It is somewhat strange to think that where once existed the solitudes of an ancient carboniferous forest now is the site of a busy underground town. For a town it really is. The various roads and passages which are cut through the solid coal as excavation of a coal-mine proceeds, represent to a stranger all the intricacies of a well-planned town. Nor is the extent of these underground towns a thing to be despised. There is an old pit near Newcastle which contains not less than fifty miles of passages. Other pits there are whose main thoroughfares in a direct line are not less than four or five miles in length, and this, it must be borne in mind, is the result of excavation wrought by human hands and human labour.
So great an extent of passages necessarily requires some special means of keeping the air within it in a pure state, such as will render it fit for the workers to breathe. The further one would go from the main thoroughfare in such a mine, the less likely one would be to find air of sufficient purity for the purpose. It is as a consequence necessary to take some special steps to provide an efficient system of ventilation throughout the mine. This is effectually done by two shafts, called respectively the downcast and the upcast shaft. A shaft is in reality a very deep well, and may be circular, rectangular or oval in form. In order to keep out water which may be struck in passing through the various strata, it is protected by plank or wood tubbing, or the shaft is bricked over, or sometimes even cast-iron segments are sunk. In many shafts which, owing to their great depth, pass through strata of every degree of looseness or viscosity, all three methods are utilised in turn. In Westphalia, where coal is worked beneath strata of more recent geological age, narrow shafts have been, in many cases, sunk by means of boring apparatus, in preference to the usual process of excavation, and the practice has since been adopted in South Wales. In England the usual form of the pit is circular, but elliptical and rectangular pits are also in use. On the Continent polygonal-shaped shafts are not uncommon, all of them, of whatever shape, being constructed with a view to resist the great pressure exerted by the rock around.
[Illustration: FIG. 31.—Engine-House and Buildings at head of a
Coal-Pit.]
If there be one of these shafts at one end of the mine, and another at a remote distance from it, a movement of the air will at once begin, and a rough kind of ventilation will ensue. This is, however, quite insufficient to provide the necessary quantity of air for inhalation by the army of workers in the coal-mine, for the current thus set up does not even provide sufficient force to remove the effete air and impurities which accumulate from hundreds of perspiring human bodies.
It is therefore necessary to introduce some artificial means, by which a strong and regular current shall pass down one shaft, through the mine in all its workings, and out at the other shaft. This is accomplished in various ways. It took many years before those interested in mines came thoroughly to understand how properly to secure ventilation, and in bygone days the system was so thoroughly bad that a tremendous amount of sickness prevailed amongst the miners, owing to the poisonous effects of breathing the same air over and over again, charged, as it was, with more or less of the gases given off by the coal itself. Now, those miners who do so great a part in furnishing the means of warming our houses in winter, have the best contrivances which can be devised to furnish them with an ever-flowing current of fresh air.
Amongst the various mechanical appliances which have been used to ensure ventilation may be mentioned pumps, fans, and pneumatic screws. There is, as we have said, a certain, though slight, movement of the air in the two columns which constitute the upcast and the downcast shafts, but in order that a current may flow which shall be equal to the necessities of the miners, some means are necessary, by which this condition of almost equilibrium shall be considerably disturbed, and a current created which shall sweep all foul gases before it. One plan was to force fresh air into the downcast, which should in a sense push the foetid air away by the upcast. Another was to exhaust the upcast, and so draw the gases in the train of the exhausted air. In other cases the plan was adopted of providing a continual falling of water down the downcast shaft.
These various plans have almost all given way to that which is the most serviceable of all, namely, the plan of having an immense furnace constantly burning in a specially-constructed chamber at the bottom of the upcast. By this means the column of air above it becomes rarefied under the heat, and ascends, whilst the cooler air from the downcast rushes in and spreads itself in all directions whence the bad air has already been drawn. On the other hand, to so great a state of perfection have ventilating fans been brought, that one was recently erected which would be capable of changing the air of Westminster Hall thirty times in one hour.
