EXPLOSIONS IN COLLIERIES AND I HAVE read Mr. Plimsoll's article in the December number of the Nineteenth Century, on Explosions in Collieries and their Cure;' and, agreeing with him that their cure is within the possibilities of science, beg to add my appeal on behalf of the miner to scientific men. For mining is now no longer a matter of rule of thumb, and we cannot hope for any real improvement except from persons who are thoroughly well acquainted with those natural laws upon which all science is based. But before they are in a position to grapple with the question, it seems to me essential that the way should be cleared for them by some one practically acquainted with mining, lest their energies be wasted over impracticable schemes, or in the solution of problems not directly bearing upon the point at issue. I propose, therefore, first, to point out one or two errors into which, it appears to me, Mr. Plimsoll, in common with more than one person of the highest scientific attainments, but, as I may conclude, practically unacquainted with mining, has fallen; and, secondly, to lay before your readers the real problem which I believe must be solved before we can hope to place any definite limit to these disastrous accidents. Perhaps I should premise, in order to elucidate further a subject so technical as mining, that coal is found in beds varying in thickness from a few inches up to several feet, and extending with great regularity over large areas. These beds are seldom found lying either quite horizontally, or quite vertically, but are found inclined at all angles between these two extremes. There is also a great variety in the quality of the seams of coal, in the quantities of gas that exude from them, and in the character of the rocks between which they lie. We should, therefore, be naturally led to anticipate, and rightly so, that there are many systems of working coal so as to suit these varying conditions of its occurrence. It would be impossible, within the limits of this paper, to describe even the more important of these methods, but I will try, in a few words, to make one of them-viz. the 'Board and Pillar' system of the North of England-sufficiently intelligible to your readers for my 6 purpose. I choose this method of working the coal for explanation in preference to others, because in connection with it goaf-drainage was, I believe, first mooted. This system of coal working will be readily understood from a consideration of it, as illustrated by the name échiquier' which it bears in France and Belgium. The black and white squares represent the pillars of coal left during the first working to support the roof of the mine. The lines separating these squares are the drifts or excavations made in the coal during the first working, or in working the whole,' as it is called. Afterwards the black and white squares, i.e. the pillars which have been left to support the stråta above, are removed; and this, the second working, is called working the broken,' or 'working out the pillars." The empty area left by the extraction of the coal, which, however, is soon filled up by falls of stone from the strata overlying the bed, is called the 'goaf.' This term 'goaf,' plural 'goaves,' is applied to the area from which the coal has been extracted, whatever be the system of working employed. I shall have more to say about the character of a goaf presently. A seam, when first cut, gives off inflammable gases in larger or smaller quantities, according to the character of the coal, which gases, as Mr. Plimsoll has pointed out, being lighter than air, tend to collect in the higher parts of the workings. When mixed with air, in the proportion of one volume of gas to from five to fourteen volumes of air, they become explosive; and one of the principal objects of ventilation is to dilute these gases with sufficient air, so as to render them harmless, and then to carry them off out of the mine. By gas I shall here mean these inflammable gases, and by fire-damp an explosive mixture of these gases and air. I shall pass quickly over the first four of Mr. Plimsoll's suggestions. Three of them-viz. mordants, collodion balloons, and absorption-would no doubt render valuable aid to the miner if practicable; but whether they are so or not I must leave to chemists to decide. One, the absorption of the gas, has already been attempted, but hitherto without success. The fourth suggestion, the explosion of the gas in regulated quantities after careful examination of its first beginning to accumulate, was the system in vogue before the invention of the safety-lamp. Simonin mentions it in his book, La Vie souterraine, page 179, where also may be seen an engraving of the miner in the dress specially adapted to his dangerous work. I cannot do better than quote his description : En France, à Rive-de-Gier, on se rappelle encore le temps où un homme, courageux entre tous, venait tous les soirs enflammer le gaz dans la mine, en provoquer l'explosion, pour que les chantiers fussent de nouveau accessibles le lendemain. 