At around 6 am, a flash was produced during operations in a chemical plant. The accident took place between 2 production campaigns. On the 7 and 8 February, the hydrogenation reactor was cleaned, deodorised and dried to eliminate residual waste from the previous production cycle and prepare the reactor for the following one. On 12/02 at 5 am, the production supervisor issued specific instruction on a new production cycle to a technician. The technician did not follow them in the right sequence as indicated in the verification instructions before staring production: to save time when pressurising the device at 9 bar of nitrogen, he simultaneously made several adjustments and carried out several checks (opening the manual H2 valves of the storage tank, the emergency shutdown valve just in front of the workshops, etc.). The reactor and safety process valves in front of the reactor were protected by a check valve that remained closed. The reactor was pressurised using nitrogen. The operator observed N2 leaking from a manhole. He decompressed the reactor and removed the fastening bolts from the lid to change the joint. During this operation, he heard a leaking noise at the joint. Believing it to be a H2-leak, he blocked the reactor and triggered the emergency shutdown. He was convinced that the reactor was clean and the residual volume in the pipe was low and proceeded to change the joint with assistance from a fellow technician. The two technicians were projected backwards in an explosion that ensued. The internal emergency plan and ETARE plan (emergency plan drafter by the regional fire service) were triggered.

Both the technicians sustained burns on their faces and hands and were initially hospitalised in Nice then transferred to a specialised unit in Toulon. A safety alert was sounded in the workshop. The gendarmerie (FR military police) carried out an enquiry to determine the cause of the accident. The operator decided to shut down the site for 48 hours.

The commissioned expert explained that the explosion occurred as a small quantity of H2 ignited upon contact with the catalyst in presence of oxygen coming from the manhole. He also noted that the tightness of the reactor was checked and the pipe pressurised at the same time without following the guidelines, no tightness test was planned on the valves of the H2 pipe and that there was not specific instruction on opening the manhole during normal or degraded mode as well as for changing the joint. The current Le montage H2 sampling and introduction assembly increases the risk of leak on valves before the reactor and in the presence of a catalyst in the reactor. The drying conditions may have contributed to have increased the pyrophoric nature of the catalyst. Changes have been planned in the hydrogenation equipment (installing pressure sensors, flame guards on regulator vents) and procedures (risk analysis,pipe verification,de-commissioning the H2 pipe before opening the manhole.