Having procured a current of sufficient power, it will be at once understood that, if left to its own will, it would take the nearest path which might lie between its entrance and its exit, and, in this way, ventilating the principal street only, would leave all the many off-shoots from it undisturbed. It is consequently manipulated by means of barriers and tight-fitting doors, in such a way that the current is bound in turn to traverse every portion of the mine. A large number of boys, known as trappers, are employed in opening the doors to all comers, and in carefully closing the doors immediately after they have passed, in order that the current may not circulate through passages along which it is not intended that it should pass.
The greatest dangers which await the miners are those which result, in the form of terrible explosions, from the presence of inflammable gases in the mines. The great walls of coal which bound the passages in mines are constantly exuding supplies of gas into the air. When a bank of coal is brought down by an artificial explosion, by dynamite, by lime cartridges, or by some other agency, large quantities of gas are sometimes disengaged, and not only is this highly detrimental to the health of the miners, if not carried away by proper ventilation, but it constitutes a constant danger which may at any time cause an explosion when a naked light is brought into contact with it. Fire-damp may be sometimes heard issuing from fiery seams with a peculiar hissing sound. If the volume be great, the gas forms what is called a blower, and this often happens in the neighbourhood of a fault. When coal is brought down in any large volume, the blowers which commence may be exhausted in a few moments. Others, however, have been known to last for years, this being the case at Wallsend, where the blower gave off 120 feet of gas per minute. In such cases the gas is usually conveyed in pipes to a place where it can be burned in safety.
In the early days of coal-mining the explosions caused by this gas soon received the serious attention of the scientific men of the age. In the Philosophical Transactions of the Royal Society we find a record of a gas explosion in 1677. The amusing part of such records was that the explosions were ascribed by the miners to supernatural agencies. Little attention seemed to have been paid to the fact, which has since so thoroughly been established, that the explosions were caused by accumulations of gas, mixed in certain proportions with air. As a consequence, tallow candles with an exposed flame were freely used, especially in Britain. These were placed in niches in the workings, where they would give to the pitman the greatest amount of light. Previous to the introduction of the safety-lamp, workings were tested before the men entered them, by "trying the candle". Owing to the specific gravity of fire-damp (.555) being less than that of air, it always finds a lodgement at the roofs of the workings, so that, to test the condition of the air, it was necessary to steadily raise the candle to the roof at certain places in the passages, and watch carefully the action of the flame. The presence of fire-damp would be shown by the flame assuming a blue colour, and by its elongation; the presence of other gases could be detected by an experienced man by certain peculiarities in the tint of the flame. This testing with the open flame has almost entirely ceased since the introduction of the perfected Davy lamp.
The use of candles for illumination soon gave place in most of the large collieries to the introduction of small oil-lamps. In the less fiery mines on the Continent, oil-lamps of the well-known Etruscan pattern are still in use, whilst small metal lamps, which can conveniently be attached to the cap of the worker, occasionally find favour in the shallower Scotch mines. These lamps are very useful in getting the coal from the thinner seams, where progress has to be made on the hands and feet. At the close of the last century, as workings began to be carried deeper, and coal was obtained from places more and more infested with fire-damp, it soon came to be realised that the old methods of illumination would have to be replaced by others of a safer nature.
It is noteworthy that mere red heat is insufficient in itself to ignite fire-damp, actual contact with flame being necessary for this purpose. Bearing this in mind, Spedding, the discoverer of the fact, invented what is known as the "steel-mill" for illuminating purposes. In this a toothed wheel was made to play upon a piece of steel, the sparks thus caused being sufficient to give a moderate amount of illumination. It was found, however, that this method was not always trustworthy, and lamps were introduced by Humboldt in 1796, and by Clanny in 1806. In these lamps the air which fed the flame was isolated from the air of the mine by having to bubble through a liquid. Many miners were not, however, provided with these lamps, and the risks attending naked lights went on as merrily as ever.
In order to avoid explosions in mines which were known to give off large quantities of gas, "fiery" pits as they are called, Sir Humphrey Davy in 1815 invented his safety lamp, the principle of which can be stated in a few words.
