EXPLOSIONS IN CONNECTION WITH COAL DUST. BY EDWARD DAVIES, F.C.S. THE causes which lead to explosions in coal pits are deserving of such careful consideration, whether we consider the serious loss of life which so often attends them, or the minor point of the additional cost of coal which the dangerous character of the work entails, that I feel no excuse is necessary for bringing the subject before you. To many persons it will be a revelation that fire-damp, or light carburetted hydrogen, is not the only agent capable of spreading ruin and death in coal mines, and that in mines practically free from gas, or where every precaution in the way of ventilation and the use of the most improved safety lamps is taken, a badly tamped blast may give rise to an explosion in no way less destructive than a fire-damp explosion, either in its direct violence, or in the after suffocation which the gases generated by the explosion produce beyond the range of the actual flame and shock. Yet, just 50 years ago, two of our most distinguished scientific men, Faraday and Lyell, in a report on an explosion in Haswell Colliery, in September, 1844, called attention to the action of coal dust in colliery explosions in the following words : -- “In considering the extent of the fire from the moment of the explosion it is not to be supposed that fire-damp was its only fuel; the coal dust swept by the rush of wind and flame from the floor, roof, and walls of the works would instantly take fire and burn, if there were oxygen enough present in the air to support its combustion; and we found the dust adhering to the faces of the pillars, props, and walls in the direction of, and on the side towards, the explosion, increasing gradually to a certain distance as we neared the place of ignition. This deposit was in some parts half an inch, in others almost an inch, thick; it adhered together in a friable coked state. When examined with the glass it presented the fused round form of burnt coal dust; and when examined chemically and compared with the coal itself reduced to powder, was found deprived of the greater portion of the bitumen, and in some instances entirely destitute of it. There is every reason to believe that much coal gas was made from this dust in the very air itself of the mine, by the flame of the fire-damp which raised and swept it along, and much of the carbon of this dust remained unburnt only from want of air. At first we were greatly embarrassed by the circumstance of the large number of deaths from choke damp, and in the evidence that that had been present in very considerable quantities compared with the small proportion of firedamp, which in the opinion of those in and about the works just before, must have occasioned the explosion. But, on consideration of the character of the goaves and reservoirs for gaseous fuel, and the effect of dust in the mine, we are satisfied that these circumstances fully account for the apparent discrepancy." Subsequently, at the Royal Institution, Faraday said, "The ignition and explosion of the fire-damp mixture would raise and then kindle the coal dust which is always pervading the passages, and these effects must in a moment have made the part of the mine which was the scene of the calamity glow like a furnace." A better instance of the superiority of a thoroughly trained scientific mind over merely practical experience in tracing the cause of obscure phenomena could hardly be found, when two men who probably had no experience in the working of mines, or in the effect of explosions, at once detected a new danger, which generations of practical men had not suspected, and which many of them have since resolutely refused to admit. Notwithstanding this clear and definite warning, twenty years elapsed before any notice was taken of it, and fortythree years before legislation was passed to carry it into effect in the Mines Act of 1887. In 1867, M. Verpilleux made some experiments in France, which convinced him of the important part played by coal dust in colliery explosions. In 1870, Mr. W. Galloway, an inspector of coal mines in Scotland and Wales, began to study the question. As the result he came to the conclusion "That the usual attempted explanation of explosions by supposing outbursts of gas to have taken place was quite untenable, and that there must be some other cause which had not been yet discovered.” This investigation at length convinced him "That coal dust was really the one element which had been up to that time practically lost sight of." In 1875 he made experiments which led him to the conclusion "That if coal dust and air did not form an inflammable mixture, a small addition of fire-damp would certainly make it so," and, as a necessary consequence that "a mixture of air and fire-damp, which would not be inflammable alone, would become inflammable when coal dust was added." Further experiments and examination of the circumstances attending explosions led him to the opinion "That fire-damp is altogether unnecessary for the propagation of flame with explosive effects by a mixture of dry coal dust and air." These views were by no means generally accepted, but attention was now drawn to the subject, and experiments were made in England, France, and Prussia, which on the whole gave support to all these theories; and to the experiments made by Mr. Hall, inspector of mines for the South Lancashire district, I will now draw your attention. It had been accepted as a fact that danger from coal dust did not arise unless there was a great disturbance of the dust and a large body of flame, such as would be created by a blown out shot of gunpowder. To imitate this, a small cannon was used as the igniting agent. To render the conditions as nearly as possible like those in the actual working of a mine, and as it was impossible to diffuse the coal dust in a horizontal roadway, a disused pit shaft was employed. A large quantity of fine coal dust was obtained from coal pits where it had deposited in empty spaces along the roadways, and from the timbers which supported the roofs, and this was distributed down the shaft by a sieve. MR. HALL'S EXPERIMENTS. White Moss Colliery Co., Ormskirk, 1890. Shaft 50 yards deep and 7 feet diameter. A cannon, 2 feet 6 inches long and 2 inches bore, was fixed at bottom and pointed directly upwards. It was fired by electricity. Coal dust was sifted from the top into the shaft. 1. 2 cwt. Coal dust, & lb. Gunpowder-No explosion. 2. 2 cwt. 1 lb. Violent explosion, flame 20 feet above top of shaft. Dust ignited, flame 20 feet above top. Cannon fired 20 minutes after dust was put in. 4 oz. Roburite- No ignition. |