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 indicative of 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.

“Inasmuch as no explosive manufactured for use in mining is flameless,
and as no such explosive is entirely safe under all the variable
mining conditions, the use of the terms ‘flameless’ and ‘safety’ as
applied to explosives is likely to be misunderstood, may endanger
human life, and should be discouraged.

“JOSEPH A. HOLMES,
“_Expert in Charge Technologic Branch_.

“Approved, May 18, 1909:
“GEO. OTIS SMITH,
“_Director_.”

In the meantime, many of the explosives submitted, which heretofore had
been on the market as safety explosives, were found to be unsafe for
use in gaseous or dusty mines, and the manufacturers were permitted
to withdraw them. Their weaknesses being known, as a result of these
tests, the manufacturers were enabled to produce similar, but safer,
explosives. Consequently, applications for further tests continued