The Chemistry of Powder and Explosives - Sciencemadness Dot Org

PERMISSIBLE EXPLOSIVES 347
that one blast will stir up clouds of dust which the next blast will
cause to explode. Accidents from this cause became more and
more frequent as the industrial importance of coal increased
during the nineteenth century and as the mines were dug deeper
and contained more fire damp, until finally the various nations
which were producers of coal appointed commissions to study
and develop means of preventing them. The first of these was
appointed in France in 1877, the British commission in 1879, the
Prussian commission in 1881, and the Belgian and Austrian commissions
at later dates. The Pittsburgh testing station of the
U. S. Geological Survey was officially opened and regular work
was commenced there on December 3, 1908, with the result that
the first American list of explosives permissible for use in gaseous
and dusty coal mines was issued May 15, 1909. On July 1, 1909,
the station was taken over by the U. S. Bureau of Mines, 22 which,
since January 1, 1918, has conducted its tests at the Explosives
Experiment Station at Bruceton, not far from Pittsburgh, in
Pennsylvania.
Explosives which are approved for use in gaseous and dusty
coal mines are known in this country as permissible explosives,
in England as permitted explosives, and are to be distinguished
from authorized explosives which conform to certain conditions
with respect to safety in handling, in transport, etc. Explosives
which are safe for use in coal mines are known in France as
explosifs antigrisouteux, in Belgium as explosifs S. G. P. (securite,
grisou, poussiere), in Germany- as schlagwettersichere Sprengstoffe
while the adjective handhabungssichere is applied to those
which are safe in handling. Both kinds, permissible and authorized,
are safety explosives, explosifs de surete, Sicherheitssprengstoffe.
A mixture of air and methane is explosive if the methane content
lies between 5 and 14%. A mixture which contains 9.5% of
methane, in which the oxygen exactly suffices for complete combustion,
is the one which explodes most violently, propagates the
explosion most easily, and produces the highest temperature. This
mixture ignites at about 650° to 700°. Since explosives in general
produce temperatures which are considerably above 1000° ? explo-
22 A few of the interesting and important publications of the U. S. Bureau
of Mines are listed in the footnote, Vol. I, pp. 22-23.