If a piece of fine wire gauze be held over a gas-jet before it is lit, and the gas be then turned on, it can be lit above the gauze, but the flame will not pass downwards towards the source of the gas; at least, not until the gauze has become over-heated. The metallic gauze so rapidly conducts away the heat, that the temperature of the gas beneath the gauze is unable to arrive at the point of ignition. In the safety-lamp the little oil-lamp is placed in a circular funnel of fine gauze, which prevents the flame from passing through it to any explosive gas that may be floating about outside, but at the same time allows the rays of light to pass through readily. Sir Humphrey Davy, in introducing his lamp, cautioned the miners against exposing it to a rapid current of air, which would operate in such a way as to force the flame through the gauze, and also against allowing the gauze to become red-hot. In order to minimise, as far as possible, the necessity of such caution the lamp has been considerably modified since first invented, the speed of the ventilating currents not now allowing of the use of the simple Davy lamp, but the principle is the same.
During the progress of Sir Humphrey Davy's experiments, he found that when fire-damp was diluted with 85 per cent. of air, and any less proportion, it simply ignited without explosion. With between 85 per cent. and 89 per cent. of air, fire-damp assumed its most explosive form, but afterwards decreased in explosiveness, until with 94-1/4 per cent. of air it again simply ignited without explosion. With between 11 and 12 per cent. of fire-damp the mixture was most dangerous. Pure fire-damp itself, therefore, is not dangerous, so that when a small quantity enters the gauze which surrounds the Davy lamp, it simply burns with its characteristic blue flame, but at the same time gives the miner due notice of the danger which he was running.
[Illustration: FIG. 32.—Gas Jet and Davy Lamp.]
With the complicated improvements which have since been made in the Davy lamp, a state of almost absolute safety can be guaranteed, but still from time to time explosions are reported. Of the cause of many we are absolutely ignorant, but occasionally a light is thrown upon their origin by a paragraph appearing in a daily paper. Two men are charged before the magistrates with being in the possession of keys used exclusively for unlocking their miners' safety-lamps. There is no defence. These men know that they carry their lives in their hands, yet will risk their own and those of hundreds of others, in order that they may be able to light their pipes by means of their safety-lamps. Sometimes in an unexpected moment there is a great dislodgement of coal, and a tremendous quantity of gas is set free, which may be sufficient to foul the passages for some distance around. The introduction or exposure of a naked light for even so much as a second is sufficient to cause explosion of the mass; doors are blown down, props and tubbing are charred up, and the volume of smoke, rushing up by the nearest shaft and overthrowing the engine-house and other structures at the mouth, conveys its own sad message to those at the surface, of the dreadful catastrophe that has happened below. Perhaps all that remains of some of the workers consists of charred and scorched bodies, scarcely recognisable as human beings. Others escape with scorched arms or legs, and singed hair, to tell the terrible tale to those who were more fortunately absent; to speak of their own sufferings when, after having escaped the worst effects of the explosion, they encountered the asphyxiating rush of the after-damp or choke-damp, which had been caused by the combustion of the fire-damp. "Choke-damp" in very truth it is, for it is principally composed of our old acquaintance carbonic acid gas (carbon dioxide), which is well known as a non-supporter of combustion and as an asphyxiator of animal life.
It seems a terrible thing that on occasions the workings and walls themselves of a coal-mine catch fire and burn incessantly. Yet such is the case. Years ago this happened in the case of an old colliery near Dudley, at the surface of which, by means of the heat and steam thus afforded, early potatoes for the London market, we are told, were grown; and it was no unusual thing to see the smoke emerging from cracks and crevices in the rocks in the vicinity of the town.
From fire on the one hand, we pass, on the other, to the danger which awaits miners from a sudden inrush of water. During the great coal strike of 1893, certain mines became unworkable in consequence of the quantity of water which flooded the mines, and which, continually passing along the natural fractures in the earth's crust, is always ready to find a storage reservoir in the workings of a coal-mine. This is a difficulty which is always experienced in the sinking of shafts, and the shutting off of water engages the best efforts of mining engineers.
Added to these various dangers which exist in the coal-mine, we must not omit to notice those accidents that are continually being caused by the falling-in of roofs or of walls, from the falling of insecure timber, or of what are known as "coal-pipes" or "bell-moulds." Then, again, every man that enters the mine trusts his life to the cage by which he descends to his labour, and shaft accidents are not infrequent.
