At around 11.45 p.m., a 250m³ tank of crude ethanol (flammable liquid) overflowed in a manufacturing plant for bioethanol and other products intended for human and animal consumption. The operator put in place a preventive layer of foam. A quantity of 40m³ of crude ethanol spilled into the tank retention basin. The mixture in the retention system was pumped and sent to waste management.

On the day of the event, two tanks of crude ethanol had been filled above the “very high” level after unloading several lorries. The technicians disabled the very-high-level safety devices in order to start the discharge pump to draw the ethanol off from one of the tanks for use in the process. Despite starting this pump, the tank level did not decrease. The technicians noticed a misalignment: the draw-off valve was closed and two valves for sending product back to the storage tank were open. Overflowing occurred.

The draw-off valve had been closed during loading, but this was not indicated in the dedicated shift handover log. The tank high-level safety bypass had not given rise to compensatory measures or tests and had been implemented without following the procedure established by the operator. Before starting the draw-off pump, no alignment check had been performed.

The tank was not considered to be a possible cause of a major accident in the hazard analysis, and was not equipped with a device that was independent of the in-service measuring system to prevent the risk of overflowing.

After the overflowing, the operator took the following measures:

• locking of the bypass valve;
• a reminder to the management teams that alignment checking is mandatory before starting transfers;
• a reminder to the production and logistics teams to note all modifications in the dedicated shift handover log;
• a reminder regarding the obligation to issue bypass permits and to systematically check the correct use of permits;
• review of the strategy for filling the alcohol tanks (daily adjustment of lorry deliveries based on production and consumption, and blocking of transfers that could trigger tanks’ high-level safety systems);
• unannounced targeted spot checks on compliance with procedures for the plant’s critical systems at the request of the authorities.

The operator also performed risk analysis of all flammable liquid storage systems in order to establish an overflow prevention threshold independent of the control systems.

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