A fuel cell (FC) system operating as its own hydrogen leak detector. The system including at least one cathode and cathode conduit for passage of oxidant to to the cathode and a housing containing one or more FCs and defining a plenum around the FC. A ventilation system forces air from the plenum into the cathode conduit and a control system monitors the FC voltage and detects a drop in voltage attributable to hydrogen in the cathode conduit. A control system may include actual cell voltage monitoring of the FC or of one or more cells in the FC stack and a processor for receiving inputs indicative of the operation of the FC or FC stack and/or to determine an expected voltage of FC(s) being monitored and whether the difference between the actual and expected voltage(s) exceeds a predetermined threshold indicative of a predetermined level of hydrogen in the cathode conduit.