The following table shows the number of deaths from colliery accidents for a period of ten years, compiled by a Government inspector, and from this it will be seen that those resulting from falling roofs number considerably more than one-third of the whole.
—————————————————————————————————- | Causes of Death. | No. of | Proportion | | | Deaths. | per cent. | —————————————————————————————————- | Deaths resulting from fire-damp | | | | explosions | 2019 | 20.36 | | | | | | Deaths resulting from falling | | | | roofs and coals | 3953 | 39.87 | | | | | | Deaths resulting from shaft | | | | accidents | 1710 | 17.24 | | | | | | Deaths resulting from miscellaneous | | | | causes and above ground | 2234 | 22.53 | | |——————|——————| | | 9916 | 100.00 | —————————————————————————————————|
Every reader of the daily papers is familiar with the harrowing accounts which are there given of coal-mine explosions.
This kind of accident is one, which is, above all, associated in the public mind with the dangers of the coal-pit. Yet the accidents arising from this cause number but 20 per cent. of those recorded, and granted there be proper inspection, and the use of naked lights be absolutely abolished, this low percentage might still be considerably reduced.
A terrific explosion occurred at Whitwick Colliery, Leicestershire, in 1893, when two lads were killed, whilst a third was rescued after a very narrow escape. The lads, it is stated, were working with naked lights, when a sudden fall of coal released a quantity of gas, and an immediate explosion was the natural result. Accidents had been so rare at this pit that it was regarded as particularly safe, and it was alleged that the use of naked lights was not uncommon.
This is an instance of that large number of accidents which are undoubtedly preventable.
An interesting commentary on the careless manner in which miners risk their lives was shown in the discoveries made after an explosion at a colliery near Wrexham in 1889. Near the scene of the explosion an unsecured safety lamp was found, and the general opinion at the time was that the disaster was caused by the inexcusable carelessness of one of the twenty victims. Besides this, when the clothing of the bodies recovered was searched, the contents, taken, it should be noted, with the pitmen into the mines, consisted of pipes, tobacco, matches, and even keys for unlocking the lamps. It is a strange reflection on the manner in which this mine had been examined previous to the men entering upon their work, that the under-looker, but half an hour previously, had reported the pit to be free from gas.
Another instance of the same foolhardiness on the part of the miners is contained in the report issued in regard to an explosion which occurred at Denny, in Stirlingshire, on April 26th, 1895. By this accident thirteen men lost their lives, and upon the bodies of eight of the number the following articles were found; upon Patrick Carr, tin matchbox half full of matches and a contrivance for opening lamps; John Comrie, split nail for opening lamps; Peter Conway, seven matches and split key for opening lamps; Patrick Dunton, split nail for opening lamps; John Herron, clay pipe and piece of tobacco; Henry M'Govern, tin matchbox half full of matches; Robert Mitchell, clay pipe and piece of tobacco; John Nicol, wooden pipe, piece of tobacco, one match, and box half full of matches. The report stated that the immediate cause of the disaster was the ignition of fire-damp by naked light, the conditions of temperature being such as to exclude the possibility of spontaneous combustion. Henry M'Govern had previously been convicted of having a pipe in the mine. With regard to the question of sufficient ventilation it continued:—"And we are therefore led, on a consideration of the whole evidence, to the conclusion that the accident cannot be attributed to the absence of ventilation, which the mine owners were bound under the Mines Regulation Act and the special rules to provide." The report concluded as follows:— "On the whole matter we have to report that, in our opinion, the explosion at Quarter Pit on April 26th, 1895, resulting in the loss of thirteen lives, was caused by the ignition of an accumulation or an outburst of gas coming in contact with a naked light, 'other than an open safety-lamp,' which had been unlawfully kindled by one of the miners who were killed. In our opinion, the intensity of the explosion was aggravated, and its area extended, by the ignition of coal-dust."
