“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