On a site that produces sodium and chlorine, several chlorine discharges happened during the power build-up in a new electrolysis room. During the thunderstorm activity on June 3, the activation of compressors for several-hour stretches caused the shutdown of both the overriding power rectifiers and the electrolysis rooms. 20- and 18-kg bursts of Cl2 during two of these shutdowns were perceived in a neighbouring village (through odours). These malfunctions resulted from continuing to run (for some unexplained reason) a power rectifier during the period of compressor shutdown. The lack of procedural compliance and design flaws were recorded: compressors with an electrical starter whose frequency-based control serves to increase sensitivity to micro outages and voltage variations, valves open in the safe position, risk of losing a liquid trap. The trap was eliminated, a power inverter installed, automated mechanisms modified and the compressors regulated based on speed, etc.