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AND PRECAUTIONS TO BE TAKEN IN THEIR USE.
This circular contains the names of permissible explosives that have been tested by the Bureau of Mines at Pittsburg, Pa., and precautions to be observed when these explosives are used in coal mines. Permissible explosives give a short and relatively cool flame that is less likely to ignite inflammable gas or coal dust than is the longer and hotter flame of dynamite or the longer and much more lasting flame of black powder, and are intended for use in those coal mines where the presence of such gas or dust may render a mine explosion possible. Because they can be used with greater safety, permissible explosives have taken the place of other explosives in many coal mines in the United States during the last two years, and their use is increasing rapidly.
Whether or not an explosive has the good qualities of those explosives classed as "permissible” is something that can be found out only by careful tests. To carry on such tests the Government has placed suitable equipment in a mining experiment station at Pittsburg, Pa. The station is under the charge of the Bureau of Mines, which is directed by law to search for means by which the work of the miner can be made safer,
This circular states the conditions under which explosives are accepted for testing, the tests the explosives now have to pass, the names of the explosives that have passed the tests, and some of the dangers that should be avoided in storing and using explosives. The United States Geological Survey, which formerly had charge of the station at Pittsburg, Pa., has published in three circulars the names of the explosives that passed similar tests prior to May 16, 1910. All of those explosives, and all permissible explosives tested subsequent to May 16, 1910, and prior to January 1, 1911, except such as bave been withdrawn by the makers or have not satisfied later tests, are named in this circular.
CONDITIONS UNDER WHICH EXPLOSIVES ARE TESTED.
The conditions under which the Bureau of Mines tests explosives to determine whether they shall be placed on its list of permissible explosives are as follows:
1. The manufacturer is to deliver to the BUREAU OF MINES, FORTIETH AND BUTLER STREETS, PITTSBURG, Pa., three weeks prior to the date set for tests, 100 pounds of each explosive that he desires to have tested. He is to be responsible for the care, handling, and delivery of this material to the testing station and he is to have a representative present during the tests. In order to avoid duplication of work, it is requested that the smallest size of cartridge that the manufacturer intends to place on the market be sent for these tests.
2. No one is to be present at or participate in these tests except the necessary Government officers at the experiment station, their assistants, and the representative of the manufacturer of the explosives to be tested.
3. The tests will be made in the order of the receipt of the applications for them, provided the necessary quantity of the explosive is delivered at the testing station by the date set, of which date due notice will be given by the Bureau of Mines.
4. A list of the explosives which pass certain requirements satisfactorily will be furnished to State mine inspectors and will be made public in such other manner as may be considered desirable.
5. The details of results of tests are to be considered confidential by the manufacturer and are not to be made public prior to official publication by the Bureau of Mines.
6. From time to time field samples of permissible explosives will be collected, and tests will be made of these explosives as they are supplied for use in coal mines in the various States.
TEST REQUIREMENTS FOR EXPLOSIVES.
The tests will be made by the engineers of the United States mining experiment station at Pittsburg, Pa., in gas and dust gallery No. 1. The charge of explosive to be fired in tests 1, 2, and 3 shall be equal in deflective power, as determined by the ballistic pendulum, to one-half pound (227 grams) of 40 per cent nitroglycerin dynamite in its original wrapper, of the following formula:
100 Each charge shall be fired with an electric detonator (exploder or cap) strong enough to completely detonate or explode the charge, as recommended by the manufacturer. The explosive must be in such
condition that the chemical and physical tests do not show any unfavorable results.
In order that the dust used in tests 2, 3, and 4 may be of the same quality, it is always taken from the same mine, ground to the same fineness, and used while still fresh.
The following are the tests to which are subjected the explosives that the Bureau of Mines is asked to place in the list of permissible explosives:
Test 1. Ten shots each with the charge as described above, in its original wrapper, shall be fired, each tamped with 1 pound of clay stemming, at a gallery temperature of 77° F., into a mixture of gas and air containing 8 per cent of gas (methane and ethane). An explosive is considered to have passed the test if no one of the ten successive shots ignites this mixture.
