104 THE VENTILATION OF COAL MINES. The ventilation of mines is a subject which has engaged the attention of many; numerous schemes, some of them rather strange in their suggestions, have from time to time appeared. Amongst others, safety stalls have been proposed for the miners to fly to whenever explosion of fire-damp threatened or occurred. Bore-holes have been also suggested, four hundred or five hundred yards in depth, to drain off the gas; india-rubber and gutta percha pipes to be scattered about the mines with similar intent; cast-iron pipes to blow the gas out, or to suck it up to the surface, and chemical compounds which should neutralize its effects. Many similar schemes have been suggested, tried, and failed. And yet in order properly to conduct the workings of a mine, a good system of ventilation is imperative; especially where the workmen are constantly exposed to the efflux of explosive gas, it becomes absolutely necessary to adopt the means of removing, as rapidly as possible, the air by which the workmen are surrounded. Ventilation should convey not only a continual supply of atmospheric air through the workings, which must be sufficiently powerful to enable the men to breathe freely, but also carry off the continual effusion of carburetted hydrogen, or carbonic acid gases, which are inseparable from the workings of mines. Of these gases the most easily managed is the carbonic acid. The plan generally pursued in the sinking of a pit, is to carry a series of pipes, connected with one another; these are laid along the pavement, or else attached to an angle of the mine along the roof. These pipes are prolonged with the galleries, by which means the gas at the forehead is drawn up the pipes and replaced by atmospheric air, which descends by the shaft in an equable current, and is regulated by the draught of the furnace at the pit's mouth. This circulation is continued until the miners cut through upon the second shaft, when the air-pipes become useless, as the air will descend along the first shaft, and after traversing the gallery below, will ascend in the second. The reason of this is, that the atmospheric air which descends by the first shaft, is of the same temperature as the air above, but, in traversing the galleries, it becomes warmed and rarefied by the greater heat below, and consequently is lighter, and thus enabled to ascend by the second outlet. In very deep and extensive collieries the circulation is made active by rarefying the air at the upcast shaft, by means of a very large furnace placed either at the bottom or top of the pit; when the furnace is situated at the top, the compartment is made airtight above, by placing strong beams across the pit, on which a close scaffolding of planks is laid, which is well plastered with adhesive clay. A little below this scaffold a passage is previously cut, either in a sloping direction, to connect the current of air with the furnace, or it is laid horizontally, and then communicates with the furnace by a vertical opening. The plan of placing the furnace at the bottom of the pit is, however, more advantageous, because the shaft, through which the air ascends to the furnace at the pit's mouth, is always of the ordinary temperature, so that, whenever the top furnace is neglected, the circulation of air throughout the mine becomes languid, and dangerous to the workmen; whereas, when the furnace is situated at the bottom of the shaft, its sides get heated, like those of a chimney, throughout its whole length, so that though the heat of the furnace be allowed to decline, or even become extinct for awhile, the circulation will still go on; the air in the upcast shaft being rarefied by the heat remaining in the sides of the shaft. Attempts have also been made to introduce a system of ventilation by means of a steam jet. This plan was first introduced into the colliery of Seaton Delaval, in the year 1848, by Mr. Forster. Concerning the working of this plan, the following is his explanation, upon his examination before the House of Lords, in September, 1849: "The colliery had four downcast shafts, of eight feet in diameter each, and two upcast shafts, one eight and the other nine feet; each upcast shaft having a spacious furnace. "By this means only 53.058 cubic feet of air could be accomplished, and this ventilation was not sufficient to work the colliery with safety. The rapidity of the current was from six to sixteen feet per second. "After the steam jet was in operation 79.359 cubic feet per minute, being an increase of 26.000. Afterwards one furnace and upcast shaft was dispensed with, and he obtained 85.690 cubic feet per minute." From the examination of many other viewers and coal owners, it would seem that the principle of the steam jet was superior to the ordinary furnaces, only that the furnace produces more air than the jet, in proportion to the fuel consumed, M In ventilating the very thick coal of Staffordshire, though there is much inflammable air, less care is needed than in the north of England collieries, as the workings are very roomy, and the aircourses of comparatively small extent. The air is conducted down one shaft, carried along the main road, and distributed into the sides of the work. A narrow gallery, termed the air-head, is carried into the upper part of the coal in the rib walls, along one or more of the sides. Lateral openings, named spouts, are led from the air-head gallery into the side of the work; and the circulating stream, mixed with the gas in the workings, enters by these spouts, and returns by the air-head to the upcast pit. Throughout Lancashire and Cheshire the strata are of such a quality that they emit little fire-damp; and they are so much inclined in the dip that this gas, which is of lighter gravity than common air, easily escapes without danger. Davy lamps are there seldom used except in trying a mine. Ventilation, however, is nowhere exhibited to such advantage as in the coal mines of Northumberland and Durham. In 1760, the plan of coursing was introduced by Mr. James Spedding; he converted the whole of the passages into air-pipes, and drew the current of air from the downcast pit; then traversed it up and down through the several sheaths of the workings, so that no particular gallery was left without a current of air. In 1807, Mr. Buddle devised his plan of a divided current; he divided the main current into two separate streams at the bottom of the pit; the purer air was coursed through the various galleries, and inflammable gas was led off towards the dumb furnace, which communicated with the hot upcast shaft, out of reach of the flame, and thence derived its power of draught. As the inflammable gas exudes from the innumerable cavities or pockets in the coal, it follows that in the first opening of the mine the discharge of gas is generally more copious than afterwards. Hence, in the working of fiery mines, there is a necessity for having a powerful current of air up to the front where the workmen's candles are employed; and as the principle of conducting the operations is to provide an intake and return for the air, it frequently happens that the discharge of gas is so important that it is unsafe to proceed even from holing to holing without some additional ventilation. This was formerly effected by a brattice of thin deal slightly nailed to props set up for the purpose, and the direction of the air current is aided by a door in the tramway, for the purpose of forcing a portion of the The main current up one side of the brattice and down another. brattice is continued until this working is holed into the back drift, which is then made to receive the main currents; the former holing being made up. If the brattice is to be permanent it is sometimes made of brick. Mr. Lever, of Manchester, has an improved brattice, which possesses the qualities of being not only water-proof and airproof, but also proof against the injurious effects of foul air. This recommends itself to colliery proprietors and managers by its triple qualities; as it is well known that the old deal brattice is continually splitting and cracking by contraction; and if taken down will seldom do for the same purpose again. Canvas had been used in the Scotch, Lancashire, and Welsh collieries, but it was in the woven state, without any after processes of preparation. This method of dividing currents of air for the ventilation of mines has become very popular. In some of the very fiery coal seams of the South Wales coal-field, the ventilating fan of Mr. Nasmyth has been erected; the speed at which it is usually worked is about sixty revolutions per minute, giving a velocity at the circumference of the fan of 2,545 feet a minute; 45,000 cubic feet of air per minute are thus drawn up the mine, nearly one third of which ventilates the upper workings, and the rest passes through the lower workings. SUMMARY OF FATAL ACCIDENTS IN THE COAL MINES OF GREAT BRITAIN DURING THE YEAR ENDING DECEMBER 31, 1859. Derbyshire, Nottinghamshire, Lei- 2 17 11 6 23 88 67 56 36 7 24 7 Shropshire South Staffordshire and Worcester Gloucestershire, Devonshire South Wales Somersetshire, Breconshire, and Eastern District of Scotland.. ..... ........ 43 39 |