At around 9:00 a.m., black smoke was visible from the flare stacks of the steam cracking unit of a petrochemicals plant. At 1:50 p.m., flames were seen coming out of a flue-gas stack. Two separate events were underway: a loss of steam supply to the entire platform and a fire in a furnace in the steam cracking unit. The operator implemented the site’s internal emergency plan at 2:30 p.m. As a preventive measure, the police blocked traffic on the road running alongside the plant. The plant’s first responders and the firefighters set up a command post to monitor the situation. The operator cut off the supply of hydrocarbons to the steam cracking furnace. This progressively decreased the fire’s intensity. The facilities downstream of the furnace were purged with nitrogen. The fire was brought under control and the furnace was safely shut down at around 3:00 a.m. the next morning. To compensate for the loss of the steam supply, the plant restarted the boilers at around 5:30 p.m. The prefecture and the operator issued a joint press release at around 6:00 p.m. The internal emergency plan was lifted at 7:30 a.m. the next morning. The boilers were restarted, which reduced flaring. However, black smoke was still visible until the next day. A total of 1440 t of hydrocarbons was sent to the flare stacks.

A loss of the main and then emergency power supply resulted in the loss of steam supply to the platform and, more particularly, to the steam cracking unit and consequently to the flaring system. The steam supply that was restarted at around 5:30 p.m. but was insufficient to completely eliminate the flaring because several boilers were still shut down. The operator’s steam-load shedding strategy was to first cut off the steam supply to the flare stacks (was necessary to improve combustion) and then cut off the steam supply to the production units. Flaring was ultimately reduced by restarting the production units and starting up secondary boilers.

The power supply was lost due to faults on junction boxes between two sections of large-diameter buried cables. At the time of writing, these boxes were being analysed by an expert to determine the causes of the faults.

As for the fire in the steam cracking furnace, it was started by hydrocarbons that ignited after the pipes carrying them broke and fell to the furnace’s bottom. The loss of steam caused the furnace to abruptly shut down and result in a thermal shock that damaged the pipes.

During the two visits conducted by the inspection authorities for classified facilities following the event, the operator brought up the following two areas for improvement in particular:

• revision of the steam-load shedding strategy to reduce the amount of gases released by the flare stacks;
• rethinking of the steam cracking unit’s operation in the event of a loss of steam supply.