A fire broke out at around 11:15 pm in the heavy filler thermal cracking unit at a refinery. The internal emergency plan was activated. The flames that could be seen for kilometres rose to 50 m, and the area affected covered 200 m². The supplies to the units in the area were cut off. Significant backup from the Urban Community (120 fire-fighters/25 vehicles) were provided for the site’s operational crisis centre: 2 foam hoses (7,500 and 2,500 l/min) contained the fire while all of the supplies were cut off, 2 water hoses were used to protect the area immediately surrounding the fire and prevent it from spreading. The law enforcement agencies closed off the slip roads to the A4 and A35 motorways, and the traffic on CD 37 and 301 minor roads; the perimeter affected extended as far as 1 km north of the site. The detection of an H2S concentration of nearly 9 ppm (sewer discharge) by one of the site’s sensors led the emergency services to map the H2S concentration in the area concerned equipped with self-contained breathing apparatuses (SCBA), without in any way confirming the presence of a toxic atmosphere. The fire was controlled at around 1:30 am As a result of the persistence of small isolated fires, due to the difficulties in totally isolating certain circuits, the internal emergency plan was not lifted until 8.30 am. There were no casualties but the accident caused significant material damage: the unit was shut down for several months for repairs. The inspection authorities for classified facilities recommended that the Prefect issue an emergency order supervising its restart. According to the operator, a configuration error (alignment) on the charging pump discharge circuit had caused the accident: an error occurring during this start-up sequence for this pump (45 bar at the discharge nozzle) caused a circuit that was normally expected to operate at 10 bar to be pressurised to 45 bar. In fact, a temporary connection between the two circuits had been installed prior to the start-up in order to warm up the charging pump. This connection, normally removed before the start-up, remained in place on the day of the accident. A rupture occurred in line with one of the low pressure heat exchangers and leaks occurred on various flanges of the section. The vacuum-distilled product (estimated at less than 35 m³) thus sprayed ignited due to the temperature (350 °C).