At around 3:00 a.m., an explosion followed by a fire occurred in a vacuum chamber at a hazardous waste treatment plant. Firefighters prevented the flames spreading to the five other treatment chambers. The fire was contained at 4:00 a.m. The foam-laden firewater was contained in the building and subsequently pumped into IBCs. The water used to wash the firefighters’ turnout gear was sent to the firewater retention basin. The explosion blew out a 10 m² smoke vent. A tarpaulin was laid over the opening at around 9:00 a.m. to prevent the spread of residual smoke.

The fire caused some material damage in one of the production rooms: the door of the chamber was ripped off its hinges and sent flying, a portion of the waste inside the chamber was hurled out, and several components were flung into the shop.

An emergency prefectural order was issued to compel the operator to test grass, milk, and vegetables in the environment in the vicinity of the site in order to assess the pollution caused by the accident (in particular PCBs and dioxins and furans). The consequences of the explosion caused the market threshold for fodder produced to rise to 1500 m east of the plant. The plant’s safety report had not identified any toxic effects beyond its boundaries. Resumption of the site’s operations was conditioned on the provision of a report presenting the causes of the accident and the corrective measures taken. The plant resumed operations on 20 March 2018.

A cycle to treat an electrical transformer contaminated with PCBs had just been started when the fire occurred. There were two successive explosions. The first occurred inside the tank of the transformer as it was being processed and the second went off inside the chamber. The primary explosion was caused by the unexpected presence in the transformer of:

• sludge/pasty residues (combustibles likely to become explosive under certain pressure and temperature conditions);
• or a metal cleaning product (which, in the presence of organic compounds, can create exothermic reactions).

Following the primary explosion, which damaged the chamber’s door, the oil and PCB residues at the chamber’s bottom vaporised (the ambient temperature was 240 °C), filling it with fine particles and organic compounds. These aerosols then mixed with the air in the chamber and self-ignited. This situation had not been taken into account in the plant’s safety report.

The operator implemented a number of corrective measures:

• It modified the plant’s operating and maintenance procedures:
  • before transformers are placed in the chamber, their fins are cut off to avoid the build-up of pasty residues or sludge and their covers are removed to avoid creating confined spaces;
  • transformer tanks are visually checked for foreign bodies before being placed in the chamber;
  • the instructions on cleaning the treatment chambers are now more stringent to ensure that all residues at the bottom are removed;
  • the system used to control the temperature in the treatment chambers was improved to control the temperature homogeneity (which enables all compounds contained in the treated devices to be vaporised).
• Constructional measures:
  • a control system that electrically locks the door while the chamber is operating was installed;
  • a control system ensuring that the chamber is inerted with nitrogen it may heat up to 240 °C was installed;
  • the chamber door’s thermal insulation was improved.
  • the chamber door was weakened so that it opens more easily in the event of overpressure and a device was fitted to prevent it being flung through the air in an explosion.

Multiple fires have occurred at this plant in recent years (ARIA 49388, 41794, 41617).