"Subject to the provisions named below, a permissible explosive is defined as an explosive which is in such condition that the chemical and physical tests do not show any unfavorable results; which has pa.s.sed gas and dust gallery tests Nos. 1 and 3, as described in circular No. 1; and of which, in test No. 4, 1 pounds (680 grams) has been fired into the mixture there described without causing ignition.
"_Permissible explosives tested prior to October 1, 1909._
"[Those reported in Explosives Circular No. 1 are marked *.]
------------------------------+------------------------------------- Brand. | Manufacturer.
------------------------------+------------------------------------- *aetna coal powder A | aetna Powder Co., Chicago, Ill.
aetna coal powder AA | Do.
*aetna coal powder B | Do.
aetna coal powder C | Do.
Bituminite No. 1 | Jefferson Powder Co., Birmingham, | Ala.
Black Diamond No. 3 | Illinois Powder Manufacturing Co., | St. Louis, Mo.
Black Diamond No. 4 | Do.
*Carbonite No. 1 | E. I. Du Pont de Nemours Powder Co., | Wilmington, Del.
*Carbonite No. 2 | Do.
*Carbonite No. 3 | Do.
*Carbonite No. 1-L. F. | Do.
*Carbonite No. 2-L. F. | Do.
*Coalite No. 1 | Potts Powder Co., New York City.
*Coalite No. 2-D. | Do.
*Coal special No. 1 | Keystone Powder Co., Emporium, Pa.
*Coal special No. 2 | Do.
*Collier dynamite No. 2. | Sinnamahoning Powder Manufacturing | Co., Emporium, Pa.
*Collier dynamite No. 4. | Do.
*Collier dynamite No. 5. | Do.
Giant A low-flame dynamite. | Giant Powder Co. (Con.), Giant, Cal.
Giant B low-flame dynamite. | Do.
Giant C low-flame dynamite. | Do.
*Masurite M. L. F. | Masurite Explosives Co., Sharon, Pa.
*Meteor dynamite. | E. I. Du Pont de Nemours Powder Co., | Wilmington, Del.
Mine-ite A. | Burton Powder Co., Pittsburg, Pa.
Mine-ite B. | Do.
*Mon.o.bel. | E. I. Du Pont de Nemours Powder Co., | Wilmington, Del.
Tunnelite No. 5. | G. R. McAbee Powder and Oil Co., | Pittsburg, Pa.
Tunnelite No. 6. | Do.
Tunnelite No. 7. | Do.
Tunnelite No. 8. | Do.
"_Provided:_
"1. That the explosive is in all respects similar to sample submitted by the manufacturer for test.
"2. That No. 6 detonators, preferably No. 6 electric detonators (double strength), are used of not less strength than 1 gram charge, consisting by weight of 90 parts of mercury fulminate and 10 parts of pota.s.sium chlorate (or its equivalent), except for the explosive "Masurite M. L. F.," for which the detonator shall be of not less strength than 1 grams charge.
"3. That the explosive, if frozen, shall be thoroughly thawed in a safe and suitable manner before use.
"4. That the amount used in practice does not exceed 1 pounds (680 grams), properly tamped.
"The above partial list includes all the permissible explosives that have pa.s.sed these tests prior to October 1, 1909. The announcement of the pa.s.sing of like tests by other explosives will be made public immediately after the completion of the tests.
"With a view to the wise use of these explosives it may be well in this connection to point out again certain differences between the permissible explosives as a cla.s.s and the black powders now so generally used in coal mining, as follows:
"(_a_) With equal quant.i.ties of each, the flame of the black powder is more than three times as long and has a duration three thousand to more than four thousand times that of one of the permissible explosives; the rate of explosion also is slower.
"(_b_) The permissible explosives are one and one-fourth to one and three-fourths times as strong and are said, if properly used, to do twice the work of black powder in bringing down coal; hence only half the quant.i.ty need be used.
"(_c_) With 1 pound of a permissible explosive or 2 pounds of black powder, the quant.i.ty of noxious gases given off from a shot averages approximately the same, the quant.i.ty from the black powder being less than from some of the permissible explosives and slightly greater than from others. The time elapsing after firing before the miner returns to the working face or fires another shot should not be less for permissible explosives than for black powder.
