In a depot for flammable crude and refined liquids, an ignition incident occurred during works on a pipeline. These works were ordered after observing external corrosion on the 20-inch pipe running near sheet piling separating a retention basin, thus causing the pipe to shift. Operations were scheduled over 4 phases: 1) bleeding, cleaning and degassing of the pipeline followed by rinsing with water (3 times 60 m³, or 200 m³ in all) on 24th Sept, before a sequence of draining then measuring flammable gas detection; 2) preparation of the works (lockout of valves on the manifold, plugging of the pipe with an inflatable diaphragm seal, removal of the section to be replaced); 3) welding of the flange (where the new section would connect), performed on 24th Sept and completed on the 26th at 12:30 am by one of the company’s regular subcontractors for such jobs; and 4) final compliance testing of circuits by means of realignment beginning on the 26th around 8 am. A site safety inspector oversaw gas detection controls, accompanied by 2 subcontracted employees. An initial inspection downstream of the plug revealed nothing out of the ordinary, as was the case for a pipe inlet inspection performed after removing the plug. The safety inspector sprinkled the end of the pipe with a misting jet placed inside the pipe for 2 to 3 min before transitioning to a solid stream jet. Ignition happened at this very moment; 1.5 m from the pipe end at the bottom of the trench, the inspector sustained serious burns to his hands, face and arms. Employees tended to his injuries and contained the fire outbreak. The internal emergency plan was activated at 8:40 am. The causes of this accident are not precisely known. During the afternoon following the accident, experts recorded measurements indicating the presence of a residual flammable gas in the pipe. The presence of a hot spot might have had several origins: mechanical, chemical (calamine), but also electrostatic.

The inspection authorities for classified facilities requested the depot operator to submit a report on the incident and proposed subjecting facility start-up to testing the electrical continuity on the hazardous line under conditions giving rise to the accident.