The accident occurred in the hexane-based rapeseed oil extraction process. After grinding the seed and obtaining meal that is then steam-cooked (100°C), pressing in a continuous screw press is used to obtain 2/3 crude oil and flakes containing 1/3 oil. This oil is extracted from the flakes in the extraction process: the flakes are transported through the extractor while a mixture of hexane and oil (miscella) is sprayed against the flow.
The previous day, flakes (seeds after pressing) had become jammed in the extractor, causing the shutdown of the extraction process and holding up the whole production line. A sub-contractor was contacted to unjam the extractor. The explosion occurred at 11 a.m., while the subcontractor was working on the extractor. The blast was heard over a distance of several hundred meters. At around 11.30 a.m., the operator shut off the building’s hexane supply. This supply was stored in a 60m³ underground tank containing 43m³.
When the emergency services arrived, at around 11.40 a.m., the 5-floor building was totally ablaze, and 2 people were declared missing. Firefighters set up a 300m security perimeter and evacuated 7 homes located in this zone. The nearby road was closed to traffic and the electricity supply was cut off around the site until 5 p.m. The fire was brought under control after 3 hours of work with foam cannon hoses. Residual fires were extinguished with water. The extractor was cooled with 4 hoses, but the fires inside remained inaccessible. The firefighters let the final residue burn under control. The tanks of flammable liquids located in the building (hexane and effluent) were not a priori damaged by the incident. Security was set up on the site for the weekend. The fire was declared extinguished the next day at around 5 p.m.
THE ORIGIN, CAUSES, AND CIRCUMSTANCES SURROUNDING THIS ACCIDENT
During the unjamming of the extractor, one of the sub-contractors entered the machine, equipped with breathing apparatus due to the presence of residual hexane vapor.
The operation consisted of sucking up the substance with a hose connected to a sewer cleaning truck.
No information is available on the extractor’s degassing status at the time of the accident.
According to the press, some factors that may have contributed to the explosion need to be cleared up, such as the absence of “lockout-tagout”, the use of inappropriate tools near the extractor, and the presence of static electricity, the presence of oxygen in the extractor, etc.
The company doing the work was not the usual company because the latter did not have a sewer cleaning truck.
The work was carried out urgently.
LESSONS LEARNT
The accident, of which the causes are not yet known, demonstrates the risks associated with the presence of an explosive atmosphere (in this case due to hexane vapor).
The accident underlines that during work by a sub-contractor and in spite of the urgent need to restart a facility blocking the whole process, it is essential to take the time to:
- coordinate the actions of both sub-contractor and operator;
- assess any risks involved in the planned operation;
- make sure workers are trained;
- make sure that equipment used meets specific operational requirements (ATEX equipment, etc.);
- make sure workers are effectively protected (breathing apparatus if necessary, safety equipment, etc.);
- in case of hot work, draw up a welding and cutting permit taking account of all the risks involved in the operation
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