Coal and the coal mines

by Homer Greene

One of the chief dangers to which workmen in the mines are subject arises from the gases given off by minerals and metals. Though these deleterious gases are commonly found in more or less abundance in the coal mines, and are usually considered in connection with such mines, they are, nevertheless, not confined to the coal measures. They have been noticed also in mines of lead, sulphur, salt, and other substances. It is said that anthracite contains a much larger proportion of these gases than do bituminous or other coals, but that being hard it holds them more tenaciously, and is therefore worked with less risk. The soft coals, on the contrary, being porous as well as soft, allow the gases to escape from them much more readily, and so increase the danger at the working faces of the mines. The gas given out most abundantly by the coal is light carbureted hydrogen, known as marsh gas, from the fact that being a product of vegetable decomposition under water, bubbles of it rise to the surface on stirring the waters of a marsh. This is the gas that is known to miners as fire damp. The French call it grisou. Marsh gas, in its simple form, consists of four parts of hydrogen to one of carbon. It is about one half the weight of air, and therefore rises and gathers at the roof of a mine chamber, extending downward as it accumulates. When it is mixed with from four to twelve times its volume of atmospheric air it becomes violently explosive. If the mixture is above or below this proportion it is simply inflammable, burning without explosive force, with a pale blue flame. The value of a perfect ventilating current across the faces of chambers which are making gas rapidly can now be appreciated. It is not only necessary that the supply of air should be sufficient to make the gas non-explosive, but that it should be sufficient to dilute it beyond even the point of inflammability. For to its inflammable more than to its explosive quality is due most of the disasters with which it is accredited. A peculiar and dangerous feature of this gas is that it does not always escape from the coal at a uniform rate, but often comes out suddenly in large compact bodies. These are called “blowers.” They are found most commonly in faults, in cracks in the coal seams, or in open spots in the body of coal, where they have opportunity to accumulate. They contain, besides marsh gas, less than one per cent. of carbonic acid, and from one to four per cent. of nitrogen. It is impossible to anticipate their coming; the miner’s drill may strike into one and free it at any time without a moment’s warning. It may even burst through the face by its own power. In such cases danger is imminent, disaster is most common.

When the naked light of the miner comes into contact with any considerable quantity of fire damp in an explosive state the shock that follows is terrific. Men and mules, cars and coal, are hurled together to destruction. Walls are swept out, iron rails are bent double, doors are torn from their fastenings, the mine is laid waste. The damage which results from an explosion of gas is of course much greater than that which is due to mere ignition and burning without the explosive force. In the latter case, however, the danger to the miner is but slightly diminished. He is liable to receive injuries which may prove immediately fatal. His burning lamp no sooner touches the body of fire damp than it bursts into flame, which, propelled by expansive force, passes swiftly down along the roof of the chamber. Taking up enough oxygen from the atmospheric air to make combustion more fierce, it returns to the face of the chamber with a violent contractile surge, scorching everything in its path, and then, perhaps after another brief sally, it burns itself out.

The miner who accidentally fires a block of fire damp falls suddenly flat on his face on the floor of the mine, burying his mouth, nose, and eyes in the dirt to protect them from the flame and intense heat. Then he clasps his hands over the back of his head and neck to protect these parts from injury, and lies waiting for the minute or two to pass before the fire shall have burned itself out. But he must not wait too long. The fatal after damp follows quick upon the heels of the flame, and his only safety from certain death lies now in immediate flight.

The danger from inflammable gases was known and appreciated very early in the history of mining. But it was long thought to be an unavoidable danger. Light must be had or no work could be done, and the only light that could be obtained was from the flame produced by combustion. Candles were commonly used. They were stuck into a ball of clay and fastened to the sides of the working places at the most advantageous points. The bituminous mines of England were peculiarly prolific of inflammable gases; accidents were almost of daily occurrence. On the 25th of May, 1812, a great disaster occurred at Felling Colliery, near Newcastle, in which eighty-nine persons lost their lives by explosion of fire damp, and public attention and the public conscience were directed to the matter of safety in mines more intensely than ever. Sir Humphrey Davy was then in the zenith of his fame. In April, 1815, he returned to London after a triumphal tour through France and Italy, in which his progress had been marked by a series of brilliant experiments. He had no sooner reached home than he was asked by Mr. Buddie, a well-known colliery owner of that day, to turn his attention toward improved methods of lighting the mines. Specimens of the dangerous gas were sent to him from Newcastle, and he experimented with them. He found that the flame from them would not pass through a small tube, nor through a set of small tubes standing side by side. He found also that the length of the tube was immaterial. He therefore shortened them until they were mere sections, until his set of parallel tubes became simply wire gauze. The proper proportion between the substance of the wire and the size of the aperture was found to be twenty-eight wires to the linear inch, and seven hundred and eighty-four apertures to the square inch, a proportion that is still in use. This wire gauze was then made into the form of a cylindrical tube about six inches long and one and one half inches in diameter, with a flat gauze top. To the bottom of this tube was fastened a small cylindrical oil vessel, and to the top a ring handle. The wick extended up from the oil vessel inside the tube.

