In a bituminous materials depot run by the BTP company and comprising 17 tanks, one of which contained hydrochloric acid, the vapour space of a vertical container filled to half its “cut-back 0/1” capacity (i.e. 18 tonnes of liquefied bitumen with 40% kerosene / flash point < 55°C) exploded around 2:30 pm, during the installation of walkways and guardrails between the tanks. The container was thrust some 20 metres and the 2 employees, who were already at the scene with a trimming machine close to the tank vent, died after being thrown a 30-m distance. The liquefied bitumen spread causing a fire and, less than 5 minutes later, the explosion of an empty, non-degassed bitumen container that wound up on the roof of a depot building some 10 metres away. Traffic was halted on the adjacent street leading to a shopping centre. Local residents and customers of a nearby shop, as well as all bystanders, were evacuated. The fire also ignited a row of trees planted on the property line; the emergency response team's quick arrival on the scene enabled containing and extinguishing the blaze.
The two containers broke at the level of the shell / bottom interface. The HCl storage capacity melted when exposed to the effect of heat; moreover, 12 other tanks and the roof of the adjacent production unit were damaged. 7 company vehicles were destroyed. The retention basins were also extensively damaged. Total property loss was valued at 5 million francs.
During its investigation, the classified facilities inspection authority found that the operating instructions posted near the depot made no mention of prohibiting presence in the vicinity of any installation with devices capable of generating sparks or hotspots, and moreover that no risk analysis had been conducted prior to these works. Instructions were only being transmitted verbally, and lastly the site operator was unfamiliar with the combustibility characteristics of “cut-back 0/1”, which is a Category 1 combustible liquid.
The initial inflammation was most likely triggered by a spark or hotspot during onsite works, which then ignited a vapour space outside the “cut-back 0/1” tank. The resulting vapours were able to “form” either at the end of the 6-m long hose set into place by workers to redirect vapours to the bottom of the container, or at the hose-vent junction (had the hose not been perfectly sealed), or at a tank cover opening designed for tank instrumentation (level measurement cable). After ignition of the vapours in an unconfined space, the flame penetrated into the tank causing the explosion and ejecting the tank.
Subsequent to the accident, the site operator proceeded by: installing a new depot with a storage capacity of less than 150 tonnes of emulsion, published a safety manual for nationwide dissemination, and organised a safety training course for site personnel. The installation was definitively closed on October 5th, 2007.
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