March 24, 1916. THE COLLIERY GUARDIAN. 559 whilst with rapid falls there would be increased evolu- tion of blackdamp outwards. In both these cases fluctua- tions in pressure would occur which would be shown on the water gauge, though slow barometric fluctuations would not, as the changes would be counter-balanced by leakage as they occurred. Influence of Changes in Atmospheric Temperature. This factor leads to somewhat complicated pheno- mena. Suppose an abrupt fall occurs in the atmospheric temperature. The temperature of the return air in a deep mine would be constant, and, therefore, with the greater difference in temperature between intake and return, there would be a greater difference in pressure between the twTo; and, if the previous illustration be taken as an example, the water gauge placed at F would show a static increase of pressure. Furthermore, with such increased difference in pressure, a dynamic action would occur, and an increased quantity of air would pass through the fire area, producing increased combus- tion and increasing the pressure in the fire area. This increase in pressure would continue as long as the fall in temperature continued. Then, however, a condition of equilibrium would be set up, the increased pressure in the fire area tending to reduce the leakage, and therefore combustion would slacken. If now the temperature began to rise, this would show itself by a drop in the water gauge between the fire area and the return. The pressure differences between intake and return would be reduced, the quantity of air chort-circuiting from intake to return would decrease, and combustion would decrease. The ultimate effect would be increase of com- bustion with decrease of temperature, and vice versa, as was actually the case at Senghenydd. A snap of cold weather accelerated combustion to a marked extent, whilst a fairly prolonged spell of mild weather was invariably accompanied by favourable analytical results. Influence of Changes in Atmospheric Humidity. Theoretical considerations point to the fact that atmo- spheric humidity would have an appreciable effect on mine fires. No observations, however, were made at Senghenydd with regard to this point; and in the absence of such records it would be inadvisable at pre- sent to do more than point out the possibility of this influence. Effect of Changes in Ventilation. The balance of pressure between intake and return is often seriously affected by changes in ventilation, and an instance of this has already been given. A number of smaller variations may also produce appreciable differ- ences in pressure, with consequent appreciable differences in the amount of leakage. The opening of doors, variations in the speed of the fan, falls in the fire area, and the small changes of ventilation that daily take place in every colliery—all these innumerable small factors have quite an appreciable cumulative effect on the progress of a mine fire. From charts prepared showing the relation between water gauge pressure and combustion, it was found that a damping effect first began to appear on January 15; and on January 16 the analysis gave indications of a cessation of combustion. From January 16 to January 20, the fluctuations became less marked. From January 20 to January 23 there was a period of fluctu- ations, which did not correspond to any atmospheric pressure or temperature changes. This probably meant that a fresh outburst of combustion had occurred. The curve showed very little fluctuation from the 23rd until the ,31st, when a slight outbreak occurred. On February 5 a sample gave the following results :— Methane, 1-35 per cent.; carbon dioxide, 18-70; carbon monoxide, 0-41; hydrogen, 0-49; ethane, 0-12; oxygen, 1-86; nitrogen, 77-86 per cent. Although the carbon monoxide was high, the percent- ages of hydrogen and ethane showed that combustion was probably ended; and the fairly steady character of the curve until February 23, when a rather serious depression in the water gauge was followed by marked fluctuation. The depression probably caused serious leakage of air inwards which again set combustion going, and on February 26 the following analysis was obtained : Methane, 1 per cent.; carbon dioxide, 18-80; carbon monoxide, 0-60; hydrogen, 0-40; ethane, 0-15; oxygen, 1-65; nitrogen, 77-40 per cent. The high percentage of carbon monoxide indicated a rather serious outburst, and to cope with it the carbon dioxide was increased to 1,000 cu. ft. an hour, and kept at that quantity for about three days. This had the desired effect, and by March 1 the water gauge curve showed that things were again becoming normal, whilst an analysis of a sample taken on March 20 gave the following results:—Methane, 0-91 per cent.; carbon dioxide, 1-65; carbon monoxide, 0-25; hydrogen, 0-23; ethane, 0-05; oxygen, 1-79; nitrogen, 78-92 per cent. From March 1 onwards the curve showed very little fluctuation, and there was no doubt that the combustion had decreased to practically a minimum. The CO2 plant was stopped on March 28, and, despite the con- siderable leakage of air evident in the analyses after that date, the products of combustion were present in such small quantities that there was every reason for believing that very little actual burning was taking place. The general character of the curve indicated that the con- stant addition of the carbon dioxide exerted a small but continuous checking of the violent fluctuations produced by the breathing action of the fire. The extremes of pressure gradually approached closer and closer until, finally, the