When Sir Humphrey had perfected his lamp to a point of safety he took it and went with Mr. Buddie down to Newcastle, and together they traversed with impunity some of the most dangerous parts of the Bentham seam, at that time one of the most fiery coal beds known. At about the same time the celebrated George Stephenson also invented a safety lamp similar in most respects to the Davy, so also, later, did Clanny and Museler, and all four kinds are in general use. Other styles have been invented also, but for the purposes to which a safety lamp is properly applied the Davy doubtless still excels all others. Those purposes are principally the investigation of workings to discover the presence of gas, and to aid in the erection of proper appliances for driving it out. It is not necessary, in these days of powerful ventilating machinery, to allow dangerous gases to remain in working places and to mine the coal there by the light of safety lamps. It is far safer, and better in every way, to sweep the chambers clean from foul air by strong ventilating currents, so that the miner may work by the light of his naked and most convenient common tin lamp. The objection, therefore, to the Davy lamp, that the light given out by it is too dim, need not be considered a serious one. The size of the flame cannot be increased without destroying the proportion between it and the gauze cylinder, and the size of the cylinder cannot be increased without making a dangerously large chamber for the accommodation of explosive gas. Therefore the light given out must, of necessity, be dim.

But the safety lamp itself must be used with care and prudence, otherwise it may become no less an instrument of danger than the naked lamp. When it is carried into a chamber that contains fire damp the gas enters freely through the gauze into the cylindrical chamber, and is there ignited and consumed without communicating its flame to the outside body. The presence of gas is indicated by the conduct of the flame of the lamp. If the percentage of marsh gas is small the flame simply elongates and becomes smoky. If it is mixed with from eight to twelve or fourteen times its volume of atmospheric air the flame of the wick disappears entirely, and the interior of the cylinder becomes filled with the blue flame of burning gas. It will not do to hold the lamp long in this mixture, the wires will become red with heat, and the outer gas may then become ignited from them. Neither will it do to hold the lamp in a current of gaseous air moving at a greater rate of speed than six or eight feet per second, since in that case the flame is apt to be driven through the gauze and to set fire to the gas outside. There is also danger if the lamp be thrust suddenly into an explosive mixture that the force of the explosion inside the wire-gauze cylinder will force the flame through the mesh. It will be seen, therefore, that even the safety lamp is not an absolute protection against danger from explosive and inflammable gases.

The position and duties of the fire boss at each colliery have already been referred to. He goes into the mine about four o’clock in the morning and makes his round before the men arrive. If gas has been found in an inflammable or explosive condition the workmen are not allowed to enter the place until it has been cleared out by the erection of brattices and other ventilating appliances. If only an insignificant quantity has been found in any chamber, the miner who works the place is warned of its existence and told to brush it out. In obedience to this order he goes to the working face, sets his lamp on the floor, and removing his coat swings that garment vigorously over his head, thus mixing and diluting the gas and driving it down into the current.

It is not in the working chambers, however, that the most dangerous accumulations of fire damp are found, but in the worked out and abandoned portions of the mine. Here it may collect unnoticed until large bodies of it are formed, and then when some one blunders into it with a naked lamp a terrific explosion is the inevitable result. The act of 1885 recognizes this especial danger, and makes it obligatory on operators to keep old workings free of dangerous bodies of gas; and to this end it directs that they shall be inspected at least once a week by the fire boss or his assistant. Where it is known that such gas exists, or is liable to accumulate in old workings, the entrances to such places are barred across, and the word “Fire!” is written conspicuously at the opening to them. But notwithstanding all rules and precautions, ignitions and explosions of fire damp are still dangerously common. Among the thousands of mine workers there is always some one who is careless, some one who blunders; the lessons of perfect watchfulness and obedience are hard lessons to be learned.

As has already been intimated, the danger which results from the burning of fire damp lies not alone in the fierce flame given forth, but also, and perhaps in a still greater degree, in the product of its combustion. This product is known to the miner as “after damp,” and consists principally of carbonic acid gas with some nitrogen. It is irrespirable, and a single inhalation of it, in its pure state, will produce immediate insensibility and speedy death. It is heavier than atmospheric air and therefore falls to the bottom of the mine as soon as it is formed from the combustion of the light carbureted hydrogen. It is for this reason that the miner, who has fallen on his face on the floor of the mine to escape the flame of the burning fire damp, rises as soon as that flame has disappeared and hastens, if he is able, to a place of safety. Indeed, it is easier to protect one’s self from the surging fire above than from the invisible and insidious gas below, so quickly does it form, so deadly is it in effect.

One of the most characteristic disasters of recent times, resulting from the explosion of fire damp and the accumulation of after damp, occurred on Monday, August 14, 1871, at the Eagle Shaft, situated about a mile below the town of Pittston, in Luzerne County, Pennsylvania. At nine o’clock on the morning of that day a driver boy by the name of Martin Mangan was passing along an upper gangway, driving a mule with a trip of mine cars. Just above him lay a section of the mine that had been worked out and abandoned, in the old chambers of which a large body of fire damp had been allowed to accumulate. At the hour mentioned there came a sudden and extensive fall of roof in these old workings. The impulse given to the air by this fall drove it out into the working galleries, and with it the inflammable gas. When the fire damp reached the heading and touched the flame of Martin Mangan’s lighted lamp there was a terrific explosion. At the mouth of the shaft timbers were cracked, clouds of dust poured out, and débris from the mine was thrown violently into the outer air. People who were a mile away heard the noise of the explosion and hastened to the scene. Mining experts knew at once what had occurred. As soon as sufficient repairs could be made to the shaft a rescuing party, led by Superintendent Andrew Bryden of the Pennsylvania Coal Company’s mines, descended into the mine and began to search for victims. Those workmen who were on the other side of the shaft from where the explosion took place were rescued and brought out alive. But little progress could be made, however, toward the region of the trouble on account of the after damp which had accumulated. Up to two o’clock on Tuesday morning five dead bodies had been discovered, and during that day twelve more were taken out; all who had worked in that section of the mine. The positions of these bodies showed that the men had fallen where they chanced to be when the explosion occurred. The first wave of after damp that touched them had made them insensible, and death speedily followed. They died from asphyxia.