During the past years, the safe and efficient lighting of the coal mines of this country has received an ever-increasing amount of attention. Several States have passed laws attempting to regulate the type of lamp to be used and the nature of the fuel to be burned, and the mining departments of coal-mining States have generally shown a keen and intelligent interest in this subject. The passage of the recent Employers Liability Act in Pennsylvania has made it necessary for many coal-mining companies to take out liability insurance, and the companies underwriting such insurance have made it desirable for the insured to permit the use of none but illuminants of established worth. While these conditions have not obtained for a sufficient length of time to permit the statement that the illumination of coal mines by portable lamps has been standardized, still, considerable progress has been made and the direction of future practice in this branch of coal-mining technology is very evident. Under these conditions it seemed that a review of the methods now used in coal mine illumination, together with a brief consideration of the principles underlying these methods, might be of some interest. 
Miners’ lamps may be divided into three classes: The open light, the electric cap lamp and the flame safety lamp. It will be desirable to consider each of these classes separately, as each has properties peculiar to itself and one class is hardly comparable with another.
In this country, without question, the open light is the most generally used of all miners’ lamps. This fact is explained by the relative freedom of a large proportion of our mines from gaseous conditions, and by the admirable systems of ventilation installed in those that show a tendency toward such conditions. In the metal mines, the miner’s candle has had and still has considerable vogue. Because of the small amount of ventilation usually supplied in metal mines, the freedom of the candle from any tendency to produce noxious gases or offensive odors, and the small amount of air it consumes, are valuable assets, while, because of the light color of the rocks in which workings are driven, the meager light is not a serious handicap.
In coal mines, however, conditions are very different. Because of the considerable volume of air passed through the workings, the small air consumption of the candle is of little moment, and its feeble rays are so completely absorbed by the dusky background that its light is entirely inadequate. Moreover, the cost of the candle is relatively high. For these and other less obvious reasons the metal miner’s candle is, practically unknown to the coal miner.
Up to a few years ago the open oil lamp had no rival in non-gaseous mines and it is still very largely used, though its use is becoming limited, as will be shown later. The oil lamp has many disadvantages and the legislatures of a number of States have endeavored from time to time to remedy these defects by law. As the service given by an oil lamp varies largely according to the character of the oil, efforts have been made to fix by law the quality of the oil that may be sold to miners for use in these lamps. These efforts, unfortunately, have proven rather ineffectual, as the result has generally been to increase the cost of oil to the miner, without,increasing its quality in anything like the same proportion. These laws, therefore, may well be considered one of the most potent of the forces that have driven the oil lamp out of its once strong position.
An example of the manner in which a law, that was honestly intended to be beneficial to the miner, failed of its purpose is found in the Bituminous Mining Law of 1911 of the State of Pennsylvania. This law stipulated that oils sold for use in miners’ lamps should not yield more than 0.11 per cent, of soot when burned in. a miner’s lamp under standard conditions. One of these conditions was that the flame of the lamp should be 1½ in., long. Now, low-grade oils when burned under these conditions yield as much as 1 per cent, of soot, while high-grade oils will give as little as 0.03 per cent. Thus it would seem, at first glance that this law would considerably better conditions in the mines.
Such is not the case, however. Oils to pass this test must be very largely composed of costly fatty oils and this so greatly increased the cost to the miner that he was obliged to look for some cheaper illuminant. Moreover, instead of a flame 1½ in. long, the miner burns one of a maximum length because he wants as much light as he can get. The writer has found that while costly oils, containing high percentages of fatty ingredients, will produce much less soot than oils of medium price, and less fatty material, when burned under legal test conditions, these differences very largely disappear when these oils are burned under the conditions that obtain in the mines. With very long flames the high-priced oils still show a superiority to the medium grade, but the differential is so slight as to be of little real moment.
Indeed, the soot-forming propensities of both these oils under the conditions of use are so great that it is idle to attempt to classify one as better than the other. They are both very bad. Thus with a legal requirement of 0.11 per cent. soot or lower, we find the oil passing this test will give about 8 per cent, of soot when burned as it would be in the mines—that is, with a flame 5 to 6 in. long—while the oil that will not pass the legal requirement, giving under test conditions, let us assume, 0.5 per cent, soot, will make under actual working conditions about 9 to 10 per cent. soot. Thus we may say that despite the greatly increased cost of the legal-test oil it is practically no better than many oils that may be secured at half or one-third the price. It is to be understood that many oils are of so low a grade as to be entirely unsuited for use in miners’ lamps and, of course, these remarks do not apply to them. The point is that, the tendency of many of the State laws is to increase the cost of oil very considerably to the miner and mine operator without proportionately improving its quality.
