At about 1 a.m., in a Seveso low threshold fireworks storage and assembly company, a lightning strike during a severe thunderstorm shut down the electronic surveillance and fire detection system. The remote surveillance company alerted the site manager, who conducted a 1.5-hour visual inspection while remaining outside the installations. As the fire detection system was still faulty, rounds were performed until the employees arrived at 8:30 a.m.

At 9 a.m., employees noticed smoke and flames at the base of the southernmost cypress hedge of the depot, 80 m from a storage building. Two cypress trees were struck by lightning, and the fire spread from tree to tree. The employees attempted to put out the flames with fire extinguishers, while the fire brigade was alerted. Despite the low risk of the fire spreading to the installations, the manager decided to evacuate all the employees. The emergency services arrived around 9:20 a.m. and flooded the area around the hedge that caught fire. They left the premises at 11:00 a.m., and then the employees return to the site at noon after conducting a final check. The staff monitored the burnt area throughout the day while occasionally spraying it down with water as a preventive measure.

The company in charge of inspecting “lightning protection” installations noted a strike on the meter of the building closest to the trees. A check performed of this building did not reveal any malfunctions. In the late afternoon, the company that maintains the surveillance and fire detection installation found that the electronic boards were damaged by the lightning strike near the cypress trees. A permanent security guard was posted on site until the next day, while the installation was being repaired.

The trees along the hedge were replaced over a distance of 45 m.

The operator organised a meeting with all its staff to try to draw lessons from the event. Training in the use of the fire extinguishers was scheduled. The vehicles used on site will be equipped with a sufficient number of fire extinguishers to respond to emergency situations.