black blasting powder

Black blasting powder is a classic example of a low explosive.  It was used in coal mines, for example, to shatter the coal in the seam so that it could be removed.  A hole was drilled in the coal face, a charge of black powder was tamped into the hole, the hole sealed with a foot or so of tamped clay, and the powder exploded either by a fuse or, preferably, an electric squib.

Small grains burn faster and are consumed before large ones.  If the grains in a charge did not have a uniform size, the fast combustion of the smaller grains would blow the large grains—still burning—out into the mine, possibly igniting any methane or coal dust that was present in the air. 

Black Blasting Powder Grain Sizes
Commercial
designation
Passes through holes
of this size
(in inches)
Passes over holes
of this size
(in inches)
CCC 40/64 32/64
CC 30/64 24/64
C 27/64 18/64
F 20/64 12/64
FF 14/64 7/64
FFF 9/64 3/64
FFFF 5/64 2/64

“Fine-grained powders are quicker, and tend to shatter the material more, while coarse grained powders are slower and have more of a lifting effect.”1

1. E. N. Zern, editor.
Coal Miners' Pocketbook. Twelfth edition.
New York: McGraw-Hill Book Company, 1928.

Page 665.

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