The subject of colliery explosions has engaged the attention of mining engineers for nearly a century, and experience and science have devised many precautions, with the result that the number of disasters have been greatly reduced during each succeeding decade. Explosions, however, still occur in the best arranged collieries, showing that there are some phenomena not yet fully recognized and understood ; and, with this fact as a justification, the author ventures to offer this paper to the members.

The author had the advantage of investigating the first and second recorded explosions in mines that yield no fire-damp — viz., the disasters at the Camerton and Timsbury collieries, Somersetshire, in November, 1893, and February, 1895, respectively. These disasters provided opportunities for observing the phenomena of two explosions not complicated by the presence of fire-damp. They exhibited the effects produced by an explosive agent, and therefore pronounced its identity, as every agent is identified by the phenomena it produces. The records have this value : they demonstrate that explosions are produced in mines by gases derived from coal-dust and that the processes are originated under ordinary working-conditions and operations ; they also disclose the phenomena which identify explosions from this agent.

The effects of the disaster at the Cammerton collieries were visible from the point of origin for 828 feet towards the coal-faces, and for 3,714 feet in the opposite direction towards the downcast shaft. The phenomena were equally clear at the Timsbury collieries, from the seat of origin to the upcast shaft, a distance of 2,900 feet, and into the several districts that branched off at intermediate points.

In the paths of the explosions, there were several exhibitions of destruction, where men had been exposed to violent forces ; trams of coal hurled off the rails, crumpled up, and their contents scattered abroad ; empty trams broken ; the roof ripped down in large falls ; timber structures reduced to matchwood ; and wrought and cast-iron fittings and pipes torn or broken to pieces. These scenes of destruction were separated by intervals varying from 114 feet to 1,030 feet in length ;¹ and in the intervening spaces the men had suffered no violence, the trams of coal were standing undisturbed, the empty trams were uninjured, the timber and fixtures were in their normal positions, and the iron fittings and pipes were not damaged or displaced. The phenomena of explosive violence at distinct points along the paths of the explosions, and the positive absence of such phenomena in the intervening spaces, demand for their explanation distinct modes of energy.

An examination of the local disturbances, in parallel passages, showed that the materials were displaced in opposite directions ; and where the destruction occurred at junctions, the wreckage was distributed in the entrance of each road. The positions occupied by the displaced materials, indicated the exertion of explosive forces from a common centre, and exhibited the phenomena that must arise in a gaseous explosion, in which disruptive forces are necessarily exerted in radial lines, hurling movable objects in all directions around the gaseous body within a local area. The evidence in the disturbances and in the spaces between them left no room to question the occurrence of distinct local disruptions along the paths of the coal-dust.

Between the points of origin and the first disturbances, there were considerable lengths of road in which the men were found who fired the originating shots, also their cotton food-bags, loaded and empty trams, and timbering. The men had suffered no violence not a bone was broken, nor their clothing disturbed, the food-bags were still hanging from the roof by cotton-tapes, the loaded and empty trams were alike undisturbed, and the timber standing in its ordinary position. Consequently there could not have been either explosive violence or a rapid gaseous movement between the shots and the first disturbances ; the distances were 408 feet, 420 feet, and 573 feet respectively ; and this undisturbed condition of road was repeated between every propagated explosion.

The author numbered the local explosions for facility of reference, and referring to the disaster at the Camerton collieries, he observed six loaded trams of coal in the road between No. 5 and No. 6 explosions, which threw some light upon gaseous movement in the interval of 492 feet that separated these propagated explosions. The trams have an open end, in which lumps of coal are built up, and this wall of coal in the last tram faced the emergent gases of No. 5 explosion. About 60 lbs. of this exposed coal, in lumps of 1/4 lb. To 4 or 5 lbs. each, had disappeared. If the coal had been removed by mechanical force, the lumps or their fragments must have been present somewhere in the road, but the author could not discover any trace of them. He, however, observed heavy deposits of coked coal along the opposing faces of two rods or collars (6 feet long each) fixed next to the roof, almost immediately over the tram referred to. This coke and some fine carbon were the only visible remains of the missing coal, which had evidently been reduced to globules of coke by gases at an exalted temperature. ² Had there been a great velocity in the horizontal movement of the gaseous body that attacked the coal, the particles of coke must have been swept along as they were produced ; but they ascended almost vertically to the faces of the overhanging timber, and were deposited there, indicating a comparatively slow onward movement of the gaseous body, and showing that the disruptive forces of No. 5 explosion were expended in the immediate vicinity of their production, about 120 feet from the tram of coal.

In a stall at the Timsbury collieries, about 210 feet from No. 6 explosion, a tram of coal was found undisturbed upon the rails ; the blocks of coal standing from 15 to 18 inches above the woodwork, the top surface reaching a height of 4 feet above the floor. The hard faces of these blocks of coal all round the tram had been made to burst out into globules of bituminous matter, which underwent further destructive distillation, leaving residues of comminuted coke. Some globules remained attached to faces of coal in different stages of production ; and every ledge of coal, the edges of the woodwork of the tram, and the buffers were loaded with accumulated particles of coke resembling small shot or coarse sand. ³ These particles of coke did not ascend to the roof but gravitated down to the resting-places where they were found ; showing an inadequate horizontal movement, in the gaseous body that attacked the coal, to carry the particles forward ; and that the disruptive forces in No. 6 explosion, which were necessarily of an enormous velocity, were also expended in the immediate vicinity of their production.

