When men were outside the chamber, the choice was made in the same manner, except in the case of detection of the gas by throat irritation. In this case the mouthpiece was attached to two or three lengths of breathing tubes and a separate noseclip was used. The facepiece was not needed and the men were much more comfortable without it.
Disinfection of Masks. Mouthpieces are disinfected after use by first holding them under a stream of running water and brushing out thoroughly with a test tube brush; then the latter is dipped into a 2 per cent solution of lysol, and the inner parts of the mouthpiece are brushed out well; finally the mouthpiece and exhaling valve are dipped bodily into the lysol solution and allowed to dry without rinsing. Tissot masks are wiped out with a cloth moistened in alcohol, followed by another cloth moistened in 2 per cent lysol solution. The flexible tubes are given periodic rinsings with 95 per cent alcohol.
Applicability of Man Tests. Man tests are applicable to all gases which can be detected by the subject of the test before he breathes a dangerous amount.
The man test laboratory described above provides facilities for obtaining information concerning the efficiency of canisters, facepieces, etc., within very short periods of time, without waiting for the construction of special apparatus required for machine tests. To get satisfactory results from machine tests, a delicate qualitative chemical test for the gas is essential. Man tests can be made when such a qualitative test is not known. Further, man tests can be made with higher concentrations of some gases than is practicable with machines. Evolution of excessive amounts of moisture when high concentrations of some gases are used causes much more trouble with machine tests than with man tests.
On the other hand, man tests are adversely affected by the varying sensitiveness and lung capacities of the men, and the humidity of the air-gas mixture is not subject to as exact control as is the case with machine tests.
Field Tests
It will be observed that all of the above tests are concerned only with the efficiency of the absorbent and its packing in the canister. No attempt was made to determine the comfort and general “feel” of the mask. For this purpose field tests were devised, covering periods from two to five hours. The first test was a five-hour continuous wearing test. It was assumed that any mask which could be worn for five hours without developing any marked features of discomfort could, if the occasion demanded it, be worn for a much longer period of time. A typical test follows:
| 8:00 to 8:30 | Instruction and adjustment of gas mask. |
| Gas-chamber tests | |
| 8:30 to 9:30 | Games involving mental and physical activity |
| 9:30 to 11:30 | Cross-country hike with suitable periods of rest |
| 11:30 to 12:00 | Tests of vision |
| 12:00 to 12:30 | Games to test mental condition of subjects |
| 12:30 to 1:00 | Gas-chamber fit test |
Fig. 79.—Hemispherical Vision Chart.