Test 2. Ten shots each with the charge as described above, in its original wrapper, shall be fired, each tamped with 1 pound of clay stemming, at a gallery temperature of 77° F., into a mixture of gas and air containing 4 per cent of gas (methane and ethane) and 20 pounds of bituminous coal dust, 18 pounds of which is to be placed on shelves along the sides of the first 20 feet of the gallery, and 2 pounds to be so placed that it will be stirred up by an air current in such manner that all or part of it will be suspended in the first division of the gallery. An explosive is considered to have passed the test if no one of the ten successive shots ignites this mixture.
Test 3. Ten shots each with the charge as described above, in its original wrapper, shall be fired, each tamped with 1 pound a of clay stemming, at a gallery temperature of 77° F., into 40 pounds of bituminous coal dust, 20 pounds of which is to be distributed uniformly on a steel trestle placed in front of the cannon and 20 pounds placed on side shelves in sections 4, 5, and 6. An explosive is considered to have passed the test if no one of the ten successive shots ignites this mixture.
Test 4. A limit charge will be determined within 50 grams by firing charges in their original wrappers, without stemming, at a gallery temperature of 77° F., into a mixture of gas and air containing 4 per cent of gas (methane and ethane) and 20 pounds of bituminous coal dust, to be arranged in the same manner as in test 2. This limitcharge test is to be repeated five times under the same conditions before being established.
DEFINITION OF PERMISSIBLE EXPLOSIVE. An explosive is called a permissible explosive when it is similar in all respects to the sample that passed certain tests by the national Bureau of Mines, and when it is used in accordance with the conditions prescribed by that bureau.
a Two pounds of clay stemming are used with slow-burning explosives.
The tests now prescribed as those a permissible explosive must have passed are those given above. But even the explosives that have passed those tests and are published as permissible explosives are to be considered as permissible explosives only when used under the following conditions:
1. That the explosive is in all respects similar to the 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 potassium chlorate (or their equivalents), except for the explosives "Bental coal powder No. 2,” “ Detonite special,” “ Hecla No. 2,” “Kanite A," "Masurite M.L. F.," "Titanite No. 7-P," and "Titanite No. 8-P," for which the detonator shall be of not less strength than the No. 7 (1} grams charge of the same mixture).
3. That the explosive, if frozen, shall be thoroughly thawed in a safe and suitable manner before use.
4. That the quantity used for a shot does not exceed 14 pounds (680 grams), properly tamped.
It must not be supposed that an explosive that has once passed the above-mentioned tests and has been published in lists of permissible explosives is thereafter to be considered a permissible explosive, regardless of its condition or the way in which it is used. Thus, for example, an explosive named in the permissible list, if kept in a moist place until it undergoes a change in character, is no longer to be considered a permissible explosive. If used in a frozen or half-frozen condition, it is not when so used a permissible explosive. If used in excess of the quantity specified (1) pounds), it is not when so used a permissible explosive. And when the other conditions have been met, it is not a permissible explosive if fired with a detonator of less than the prescribed strength.
Moreover, even when all the prescribed conditions have been met no permissible explosive should necessarily be considered as permanently being a permissible explosive, but any permissible explosive when used under the prescribed conditions may properly continue to be considered a permissible explosive until notice of its withdrawal or removal from the list has been officially published, or until its name is omitted from a later list published by the Bureau of Mines.
Furthermore, the manufacturers of a permissible explosive may withdraw it at any time when introducing a new explosive of superior qualities. And after further experiments and conferences, the Bureau of Mines may find it advisable to adopt additional and more severe tests to which all permissible explosives may be subjected, in the hope that the lives of miners may be safeguarded better through the use of only those explosives that may pass the more severe tests.