Modular NBC filtration system for protection shelters

A method of operation of a modular, NBC filtration system for protection shelters, comprising the steps of:

• a. providing a mounted NBC filtration system comprising:
• a filter unit positioned along a top portion of a wall of the protection shelter;
• a blower driven by an electric motor, said blower is positioned along said filter unit;
• an air exchange backup unit comprising a plurality of hinged segments serially linked to each other, forming a foldable arm, a first end of said air exchange backup unit is swiveably attached to said electric motor and a second end of said air exchange backup unit carries a detachable hand crank;
• a status indicator interface configured to exhibit an airflow-rate of said blower;
• an adjustment knob configured for tuning the speed of said motor;
• and
• a changeover valve, selectively airflow coupling said filter unit and said blower, said changeover valve comprising a state selector handle for switching said changeover valve between ventilation and filtration states;
• b. powering on said electric motor driving the blower in any event requiring entrance into the protection shelter;
• c. observing said status indicator interface and adjusting said adjustment knob if required;
• and
• d. powering off said electric motor driving said blower, and leaving the protection shelter when back to normal or exit shelter is declared.