NOVELTY - The system has an air outlet portion (100) which is provided on anode (20) of fuel cell. A controller (200) is provided for measuring cleaning period of re-circulated hydrogen (H1) and operating temperature of fuel cell and for actuating air outlet portion on basis of measured cleaning period and the operating temperature, in order to prevent poisoning of anode. The air outlet portion is provided in hydrogen circulation spacer and hydrogen supply line (H). The air outlet portion is frequently operated, if cleaning of re-circulated hydrogen decreases.    USE - Fuel cell system used in vehicle. Uses include but are not limited to motor car such as passenger car, comfort jeep and sport utility vehicle, bus, truck, commercial vehicle, water motor vehicle such as boat and ship, aircraft, hybrid vehicle, electric car, plug in hybrid electric car, vehicle with hydrogen pulsation and vehicle with alternative fuel.    ADVANTAGE - The increase in carbon monoxide concentration and carbon monoxide poisoning of anode in hydrogen-side recirculation system is prevented effectively, when hydrogen side fuel starvation occurs during operation of fuel cell vehicle. The stack performance is restored by air that is blown off during idle/halt or switch-off of fuel cell vehicle to hydrogen side to restore stack of fuel cell. The efficiency of fuel cell is improved efficiently. The state of fuel cell is optimally maintained by accurate air cleaning without the use of separate hydrogen concentration sensor or carbon monoxide sensor.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a method for operating fuel cell system; and    (2) a non-volatile machine-readable medium storing program for operating fuel cell system.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the fuel cell system. (Drawing includes non-English language text)    Anode (20)    Air outlet portion (100)    Controller (200)    Hydrogen supply line (H)    Re-circulated hydrogen (H1)