1 I see, in connection with the Penygraig accident, which happened so recently as December 10, that the Rev. T. Jones, of Rhymney, is confident that he has now discovered the solution of his problem. Roulé dans une couverture de laine ou de cuir, la figure protégée par un masque, la tête couverte d'un capuchon analogue à la cagoule des moines, il rampait sur le sol pour se tenir autant que possible dans la couche d'air respirable, car le grisou, plus léger que l'air, monte toujours au sommet des galeries. Il tenait d'une main un long bâton, au bout duquel était une chandelle allumée; et il allait seul, perdu dans ce dédale empoisonné, provoquant les explosions par l'approche de sa lampe et décomposant ainsi le gaz pernicieux. On l'appelait le pénitent, à cause de la ressemblance de son costume avec celui des ordres religieux; et ce mot semblait en même temps dicté par une dérision amère, car souvent le pénitent, victime sacrifiée d'avance, ne revenait pas, emporté par l'explosion. Sur d'autres mines on nommait ce brave houilleur le canonnier. Quand le grisou le tuait sur place, on disait que le canonnier était mort à son poste, au champ d'honneur, et c'était là toute son oraison funèbre. Le même ouvrier portait dans les mines anglaises le nom expressif de fireman, ou l'homme du feu. I need hardly add, that though this system, under very careful management, might do some good service, it has long since been abandoned. The method of ventilation proposed by Mr. Plimsoll is good; for not only is the gas lighter than air, as he has pointed out, but the air of the mine, being heated by contact with the warm surface of the stony strata, is lighter than the cool air coming down from the surface, and for the same reason it becomes lighter and lighter the further it travels through the passages of the mine. Its natural tendency is, therefore, to rise, like the gas, as it proceeds on its course towards the upcast shaft; and accordingly the current of air, as well as the gas, is most easily kept in circulation when this natural tendency is not obstructed. The downcast, or shaft for entry of air, should therefore be placed near the lowest point of the area of the coal working; the upcast, or shaft for exit of air, near the highest (the area being in almost all cases on an incline). This, a fact well known to mining engineers, is called ascensional ventilation, and is always carried out in the working where practicable; but sometimes it is impossible to carry it out effectually, for many conflicting interests may interfere with the choice of a situation for the shafts of a mine. I now come to Mr. Plimsoll's principal suggestion-viz. that the gas should be drained off by means of a pipe placed in a hole or sump 'made for it in the roof of the upper exhausted spaces in a pit, ie. in the highest point of the goaf, and carried from this sump to the upcast shaft. This idea was brought forward, whether for the first time or not I cannot say, by Messrs. Faraday and Lyell at the Haswell Colliery explosion in 1844. A description of their apparatus was published by them in the Philosophical Magazine (third series, vol. xxvi. p. 16). A committee of mining engineers was appointed by the coal-trade of the north of England to examine and report upon this scheme. After a most careful consideration of the matter, they pronounced it not only infeasible, but of very doubtful benefit, even could it be carried out. Their report 2 is too long for quotation in full, but a summary of the parts bearing upon this question will show the impracticability of the scheme. Goaves are not limited in their dimensions, but ultimately, by the continued progress of the pillar excavations, come to be coextensive with the tract of coal-field which is being worked. It thus happens that there will be a greater or less magnitude of goaf, corresponding with the quantity of coal extracted, and that, at last, the mine will consist exclusively of goaf in any seam the coal of which has been entirely removed. It must further be remarked that there is not any certainty of an open communication between one part of a goaf and another part of the same goaf: the contrary is indeed the rule, as may be easily understood from the following considerations. The immediate effect of the removal of a pillar of coal is to produce a fall from the bed of stone resting upon the coal; and the cavity made by this fall of stone is necessarily of a conical form. As the coal continues to be removed, the sides of the cavity lose their support, the cone is extended; and this process goes on until the superimposed strata, no longer sustained by the converging