1122

THE COLLIERY GUARDIAN

November 27, 1914

that the most effectual method is to place the dust on
cross-shelves, and on overhead timbering, if there be
such ; then the advance air wave causes the entire dust
load to fall in a shower and practically all of it is brought
into play, whereas when placed along the ribs and floor
it is not so easily brought into suspension when the
explosion pressures are low. With this cross-shelf
arrangement, which is practically a continuous Taffanel
barrier, the greater specific gravity of the limestone
dust has no appreciable disadvantage since, after tests,
it is found widely scattered, and on the other hand there
is some liberation of carbon dioxide, which further tends
to quench the combustion.

In connection with the extinguishment of the flame
of an explosion, it is interesting to note that in an effort
to start a strong ignit.on of coal dust 75 lb. of coal dust
was placed on eight cross-shelves from immediately in
in front of the cannon to 50 ft. distant. To the surprise
of all present at the test, the flame did not pass beyond
these cross-shelves. The test was repeated five times in
all, with the same results except in one case when
propagation occurred. Subsequently M. Watteyne of
Belgium reported he had tried the same experiment,
and obtained confirmatory results. Coal dust placed in

There are two forms of these: One the box barrier,
where six boxes containing about 700 lb. of dust are
hung from the roof and timbers across the entry. In
the final design (figs. 3 and 4) the arrangement com-
prises a light open box hung by four freely suspended
rods, with eyes, from open hooks fastened in the roof or
overhead timbering. The box within limits may swing
freely; when, however, the movement is over fin. Or
thereabouts from the middle position, the two suspending
rods on the side toward which the movement is directed,
which fasten to the bottom edge of the box, are struck
by cleats fastened to the upper edge of the box, and if
the movement is sustained by the advance wave of the
explosion, the eyes of the suspending rods are pushed
off the open hooks and the box swings downward,
pivoting on the points of suspension of the rods on the
opposite side of the box. The rock dust in the box is
partly discharged, but some is held by the bottom of the
box, which is constructed of two loose boards resting on
clea ts attached to the side of the box. The boards are hung
by chains attached to the roof or overhead timbers,
which permit the boards to drop 3 or 4 inches, then
they are caught by the chains so that a portion of the
rock dust is held on them, unless the explosion is so

figs. 5 and 6, is termed the “ concentrated barrier.” In
this the rock dust is placed on a large platform hung
close to the roof. The platform consists of boards,
hinged separately to a cross timber, and held up at the
other end by an angle iron. This angle iron, in turn, is
held up by a system of levers, which are tripped by
vanes. There are advance vanes connected by a wire
with the lever which pushes upon the tripping lever.
In the experiments at Bruceton the advance vane has
been placed about 100 ft. from the concentrated barrier.
As erected in a commercial mine there would be a
similar vane on the other side, as the barrier is symmet-
rical, and will extinguish an explosion approaching
from either side. In case of possible accidental
tripping, and danger when a man or trip of cars is
passing, the inner end of each of the platform boards is (
fastened by a loose chain to the roof, or to a cross
timber, permitting only a limited drop. As hitherto
arranged, half of the boards dropped about 9 in., and
the other half about 18 in. The platform holds about
3 to 4 tons of rock dust, and is quite compact, occupying
the space between timber sets, which are placed 7 ft.
apart. In mines with low roof it may be necessary to
brush down the top to make room. The appearance of

Fig. 4.—Box Rock-dust Barbier.

	





Fig. 5.—Concentrated Barrier, showing Undee-side of same, and
Bumping Vane in Front; also Tripping Wiee from First Vane,
100 ft. in Advance.



I

Fig. 7.—Rock-dust Protected Door with Front Bjiard Removed to
Show Loose Chains to Support Boards Over Door Frame if
Explosion Occurs.

Fig. 6 — Concentkated Barrier after Light Explosion, which

■ it Extinguished.

this way appeared to have acted like a rock-dust
barrier; the coal dust falling rapidly across the path of
the flame cooled it below the ignition point of the dust.
It must be clearly understood, however, that an excess
of coal dust is not a protection even in an ignition under
any ordinary circumstances, as it is almost impossible
to conceive of its being similarly placed under working
conditions. It was interesting to note that in each case
there was much burning dust found on the platform in
front of the cannon alter the test.

Rock Dust Barriers.

At the experimental mine the barriers, which in com-
pliment to Mr. Taffanel are termed “ Taffanel barriers,”
were employed to limit the zone of violence. The
barriers proved uniformly successful in stopping explo-
sions, except in a few instances of very light explosions
or other inflammations where the flame passed the
barrier. There is also the disadvantage that where the
air current was strong, as it generally is along the
haulage ways of American mines, the dust was blown
from the shelves. Again, in mines where the watering
system is employed, the dust will likely become
dampened, and when wet it is, of course, ineffectual in
quenching explosions.

These disadvantages led Mr. Rice to design some
special forms of enclosed barriers which would operate
with lighter pressures than the Taffanel open barriers

violent that all parts of the box are ruptured. In the
latter event the rock dust is automatically launched
and mixed with the air and coal dust cloud. The
arrangement of hanging the bottom boards, which
allows some of the retained dust to sift down slowly, is
to take care of the more difficult situation brought
about in light explosions, when there may be a con-
siderable time interval between the advance air wave
and rhe flame. It has the further merit that if a box is
accidentally tripped off, the bulk of the weight is
caught by the chains, and it is not believed a serious
injury would be caused to a man who might be caught
underneath.

To protect the rock dust, in an ordinary mine working,
from becoming damp or admixed with float coal dust,
the box should be covered by a waterproof cloth attached
over the centre line of the box to the roof, so that as
the box dumps the cloth is automatically pulled from
its top.

As indicated above, there is less difficulty in stopping
a violent explosion than a light one, because in the
violent explosion the whole mass is disrupted, and the
rock dust forms a thick cloud of inert dust. Many
tests have shown that the rock dust from the boxes is
very widely distributed, and when limestone dust is
used it can be observed ejected from the mouth of the
mine by the air blast.

Another form of barrier, which is illustrated by

the barrier in passing under it is like that of an
ordinary overcast.

The leverage system of operating the concentrated
barriers can be arranged so that it will operate with
almost any desired pressure. As arranged at the
experimental mine, it will not discharge until the
pressure is equivalent to that of a wind of about
40 miles per hour (3,500ft. per minute)—in other words,
a heavy gale. It is thought that the proper places for
such concentrated barriers are at intervals in the main
entries, and in each side entry near its mouth, so that if
the mine is panelled an explosion will be confined to
one panel.

It is interesting to note that Mr. Taffanel had indepen-
dently decided that it was desirable to have such enclosed
barriers, and had designed a concentrated barrier just
prior to his coming to Pittsburg recently for collabora-
tion on special tests. This was also tried out success-
fully at the experimental mine, but it did not have the
advance vane for tripping it, and this Mr. Taffanel
thought was a considerable gain to provide for very
rapid explosions.

As far as the tests have gone, the box barriers and
the concentrated barriers are equally effectual, and the
adoption of one or the other at the commercial mines
wjll perhaps depend somewhat on local conditions.

The success of the foregoing barriers led to the
designing of a rock-dust protected ventilating door,