The blasts occurred around 3 am in the storage zone of a petrochemical plant: 2 tanks ignited and their floating roofs were damaged. The 1st tank contained 11,300 m³ of pyrolysis gasoline (a mix of diesel, butene, toluene and butadiene). The 2nd tank, located 300 m away, was holding 48,000 m³ of naphtha. On-site fire-fighters, backed up by neighbouring facilities’ response teams, arrived on the scene in large numbers. The complex operator activated the internal emergency plan and notified local emergency services. A vast plume of black smoke was visible at dawn several kilometres around.
Triggering of the external emergency plan
Authorities implemented the external emergency plan at 5:35 am. By 6:30, the rail line running adjacent to the facility was closed to traffic for 3 hours, 45 minutes. A motorway exit ramp was also shut down, for 7 hours, by local police. Both county highways leading to the site remained closed for 12½ hours. Access restrictions were imposed on routes leading to the storage zone.
Fire-fighters reached the scene around 4:20 am with a contingent of 120 men and 64 vehicles. Six 1.8-km long sprinkler lines drew water from the nearby pond to cool the tanks and produce a high flow of foam to spray the tops of the tanks.
The fire on the first tank was brought under control by around 6 am; its structure had remained intact. The second tank fire was fully extinguished at 11:25 that morning. Despite fears to the contrary when extinction operations got underway, this second tank never collapsed. Its floating roof wound up sinking 48 hours later. Fire-fighters left the site around 8:30 pm.
Discovery of a third damaged tank
The next morning around 11 am, an inspection of the floating roof of an adjacent tank containing 25,000 m³ of condensate revealed the presence of an ignition system and a 4-m² gash in the middle section. The roof was partially submerged, though it did not sink.
Drainage took place on the third tank within the week following the accident; on the first tank beginning on Day 8 and on the second tank as of Day 10. All three tanks were then degassed, skimmed and ventilated. The structural integrity of their shells was also verified.
The earthen basins of the first 2 tanks contained a mix of runoff collected from stormwater recovery drains installed on the damaged roofs, plus fire extinction water and emulsifiers. These basins were also drained.
The ensuing pollution created nuisances for the neighbouring population
During draining, the evaporation of hydrocarbons caused air pollution, over roughly 10 days, due to VOC (volatile organic compounds) and BTEX (a highly toxic and ecotoxic family of VOCs, consisting of: benzene, toluene, ethylbenzene, and xylenes).
As of the morning following the accident, the air quality monitoring association measured pollutant concentration peaks (of BTEX, ozone) in the adjoining municipality of BERRE. Two days after the accident, residents in the vicinity complained about the smell of hydrocarbons, headaches and irritations to their eyes, throat and nose.
Subsequent to a series of pollution mitigation measures, these concentrations slowly abated and ultimately on Day 8 dropped substantially, though they remained above local background levels. Depending on prevailing wind direction, complaints stemming from residents of neighbouring municipalities (BERRE, VITROLLES, ROGNAC) were recorded throughout this period.
A foam blanket was installed on the first two tanks on the day after the accident. The third tank was not covered with foam so as to prevent its roof, which had already been weakened by the blast, from breaking.
The second tank’s basin, which had been filled to the highest level (1,500 m³), was pumped as a priority step in order to release the tank’s drain valve. On Day 4 owing to complaints filed by local residents, drainage of the third tank was accelerated while its basin contents were rerouted from the above-ground settling tank to an enclosed stormwater retention tank.
Pollution control dams were set up at outfalls along Berre Pond. Values recorded on treatment plant outflow remained within the normal range. The results of water table monitoring southeast of the site revealed the presence of supernatant in the piezometers, along with high BTEX concentrations in certain spots. The pollution originating from this accident might have “propelled” pre-existing pollution into this zone. On Day 13, supernatants appeared around a surface resurgence located some 100 m from the site’s storage zone. These supernatants were ultimately pumped.
Clues pointing to an act of malicious intent
Initial findings from the investigation indicated an act of malicious intent due to: simultaneity of the explosions, and discovery of ignition devices adjacent to the damaged tanks and on the roof of Tank 3. Moreover, the site’s fence had been cut open at several spots.
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