In a microelectronics plant, a fire broke out inside a workshop (circuit etching), originating at one of the gas treatment devices fitted onto the production machines. This device is responsible for incinerating process gases (with high C2F6 content) through the use of methane, as well as for water cooling before inflow onto the site’s general gas treatment installation (including washers). In equipping each of the 19 machines, the device features an array of safety controls: water flow rate and pressure to ensure site security, incineration temperature, methane and fluorine detection individually controlled by methane supply cut-off, water level. The likely chronology is as follows: violent thunderstorms caused the destruction of water supply pump controls as well as the network pressure drops. The alarms that sounded did not shut down the gas abatement device, as system design indicates. On-call personnel were mobilised. An alarm on the CH4 detection sounded without triggering closure of the supply valve. The personnel were then evacuated and the Internal Response Plan implemented. 3 sprinklers heads were activated above a single machine. The fire department was called. Reliance on the emergency water network and after a general gas supply shutoff, the fire was brought under control. Effluents were drained in the direction of the site treatment plant. The emergency water supply procedure was scheduled for review.