One of the drawbacks to the use of the open oil lamp is the greatly increased fire risk where such lamps are used in dry workings. It is necessary for the user of such a lamp to renew its wick or lamp cotton at frequent intervals, and it is customary to pull out the old cotton and insert the new while the old lies blazing on the ground. When the new cotton is in place and alight the miner, places his heel on the blazing remains of the old, and perhaps extinguishes it; at any rate, he goes away and leaves it, to burn or not as may be. Another source of fire is the shower of sparks that is blown from the wick when the wearer of the open oil lamp is traveling against a strong ventilating current. Together these are the possible causes of mine fires that have disposed thoughtful mine operators, to look with disfavor upon this source of illumination.
Of recent years a substitute for miner’s oil, called “Miner’s Wax” and a host of proprietary and brand names, has been placed upon the market. It is a paraffin wax obtained in the refining of petroleum and possesses the property of burning with a whiter flame than miner’s oil and giving somewhat less soot. It must be used in a special lamp, however, as means must be provided for keeping it in a molten condition in the lamp fount. This is accomplished by conducting heat from the flame, to the fount. Its use, though considerable, is decreasing because the fire hazard with this illuminant is as great as with miner’s oil, and it is troublesome to handle.
Undoubtedly the greatest advance made in the illumination of non-gaseous mines is the acetylene or “carbide” miner’s lamp. This lamp has come into general use during the past 7 years and is now probably the most widely used of miners’ lights. The reasons for its popularity are not far to seek; in brief, it gives far more light than any other portable miner’s lamp and costs less to operate. It gives a clear, white light in which objects have very much the same color value as in daylight. It makes no smoke or soot and its demands on the oxygen of the mine air are moderate. It gives more reliable indications of, the presence of dangerous proportions of black damp than theoil-fed flame. It gives off no sparks and hence decreases the fire, hazard very considerably. It may thus be seen that this type of miners’ lamp has benefits for the mine operator and the worker and is liked by both. The writer understands that insurance companies underwriting the insurance of many coal-mining companies under the new Pennsylvania Compensation Act have recognized the safety features of the acetylene miners’ lamp by giving credits on the insurance rate where such lamps are used in non-gaseous mines.
Some years ago, considerable uneasiness was felt among mining men because it was thought that the acetylene lamp failed to give adequate warning of the presence of black damp. In the past, black damp had been believed, by many, to be an atmosphere in which a lamp would not burn, the reasoning being along these lines. If an oil lamp goes out, it is because there is not enough air (meaning oxygen). Now it is a fact that 1 the acetylene lamp will burn where an oil lamp will not. Hence, if the oil lamp will not burn there is no air, and as the acetylene lamp continues to burn, this indicates that the, acetylene lamp will burn without air. Therefore, a man may carry an acetylene lamp into an atmosphere containing so little air that he may be rendered unconscious, and still his lamp will give no indication of the dangerous condition of the atmosphere.
The facts of the matter are these: The oil-fed flame requires a minimum of about 17½ per cent, of oxygen for its maintenance; the acetylene flame requires about 12½ per cent. and a man’s life is endangered should the oxygen content fall much below 10 per cent. At about 14 per cent. of oxygen, however, the color of the acetylene flame changes markedly. It loses its brilliance and illuminating power, and becomes greatly elongated and unstable. From these data it will be seen that the miner is given obvious and adequate warning of the vitiation of the atmosphere through deficiency in oxygen. While this warning is not so peremptory as that given by the oil lamp, still it is of ample distinctness for men to appreciate and value, and above all, it is essentially a real danger warning.
On the other hand, the warning of the oil-fed flame is given with so high an oxygen content that miners have learned to disregard it, and will frequently go into workings containing air in which their oil lamps, will not burn. They know that they can live in an atmosphere in which these lamps will not burn, but do not realize that, once in the dark, they have no further guide to the quality of the atmosphere and that in a few feet it may become lethal. Such is not the case with the acetylene lamp its warnings are given so near to the danger point that men will, have a wholesome respect for them, to the great increase of their own safety.
While the writer has heard of cases in which men after working with acetylene lamps in sections in which oil lamps, would not burn became sick when brought into fresh air, these always proved to be based upon a fallacy. Upon investigation, the fact has always developed that the disability of the men was due to other causes; too high a temperature of the workings or carbon monoxide being the most usual. In any case the presence of the disturbing agency would not have been detected by the use of oil lamps. Indeed, the writer has many times seen men fall like flies in a place they had considered safe, because their oil lamps gave no indication of anything abnormal in the composition of the atmosphere.
