Report to the secretary of state for the home department on the causes of death in colliery explosions and underground fires, with special reference to the explosions at Tylorstown, Brancepeth and Micklefield / by John Haldane.

  • John Scott Haldane
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: Report to the secretary of state for the home department on the causes of death in colliery explosions and underground fires, with special reference to the explosions at Tylorstown, Brancepeth and Micklefield / by John Haldane. Source: Wellcome Collection.

Provider: This material has been provided by London School of Hygiene & Tropical Medicine Library & Archives Service. The original may be consulted at London School of Hygiene & Tropical Medicine Library & Archives Service.

    14/52 (page 12)
    When fire-damp is said to be sharp, this seems usually to signify nothing else than that the line of demarcation between the fresh air and fire-damp is very sharp. Under favourable conditions this line will be far sharper than that between a layer of pure air and black-damp, since the difference in specific gravity (about 80 per cent.) between pure fire-damp and air is far greater than that between air and pure black- damp (about 4*5 per cent.). In many cases the line of demarcation is so sharp that there can be only a very thin intermediate explosive layer. The gas above this layer will be inexplosive, on account of the presence of more than 11 or 12 per cent, fire- damp. This upper layer will burn quietly when it is in contact with fresh air below. The facts just referred to make it evident that in m©st fire-damp explosions there must be, in parts of the explosion, not sufficient oxygen for complete combustion. In such a case the chemical reaction is complicated, and without further experimental data it would be difficult to say exactly what the quantities would be of the various products formed under the conditions which prevail in a pit. Instead of carbon dioxide and aqueous vapour, a variable mixture of carbon dioxide, carbon monoxide, aqueous vapour, and probably hydrogen, will be formed, and these, when mixed with about 80 per cent, of nitrogen, and any undecomposed fire-damp, will constitute the after-damp. The latter will evidently always contain less than 12 per cent, of carbonic acid, but what is of more interest in connexion with the present inquiry, is the propor- tion of carbon monoxide liable to be formed. There are reasons for believing that this proportion is by no means high. It is well known that in ordinary laboratory experi- ments it is impossible to explode, either by introducing a flame or by means of the spark yielded by the common induction coil, mixtures of air and fire-damp containing more than a very slight excess of the latter gas. The excess of fire-damp in some way prevents the explosion. A similar excess of an indifferent gas, such as nitrogen, does not exercise this influence. As the result of a recent investigation, Professor Clowes finds that mixtures containing more than 11 to 13 per cent, of methane will not explode. In experiments with natural fire-damp,* I have myself found that an ordinary spark would not inflame a mixture containing ll'l per cent, of fire-damp in air, although with 1O0 per cent, a violent explosion occurred. With the latter propor- tion 9'34 per cent, of carbonic acid, and (according to a calculation), about 27 percent, of carbon monoxide were present in the residual gas or after-damp. Hence it would seem probable that in an explosion with an excess of fire-damp, and without dust, not more than about 3 or 4 per cent, of carbon monoxide will be formed in any part of the track of the explosion. The matter, however, certainly requiries further experi- mental investigation, under conditions such as occur in an actual pit explosion. The case of the after-damp from a dust explosion is, of course, by far the most impor- tant. In all the great colliery explosions the flame seems to be propagated by dust, although in some cases the firing of a small collection of fire-damp has originated the explosion.f Since the explosion usually passes along the intake air-ways, which are free from fire-damp, it may also be assumed that the after-damp is practically due to the explosion of dust and air alone, and not of a mixture of dust, fire-damp, and air. The physical and chemical conditions which prevail along the track of an explosion as it sweeps along the roads of a pit are as yet by no means clear. It seems probable, however, that there is not a complete combustion of the particles of coal dust, and that what burns in the explosion is gas distilled off by these particles. After an explosion the bodies of the men (see above, p. 3) and the timbers (especially in places where little force has been developed) are often found encrusted with melted, or partially coked dust. The half melted particles of dust have evidently lost part of the gas which they yield on dry distillation; and, doubtless, this gas feeds the flame. Each particle will be protected against complete combustion by the absorption of heat which must occur in the process of heating and dry distillation, and the consequent impossibility of the occurrence of a sufficient rise of temperature in the particle to render complete combustion possible before the surrounding oxygen is consumed. As to the products of combustion, there must, in the absence of experimental data (obtained under the conditions prevailing in a pit), be much uncertainty. The gas given off by the coal dust will probably somewhat resemble crude (unpurified) coal gas; most of this will probably be burnt, but an unburnt excess may remain behind to swell the volume of after-damp. Ordinary crude coal gas is a variable mixture, * Artificially prepared fire-clamp usually contains hydrogen. The pit gas employed contained 86'] 8 per cent, of fire-damp. t According to Mr. Robson's evidence, the Tylorstown explosion -was probably originated by the flame from a blasting shot in the roof of a stall igniting a small collection ot fire-damp, which in its turn ignited the dust.