TM 3-4240-286-20&P
Section Ill. PRINCIPLES OF OPERATION
partment control module automatically ad-
just the airflow valve to maintain a positive
SYSTEM.
pressure in the shelter.
a. The M56 gas-particulate filter unit removes
toxic gases and dust from the air supplied to
b. The M12 protective entrance provides a
the M12 protective entrance and shelter.
pressurized transition area between the
outside and return air are drawn through
shelter and the outside contaminated zone.
the air inlet of the filter unit by the main fan.
Personnel entering from the outside must
From the main fan, the air is pushed
wait five minutes within the protective en-
through the particulate and gas filters to the
trance before entering the shelter. Con-
airflow valve. The filtered air passes
tamination is purged by the flow of the fa-
through the airflow valve and is carried by
ltered air. The protective entrance control
airduct hoses to the protective entrance
module automatically adjusts the airflow
through the airflow valve and silencer and to
valve and silencer assembly to maintain the
the shelter through the air conditioner.
proper air pressure inside the protective
Pressure sensing components in the com-
entrance.
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