"The use of permissible explosives should be considered as supplemental to and not as a subst.i.tute for other safety precautions in mines where gas or inflammable coal dust is present under conditions indicating danger. As stated above, they should be used with strong detonators, and the charge used in practice should not exceed 1 pounds and in many cases need not exceed 1 pound.
"JOSEPH A. HOLMES, "_Expert in Charge Technologic Branch._ "Approved, October 11, 1909.
"H. C. RIZER, "_Acting Director._"
The second list contains 31 explosives which the Government is prepared to brand as permissible, and therefore comparatively safe, for use in gaseous and dusty mines. An equally large number of so-called safety powders failed to pa.s.s these tests. Immediately on the pa.s.sing of the tests, as to the permissibility of any explosive, the facts are reported to the manufacturer and to the various State mine inspectors. When published, the permissible lists were issued to all explosives manufacturers, all mine operators in the United States, and State inspectors. The effect has been the enactment, by three of the largest coal-producing States, of legislation or regulations prohibiting the use of any but permissible explosives in gaseous or dusty mines, and other States must soon follow. To prevent fraud, endeavor is being made to restrict the use of the brand "Permissible Explosive, U.S. Testing Station, Pittsburg, Pa.," to only such boxes or packages as contain listed permissible explosives.
As these tests clearly demonstrate, both in the records thereof and visually to such as follow them, that certain explosives, especially those which are slow-burning like black powder, or produce high temperature in connection with comparative slow burning, will ignite mixtures of gas and air, or mixtures of coal dust and air, and cause explosions. The results point out clearly to all concerned, the danger of using such explosives. The remedy is also made available by the announcement of the names of a large number of explosives now on the market at reasonable cost, which will not cause explosions under these conditions. It is believed that when permissible explosives are generally adopted in coal mines, this source of danger will have been greatly minimized.
_Explosives Investigations._--Questions have arisen on the part of miners or of mine operators as to the greater cost in using permissible explosives due to their expense, which is slightly in excess of that of other explosives; as to their greater shattering effect in breaking down the coal, and in giving a smaller percentage of lump and a larger percentage of slack; and as to the possible danger of breathing the gases produced.
Observations made in mines by Mr. J. J. Rutledge, an experienced coal miner and careful mining engineer connected with the Geological Survey, as to the amount of coal obtained by the use of permissible and other explosives, tend to indicate that the permissible explosives are not more, but perhaps less expensive than others, in view of the fact that, because of their greater relative power, a smaller quant.i.ty is required to do the work than is the case, say, with black powder. On the other hand, for safety and for certainty of detonation, stronger detonators are recommended for use with permissible explosives, preferably electric detonators. These may cost a few cents more per blast than the squib or fuse, but there is no danger that they will ignite the gas, and the difference in cost is, in some measure, offset by the greater certainty of action and the fact that they produce a much more powerful explosion, thus again permitting the use of still smaller quant.i.ties of the explosive and, consequently, reducing the cost. These investigations are still in progress.
Concerning the shattering of the coal: This is being remedied in some of the permissible explosives by the introduction of dopes, moisture, or other means of slowing down the disruptive effect, so as to produce the heaving and breaking effect obtained with the slower-burning powders instead of the shattering effect produced by dynamite. There is every reason to believe that as the permissible explosives are perfected, and as experience develops the proper methods of using them, this difficulty will be overcome in large measure. This matter is also being investigated by the Survey mining engineers and others, by the actual use of such explosives in coal-mining operations.
Of the gases given off by explosives, those resulting from black powder are accompanied by considerable odor and smoke, and, consequently, the miners go back more slowly after the shots, allowing time for the gases to be dissipated by the ventilation. With the permissible explosive, the miner, seeing no smoke and observing little odor, is apt to be incautious, and to think that he may run back immediately. As more is learned of the use of these explosives, this source of danger, which is, however, inconsiderable, will be diminished. Table 1 gives the percentages of the gaseous products of combustions from equal weights of black powder and two of the permissible explosives. Of the latter, one represents the maximum amount of injurious gases, and the other the minimum amount, between which limits the permissible explosives approximately vary.