curve, considered apart from the other influences, tended to become a straight line. Water Gauge and Atmospheric Temperatures. The relation between changes in atmospheric temper- atures and the water gauge was clearly shown by a chart. The curves of temperatures and pressures were svmmetrically opposite to one another, the water gauge rising with a decrease in atmospheric temperature, and falling with a rise in the latter. An upward loop in the temperature curve between January 7 and January 11 corresponded with a downward loop in the water gauge between the same dates. Similar results were found between January 23 and February 9, between February 11 and February 17, and between March 10 and March 18. Furthermore, as a general rule, greater fluctuations occurred in the depressions of the water gauge curve than in the elevated portions, because depressions represent periods of low pressure, during which leakage from the intake side would be greater than normally, and the leakage would be followed by greater combustion. Water Gauge and Barometric Variation. In very few instances could the effect of barometric variation be perceived. This was only to be expected, as slow movements would be readily counteracted by leakage, and only very rapid changes would be shown. One particular instance of a marked character occurred on February 2, where a rapid rise of barometric pressure began. This was followed by an abrupt fall in the water gauge readings, succeeded by a slow rise, lagging several hours behind the barometric rise. This rapid decrease in pressure in the fire wave produced, for a short time, a serious renewal of combustion. Similar instances could be noted in the sudden baro- metric fluctuations in the period March 8 to 26, whilst, speaking generally, the water gauge curve showed a distinct lag after the barometric curve. Changes of Ventilation and Miscellaneous Factors. Apart from the effects of big changes of ventilation, the influence of such factors as the opening of doois was noticed. As a general rule, the most marked fluctua- tion each day—especially if the temperature' and baro- metric effects be eliminated—occurred between 9 p.m. and 3 a.m. In many instances several fluctuations of about 0-05 in. occurred in these few hours. It was the practice to take all the chemicals for the following 24 hours to the plant in the night, and during this period the doors were opened far more frequently, and to a greater extent, than in the day time, so that small fluctuations in the water gauge occurred more frequently. The water gauge is a most valuable instrument in the detection and control of mine fires. Preferably it should be of a recording type, and its readings should be corre- lated as far as possible with the readings of a recording barometer and with readings of atmospheric tempera- ture. Supplemented by periodical chemical analysis, the information so obtained is far more comprehensive in character than temperature measurements alone. Summary and Conclusions. The chief effect of a comparatively small but regular quantity of inert gas pumped into a fire lies not so much in its extinguishing power as in its gradual damping down of pressure changes in the fire area. These pressure changes are produced by the breathing action of the fire, by changes in ventilation, and by changes in atmospheric temperature and pressure; and it is the leakage of air resulting from these changes that allows combustion to proceed. Provided leakage is reduced to a minimum, it is only a matter of time before combustion is absolutely extin- guished, the length of time depending on the extent of the fire and the magnitude of the inevitable leakage. Unfortunately, however, inert gas has a rather serious limitation, that was pointed out by Mr. W. H. Chambers nearly 20 years ago (Proceedings Fed. Inst., p. 165, vol. xviii., p. 154). There is no doubt that in time it can extinguish a mine fire, but it can only reduce the temperature by a very slight extent, unless used in the liquefied form, and in such quantities that its vaporisa- tion will absorb sufficient heat to reduce the temperature io normal. Under such conditions, and injected at a number of different points, it has proved efficacious, both in the extinction of combustion and in the reduction of temperature, in the case of very large fires in the hold of ships. In such cases a -quantity varying from 4,000 to 10,000 cu. ft. of C()2 is injected in a few hours through pipes already fitted around the liold of the ship, and several cases are on record of exceedingly rapid temperature reductions, even when masses of coal, amounting to thousands of tons, have been on fire. Difficulty would perhaps be found, in mining practice, in applying the liquid CO2 at a sufficient number of points to ensure a sufficient.reduction of temperature at every point of the burning mass to cause extinction. The temperature difficulty, therefore, will always be a serious one in mining practice. The only outlet for the temperature is by conduction through the strata, and the enormous store of heat in a large mine fire might possibly take wears to dissipate. This was the difficulty experienced at Senghenydd. Despite the favourable analytical results, the temperature measurements declined so very slowly that the management always had present in their minds the possibility of combustion re-starting. It was therefore decided to adopt other measures with a view to absolutely preventing the possi- bility of any future recurrence of combustion. The out- side bashing was opened during the last week in July, and the following analyses show that combustion re-started immediately. Analyses of Samples taken July 24 and August 17. July 24. August 17. Per cent Per cent. Methane 0*35 ... 