We have mentioned that accidents have frequently occurred from the falling of "coal-pipes," or, as they are also called, "bell-moulds." We must explain what is meant by this term. They are simply what appear to be solid trunks of trees metamorphosed into coal. If we go into a tropical forest we find that the woody fibre of dead trees almost invariably decays faster than the bark. The result is that what may appear to be a sound tree is nothing but an empty cylinder of bark. This appears to have been the case with many of the trees in coal-mines, where they are seen to pierce the strata, and around which the miners are excavating the coal. As the coaly mass collected around the trunk when the coal was being formed, the interior was undergoing a process of decomposition, while the bark assumed the form of coal. The hollow interior then became filled with the shale or sandstone which forms the roof of the coal, and its sole support when the coal is removed from around it, is the thin rind of carbonised bark. When this falls to pieces, or loses its cohesion, the sandstone trunk falls of its own weight, often causing the death of the man that works beneath it. Sir Charles Lyell mentions that in a colliery near Newcastle, no less than thirty sigillaria trees were standing in their natural position in an area of fifty yards square, the interior in each case being sandstone, which was surrounded by a bark of friable coal.
[Illustration: Fig. 33—Part of a trunk of Sigillaria, showing the thin outer carbonised bark, with leaf-scars, and the seal-like impressions where the bark is removed.]
The last great danger to which we have here to make reference, is the explosive action of a quantity of coal-dust in a dry condition. It is only now commencing to be fully recognised that this is really a most dangerous explosive. As we have seen, large quantities of coal are formed almost exclusively of lepidodendron spores, and such coal is productive of a great quantity of dust. Explosions which are always more or less attributable to the effects of coal-dust are generally considered, in the official statistics, to have been caused by fire-damp. The Act regulating mines in Great Britain is scarcely up to date in this respect. There is a regulation which provides for the watering of all dry and dusty places within twenty yards from the spot where a shot is fired, but the enforcement of this regulation in each and every pit necessarily devolves on the managers, many of whom in the absence of an inspector leave the requirement a dead letter. Every improvement which results in the better ventilation of a coal-mine tends to leave the dust in a more dangerous condition. The air, as it descends the shaft and permeates the workings, becomes more and more heated, and licks up every particle of moisture it can touch. Thorough ventilation results in more greatly freeing a mine of the dangerous fire-damp, but the remedy brings about another disease, viz., the drying-up of all moisture. The dust is thus left in a dangerously inflammable condition, acting like a train of gunpowder, to be started, it may be, by the slightest breath of an explosion. There is apparently little doubt that the presence of coal-dust in a dry state in a mine appreciably increases the liability of explosion in that mine.
So far as Great Britain is concerned, a Royal Commission was appointed by Lord Rosebery's Government to inquire into and investigate the facts referring to coal-dust. Generally speaking, the conclusion arrived at was that fine coal-dust was inflammable under certain conditions. There was considerable difference of opinion as to what these conditions were. Some were of opinion that coal-dust and air alone were of an explosive nature, whilst others thought that alone they were not, but that the addition of a small quantity of fire-damp rendered the mixture explosive. An important conclusion was come to, that, with the combustion of coal-dust alone, there was little or no concussion, and that the flame was not of an explosive character.
Coal-dust was, however, admittedly dangerous, especially if in a dry condition. The effects of an explosion of gas might be considerably extended by its presence, and there seems every reason to believe that, with a suitable admixture of air and a very small proportion of gas, it forms a dangerous explosive. Legislation in the direction of the report of the Commission is urgently needed.
We have seen elsewhere what it is in the dust which makes it dangerous, how that, for the most part, it consists of the dust-like spores of the lepidodendron tree, fine and impalpable as the spores on the backs of some of our living ferns, and the fact that this consists of a large proportion of resin makes it the easily inflammable substance it is. Nothing but an incessant watering of the workings in such cases will render the dust innocuous. The dust is extremely fine, and is easily carried into every nook and crevice, and when, as at Bridgend in 1892, it explodes, it is driven up and out of the shaft, enveloping everything temporarily in dust and darkness.
In some of the pits in South Wales a system of fine sprays of water is in use, by which the water is ejected from pin-holes pricked in a series of pipes which are carried through the workings. A fine mist is thus caused where necessary, which is carried forward by the force of the ventilating current.
A thorough system of inspection in coal-mines throughout the world is undoubtedly urgently called for, in order to ensure the proper carrying out of the various regulations framed for their safety. It is extremely unfortunate that so many of the accidents which happen are preventable, if only men of knowledge and of scientific attainments filled the responsible positions of the overlookers.