Mining Practices and Safety at the Lava Cap Gold Mining Corporation Mines, Nevada City-Grass Valley District, California Page: 13
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UNDERGROUND MINING METHODS, CONDITIONS, AND EQUIPMENT 13
BLASTING PRACTICE
Forty-five-percent dynamite (fume class 1) complying with the
California Safety Orders 9 is used in all work.
The cartridges are 1 % by 8 inches. No. 6 electric detonators with
iron legs short-circuited are used for delay blasting and No. 6 caps
for blasting. Firing is done electrically from power circuits and by
fuse and caps, using hot-wire spitters.
Electric blasting is done in long crosscuts, long drifts,.wet headings,
shaft sinking, and long and wet raises. The power blasting circuits
are equipped with two double-throw switches; these are locked in the
open positions except at firing time, when they are operated by the
men doing the blasting, who have and keep the keys. A plug and
receptacle are placed on the blasting line between the blasting switch
and explosives charge when blasting is to be done. These are stretched
across the passageway so that the circuit must be opened before
anyone can pass and when not in use provide a wide gap in the blast-
ing circuit. The outside and face end of all blasting lines are kept
short-circuited until the lines are to be energized.
The rounds consist of 6 to 30 holes 6 to 8 feet deep. Mixed charges
of explosives are not used; the primer is placed next to the bottom
stick in the hole, and the detonator points toward the bottom of the
hole. The prescribed practice for making the hole in the cartridge for
the detonator is to use a wood stick, although some miners use a
sixpenny nail-by no means a good practice.
The holes are loaded by the miner, and cartridges are slit. Air
spacing is avoided, and wood tamping sticks are used to insert the
charge. Holes are cleaned out by a blowpipe and compressed air.
Stemming is required in all holes, one or two sticks or dummies to
a hole. The dummies are made of clay and slime from mill tailings
and are 1Y4 inches in diameter and 8 inches long; they are wrapped in
pink paper as a means of identification in handling the explosive,
loading the holes, and protecting against unexploded dynamite
following blasting.
Blasting by fuse is done by the miner and his helper. The shots are
blasted at the end of the shift when the men are ready to leave the
mine. No tests for noxious gases and no fire runs are made after
blasting. Ample verbal warning appears to be given before the shots
are fired; warning is particularly necessary for protection of workers
when two places are coming together. In such instances the shift boss
usually takes charge.
MISFIRES
Probably no single factor would contribute more to reduction of
explosives accidents than the prevention of misfires. Explosives
accidents are so common in California mines that they are no longer
news, and as long as coroners' inquests held in mining communities
after explosives accidents return verdicts using the stock terms
"premature," " unexpected," and "unavoidable" public opinion will
not be aroused to needless sacrifice of life from this cause.
Misfires at the Lava Cap are reshot by the miners. As all shots are
blasted at the end of the shift, the 5-hour period between shifts is
SSee footnote 8.
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Ash, S. H. Mining Practices and Safety at the Lava Cap Gold Mining Corporation Mines, Nevada City-Grass Valley District, California, report, 1941; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc66443/m1/21/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.