At around 4:45 a.m., a chlorine leak (CL2, toxic gas) occurred in a chlorochemical plant on a reactor in the bleach manufacturing workshop. The detectors in the premises were triggered at 4.5 and 40 ppm, causing the upstream chlorine electrolysis operation to shut down. The operator informed his supervisor, who had a maintenance technician and the personal of the external company in charge of reactor maintenance come in around 8 a.m. Using a portable detector, the leak was located on a flange seal on one of the 6 Cl2 injectors on the damaged reactor. The injector was disconnected, its seal replaced and a leak check was performed following a test at 100 mbar. Production was resumed at 2:30 p.m. For 5 minutes, 200 g of Cl2 was released into the workshop. The external sensors did not record anything.

The workshop resumed operations after a period of maintenance. The investigation revealed that the mating faces of the injector’s flanges were not plane, and went undetected prior to restart. This defect resulted in the loss of seal integrity. Before bringing the reactors back online, the operator had not inspected the work performed on the injectors by an outside company. The Cl2 network had also not been checked for leaks. No procedure had been drawn up regarding how the reactors were to be brought back online following servicing. Communication difficulties were noted during this maintenance operation between the production, maintenance and safety departments.

As a result, the operator has set up instructions to be followed before the bleach manufacturing reactors are restarted. The injector installation method has been modified to compensate for any flatness defects and there are plans to inspect the flatness of the damaged injector during the next shutdown.