sides of the cone, subside, and rest upon the broken fragments of the fallen stones, which occupy a much larger space than did the same rocks when in a solid state. The summit of the cone does not then continue to extend upwards, but, as the excavation progresses, the strata rest upon the mass of stones forming the goaf, and the upper portion of the goaf becomes parallel with the lines of stratification. This is proved by the state of the upper beds of coal a few fathoms above the lower bed, which has already been extracted. The settlements and fissures there show that in some parts the fallen mass must be crushed extremely close, and that, in others, cavities may exist; the effect produced being, in fact, that of rendering the interior either, practically speaking, solid, or of dividing it into compartments which are isolated one from another. It must too be noticed that a passage will not remain open between the bounding edges of the goaf and the remaining coal yet unworked. Accordingly, the cavities in a goaf being isolated and detached, a pipe placed at its upper edge could not be depended upon as draining it throughout its entire space, and it would therefore be necessary to have a separate pipe at each avenue leading into each goaf. Further, at Haswell Colliery, to carry but one cast-iron pipe of the dimensions proposed by Messrs. Faraday and Lyell (twelve inches diameter and half an inch thick in the shell) from each of the fourteen goaves to the upcast shaft would require rather more than twelve miles of pipes, and would cost about 21,000l. As regards the current expense of maintenance, it is impossible to form any accurate estimate; but it would be extremely difficult to keep the goaf ends of the pipes in working condition, and a Published by I. H. Veitch, the Chronicle office, Durham, 1845. fracture there, which is very likely to occur, would destroy the entire value of the apparatus. Moreover, the constant attention which would be required to keep in order the goaf terminations of the several ranges of pipes must without doubt, in so dangerous a situation, be attended with risk of frequent loss of life from falls of the broken strata. I will now quote the last few lines of that portion of the report which refers to my subject: Your Committee have shown that the actual state of goaves is incompatible with that required for the efficient working of the apparatus suggested by Messrs. Faraday and Lyell; and, having also duly considered and explained the extreme difficulty, expense, and almost, in their opinion, impracticability, of carrying into execution the plan recommended by those gentlemen, together with the extreme uncertainty of its success, they regret exceedingly that they cannot recommend it for adoption. The proposed scheme of gas drainage, introduced to your readers by Mr. Plimsoll, is, as I have already said, identical with the above. It has been before the public for thirty-six years, but no one, as far as I am aware, has attempted to put it into practice. Several other plans have been proposed at different times with the same object in view, i.e. the draining off of the gas. Many of them are quite impracticable; but two, I think, are deserving of the consideration of mining engineers, viz. : Where an inferior seam of coal exists, of sufficient thickness, a few fathoms above the one which is being worked, drifts might be driven in it and boreholes put down from these drifts into the goaves and other places where gas was known to be, or thought likely to accumulate; and these drifts being put in communication with the upcast shaft, a current of air would sweep through the goaves and up through the boreholes into them, carrying with it the gas. These drifts would have to be driven a considerable distance ahead of the workings in the lower seam, so as not only to offer a vent for the accumulations of gas in the goaves, but to tap the gas also in the solid coal. In this way these excavations would also become exploring drifts, and would prove the existence of faults and other geological features of the area, thus enabling the engineer to lay out his workings in the lower and more valuable seam to the best advantage. Another idea, which was carried out with considerable success at Springwell Colliery, in Durham, is to drive drifts in the solid coal a few yards to the rise' of each goaf and parallel to it (meaning by the rise any spot higher up the slope formed by the inclination of the bed). These drifts may be connected with the goaf, where deemed expedient, by means of other short drifts, and, the first being put into communication with the upcast shaft, a current of air is carried through the goaf into them, and the gas along with it. There are, indeed, difficulties in the way of carrying out both these schemes, which will be patent to members of my profession; |