Transactions of the American Society of Civil Engineers, vol. LXX, Dec. 1910 | Page 8

1 pound of a permissible explosive or 2 pounds of black
powder, the quantity of noxious gases given off from a shot averages
approximately the same, the quantity 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 substitute 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 1½
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 pass these tests. Immediately on the passing 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 quantity 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 quantities 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,