At around 10.45 a.m., when the gas supply was restored following renovation work on part of the interconnection station, an explosion followed by a gas leak occurred on a portion of the pipeline (609mm, 80 bar). The explosion occurred at around 20 bar. The detonation could be heard for several kilometres around. Debris was ejected as far as 500m away. The personnel was evacuated and the pipeline was isolated upstream and downstream. The emergency responders set up a 500m safety perimeter. Road traffic was stopped.

The incident caused the pipeline to pivot by 90° and to be severed in several places. Accessory pipelines were displaced, equipment ripped off and supporting structures damaged. Two people were injured slightly (ruptured eardrum and finger dislocated when falling). A psychological support system was set up. The damage was estimated at €1m. 86,000m³ of natural gas was emitted into the atmosphere. The event had no impact on gas transport and delivery.

The accident occurred at an interconnection facility whose role is to receive and treat the gas before pressure regulation and distribution to various regional supply arteries. The facility had been undergoing upgrading work since 2020. On the day of the accident, a team consisting of employees and subcontractors was on site to restore gas to the equipment. First, the technicians injected gas. Next, a technician located about fifteen kilometres away produced a pressure build-up by operating a tap.

The BEA-RI (Bureau d’Enquêtes et d’Analyses sur les Risques Industriels, i.e., industrial risk investigation and analysis bureau) indicated that the risks involved in restoring the gas supply had not been sufficiently taken into account. It concluded that this was an internal explosion of an air-gas mixture. The operating procedure for restoring the gas differed from the customary procedure. First, air was expelled. It was during the second phase, which consisted of building up pressure in several cycles, that the pressure rose in an uncontrolled manner up to 20 bar, with an air/gas mixture present in certain parts of the pipeline. The explosion occurred 1 hour later. It turned out that at this pressure, the minimum energy necessary for ignition of the air/natural gas mixture was far lower than that of atmospheric pressure (just like the ARIA 45217 event). The particular explosiveness of such a mixture at high pressure had not been pointed out. Although the technicians were experienced, they had deviated from the standard procedures without identifying any particular risk.

Immediately after the incident, the operator took precautionary measures:

• special care when removing or restoring gas in systems that are of significant size or complex, and taking of additional readings;
• general raising of technicians’ awareness of the risks involved in those phases: pressure is a highly aggravating factor.

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