The supposed danger from the use of acetylene lamps where black damp may be encountered has caused their use in pillar work and in robbing to be discontinued to some extent, thus exchanging a danger of the imagination for a very real peril. Those familiar with the coal-mining industry know what a curse miner’s asthma has been. If not caused, it is at least aggravated, by the greasy soot and oily emanations given off by the oil lamp. Now these foul vapors are at their worst in pillar work and in robbing where the ventilating current is apt to be at its lowest ebb and where black damp is obviously most likely to be encountered. Hence, as a result of trying to safeguard the miner against the hypothetical danger—of a combination of black damp, the acetylene lamp, and his own stupidity—we expose him to the very real and pressing danger of miner’s asthma, against which the most careful and most thoughtful is helpless.
The deepening of our mines, and the increased length of airways, together with the greater attention now given to the danger of gas and dust explosions, have all tended to increase the number of safety lamps in use. Safety lamps may be divided into two classes: The electric cap lamp and the flame safety lamp.
The electric cap lamp is a development of the last 7 or 8 years and its growth has been very lucidly traced by J. T. Jennings in a paper read at the 1916 meeting of the Coal Mining Institute of America. It will, therefore, be unnecessary for the writer to go deeply into this matter. European practice has tended toward the development of an electric, hand lantern. Because of the more general use of flame safety lamps there, their mine workers were satisfied with this type, being accustomed to the inconvenience of hand lamps.
In this country, however, conditions are radically different. The miners are, as a general rule, accustomed to open lights worn on the cap and rebel at the inconvenience and inefficiency accompanying the use of the electric hand lantern. Hence, when an electric miners’ lamp was developed it became essential that it should be such that the efficiency and convenience of the cap lamp would be retained. Progress was made along these lines with the result that the present very convenient equipment has been developed.
It is remarkable that so complete a standardization in general design as is now found among the product of the numerous manufacturers of this type of lamp should have been possible. The credit for this should be given without stint to the Bureau of Mines. This bureau has worked hard and faithfully with the manufacturers of electric cap lamps for the past 4 years or so, and has had a very definite, vision of what such a lamp should be. The result of this pre-natal influence is a startling similarity in the various equipments offered to the mining industry. While this method has perhaps sacrificed a little individuality, it has undoubtedly increased the average excellence of the product, and made the whole industry, more robust by weeding out the abnormalities.
Technical literature has been so full of descriptions of various types, of miners’ electric cap lamps that it will not be necessary to describe any in detail; it will suffice to touch upon the general advantages and disadvantages of this type of lamp.
Many of the underwriters of insurance under the Employers’ Liability Act have shown a marked preference for the electric cap damp when compared with the flame safety lamp. This preference has led to the penalization of companies using the flame safety lamp, to the extent of 11 c. for each $100 of pay roll, whereas, were electric cap lamps installed, this penalty would be wholly removed. This premium has led to the installation of many electric cap lamps.
This lamp throws its light into the plane of vision of the wearer so that its light is efficiently utilized. It leaves the miner’s hands free and, the light requires no attention; indeed, the outfits are so arranged and locked that it is impossible for the wearer or any unauthorized person to tamper with them. There is no fire risk with these lamps and we are assured by the Bureau of Mines that the danger of their originating a gas explosion is practically nil. These are also the safest of all lamps with which to handle explosives. They have three chief disadvantages: Their upkeep is high, the flux of light they furnish is not so great as it should be, and their wearer is in absolute ignorance, so far as the lamp enters into the matter, of the nature of the atmosphere surrounding him. It is very probable that the next few years will see these faults abated to a considerable extent.
That the flame safety damp should be so old, so widely used, and so little improved in all its years of service reflects but scant credit upon the human mind. To all intents and purposes we still have Sir Humphrey Davy’s invention in actual use, development having practically stopped , after introducing the use of a cylinder glass to surround the flame. In this country the bonneted Clanny and Wolf type are practically standard except where heavily pitching veins are encountered, as in the Schuylkill anthracite district. Here, because of its lightness and the convenience with which it is handled on the pitches, the old Newcastle Davy is still supreme.
