Around 5:10 pm, an explosion followed by a fire rocked a fuel oil desulphurisation unit at a refinery. The internal emergency plan was activated, a safety perimeter set up around the unit and a departmental highway was temporarily closed to traffic.

A response team had the main fire under control within about 50 min without requiring assistance from external emergency services, which nonetheless were at the scene for preventive purposes. The internal emergency plan was lifted at 10:35 pm.

This unit was shut down at the time for scheduled cleaning of a cooling tower with reintroduction of a gas into the system at a high H2 content. The accident was caused by the complete rupture of an 8″ heat-insulated carbon steel pipeline located along an upper rack and fed by a hydrocarbon/hydrogen mix. The accident triggered an explosion whose pressure surge was evaluated by the site operator at approx. 60 mbar at a distance of 10 m. Since the leak was being fuelled, the fire affected other pipelines as well as the exhaust valves connected to the flare system, which explains the persistence of several secondary fire outbreaks, finally extinguished around 3:30 am. The quantities released were estimated by the operator to be less than 2 tonnes of liquid hydrocarbons and 50 kg of hydrogen.

No victims were reported. The economic consequences were appraised at €500,000 of property damage and €2 million in production losses.

A prefectural order imposing emergency measures required the operator to conduct investigations in order to determine accident causes and establish the conditions for restarting service at the damaged unit. This rupture was due to external corrosion localised on the pipeline supporting structure. Over a section approx. 45 cm long on the line’s lower half-circumference, the residual pipeline thickness equalled 3 mm on average vs. 6.5 mm originally, and eventually reached 1.2 mm in certain zones. The rupture occurred in two stages: an initial break, followed by propagation of the opening as a result of the high pressure of gases circulating inside the pipeline.

Afterwards, the operator revised the risk assessment for the operational gas lines capable of corroding either under the heat insulation or at the supporting points, where the prospect of a pipe burst had to be taken into account under certain conditions, i.e.: service pressure above 25 bar; gaseous or mixed state when operating; diameter exceeding 2″; and a hazardous fluid being transported (H2, C2, C3, H2+H2S). The operator also ensured the adequate implementation procedures and good state of heat insulation; a special examination was also carried out on pipes not being stored on skids.

Moreover, the operator issued a press release.