MINING MAGAZINE: DEVOTED TO Mines, Mining Operations, Metallurgy, &c. &c. VOL. III.-JULY, 1854.-No. I. ART. L-THE VENTILATION OF MINES AND COLLIERIES.*-Br JOHN PHILLIPS, F. R. S. THE districts of Northumberland and Durham, in which coal is found, occupy a large part of these counties; but of this great area the portion formed by the mountain limestone or lead measures, (about two-thirds), and that covered by millstone grit, yield but small supplies of coal, though in some places, especially in shales, they are productive of ironstone. The total thickness of the coal series (including the millstone grit, to the top of the little limestone) was given by Mr. W. Forster in his mining section at nearly 1,600 feet. Of this thickness coal makes about 50 or 60 feet, or one-thirtieth part. The vertical section of the coal and ironstone series of Northumberland and Durham, including the millstone grit, presents the following beds of coal, of which scarcely any but the lowest seams are continuous over all the tract of the Tyne, Wear, and Tees; though almost every one has been found workable in some part or other. The inclination of the strata is, in a general sense, eastward, and, though very moderate, sufficient to render almost inaccessible near the seacoast the lowest beds of the series. The pits in the extreme eastward range have already reached the depth of 1,800 feet; but the beds are here so nearly level that, except for the purpose of reaching lower seams (which is not likely to happen), this may be esteemed nearly the utmost depth that will be realized. The heat at this great depth is considerable (at Monkwearmouth it is 86° in the workings); the fire-damp is not less abundant; the area to be wrought from one pair, or one system of shafts, becomes greater, in order that the enormous expense of these shafts may be repaid; and thus all things concur to render these deep eastern collieries more especially worthy of the application of all the resources of capital and skill. * Presented to both Houses of Parliament by command of her Majesty. The lower coal strata rising westward are exposed in so many dales and round the edges of so many hills as to have been easily traced, opened, and worked by the "old men." It was in these western tracts (I believe) that the working of coal in the Newcastle district first commenced. The superior quality of the high main (the uppermost good seam) near Newcastle drew away the trade; but as this and other good seams of the upper and middle coal series have become occupied by many establishments, capital and enterprise have again flowed to the west and north-west, and the lower coal seams have been opened afresh. Old wastes accordingly are met with; old pillars left by former coal-owners are discovered, and removed or abandoned; and the ventilation and drainage are sometimes affected by cutting into old levels and underground roads. Under such circumstances ancient plans become very valuable; for want of them water may be encountered in excess, or a barrier of unnecessary breadth left because of uncertainty. The abundance of crop workings; the ample exposure of the strata at the surface; the moderate depth of the coal seams below the surface; are circumstances which give to the western collieries a nearly entire immunity from fire-damp; choke-damp ("stythe") is perhaps rather more frequent in them than in the collieries farther east, excepting such as are established on a particular seam called on the Wear the "Five-quarter" coal. The most persistent of the coal seams are, as in Yorkshire and Derbyshire, of the lowest groups in the millstone grit, and in the series next above that rock. In the middle part of the series the Hutton seam of the Wear (Low main of the Tyne) has a great range, the High main a comparatively small extent. The quality of the seam varies with the district. The Hutton seam, for example, yields a fine house coal on the Wear, and superior steam coal in the country north of the Tyne, but in the immediate vicinity of this last-mentioned river it is of an indeterminate quality, though approved in the gas works. The High main, Bensham seam, and Hutton seam, have been found very fiery coals according to the locality; the Five-quarter seam on the Wear is remarkably otherwise, and rather disposed to yield stythe (carbonic acid gas). The issue of fire-damp takes place from the fresh-cut face of coal by the innumerable small fissures due to the cleavage or "cleat," a structure of great importance for the arrangement of the underground excavations. Larger fissures are found occasionally to yield correspondingly larger streams of gas; and in the vicinity of slip dikes (faults) discharges are generally looked for, and they have proved often so considerable as to give origin to the title of "blowers" and "bouks" or "bags" of gas. The extrication of gas is on such occasions rather rapid. In the course of 1846, a blower which was cut in Walker Colliery yielded so much gas as to "foul" a portion of the mine 641 yards long, and containing 86,306 cubic feet, in a few minutes. Jets likewise burst up from the "thill" (floor) of coal-beds, and bring (usually with water) either the gas of that coal, or what is yielded by a seam beneath. There is no district in the kingdom where the desire of abundant ventilation is more strongly felt, or more energetically carried out, than in the country which adjoins the rivers Tyne, Wear, and Tees. The deep collieries could not possibly be worked at all without the aid of artificial and powerful means of producing air currents; the shallower collieries could not be worked so extensively without the adoption of similar means; fire-damp and choke-damp almost everywhere require to be expelled, and the result is an almost universal employment of ventilation force. The efflux of gas may, so far as it is regular, be rendered quite innocuous by sweeping the working faces with strong and constant streams of fresh air; but the irregular discharges from jets or blowers have been found so large, as in some cases to overmatch the ventilation, impregnate the air to a dangerous degree, and generate explosion. The wisest precautions are required to meet these dangerous issues of gas. By borings kept well ahead toward the lines of "slip dikes," the discharges which might suddenly empty these large gas-holders, are sometimes rendered slow, regular, and easily manageable; the gas being, occasionally, with safety, lighted, and actually burnt away. By similar means, viz., boring through the thill, or sometimes into the roof, as the works proceed, gas channels become established on which pipes may be fixed, so as to exhaust, by a long and slow discharge, the gas which has been treasured up in the adjoining fissures. If these methods fail, and the gas-jets be thought