During the night, in a vegetable oil production facility, hexane was spilt in the treatment plant. The flammability of this product caused the activity in the area to be shut down at around 6 a.m. Vehicles were stopped and the fire permits were cancelled. A foam mat was deployed on the station’s intake basin and in the contaminated areas to prevent the hexane from evaporating. An ATEX truck pumped the undissolved hexane in the aqueous phase, and the alert was lifted at 6 p.m.

Of the 60 m³ of hexane spilt, 30 m³ was pumped, and 30 m³ had evaporated. Hexane concentrations at the station’s outlet were checked and were determined to be negative. The operator estimated the production loss at €33,000.

In the afternoon before the incident, the operator in charge of monitoring the extraction pumped the interface from the water/hexane decanter to the water tank. He left the pumps in automatic mode and the valves open. At the end of the shift at 9 p.m., he left without telling the control room or the night-shift crew about his intervention. In this pumping configuration, the decanter remained in communication with the water tank. Once the water level had dropped in the decanter, the pure hexane was pumped into the water tank. From there, it was sent to the buffer basin of the treatment plant. Initially, the station’s intake basin absorbed the massive influx of hexane, then overflowed. The hexane then spread across the ground, outside the ATEX zone. At 9:15 p.m., the operator in charge of the treatment plant detected odours but thought the smell was coming from the pellets nearby that were impregnated with hexane.

At 3:30 a.m., the same operator noticed that the treatment plant’s intake basin was overflowing. He stopped the rainwater network’s water transfer pump and accelerated another pump to stop the overflow.

At 4:15 a.m., an alarm was triggered on the low level of the plant’s jockey pump on the hexane storage tank. Thinking that there may be a leak, the shift supervisor went to check out the hexane pumps. He noted a smell of hexane coming out of the boiler. He also noted an abnormally high flow rate on the water tank’s overflow outlet. He took a sample and visually detected the presence of a hexane phase.

At 4:40 a.m., he sent an operator to the extraction workshop who noted that the decanter’s pumping valves were not correctly configured.

The operator fired the technician in charge of the decanter and the treatment plant operator. The following operations were planned to secure the decanter’s purge:

• provide a log book to trace the pumping phases of the decanter’s interface and the position of the valves after the operation,
• install a 3-way valve to prevent the decanter from communicating with the water tank in case of a handling error,
• install a 3-way valve on the pump near the drain sump to direct any water that may contain hexane to the hexane unloading station. A hexane detection sensor will activate the valve if hexane is present,
• install a level float adapted to the density of the hexane in the treatment plant’s intake basin.

The operator review the risk analysis of its hexane extraction unit.