An electrical network supply cut-off affected a basic plastics plant around 7:50 pm on a petrochemical platform. The interruption, which lasted a long time for the batch in progress (over 2 min), triggered protective measures for the plant workshops. The Internal Response Plan was activated and the units shut down operations at 8:15. Under these circumstances, the workshops sent the current batches to the site’s two flares. The combustion of effluents generated heavy smoke that dispersed into the atmosphere under particularly stormy weather conditions. The backup diesel generating sets of the polystyrene workshop that provide a power relay in cases such as this did not engage fast enough to cool the reactors on lines 1 and 2 during the workshop shutdown phase. A reaction acceleration occurred, and the rupture discs of two line 1 reactors and a third on line 2 burst, causing the atmospheric release of 8 tonnes of styrene. Since the weather conditions were unfavourable (i.e. weak wind), the cloud indisposed three residents from the l’Hôpital locality nearby and another two individuals living in Lauterbach (Germany), including a child who had to be hospitalised for 4 days. The sensors positioned near the petrochemical platform recorded, between 7 and 9 pm, high concentrations of dust, SO2 (585 µg/m³ in a 15-minute span) and orthoxylene (535 µg/m³ in 15 min), most likely corresponding to styrene (i.e. a close chemical structure). The high SO2 contents may be due not only to the workshops operating on the site, but also to the coking plant. It turns out that a condensate drip pot self-ignited around 4 pm on the coking plant’s gas pipeline feeding the neighbouring power plant. The emergency teams had the situation under control very quickly. The electrical supply interruption caused production losses on the order of 0.5 to 2 million euros. In application of the emergency decree signed July 6, 2005, the operator: established a report on the reasons why the electric generating sets malfunctioned, improved the start-up sequence, and more fully developed both the hazard study and the Response Plan. These actions enabled reopening the workshop. The Hazardous Installations Inspectorate proposed a complementary order that extends to the entire chemical platform a control over backup generating set operations and the completion of a study to lay out the points of potential release in the case of an incident, along with the type and quantity of products potentially discharged.