played by coal 

 dust in all great colliery explosions was soon brought forward; 

 and it became clear that many explosions occur in the complete 

 absence of fire damp, the coal dust being originally stirred up and 

 lighted by the blowing out of flame in blasting, and the explosion 

 carried on indefinitely by further stirring up and ignition. In other 

 cases the starting point is some, perhaps quite small, explosion of 

 fire damp, caused by a defective lamp, a spontaneous fire in the 

 coal, or perhaps even by a spark from falling stone. The ease with 

 which coal dust explosions may be produced by blasting when 

 even a very little coal dust is lying on a road, and the astounding 

 violence which they may develop after the flame has traveled 

 about a hundred yards, were strikingly shown in experiments 

 made with pure coal dust at Altofts Colliery under Sir William 

 Garforth's direction. 10 On account of their danger in a populous 

 neighborhood these experiments were transferred to Eskmeals on 

 the Cumberland coast; and finally showed that when an equal 

 weight of shale dust or other similar material was present along 

 with the stone dust the mixture could not be ignited by blasting 

 or gas explosions. 11 



Sir William Garforth's plan of stone-dusting all the roads in 

 collieries with shale dust, so that at no point is there more than 

 half as much coal dust as shale dust, has now been adopted very 

 generally in Great Britain ; and the only serious recent explosions 

 have been in mines where this precaution was not adopted. Stone- 

 dusting is far more efficacious and cheaper than watering the 

 dust; and indeed efficient watering is impossible in many cases, 

 owing to the effect of water on the roof and sides of a colliery 

 road. 



In the Altofts experiments, samples of afterdamp were analyzed 

 by Dr. Wheeler. The following is a typical example. 



Carbon dioxide 11.9 



Carbon monoxide 8.6 



Hydrogen 2.9 



Methane 3.1 



Nitrogen 73.5 



10 Record of British Coal-dust Experiments, 1910. 



11 Reports of the Explosions in Mines Committee, Parl. Papers, 1912-1914. 



