At about 9:50 a.m., a lightning strike ignited hydrogen exiting a stack in a chemical factory. This hydrogen, produced by the chlorine electrolysis cells, is conveyed to the stack when the manufacturing shop that consumes it is shut down. The internal emergency plan was activated. The electrolysis chain was put into minimal operation mode. Nitrogen and steam were injected into the stack, which was cooled by in-house first responders. The situation was brought under control at 10:30 a.m. The emergency plan was lifted and chlorine production resumed at its usual pace.

As the accident had already occurred once before (44133), a preventive procedure in the event of a thunderstorm hazard had been set up (including a Storm Alert subscription and preventive injection of steam into the stack to dilute the hydrogen and increase the energy needed to ignite it), but the system was not active at this time of year (storms were traditionally rarer during the winter).