Such noxious gases as may be produced by the discharge of the explosive are diluted by a much larger volume of air, and are practically harmless, as proven by actual a.n.a.lysis of samples taken at the face immediately after a discharge.
TABLE 1.
--------+---------+-------------------------- | | Permissible Explosives.
| Black |-------------+------------ | powder. | Maximum. | Minimum.
--------+---------+-------------+------------ CO_{2} | 22.8 | 14.50 | 21.4 CO | 10.3 | 27.74 | 1.3 N | 10.3 | 45.09 | 74.4 --------+---------+-------------+------------
In addition to investigations as to explosives for use in coal mining, the Explosives Section of the Geological Survey a.n.a.lyzes and tests all such materials, fuses, caps, etc., purchased by the Isthmian Ca.n.a.l Commission, as well as many other kinds used by the Government. It is thus acquiring a large fund of useful information, which will be published from time to time, relative to the kinds of explosives and the manner of using them best suited to any blasting operations, either above or under water, in hard rock, earth, or coal. There has been issued from the press, recently, a primer of explosives,[7] by Mr.
Clarence Hall, the engineer in charge of these tests, and Professor C.
E. Munroe, Consulting Explosives Chemist, which contains a large amount of valuable fundamental information, so simply expressed as to be easily understandable by coal miners, and yet sufficiently detailed to be a valuable guide to all persons who have to handle or use explosives.
In the first chapters are described the various combustible substances, and the chemical reactions leading to their explosibility. The low and high explosives are differentiated, and the sensitiveness of fulminate of mercury and other detonators is clearly pointed out. The various explosives, such as gunpowder, black blasting powder, pota.s.sium chlorate powders, nitro-glycerine powders, etc., are described, and their peculiarities and suitability for different purposes are set forth. The character and method of using the different explosives, both in opening up work and in enclosed work in coal mines, follow, with information as to the proper method of handling, transporting, storing, and thawing the same. Then follow chapters on squibs, fuses, and detonators; on methods of shooting coal off the solid; location of bore-holes; undercutting; and the relative advantages of small and large charges, with descriptions of proper methods of loading and firing the same. The subjects of explosives for blasting in rock, firing machines, blasting machines, and tests thereof, conclude the report.
The work of the chemical laboratory in which explosives are a.n.a.lyzed, and in which mine gases and the gases produced by combustion of explosives and explosions of coal-gas or coal dust are studied, has been of the most fundamental and important character. The Government is procuring a confidential record of the chemical composition and mode of manufacture of all explosives, fuses, etc., which are on the market.
This information cannot but add greatly to the knowledge as to the chemistry of explosives for use in mines, and will furnish the basis on which remedial measures may be devised.
A bulletin (shortly to go to press) which gives the details of the physical tests of the permissible explosives thus far tested, will set forth elaborately the character of the testing apparatus, and the method of use and of computing results.[8]
This bulletin contains a chapter, by Mr. Rutledge, setting forth in detail the results of his observations as to the best methods of using permissible explosives in getting coal from various mines in which they are used. This information will be most valuable in guiding mining engineers who desire to adopt the use of permissible explosives, as to the best methods of handling them.
_Electricity in Mines._--In connection with the use of electricity in mines, an informal series of tests has been made on all enclosed electric fuses, as to whether or not they will ignite an explosive mixture of air and gas when blown out. The results of this work, which is under the direction of Mr. H. H. Clark, Electrical Engineer for Mines, have been furnished the manufacturers for their guidance in perfecting safer fuses, a series of tests of which has been announced. A series of tests as to the ability of the insulation of electric wiring to withstand the attacks of acid mine waters is in progress, which will lead, it is hoped, to the development of more permanent and cheaper insulation for use in mine wiring. A series of compet.i.tive tests of enclosed motors for use in mines has been announced, and is in progress, the object being to determine whether or not sparking from such motors will cause an explosion in the presence of inflammable gas.