A chlorine leak occurred on a sodium-hydroxide scrubber located outside the foundry[br1]  of an aluminium production plant. The leak occurred while the chlorine system was being purged. The production shop is supplied by three cylinders of chlorine that are stored in a confined room along with three spare cylinders. A set of valves is used to direct the pressurised gas (3 bar) to either the foundry or purge, particularly when the cylinders are changed.

The leak was detected (1 ppm threshold) at 7:30 a.m. by a sensor located in the cylinder room. The alert was given. The technician shut off the purge valve, the foundry was shut down, and its employees were evacuated. After a search, the leak was ultimately located on the scrubber. A chlorine concentration of 328 ppm in the air was reported on the foundry’s mimic panel. The public firefighters were alerted and the internal emergency plan was implemented. Two employees were taken to hospital for examination; the results were normal. The leak was controlled at 11:00 a.m. by slowly venting the piping. The internal emergency plan was then lifted. The leak was caused by fatigue-induced failure at the stainless steel/PVC junction on the gas-scrubber inlet. This failure may have been caused by vibrations from the transfer of chlorine. The inspection authorities for classified facilities noted that there was no containment on the section of pipe conveying chlorine to the scrubber, the number of gas detectors installed outdoors could be improved (the chlorine’s high concentration enabled its detection), and there was no procedure for checking the condition of the PVC section. The inspection asked the operator to implement corrective measures.