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See Inside Scientific American Volume 105, Issue 23

The First National Mine-Safety Demonstration

Study of a Real Mine Explosion

THE work that is being done by the Government to reduce the dangers of mining was brought out strikingly in the First National Mine-Safety Demonstration which occurred at Pittsburgh, Pa., on October 30th and 31st, under the auspices of the United States Bureau of Mines with the assistance of the American National Red Cross Society and the Pittsburgh Coal Operators Association. The work of the explosive testing section was exhibited in a spectacular manner in the gas and dust gallery which is a steel tube 100 feet long and 6½ feet in diameter open at one end and closed at the other, with the exception of a small hole through which it is fired by the flame from a small cannon charged with the explosive that is being tested. The gallery is provided with explosion doors on top which are raised by the force of the explosion, and windows of heavy glass on the sides through which flame is visible when an explosion of gas or dust is produced. A portion of the tube was partitioned off by heavy paper making a chamber in which gas and air were mixed so that the mixture contained seven per cent of methane and ethane, both explosive gases. A charge of black blasting powder equal in strength to one-half pound of forty per cent nitro-glycerine dynamite was fired into the gallery igniting the gas and producing a terrific explosion. Again, an amount of permissible explosive equal in strength to the black blasting powder was fired in a gaseous mixture of the same composition. As no explosion of the gas took place, the relative safety of black blasting powder and permissible explosive was evident. This test of explosives is especially valuable in gaseous mines where there is the liability that the flame from the explosive may ignite pockets of gas which may be present near where coal is being blasted out. In another building lighted incandescent lamps were broken in an explosive mixture of gas and air illustrating- the relative safety of lamps of different candle power when operated with different voltages. In still another building, a foundry cupola was in operation to show the method of taking gas samples and temperatures in various zones of the coke bed. for the purpose of studying the fundamental principles of the process with a view to possible improvement. A gas producer was in operation burning fuel at a high temperature and capacity and in which the ash and clinker were removed by tapping off the liquid slag at stated intervals. In the fuel briquetting plant two types of briquet-ting presses were in operation one of which was producing briquets from California lignite under a pressure of 20,000 pounds to the square inch without the use of artificial binder while the other machine made briquets of ordinary bituminous slack using six per cent of water-gas pitch as a binder. These briquetting experiments have for their object the better utilization of fuel wast© and low grade fuels. The long combustion chamber of the bureau was also interesting to many of the visitors. This is essentially a Murphy stoker at one end of a long chamber built of brick and lined with fire brick at the other end of which is a water tube boiler. At several points on this chamber there are openings for the insertion of thermo-couples and the withdrawal of samples of flue gas. A large number of gas samples are taken from the various points simultaneously and the study of the analyses of tliese Samples makes it possible to determine the proper distance that the furnace should be from the cold boiler tubes in order that complete combustion may take place. This distance varies with different types of fuels and the results of these investigations will undoubtedly furnish valuable data for designers of boilers and furnaces. Another feature of the demonstration was a safety lamp test. Single and double gauze safety,lamps were placed in a testing apparatus where they were subjected to currents of air of a known velocity containing eight per cent of methane and ethane. The lamps which were safe to use did not produce an explosion of this mixture of gas and air; others did, and thus their relative safety was demonstrated'. Men in various types of breathing apparatus were exercising in a room filled with a noxious atmosphere and a glass partition permitted the visitors to see in a graphic manner how operations are carried on by the rescue corps under conditions similar to those existing after an explosion has occurred in a mine. There was also an exhibition of apparatus for the physical testing of explosives including a ballistic pendulum by means of which the relative disruptive force ipf an explosive is determined; a pressure gage for determining the pressure developed by a known weight of an explosive; a calorimeter for determining the heat of combustion of an explosive; a flame testing apparatus for the determination of length and duration of the flame of an explosive, an- apparatus for determining the rate of detonation of an explosive, a large and small impact machine for determining the force necessary to set off explosives, Trauzl and lead blocks which are also used for determining the relative power of an explosive and a cone and pendulum friction device for determining the behavior of explosives under friction. The explosibility of coal dust was shown by meana of a laboratory coal dust ignition apparatus consisting of a heavy glass vessel into the bottom of which coal dust was blown by air upon a wire heated red hot by an electric current. The force of the explosion of the coal was graphically shown by the .bursting of a thin glass flask connected to the top of the ignition apparatus. In gas and dust gallery No. 2 an inclosed electric mine motor was shown operating in an explosive mixture of gas and air without producing an explosion. Later the protecting devices were removed from this motor and an explosion of the gaseous mixture resulted. The relative safety of motors for mining purposes under the two conditions open and protected were thus demonstrated. Two of the mine rescue cars of the Bureau were on the siding at the plant and open for the inspection of visitors. In the afternoon of the first day the experimental mine of the bureau was visited by a party of about two thousand people, a I special train being pro- vided. The trip to the experimental mine was made for the purpose of seeing a demonstration of the explosibility of coal dust in a real mine. The mine is located in Bruceton, Pa., in the Pittsburgh seam of coal which at this point outcrops-on the side of a hill about 100 feet