0’10 Carbon dioxide 14*23 15’88 Carbon monoxide 0*35 0’67 Hydrogen 0*10 0’28 Ethane 0015 0’08 Oxygen 6’13 ... 5’08 Nitrogen 78’825 77*91 During' the progress of these operations the CO2 plant was of considerable service, chiefly as a means of keep- ing the fire back from the vicinity of the air bridge. Immediately the temperature at this point became excessive, CO2 was pumped in, and invariably effected a reduction to reasonable limits within a comparatively short period of time. With such a mass of burning material as that at Senghenydd, in ground permeated with crevices and fissures, with a consequent enormous leakage, it is a matter for surprise that the injection of C02 was able to accomplish as much as it did; but ultimately, to quote Mr. Shaw, “ it was water and perseverance that put the fire out, and it required big quantities of both.” DISCUSSION. The President moved a vote of thanks to Mr. Evans for his paper. The author, he said, had described the experiment as a partial failure, but at any rate he had given to the members -of the society and the mining community in general the benefit of a very interesting experience. A great deal could be learned from a failure, though perhaps not as much as from a success, and he was sure every member would feel grateful to Air. Evans for the valuable information he had placed before them. Mr. Drummond Paton (Manchester), in seconding, remarked that a failure, when it arose through a lack of detailed analysis and scientific investigation was a failure; but failure to reach a definite end or achieve success, through some inherent cause not yet defined, could not be fairly described as a failure. Instead of going blindly into the subject in a rough sort of way, Air. Evans had entered upon his task in a most analytical manner. Air. A. J. A. Orchard (St. Helens) asked why the author described the temperature of 140 degs. as “ a significant temperature,” and whether the winding of coal was proceeding while the experiment was being carried out. In connection with the later, query he was thinking of the action of the cage in the shaft. Mr. Evans replied that the temperature of 140 degs. was significant because M. Fayol had found that temperature continuously in heaps of coal set on fire by spontaneous combustion. With regard to the other question put by Mr. Orchard, the east side of the colliery was untouched by the explosion, and that shaft was being used continuously, both the upcast and downcast, during the whole period. Mr. Ross (Manchester) asked whether the samples of air submitted to analysis were always taken at the same place. His experience was that a sample might be taken from one particular place and found upon analysis to be quite different to a second sample taken about a foot away. In matters of that kind it was very important that the samples should be taken at exactly the same spot each time. Mr. Evans replied that the samples, except perhaps in the case of the Klondyke, were taken practically at the same place. Where the analysis gave indications of an imperfect sample he had not included it in his paper. Mr. John Gerrard observed that the lesson to be learnt was that unless the supply of air could be cut off the injection of C02 was ineffective. They had a record of the application of C02 to an underground fire in Lancashire in the year 1849, when Mr. James Darlington extinguished a fire in the Worsley Four-foot by sealing up the two shafts to cut off all air access and introducing CO2. With regard to the Senghenydd experiment, it was obvious that the failure during the long period of trial was due to the free access of air which had the effect of feeding the fire. Mr. Evans agreed that it was certainly due to the leakage of air, but, on the other hand, the C02 plant did ultimately put the fire out; he had no hesitation in making that statement. Their difficulty was in reducing the temperature. The only method of doing that was by conduction through the strata, and under those con- ditions the strata would probably have retained their heat for years, and even then have been ready to burst into active combustion immediately the bashings or stoppings were re-opened. Not being able to reduce the temperature was the reason for the failure, and not.so much the air leakage. They overcame the fluctuations due to barometric pressure, but could not reduce the temperature. Mr. Gerrard said he understood from the paper that the fire was extinguished several times and broke out again, a circumstance which required some explanation. Whatever the effect of the CO2 was, it seemed that the continued application of perseverance- and water was ultimately necessary to extinguish the fire completely. Mr. A. Stephenson (Tyldesley) said he had had a fair experience of fires in mines, and had often been told that he followed the wrong lines in extinguishing them by means of water. He always felt, however, that if the strata were fractured, as was the case apparently at Senghenydd, for many yards above the place where the fire was burning, it was practically impossible to put it out by means of CO2, or any other gas. He was inclined to think, from the description given by Mr. Evans, that the cause of the failure was the presence of too many fissures, which prevented them from getting the gas.to the spot where they wished it to be applied. The discussion was adjourned to a future meeting.