During the unloading of a lorry at a petrochemical plant, an acrylonitrile leak (estimated at 15 kg/min) occurred at a connection joint between the hose and the lorry. While evacuating the area, the 3 technicians on site (not equipped with self-contained breathing apparatus (SCBA)) stopped the transfer pump. The internal emergency plan was activated and water curtains were used to absorb the acrylonitrile vapours. The 300 people on-site were ordered to remain inside.

The three technicians and four people in a neighbouring workshop, potentially exposed to the gas, were hospitalised as a precaution (only one person remained under observation for 24 hours). The closest measuring station to the unloading area recorded a peak acrylonitrile concentration of 2 ppm, i.e. the average exposure value (AEV) limit.

The residual leak was isolated 40 minutes after the start of the accident by the emergency response team. The operator assessed the volume of the spillage at at least 750 kg. The deluge water and foam used to prevent the liquid from evaporating were recovered in the pits provided for this purpose. No human or environmental consequences were reported. The lorry involved, which was secured, still contained 13 t of acrylonitrile. The internal emergency plan was lifted four and a half hours after its activation.

The operator launched an investigation to determine the causes of the accident. The first elements seemed to indicate that mechanical stresses at the joint (caused by the transfer platform) had caused the accident: unloading was carried out from the top of the lorry, with a platform positioned above to allow the technician to make the connection. During the unloading operation, the tank may have have risen due to the reduction in the load (effect of pneumatic suspension) and may have collided with the connection fitting that caused the leak.

Several anomalies that occurred when unloading lorries 10 months later led the operator to review the investigation’s findings: the use of fittings of different brands that were not compatible with one another had also caused the accident. This phenomenon was accentuated by the ageing of the wear parts on the fittings.

New provisions were therefore implemented: identification of key equipment with a visual mark on each connection, revision of the specifications relating to fittings for acrylonitrile tanks, and the use of male and female fittings supplied by the same manufacturer, etc.