NOVELTY - A fuel cell system having a membrane or electrode assembly (MEA) has two fine pore plates, each at the anode and cathode side of the MEA; mechanisms for driving the fuel reactant flow, oxidant reactant flow and coolant flow at different pressures during on load operation of the fuel cell system; and a controller for activating or deactivating the reactant and the coolant flows during operation.    USE - For use in power plants.    ADVANTAGE - The fuel cell system is self-inerting. The method provides a safe procedure in flooding the reactant flow fields with coolant or water.    DETAILED DESCRIPTION - The fuel cell system (10) having a membrane/electrode assembly (MEA) (16) has:    (a) two fine pore plates (12, 14), each at the anode (18) and cathode side of the MEA;    (b) a pressurized fuel source or a fuel processing system for driving the fuel reactant flow at a first pressure, an air blower or compressor or a pressurized oxidant source for driving the oxidant reactant flow at a second pressure, and a water pump for driving the coolant flow at a third pressure during on load operation of the fuel cell system; and    (c) a controller for (de)activating the reactant and the coolant flows during operation.    The third pressure is lower than that of the first and second pressures. When the controller activates the reactant and the coolant flows during fuel cell operation, the reactant flows are maintained at higher pressure levels relative to the coolant flow. The pressure levels of reactants remaining in the reactant flow fields equilibrates with a pressure level of coolant remaining in the coolant flow field when the controller deactivates the reactant and coolant flow during fuel cell shut down. This causes the coolant to migrate through the fine pore plates and flood the reactant flow fields, displace the reactants and in turn, inert the fuel cell system. An INDEPENDENT CLAIM is also included for a method of inerting a fuel cell having a MEA comprising providing two fine pore plates as above; driving the fuel reactant flow at a first pressure, driving the oxidant reactant flow at a second pressure, and driving the coolant flow at a third pressure during on load operation of the fuel cell system; activating the reactant and coolant flows during on load operation; and de-activating the reactant and the coolant flow during fuel cell shut down.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic elevational view of one of the cells in a fuel cell power plant.    fuel cell system (10)    fine pore plates (12, 14)    membrane/electrode assembly (16)    anode (18)    projections (28, 40)    grooves (32, 44)    coolant flow field (36)    reactant flow field (38)