Methods of Conducting Tests
Three general methods of conducting man tests are followed:
(1) Canisters are placed in the brackets outside the chamber or fastened to the wall tubes within the chamber. The subjects of the test remain outside the chamber, and the facepieces of the masks are connected directly to the canisters, in the first case, and to the wall tubes connecting with the canisters, in the second case. The concentration is established and the time noted. Then the men put on the masks and breathe until they can detect the gas coming through the canisters. Reading matter is provided for the men during the test period. When gas is detected, the time is again noted and the time required for the gas to penetrate the canister is reported as the “time to break down” or “service time” of the canister. Ten canisters are tested at one time, and the average of the results for the 10 canisters is taken for that type of canister. Much less accurate results are obtained when the final figure is based on a small number of canisters. This is largely due to the various breathing rates and sensitiveness of different men.
(2) The canisters are placed as in (1), but it is only necessary to know if they will give perfect protection for a given length of time. The procedure is the same as in (1), except that the test is arbitrarily stopped at the end of the indicated time, and the number of canisters and the service times of the same noted.
(3) When the canisters are of such a type that they cannot be properly tested as in (1), or when it is desired to test the penetrability of the facepiece, the men wear the complete mask and enter the chamber. They remain until gas penetrates the canister or the facepiece, as the case may be, or until it is determined that the desired degree of protection is afforded. The service time is computed as in (1).
(4) Maximum-breathing-rate tests are made either by men in the chamber or by the men outside, in which they do vigorous work on a bicycle ergometer. In this test the average man will run his breathing rate up to 60 or 70 liters per min.
The concentration of the gas is followed throughout the test by aspirating samples and analyzing them.
Type of Masks Used. In the future the 1919 model will be used for all tests. In general, during the War, the following procedure held, although variations occurred in special cases:
When men entered a gas-chamber, the full facepiece was, of course, required. The type of facepiece was determined by the nature of the gas. If the gas was most easily detected by odor or eye irritation, a modified Tissot mask was used. If it was most easily detected by throat irritation, a mouth-breathing mask was employed.
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.