A storm surge coinciding with high tides flooded the salt caverns used to store hydrocarbons at a petrochemical site. The alert was given at around 11:00 p.m. by a technician who was conducting a patrol. The remote-controlled shut-off valves were closed to isolate the caverns. The transfer of hydrocarbons to and from the site was interrupted. The site operator worked with the government authorities to manage the flood.

All pressure equipment was secured. The wellheads of the caverns and the piping suffered relatively little damage. The electrical distribution systems, I&C systems, and especially the telemetry networks saw the most damage. Five months of intense work were needed to repair and replace the equipment, control occupational risks, and return the site to normal operation. Losses were estimated at more than €13.6m.

When the flood warnings were received, the operator implemented all the standard storm-preparedness procedures. It emptied the effluent treatment facilities, isolated all the non-essential electrical equipment, stacked sandbags around all at-risk areas (such as the switching stations), and removed all containers that were likely to float. Although some localised areas were already submerged, the flood was considered to be manageable on the day of the accident thanks to the preparations carried out. As a result, the site began clean-up operations in the early evening and resumed its normal operations. The flooding that occurred on the site at around 11:00 p.m. was caused by water that had built up in a nearby stream and swept in like a wave. This scenario had not been predicted by any flood-damage assessments or major Seveso accident scenarios.

A cement works (46151) and two chemical and oil terminals (46144 and 46149) were also flooded that day.

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