An electrochemical system includes an electrochemical device having a stack of elementary electrochemical cells each including an electrolyte interposed between a cathode and an anode; ducts for supplying the anodes and the cathodes with gas and for collecting the gases generated by the latter; an enclosure having the electrochemical device housed therein and including at least one inlet duct and one outlet duct to circulate an air flow in the enclosure; and a circuit for analyzing the air in the enclosure. The circuit includes a sensor capable of measuring an oxygen content present in the outlet duct of the enclosure; and an analysis unit capable of diagnosing a leak of the device when the measured oxygen content differs from a predetermined oxygen content in the inlet duct of the enclosure.