above the railroad. The mine was opened primarily in order to study the principles involved in dust and gas explosions and to test various methods of preventing and checking explosions in progress under actual mine conditions. When the special train arrived at the station the rain was falling steadily, but this was not sufficient to dampen the ardor of the enthusiastic visitors including several ladies. As soon as the party had climbed the steep ascent from the railroad to the mine they were invited to walk through the mine and 1,131 persons by actual count availed themselves of this opportunity. When all of the party were out of the mine again they were requested to take positions about twenty-five yards up the hillside above the mine December 2, 1911 SCIENTIFIC AMERICAN 499 to await the explosion. Between 600 and 700 pounds of coal dust had been scattered along 600 feet of the main entry which is 750 feet long and two pounds of -black powder were placed in a drill hole at the extreme inner end of the main entry in such a manner that the conditions would represent those similar to a blown-out shot in actual mining. Electric wires connected this charge of explosive with the instrument house outside of the mine. The wires were placed in circuit with a source of electric current and the powder explosion which followed ignited the coal dust in the mine resulting in a terrific explosion. It was dark by the time that the explosion occurred and the smoke and flame mounted high into the air above the entrances to the mine. The air was filled with pieces of stone, broken concrete and wood and the people involuntarily took refuge under the trees. “ There was no real danger, however, as the people were above and back of the mine entrances. The force of the explosion was manifested in the vicinity of the mine by the damage done. Near the main entry a loaded mine car had been shot back about fifty feet while another partly loaded had been blown more than one hundred yards over a bank into the valley. The big bags of sand which were used in the brattices 130 feet from the entry had been blown out into the open. The temporary fan house had been wrecked and the office building partly demolished. If any of the mining men present had any doubt as to the explosi-bility of coal dust in a mine without the presence of gas, this question was settled once and for all. It had been planned to have men equipped with oxygen helmets enter the mine immediately after the explosion to take gas samples, extinguish incipient fires and inspect the condition of the roof, but the lateness of the hour made it necessary for all to hasten to the train waiting to convey them back to Pittsburgh. Every one who saw this demonstration was profoundly impressed with the importance, of the test and many compliments were given to Director Holmes and those in charge of the experiment. On the morning of the 31st the great first-aid meet and mine safety demonstration was held at Forbes Field. The first thing on the program was the first-aid exhibition. The forty teams that participated were arranged in a row facing the seats. “While many of the teams participating came from Pennsylvania and adjoining States, there were others which came from longer distances notably those from Tacoma, Washington, Dawson, and New Mexico. The teams performed alternately in two sections, the even numbered teams working the same problems while the odd numbered teams worked other problems. The first-aid problems performed included treatment of lacerated wounds on the head and body, the treatment of fractured bones and dislocated joints, the removal of a man from an electric wire and the treatment of gas and electrical burns. Following the MrsT-aia worn: a demonstration of the behavior of a permissible explosive In the presence of coal dust was mtie in a temporary steel gallery or cylinder 133 feet long and 6 feet 4 Inches In diameter. The amount of explosive used was eaual In dlsruutive force to one-half pound of forty per cent nitro-glycer-ine dynamite. The explosive was fired into the gallery from a cannon through a small opening in the steel end of the former. The other end was open to the atmosphere. One hundred and thirty-three pounds of coal dust was distributed uniformly throughout the explosion gallery and twenty pounds of dust was placed on a wooden bench twenty feet long near the mouth of the cannon making a total of 153 pounds of coal dust. When all was ready the charge was fired from a distance through wires by means of a storage battery. No explosion of the coal dust was produced by this test which demonstrated the safety of using a permissible explosive in the presence of dust. A second demonstration was made in the same gallery with the same amount of coal dust using a charge of FFF black blasting powder equal in disruptive force to the permissible explosive used in the previous test. When this black blasting powder was ignited from a distance a tremendous explosion took place, the flame escaped from the safety doors on top of the cylinder and great clouds of dust and smoke were blown out of the end of the gallery. Immediately following this explo'sion while the gases within the gallery were still unbreathable a rescue party of foremen miners of the Bureau of Mines aided by * squads from some of the visiting first-aid teams and all of them equipped with various types of breathing apparatus, entered the gallery and recovered several supposed victims of the mine explosion bringing them from the explosion gallery and placing them in the care of squads of foremen miners and first-aid miners of the Bureau of Mines who demonstrated the various first-aid problems using the pocket first-aid packet only and such things, as might be handy in a mine after an explosion. Another interesting feature of the exhibition was the mine gas test made with the use of birds in exploring mines after explosions or mine fires at which carbon monoxide causes a large percentage of fatalities. Birds are much more sensitive to the effects of this poisonous gas (carbon monoxide), than human beings, and when birds taken with a rescue party into a mine, show signs of distress, the party (which of course is supposed to be without oxygen helmets), will ordinarily have time to retreat to safety. At Forbes Field the practicability of this test was demonstrated by a gas chemist of the bureau who entered a glass box about 2 feet wide by 5 feet long, and 6 feet high, with canaries in cages. The atmosphere of the box contained one quarter of one per cent of carbon monoxide gas (the miner's white damp). In eight minutes three of the birds were overcome and collapsed completely.

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