A resin and latex chemical plant lost its supply of electricity from the grid at around 2.30 a.m. This was the result of a power outage on the grid occurring from 12.00 midnight across the whole urban area of Le Havre (15 000 homes). The outage was linked to the malfunction of 2 pieces of electrical distribution equipment owing to high temperatures (summer season). The polymerisation unit’s reactors and detectors were supported by 1 of 2 back-up generators, the other being out of order.

The reactors’ air network and water/ammonia (NH3, toxic gas) cooling network were no longer powered as the ‘utilities’ unit supplying them had just lost its back-up generator. The extended shutdown of the NH3 compressors caused internal excess pressure of 15.2 bar. A leak occurred in the safety valves set to 15 bar in the compressor room.

The automatic safety system detected the gas and triggered the flooding system. The operator launched the internal emergency plan. In-house firefighters continued hosing down the inside of the building. The atmospheric measurements taken by the fixed and portable detectors did not show a leak outside the building. Following the loss of electricity, the operators in the control room made the 10 reactors safe by injecting a neutralisation ‘short stop’ solution, as envisaged in the event of loss of cooling. They started with the highest-risk reactions. The electricity supply was gradually restored from 4.35 a.m. and was normal again by around 6.45 a.m..  The internal emergency plan was lifted at 7.30 a.m. The reactors were drained and cleaned and their bursting discs were checked. Their contents were sent for destruction.

The release of NH3 through the roof of the building was suspected, access to the site was blocked by the gendarmes. Odours of NH3 were smelled in the building of the unit which was evacuated. At 5.20 a.m., the 1 000 employees of a neighbouring car factory who were going to work were confined to their vehicles for 2 hours due to late provision of information by the facility affected.