Another observation upon the air current at the Camerton collieries, adds to this part of the subject. Between the point of origin of the disaster and the downcast shaft, there were seven violent disturbances, in several of which, the falls were each estimated to measure from 600 to 800 tons of rock and shale. These falls were in the main intake-airway ; the last one being 2,838 feet from the downcast shaft, and the road for this distance approximated to a straight line. During the occurrence of the explosions, the onsetter was standing at the bottom of the downcast shaft, and neither felt nor heard anything unusual. He observed that the flame of his open light was momentarily reversed towards the shaft, but insufficiently to arouse a suspicion that anything was wrong. Another man was standing in the intake at an intermediate point, 1848 feet from No. 10 explosion, and he did not feel or hear anything of the explosions beyond a puff of wind that put out his candle ; he attached no importance to this as it often occurred, the air-current travelling at a high velocity. ⁴

The absence of appreciable force in the movement of the atmosphere between the shot and the first disturbances, in the spaces between the successive disruptions, and at the end of the propagations, with the phenomena of intermittent exhibitions of explosive violence, amount to demonstration that a series of local explosions occurred at the loci of the disturbances, in which disruptive forces were exerted in all directions and expended in their immediate vicinity.

The foregoing phenomena in the atmospheric movement admit the element of time antecedent to each disruption, for the destructive distillation of the coal and the production of the explosive gaseous mixtures, to the ignition of which the local explosions were due. The author has, therefore, described the lengths of undisturbed road that are observed antecedent to each explosion as gas-generating spaces.

Observations made at the loci of the disruptions disclosed the fact that they occurred at the junctions, sidings, where large cavities existed in the roof, at sharp angles in the road when the path of the explosion was against the air-current, and where the door formed a cul de sac. One condition common to these loci was a larger provision of atmospheric oxygen than could be obtained in the antecedent spaces. ⁵

Another branch of evidence was the deposition of coked coal upon the timber, trams, and floor of the workings, which appeared to be deposited in these places under special conditions, and not in the general progress of distillation. In the immediate vicinity of the shot at Camerton collieries, the floor was covered with a crust of coke, and the faces of the timber fronting the shot were thickly coated with coke to a height of 12 inches above the floor, above that point there was very little deposit.

At Timsbury collieries, a tram was standing between No. 4 and No. 5 explosions, from which the author took the following observations :—

Tram loaded with shale, standing upon the rails, had not been disturbed. Coked coal-dust upon the end facing the course of the explosions. The buffer-ends, measuring 12 inches above the floor, covered with coked coal-dust, ¾ inch thick. Many patches of coked coal upon the wooden end of the tram, thinning off to nothing at 21 inches above the floor, the upper 9 inches of the wood being clean. No trace of coke upon the angle-irons, draw-bar, link, wheel, or axles, nor upon any other part of the tram.

An obstruction in the path of the explosions will therefore retain a deposit of coke, if it present a surface at the necessary height, to which the intumescent coal-dust can adhere. The evidence at this tram, which is confirmed by many other observations, shows that the coal-dust upon the floor is subjected to distillation, the particles rising to a height in this case of 21 inches. The coal-dust on the sides and the upper parts of the timber is, no doubt, attacked by the hot educts ; but in the intervals between the explosions, the author observed coked coal near the roof in one place only, and that was at a sheltered plank, which had flakes of coked coal lying upon it. ⁶

In the vicinity of explosions, coked coal was observed upon the opposing faces of timber on opposite sides of the disruptions, and it is not difficult to conceived how the hot, pasty coal-dust would be projected against these opposing surfaces by the forces of the explosions which moved in radial lines.

Where propogations were arrested, with small coal left in suspension in a semi-distilled condition, it is also conceivable that with the atmosphere in front at normal or greater tension, and the atmosphere behind in an attenuated condition due to the chemical changes that had taken place, the suspended pasty coal would retreat and be deposited on the faces of timber contrary to the course of the explosions, and this disposition was observed at Timsbury collieries. ⁷

The deposits of coked coal on the timber lying next to the roof, over the tram between No. 5 and No. 6 explosions at Camerton collieries, will present no difficulty when it is known that the distillation was going on in the face of the incoming air-current, and, consequently, the chemical action was energetic, and the globules of coke were carried upward with the educts.

The comminuted coal at the tram, beyond No. 6 explosion at Timsbury collieries, was in a receding air-current with the supply cut off ; hence only a small quantity of coal was distilled ; and the action was not sufficiently vigorous to carry the globules of coke in resistance to gravitation.

The positions in which the deposits of coked coal were found, are explained by the hypothesis of local explosions with antecedent gas-generating spaces, and the condition of the air-currents.

Observations were made upon the nature of the atmosphere that filled the workings after the disasters. The roads had collapsed locally at many of the disruptions, and the circulation of air was suspended. The products of the gaseous explosions with the residual gases, filled the roads in the fields of disaster, and were imprisoned between the falls ; forming a series of still atmospheres, that could only be displaced by diffusion, until the final obstruction was reached and removed and the circulation of the air restored.

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1 Coal-dust an Explosive Agent, page 30 ; The Origin and Rationale of Colliery Explosions, page 30. 2 Coal-dust an Explosive Agent, pages 68 and 69. 3 The Origin and Rationale of Colliery Explosions, pages 20 and 55. 4 Coal-dust and Explosive Agent, pages 65 and 66. 5 Ibid., pages 72 to 73. The Origin and Rationale of Colliery Explosions, pages 14 and 28. 6 The Origin and Rationale of Colliery Explosions, page 32. 7 Ibid., pages 33 and 52.