The entire gallery rests on a concrete foundation 10 ft. wide, which has
a maximum height of 4½ ft. and a minimum height of 2 ft.
The concrete head in which the cannon is placed completely closes that
end of the gallery. A narrow drain extends under the entire length of
the gallery, and a tapped hole at the bottom of each section provides an
efficient means of drainage.
[Illustration: Fig. 2.
{cannon as described in text} ]
The buildings near the gallery are protected by two barricades near the
open end, each 10 ft. high and 30 ft. long. A back-stop, consisting of a
swinging steel plate, 6 ft. high and 9 ft. long, 50 ft. from the end of
the gallery, prevents any of the stemming from doing damage.
Tests are witnessed from an observation room, a protected position about
60 ft. from the gallery. The walls of the room are 18 in. thick, and the
line of vision passes through a ½-in. plate glass, 6 in. wide and 37 ft.
long, and is further confined by two external guards, each 37 ft. long
and 3 ft. wide.
In this gallery a series of experiments has been undertaken to determine
the amount of moisture necessary with different coal dusts, in order to
reduce the likelihood of a coal-dust explosion from a blown-out shot of
one of the dangerous types of explosives.
Coal dust taken from the roads of one of the coal mines in the Pittsburg
district required at least 12% of water to prevent an ignition. It has
also been proven that the finer the dust the more water is required, and
when it was 100-mesh fine, 30% of water was required to prevent its
ignition by the flame of a blown-out shot in direct contact. The methods
now used in sprinkling have been proven entirely insufficient for
thoroughly moistening the dust, and hence are unreliable in preventing a
general dust explosion.
At this station successful experiments have been carried out by using
humidifiers to moisten the atmosphere after the temperature of the air
outside the gallery has been raised to mine temperature and drawn
through the humidifiers. It has been found that if a relative humidity
of 90%, at a temperature of 60° Fahr., is maintained for 48 hours,
simulating summer conditions in a mine, the absorption of moisture by
the dust and the blanketing effect of the humid air prevent the general
ignition of the dust.
These humidity tests have been run in Gas and Dust Gallery No. 1 with
special equipment consisting of a Koerting exhauster having a capacity
of 240,000 cu. ft. per hour, which draws the air out of the gallery
through the first doorway, or that next the concrete head in which the
cannon is embedded.
The other end of the gallery is closed by means of brattice cloth and
paper diaphragms, the entire gallery being made practically air-tight.
The air enters the fifteenth doorway through a box, passing over steam
radiators to increase its temperature, and then through the humidifier
heads.