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]

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.

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.

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.

Fig. 78.—Apparatus for Determining Pressure Drop
and for Detecting Leaks in Canisters.