The flame safety lamp is principally handicapped by the meager light it gives. Its use is absolutely essential as an indicator of the quality of the mine air in all gaseous mines, and the writer would suggest that even in non-gaseous mines, where electric cap lamps have superseded open lights, the installation of a number of flame safety lamps would be an added safeguard. The principal difficulty in the use of the flame safety lamp as an indicator of atmospheric conditions, where electric cap lamps are relied upon for illumination, is that unless the flame lamp is the source of light it will come to hang unnoticed on the miner’s belt or be left neglected in a corner of his working place. In other words, unless his attention is automatically called to it from hour to hour, he will, in the long run, cease to note its warnings.
While the variations of the Davy principle on which flame safety lamps are constructed have been endless, these variations have been slight, and the principle has not been diverged from with any success. As a result, the flame safety lamps in actual use in this country are of two very similar types, the Clanny and the Wolf, as has been mentioned above, ignoring the Davy lamps used in the southern anthracite district of Pennsylvania, for these will soon disappear.
With the, design of the lamp fixed, we have but one variable to consider and that is the fuel burned. Even this disappears in the case of the Wolf lamps, as these will only function with naphtha whose composition may vary within but narrow limits. With the Clanny type lamp, however, a wide variation in the nature of the fuels is possible. Among these are sperm, peanut, lard, rape, seal, cotton seed and mixtures of these with mineral burning oils. The writer has spent much time in investigating the question of improving the quality of safety-lamp oils and has met with some success in this direction. It has been found that some of the most costly and highly prized safety-lamp oils were really inferior to mixtures containing high proportions of high-grade mineral burning oils. These mixtures burn with a whiter flame, give appreciably more light, do not crust the wick, and are much cheaper than the standard safety-lamp oils.
There is another type of lamp that holds out promise for the future. This is the acetylene safety lamp invented by T. M. Chance of Philadelphia and described in the discussion of R. R. Burrows’ paper on coal mine illumination. As this lamp is not yet a commercial fact, but little can be said of it definitely. It would seem, however, that it combines the safety and indispensable gas detecting properties of the flame safety lamp with many times the illuminating power of the electric cap lamp.
A table is appended containing data that may make more intelligible some of the statements in this paper. These data have been accumulated during the past eight years and are general averages. The photometric determinations were made upon a United Gas Improvement Co. 60-in. bar photometer. The photometric standards used were 10-volt tungsten lamps, prepared and calibrated by the National Lamp Works, and standard sperm candles. At times a secondary standard was used, consisting of a long-time kerosene burner, similar to that used in railway signal practice, standardized against one of the primary standards noted above.
It will be, noted that no estimate of the cost per day of electric cap or flame safety lamps is given in the table. In the writer’s opinion the modern electric cap lamp has not been in use long enough for an intelligent opinion of its upkeep cost to be formed. Moreover, the labor charge on both the electric cap and flame safety lamps is so large and varies so much with the size of the installation that such figures as could be given would have but little meaning.
Conclusions
- The open oil lamp has outlived its general’usefulness. It still has a field, however, in special cases, such as those of drivers, motormen, trip runners and the like, who are obliged to work in swift air currents.
- The use of the open acetylene lamp is growing in all non-gaseous mines because of its cheapness, the powerful light it gives, its reliability in the presence of black damp, and its freedom from soot and noxious vapors.
- The electric cap lamp is best, adapted to use in gaseous mines. Its flux of light is superior to that of the flame safety lamps now in use. Moreover as it leaves the hands free it is more convenient than the flame safety lamp. Under especially drastic conditions in non-gaseous mines, where the fire risk is unreasonably high due to peculiar local conditions, its freedom from fire hazard recommends its use. In all gaseous mines its use must be accompanied by that of flame safety lamps, in order that the condition of the atmosphere may at all times be known in all parts on the mine. Where it entirely replaces open lights in non-gaseous mines it is imperative that a few flame safety lamps be supplied along with the, electric cap lamps for the same purpose.
- The flame safety lamp should be used in all gaseous mines irrespective of the use of electric cap lamps. These lamps form in themselves the best and most trustworthy gas detector yet devised and their presence, is absolutely essential to the safe operation of such a mine. Even in non-gaseous mines, where, electric cap lamps have replaced open lights completely, it is good policy to have a liberal proportion of flame safety lamps. The flame safety lamp is doubtless an unsatisfactory working light, but its role is twofold. It may be used as a working light, but it must be used as a gage of the safety of the mine atmosphere.
- There is a new acetylene safety lamp that gives promise of being an admirable working lamp as well as an excellent fire damp and black damp detector.
Note.—The above candlepowers are in no sense maximum but are the average values over the field illuminated by the lamp in question and have been obtained from many determinations. These are the values that may be expected to be realized in practice under working conditions.
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