In the storage tanks of a refinery (production: 5 million tonnes/year), smoke was detected on a 94,000-m³ capacity floating roof tank containing 47,000 tonnes of light crude oil (flash point: 38°C). Shortly thereafter, the surface (4,800 m²) ignited. In the absence of a fixed protective device, the emergency response team projected foam at the tank roof using a gun mounted on an aerial platform, while protecting the adjacent tanks and cooling the walls of tank no. 11. The roof collapsed (with an estimated roof load equal to 700 tonnes). A few hours later, the requisite resources were in place: 26 pumps, 11 cisterns, 6 hydraulic platforms, and a crew of 150 fire-fighters. In conjunction with this response effort, the crude was being drawn out (at a rate of 1,700 tonnes/hr) in order to lower the tank level. A full-scale foam attack was deemed necessary, although the emulsifiers had not yet been installed; 160 m³ of the total 200 m³ were considered the minimum necessary. An emulsifier collection plan was thus launched. The rate of oil burned in the tank by fire was estimated at 300 tonnes/hr. The nearby tanks (2), which had been exposed to strong thermal radiation, had to be drained (as a result of heat insulation damage). Tank no. 11 started bubbling in its upper part and gradually subsided. 12 hours after the incident began, a boilover occurred and created a fireball (radius: 90 m; height: 150 m). Fire-fighters, surprised by the magnitude of this fireball, had to find refuge and regroup. Two vehicles were destroyed, standing pipes melted and had to be reinstalled (due to incompatible fittings). The tank overflowed, with fire propagating into the basin. Six fire-fighters were injured. 2 hours and 10 minutes later, a 2nd boilover happened. The shell/bottom bond on tank no. 11 broke in four places: fire spread throughout the basin (covering an area of 16,722 m²), bordered by 5-m dikes that were able to resist. At this point, fire-fighting crews feared a 3rd boilover and mounted a foam attack (with a flow rate of 1,773 m³/hr). A water cannon (operating at 13.6 m³/min) was introduced to improve positioning. At 2:00 am the following morning, the fire had spread once again, this time over the entire tank surface. Once the additional emulsifiers had been delivered, the fire could be controlled around 3:00 pm (over 60 hr after detection). A total of 765 m³ of emulsifier proved necessary. Causes of the accident were found to be: presence of cracks and traces of light crude on the tank roof (38°C flash point); same-day use of the flare system (height: 83 m, distance to tank no. 11: 99 m) following malfunction of the catalytic cracker compressor; and projection of incandescent carbon particles on the oil that had spread onto the single-deck tank roof. The cracks (which had undergone recurrent repairs) were due to fatigue from exposure to the region’s gusty winds. The operator had only anticipated, for floating roof tanks, the scenario of a joint catching on fire. The lack of fixed protective devices (sprinkler ring, foam box), appropriate mobile response equipment and emulsifier postponed and complicated the response, which in turn exacerbated the disaster.

Download the detailed report in .pdf format (71 Kb)