Four people were injured, three of them critically, in a hydrogen explosion at the Elkem Silicones site in Saint-Fons, south of Lyon, on Monday afternoon.
The blast occurred around 2:30 pm in an experimental workshop at the silicone materials production facility, a high-threshold Seveso-classified site in France's "chemical valley".
The explosion ignited a fire in a 600-square-metre building, which was brought under control by early evening.
Around 100 firefighters and 30 emergency vehicles were deployed to tackle the blaze. All four injured were Elkem Silicones employees. Two are in critical condition, whilst a third suffered serious injuries, authorities said.
Jean-Pierre Laurent, the site director, said the explosion was likely caused by hydrogen emanation in an experimental workshop where five people were working at the time.
Authorities activated the Orsec emergency response plan and sent FR-Alert messages to residents in Saint-Fons, Feyzin, Pierre-Bénite and Vénissieux — affecting over 100,000 people — ordering them to shelter indoors as a precaution. A 1-kilometre security perimeter was established around the facility.
The A7 motorway linking Lyon and Marseille was closed in both directions immediately after the explosion. Rail traffic on the Lyon-Valence-Marseille and Lyon-Saint-Etienne lines was also suspended, along with river navigation.
French Transport Minister Philippe Tabarot announced in the early evening that the A7 had reopened to traffic. Rail and river traffic around the sensitive chemical site also resumed.
Regional prefect Fabienne Buccio lifted the confinement order around 6 pm after the fire was brought under control. Authorities confirmed there was no risk of toxicity to the population at any time, with regular air quality monitoring conducted by regional environmental services.
The Elkem Silicones plant in Saint-Fons, which employs approximately 400 people, has experienced previous incidents.
In June 2016, a worker was killed when silicone drums caught fire in a 2,500-square-metre warehouse, with 600 square metres of the building destroyed.
In 2022, the Rhône prefecture issued a formal notice to the facility for non-compliant storage of hazardous materials and deficient fire suppression systems. Earlier this year, the site experienced a chlorosilane leak.
Elkem Silicones France is a subsidiary of Norwegian group Elkem, which is majority-owned by China National Bluestar, a Chinese state-owned chemical giant. The company operates four sites in France plus a 120-person research centre.
A Seveso-classified site is an industrial facility that handles or stores dangerous substances in quantities large enough to present major accident risks to people, the environment or property.
The classification is based on the EU's Seveso Directive from 1982, named after the 1976 industrial disaster in Seveso in Italy.
High-threshold Seveso sites, such as Elkem Silicones, face the strictest regulatory oversight due to the particularly hazardous nature of the substances they handle.