An electrochemical power generation system includes a fuel cell stack having an oxidant delivery system, an oxygen sensor for measuring the oxygen concentration of ambient air in the vicinity of the power generation system, and a hydrogen concentration sensor for measuring a hydrogen concentration in the ambient air in the vicinity of the power generation system. A controller is configured to cease operation of the power generation system, for example ceasing delivery of fuel to the fuel cell stack, when either the hydrogen concentration measured by the hydrogen concentration sensor exceeding a hydrogen concentration threshold or the oxygen concentration measured by the oxygen sensor falling below an oxygen concentration threshold.