Chapter XVIII

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MAN TESTS

The final test of the canister is always carried out by means of the so-called “man test.” Special man-test laboratories were built at Washington, Philadelphia and Long Island. These are so constructed that, if necessary, a man may enter the chamber containing the gas and thus test the efficiency of the completed gas mask. In most cases, however, the canister is placed inside or outside the gas-chamber and the men breathe through the canister, detecting the break point by throat and lung irritation.

The following brief description of the man test laboratory at the American University will give a good idea of the plan and procedure.[32]

[Footnote 32: Taken from Fieldner’s article mentioned above.]

The man test laboratory is a one-story building, 56 ft. in length and 25 ft. in width. The main part is occupied by three gas chambers, laboratory tables, and various devices for putting up and controlling gas concentrations in the chambers. A small part at one end is used as an office and storeroom.

Good ventilation is of great importance in a laboratory of this nature. This is secured by means of a 6 ft. fan connected to suitable ducts. The fan is mounted on a heavy framework outside and at one end of the building. The fan is driven at a speed of about 250 r.p.m. by a 10 h.p. motor. The main duct is 33 in. square, extending to all parts of the building. A connection is also made to a small hood used when making chemical analyses.

The gases, fumes, etc., drawn out by the fan, are forced up and out of a stack 30 in. in diameter, extending upward 55 ft. above the ground level.

The main features of each of the three gas chambers are identical. Auxiliary pieces of apparatus are used with each chamber, the type of apparatus being determined by the characteristics of the gas employed.

[Illustration: FIG. 76.—Man Test Laboratory, American University.]

Each chamber is 10 ft. long, 8 ft. wide and 8½ ft. high, having, therefore, a capacity of 680 cu. ft. or 19,257 liters. The floor is concrete, and the walls and ceiling are constructed on a framework of 2 × 4 in. scantling, finished on the outside with wainscoting and on the inside with two layers of Upson board (laid with the joints lapped) covered with a ½ in. layer of special cement plaster laid upon expanded metal lath. The interior finish is completed by two coats of acid-proof white paint. The single entrance to the chamber is from outside the laboratory, and is closed by two doors, with a 36 × 40 in. lock between them. These doors are solid, of 3-ply construction, 2½ in. thick, with refrigerator handles, which may be operated from either inside or outside the chamber. The door jambs are lined with ³/₁₆ in. heavy rubber tubing to secure a tight seal.

At the end of the chamber opposite the doors, a pane of ¼ in. wire plate glass, 36 × 48 in., is set into the wall, and additional illumination may be secured by 2 headlights, 12 in. square, set into the ceiling of the chamber and of the air-lock, respectively, and provided with 200 watt Mazda lamps and Holophane reflectors. Openings into the chamber, five in number, are spaced across this end beneath the window and 9 in. above the table top.

Fans are installed for keeping the concentration uniform.

[Illustration: FIG. 77.—Details of Canister Holder.]

Various devices have been installed for attaching the canister to be tested (Fig. 77). This arrangement allows the canister to be changed at will without any necessity for disturbing the concentration of gas by entering the chamber.

Arrangements for removing the gas from the chamber consist of a small “bleeder” which allows a continuous escape of small amounts and a large blower for rapidly exhausting the entire contents of the chamber.

Other general features of the equipment deal with the determination of the physical condition surrounding the tests, often a matter of considerable importance. The temperature of the gas inside the chamber is easily ascertained by means of a thermometer suspended inside the window in such a position as to be read from the outside. The relative humidity of the mixture of air and gas in the chamber is determined by means of a somewhat modified Regnault dew point apparatus mounted on the built-in table.

PRESSURE DROP AND LEAK DETECTING APPARATUS

Another piece of apparatus consists of a combined pressure drop machine and leak tester (Fig. 78) for measuring the resistance of canisters and testing them for faulty construction. This is mounted on a small table, with the motor and air pump installed on a shelf underneath. The resistance, or pressure drop, of canisters is measured by the flow meter _A_ and the water manometer _B_. Air is drawn through the canister and the flow meter _A_ at the rate of 85 liters per min., the flow being adjusted by the needle valve. The pressure drop across the canister is read on the water manometer _B_, one end of which is connected to the suction line, the other open to the air. The reading is generally made in inches, correction being made for the resistance of the connecting hose and the apparatus itself.

Canisters are tested for leaks by the apparatus shown at _D_ in Fig. 78. The canister is clamped down tightly by wing nuts against a piece of heavy ¼-in. sheet rubber large enough to cover completely the bottom of the canister and prevent any inflow of air through the valve. Suction is then applied, and a leak is indicated by a steady flow of air bubbles through the liquid in the gas-washing cylinder _E_. A second gas-washing cylinder, empty, is inserted in the line between _E_ and the canister as a trap for any liquid drawn back when the suction is shut off. If a leak is shown, it can be located by applying air pressure to the canister and then immersing it in water.

[Illustration: FIG. 78.—Apparatus for Determining Pressure Drop and for Detecting Leaks in Canisters.]

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.

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

[Illustration: FIG. 79.—Hemispherical Vision Chart.]

Vision was tested by means of a hemispherical chart (Fig. 79). This chart was 6 ft. in diameter and was constructed of heavy paper laid over a wire frame. A hinged head rest was provided for holding the subject’s head firmly in position with the center directly between the eyes. The subject wearing the mask took up his position, and with one eye closed at a time, indicated how far along the meridian of longitude he could see with the other eye. The observer sketched in the limit of vision by outlining the perimeter of the roughly circular field allowed by each eyepiece. The intersection of the two fields gave the extent of binocular vision possible with the mask.

Various other tests were also used, in order that the extent and nature of the vision could be accurately determined.

Aside from the problems of comfort, protection, vision and other important features of gas mask efficiency, the question arose as to whether certain designs of masks or canisters were mechanically able to withstand the rough treatment they were certain to receive in actual field service. A test was, therefore, developed to simulate such service as transportation of masks from base depots to the front, carrying of supplies and munitions by men wearing masks in the “alert” position, exposure to rain and mud, hasty adjustment of masks during gas alarms and typical mistreatment of masks by the soldiers.

All these tests were of great value in the development of a good gas mask.

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