Pollution
Humain
Environnement
Economique

At around 11 am, a gas leak occurred in a valve chamber on a gas pipeline (operating pressure 67.7 bar, diam. 250 mm) on an industrial estate. Two gas utility workers and a resident were injured: the first 2 were taken by helicopter to Geneva hospital and the latter was hospitalised in Sallanches. The gas board turned off the supply in the pipeline in question, depriving 168 homes of gas in the municipality. A 300 m safety perimeter was set up, and around one hundred employees of the industrial area were evacuated and congregated in the stadium’s changing rooms. Traffic on the A40, RN205 and railway line close by was halted; 93 people temporarily laid off. The leak occurred on an isolation valve (operational) of the ball valve type and equipped with a bleed device screwed into the valve body. On the day of the accident, 2 technicians were working on the valve to replace this mechanism with a bleed extension, made necessary by the application of resin around the valve in order to prevent corrosion. For this, they had to enter the valve chamber consisting of a brick enclosure built on a concrete slab. During the work, the pressure in the pipeline was at 25 bar. The valve was then closed and bled. When unscrewing it, the purge body was suddenly ejected causing a significant gas leak. One of the technicians attempted to install the extension, but lost consciousness before finishing. His colleague then entered the valve chamber and also fainted. The director of a company located nearby raised the alarm and a crisis unit was set up. Fire-fighters recovered the injured technicians and set up a water curtain. Assisted by the fire-fighters, the gas utilities attempted to manoeuvre the leaking valve several times but unsuccessfully. The decision to isolate the section was then made at around 6 pm. After depressurising the line, an excavation company intervened to break through one of the valve chamber walls and close the leak by welding a plug onto the hole in the body of the bleed mechanism. The safety measures and in particular the halting of traffic on the A40 were lifted at around 10 pm. Distribution was gradually re-established overnight and during the next morning.