Hydrogen fire at a chlorine chemical production plant (Seveso-classified)Hydrogen ignited in a chlorine electrolyzer unit. The facility was shutdown. The staff of the unit, present on site, triggered the fire alarm and put the installations in a safe state. The fire was extinguished after the start of the intervention of the internal fire brigade.According to the ARIA report (see reference), a variation in electrolyzer pressure was caused by the shutdown of a tank due to the malfunction of its level detection gauge. This variation caused, on one single cell, the tearing of the flexible PTFE belt whose role is to protect the cell from pressure shocks. This tearing resulted in the release of a small amount of hydrogen that spontaneously ignited. The other belts did not suffer, suggesting a structural weakness of the damaged one. These belts are regularly monitored by the operator, but their packaging during transport may have plaid a role.