A natural gas explosion and fire occurred at 6:40 am in the Works Council chamber of a plant manufacturing rolling mill cylinders and hoops for continuous aluminium casting. Fire-fighters set up a safety perimeter, evacuated the 110 plant employees and extinguished the blaze. The facility’s activity was shut down. The employee responsible for the explosion, in lighting a gas stove, sustained 2nd and 3rd-degree burns and required hospitalisation. The local gas utility service cut off the site’s supply. Some 20 soil samples extracted around the accident site indicated the presence of gas at concentrations above the lower explosive limit (LEL). The Classified Facilities Inspectorate undertook an investigation. The site’s internal gas pipeline network (pressure: 1.9 bar) was aboveground except for a section of roughly 30 metres buried 0.5 m deep. This pipe was made of steel (internal diameter: 50 mm) and ran alongside the premises destroyed by the explosion as well as beneath the foundations of an industrial facility built during the previous summer and autumn. A leak on this underground segment, which had been placed back into service just 3 weeks earlier after several months of being idle, was the suspected cause. Pipe evaluations conducted over the next 2 days (Pressur test at 3.2 bar – close-up inspection of the gas pipeline in the presence of a legal expert) confirmed this origin: a 1-cm long crack was discovered on the suspected segment. The operator decided to definitively abandon all use of this segment and installed gas detectors at various points in the plant. Two days after the accident, new gas concentration measurements had dropped below the LEL, convincing fire-fighters to end the monitoring campaign at 7 pm that evening. Following a site inspection, the expert authorised resumption of plant activity. The Inspectorate proposed that the Prefect issue an order mandating removal of the underground pipeline section, disposal of accident debris, monitoring of the presence of gas in the ground, control of the plant’s gas network with permeability testing and thickness measurements, verification of the medium-voltage electrical line passing over the destroyed premises and controls implemented on the nitrogen tank also located close to the point of explosion. Operating losses were estimated at €450,000.