The Wallace miner. [volume] (Wallace, Idaho) 1907-current, 1914-03-05

but 1t Is as great a menace and should
he treated accordingly. As much care
should be used in handling explosives
in the vicinity of electrical apparatus
as though the flashes and sparks that
it is capable of giving were constantly
in evidence.
Any source of heat may attack an
explosive from the outside, but cleo
tricity may, under certain conditions,
do more than that. An explosive that
is a conductor of electricity may come
in contact with an electric circuit in
such way that current may be pass
ed through the explosive itself, and
although no spark may occur outside
the package, ignition may take place
on the inside. The possibility Of such
an occurrence may seem, to be ex-
tremely remote, but accidents have
been reported for which no other cause
could be assigned and in which the
existence of the above conditions was
quite probable. AS mentioned in a
foregoing paragraph, 1t Is possible,
when mine cars of certain type are
use, that considerable difference Of
potential may exist between the draw
bars and those metallic parts of the
car that are in electrical connection
with the track rail. If such car were
loaded with metallic packages Of ex-
plosives, the points of different poten-
tial might be so Joined that current
would flow through the packages and
possibly through the explosive itself.
Accidents Due to Electrical Shot Firing
The accidents that occur in connec-
ton with electrical shot firing are due
for the most part, to the accidental
discharge of detonators in the vicinity
of explosives or to the premature ig-
milton of shots after holes are charg
ed. With regard to the accidental
discharge Of decorators should be kept
separate from explosives and that bat
teries and other sources Of electric en-
ergy should be kept separate from de-
tonatOrS.
With regard to the premature igni-
ton of shots, it is not the best prac-
tice to shoot electrically under condi-
tions that require one side of the de-
tonating circuit to be connected to the
earth, because whenever grounded sys-
TENS of distribution are used unex-
pected differences Of potential exist in
the earth in the vicinity of such cir
cults. IT, therefore, one side of the
detonator be purposely grounded, an
accidental ground ON the other side
of the detonator across a potential
sufficient to cause ignition. Premature
ignitions have been reported which
seemingly have been caused by the
conditions just described.
| Ignition Of Gas.
J Electric sparks will ignite mine gas
and air mixtures that contain between
and II per cent Of gas (methane)
Between these limits a comparative
ly small spark is sufficient to fire the
gaseous mixture. The size of arc or
spark that will occur when an electric
circuit is opened depends upon num-
Der Of things, such as the voltage OF
the circuit, the amount of current bro
ken, the speed Of break and the char
acter of the circuit The determine
ton of the exact influence of each OF
these factors is an interesting prob
lem. For all practicable purposes
however, it is safest to assume that al
sparks which occur around such APP
paratus and circuits as are used 70,
power and light in mine are capable
Of igniting gas. Although this assump-
ton may not be correct at all times
the continually varying conditions sur
rounding such equipment make con-
trary assumption unsafe. For instance
d motor that is so we'll designed and
SO adapted to it's load that the COM
mutating sparks are too minute to ig-
mite gas may. in starting, develop dan
gerous sparks.
The ignition Of gas by electric in
candescent lamps is now being investi-
gated by the bureau of mines. A large
number of lamps of various sizes are
being broken in different ways while
surrounded by highly explosive mix
ture Of gas and air. The results 50 fal
obtained show that certain sizes OF
lamps when broken in the presence Of
gas will ignite 1t, and that in the &C
tion of the lamps there is difference
which depends upon the size of the fill
ament, the larger filaments being more
likely to ignite gas than the smaller
ones.
Ignition Of Coal Dust.
The study of the ignition of coal dust
by electric arc and electric flashes has
ignite coal dust suspended in the at
mosphere. The bureau of mines is now
devising apparatus preparatory tc
|making an extensive investigation OF
this subject.
|