TM 3-4240-334-20&P

TM 3-4240-334-20&P
Section III. PRINCIPLES OF OPERATION
The mask protects the face, eyes, and respiratory system of the user from chemically, biologically, and
radiologically toxic environments. Positive air pressure is supplied to the facepiece by either the blower assembly,
during normal operations, or by the auxiliary blower assembly, in emergency situations. The M43A1 Mask
can also be used without a source of positive air pressure, if both blower systems should fail.
The Mower assembly motor is powered by a 12-volt dc (vdc) battery. The LED illuminates when approximately
20 minutes of blower operation remain. The LED can be tested by pressing the pushbutton switch. The
knob turns the blower assembly on and off and adjusts the speed of the blower, thereby changing the amount of
air being blown into the mask.
The auxiliary blower assembly motor is powered by two 3-volt batteries operating in parallel. It can be
operated by a sliding power switch. The auxiliary blower assembly is attached to either of the filter canisters, and
the other canister inlet is plugged with a rubber cap.
The incoming air is forced through two filter canisters, which remove contaminants from the air. The
airflow is directed three ways by the inlet valve assembly: the majority of the incoming air is directed into the
facepiece assembly for breathing; another path feeds the lens defog system which keeps the lenses free from
condensation; and the third path feeds the cooling duct, which directs air under the hood for user comfort. Two
knobs on the inlet valve assembly are used to adjust the amount of air directed toward either the lens defog
system or the hood cooling duct. The outlet valve assembly can also be adjusted to allow differing amounts of
air to exit from the mask; this determines the amount of positive pressure allowed to build up inside the mask.
Extra protection from nuclear thermal flash is provided by the nuclear hood, which is worn over the
helmet and facepiece assembly.
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