It has been recognized for some time that tank crews face a danger from
collection, within the tank, of carbon monoxide fumes caused by the firing
of tanks' guns with the hatches closed. The Canadians are now conducting tests
in a Ram II tank with an auxiliary ventilation system which it is hoped will
completely eliminate this hazard.
The ventilating device consists of an exhaust fan installed under the
ventilator in the roof of the main turret, and connected by a duct
leading to a hood or intake attached to the ceiling of the turret at a
point over the breech of the six-pounder gun. The exhaust fan is of the
electrolux type and operated by a high-speed 24-volt motor. The most efficient
design for the fan and motor was selected after various tests. The
intake is located at a point in the sponge-rubber ring near the main
turret hatch, over the recoil mechanism. The smoke is therefore
exhausted from the vicinity of the commander's position, where repeated
tests have shown that the gases tend to collect in a pocket under the cover
plates when the tank is closed up completely.
The above auxiliary ventilation system was recently tested under battle
conditions. During the firing tests, the hatches were completely closed. The
ammunition used was service-type 6-pounder AP, with a full charge of nitro-cellulose
propellant. As a result of the tests it was concluded that the ventilating
apparatus completely corrected the previously dangerous condition resulting
from firing with hatches closed. The highest average of concentration of carbon
monoxide gas during these tests was 0.09 percent, whereas in earlier trials of
other ventilating devices the average concentration had reached 0.15 percent, or
over, in every test.
Furthermore, in the previous tests the tank could not be kept fully closed
throughout the duration of the trials, whereas in the present case there was no
appreciable discomfort experienced in keeping the tank closed up until the average
concentration of carbon monoxide had dropped substantially to zero.