unconquerable, and the works are to be prosecuted, the Davy lamp must be exclusively used under strict and rigorous discipline. It is hardly possible to feel greater confidence of safety in any situation, than while traversing, candle in hand, the main. galleries of a well-ventilated mine; there is no sign of fire-damp; pure air flows in a full steady stream, which in a moment extinguishes the incautiously held light; and its cooling effect is fully equal to that of a moderate wind. As we proceed along the minor galleries, after one, two, or more "splits" of the current, and enter the working "bords,"* this feeling diminishes, the airstream is more languid, the warmth augments, the fire-damp issues silently, or with a slightly hissing or tinkling noise, by myriads of minute threads or bubbles, and we remember that except there be fifteen times as much atmospheric air, as of the inflammable gas at every point of the working space, explosive This is the usual miner's spelling of a word whose meaning, now become technical, is derived from the board-like structure imparted to coal by vertical fissures, called cleat, sline, back, &c. * combustion may ensue. It is at the working faces where the hewers are toiling to undercut the seam, with lights brought near to the issuing and resounding gas, that the necessity of a strong, equal, unintermitting pressure upon the air, to force it through the indirect and abruptly angulated passages of the mine, is fully impressed upon the mind. When, in the fresh headings of a fiery mine, we hear the gas at every crevice, and see it bubbling up in large quantity from small pools and wet places in the thill at intervals of a few fathoms, it scarcely needs the splendid experiment (often made) of lighting the gas, so as to cover the coal with a sheet of pale flame, or excite a more violent blaze on the floor, to testify to the importance of the safety lamp, which, while enlarging its own flame to give warning to the prudent, refuses to kindle the atmosphere around it, and thus often prevents the dreadful fate which one rash or ignorant miner, or one negligent manager, might bring upon a hundred souls. By what has been said, it appears that the extensive working of coal, in the deep fiery mines of the north of Ergland, is accompanied essentially with circumstances requiring on the whole more vigilance and precaution than in Derbyshire and Yorkshire, taken generally. But we have been speaking of the whole coal; it is still more the case in the broken. When the pillars left at some former period are to be removed, candles are rigorously excluded in well-managed collieries; for the difficulty of commanding and keeping a good clear ventilation is so great, that even the small quantity of gas yielded by the pillars (which are surrounded, and, in fact, drained by old air passages), and the uncertain and irregular additions from the falling roof, heaving thill, and breaking ground around, render the lamp indispensable. In such situations it is possible to breathe and work, while the lamp is filled with flame, but in every well-managed mine such an experiment is forbidden. Finally, when the passages which remain open through the waste, and touch upon the fallen materials which constitute the mysterious recesses of the goaf, are traversed by the wastemen, the lamp alone is trusted. It is saddening to reflect that powerful ventilating currents of air, and safety lamps, which, under judicious management, offer an almost impregnable guard against danger, have not been always so employed as to afford constant protection against explosion. Accidents have happened, from known and unknown causes, in the best-managed collieries, and there is certainly an impression rather general, among intelligent viewers, that they must still be counted as among the ineradicable obstacles to the satisfactory and profitable conduct of a great colliery in a fiery *This operation is called "kyrving" in the Newcastle district. This word, goaf, equivalent to the gob of Midland Counties, seems to have a Cymraic origin in ogof, a cave or hollow, seam. Before adopting this conclusion, let us survey more in detail the mode of working; gather examples of the evolution. of gas under different circumstances; discuss the methods of ventilation; and inquire into the precautionary discipline of the mine. GENERAL VIEW OF THE WORKING PROCESSES AS AFFECTING THE EXTRICATION AND ACCUMULATION OF FIRE-DAMP AND CHOKE-DAMP. Though, as might be expected, the great and numerous collieries of the northern district, sunk to various depths, to seams of different thickness and quality, lying flat or variously inclined, much or little broken by slip dikes, and traversed irregularly by whin dikes, offer a large variety of mechanical combinations to meet special cases, as bratticed shafts, two, three, or many shafts, self-acting planes, engine-planes worked from the surface, or by high-pressure steam below, there is an approach to general conformity in the methods and contrivances, according to which the coal is actually got, and brought from the working places to the main roads, and ultimately delivered at the surface. The order of the operations is this:-the coal is cut and got by hewers; it is then moved in the tubs through the first passages by putters; horses draw several of these tubs to the shaftfoot, or to stations on the main roads, according to the plan of the colliery; and their labor is completed by the steam-engine. Only one of these processes (that of the hewer) has any direct or collateral effect on the extrication of gas, but they all have an important bearing on the plan of the underground roads and the methods of ventilation. The roof which overlies the cavities made by hewers may have a tendency to fall in, and pour inflammable gas into the roadways or air channels; the thill or floor may be subject to heave and discharge gas upwards; there may be in front of the workings, especially along lines of dislocation, undiscovered reservoirs of such gas; it may accumulate in the broken ground or goaf, which, once abandoned, is almost never explored again; all these are to be expected, occasionally. as consequences of the advancing excavation; but the main source of inflammable gas in the northern collieries, that which yields by far the greater, though (with good ventilation) not the most dangerous supplies, is the cutting of the fresh coal in the ordinary process of everyday work. The method of getting coal now employed in the districts of the Tyne, Wear, and Tees, varies considerably from that formerly practised in the same parts, yet rather in degree of development than in essential points. The basis of the method is unchanged. It is to excavate straight parallel passages of a constant width, and to connect these at regular intervals by |
