Evening star., 1911-06-04
yXPLOSION GALLERY
AT PITTSBVRQ

powder has been tho commonest cause q.
coal dust explosions in mines Of thu
country Blown-out shots have started
many. and II is common belief that the
flame of black powder must come from q
blown-out shot to start dust explosion
This belief is not supported by fact. foi
explosions have started from shots that
were not blown-out, nor even overcharG
ed. IL is certain also that IL the air al
the face contains even a small percent,
age OF gas tho flame from even a props
erly placed and charged shot OF blaci
powder may start dust explosion. Tho
danger Is greatest when several shots II
the same working place are fired at tho
same time The dust made by the shot
and any gas distilled from the coal b,
the heat may be set on fire by the hanlt
of the next shot
Dynamite is fully as dangerous as black
powder. 1t is quicker than powder. hut
gives long hot flame. and many ex-
plosions have been traced to its usa
Miners have been known TO put two eSs.
plosives. like black powder and dynamite,
i'm the same hole. Such a combination ID
more dangerous than either explosive
used alone. If the quicker burning ex.
plosive is placed at the outer end of the
charge ii may blow out the stemming,
III il is placed at the bottom of the hole
1t may blow the slower explosive, while
still burning, into the dust raised by the
shot.
Explosives Of ire-damp have ranked
next to the use of long-fame explosives
as a cause OF dust explosives. Gas lie
given off more or less from all coal. al.
though most coal mines in the United
States do not have enough to be called
gaseous But If mine is dry and dusty
and long-fame explosives like black pow
der are used the presence OF a small per
centage Of gas greatly increases tho
chances OF an extensive dust explosion.
That an electric arc or glowing wire
could ignite coal dust in the air was not
thought possible few years ago. but
since then several mine explosions have
been laid to these causes. or course. II
must take combination of unusual
conditions to start an explosion In this
way, but such combination may happen
now. and then. All that Is necessary ID
to have an arc from a grounding or ar
overcharged hot wire surrounded by
thick cloud of infiammable dust. Lab
oratory experiments at Pittsburg have
shown that a small white hot wire can
set fire to cloud of dust.
Many people have contended that an
open flame could not ignite floating coal
dust unless a shock, as from a blown-out
shot, accompanied the fame. Yet floating
coal dust has caught fire about. bins and
dusty tipples. Usually there has been
little damage done because the dust waa
not confined, but a bad explosion In the
coal grinding room of a cement plant IN
New Jersey Is believed to have started
from the flame of an open lamp.
In mines, because the space is confined
In rooms and entries, there is mucl
greater chance Of the burning dust caus
ing an explosion wave. This possibiit,
was shown in recent coal mine explo
sion that started near the mouth OF
dusty drift. This drift was an intake $.
the air could not have contained any gas
A trip Of cars jumped the track ans
knocked out some timbers, thus makinl
dense dust cloud that was probabl.
fired by the flame Of trip riders lamp
The explosion travelled a long distance
into the mine. and gained strength az 4
travelled
An fncipient dust explosion started b.
the flame of an open lamp. was seen at
mine In Yorkshire. England The dus
that ignited was raised by a passing tril
OF cars. The flame followed the trip SOM
distance and then ran back
Uncle Sam, through his experiments q
the station at Pittsburg. makes man,
recommendations for the laying OF thf
coal dust. chief among which is that TIN
dust should be kept wet. He also recon-
mends the use of what is termed per
missible explosves"-that is, explo
sives which have been tested at the ex
can be used with safety. The use of cal
cium chloride for the laying of coal dus
is recommended. because II slowly dis
solves by absorbing moisture from the Of