Third Buncefield progress report points to failures of safety systems
Buncefield Investigation Manager Taf Powell, explains: “I am able to explain with reasonable clarity and confidence that Tank 912 in bund A on the Hertfordshire Oil Storage Ltd (HOSL) West site overflowed at around 05.30 hours on 11 December while being filled at a high rate. “The environmental conditions, flow rate of fuel, and physical configurations of the tank top and wall provide a suitable mechanism for rapid formation of a fuel-rich vapour that flowed off site following the ground topography. “As the vapour flowed off site, driven by gravity and the formation of more vapour in bund A, it would have mixed with more air and by the time it reached the Fuji and Northgate car parks, may have become an almost ideal flammable mixture. “Several likely sources of ignition are discussed [in the report] , a primary one on site and another in the Northgate car park. The explosion sequence is also discussed, but here there is far less confidence in the mechanism for the high overpressures seen and modelling of this may take some time. Nonetheless I believe the most important facts leading up to the explosions at Buncefield are known with reasonable confidence and they are presented [in the report].” The report sets out a timeline of events: 10 December 2005 11 December 2005 From approximately 03.00, the level gauge for Tank 912 recorded an unchanged reading. However, filling of Tank 912 continued at a rate of around 550 m3/hour. Calculations show that at around 05.20, Tank 912 would have been completely full and starting to overflow. Evidence suggests that the protection system which should have automatically closed valves to prevent any more filling did not operate. From 05.20 onwards, continued pumping caused fuel to cascade down the side of the tank and through the air, leading to the rapid formation of a rich fuel/air mixture that collected in bund A. At 05.38, CCTV footage shows vapour from escaped fuel start to flow out of the north-west corner of bund A towards the west. The vapour cloud was about 1 m deep. At 05.46, the vapour cloud had thickened to about 2 m deep and was flowing out of bund A in all directions. Between 05.50 and 06.00, the pumping rate down the T/K South pipeline to Tank 912 gradually rose to around 890 m3/hour. By 05.50, the vapour cloud had started flowing off site near the junction of Cherry Tree Lane and Buncefield Lane, following the ground topography. It spread west into Northgate House and Fuji car parks and towards Catherine House. At 06.01, the first explosion occurred, followed by further explosions and a large fire that engulfed over 20 large storage tanks. The main explosion event was centred on the car parks between the HOSL West site and the Fuji and Northgate buildings. The exact ignition points are not certain, but are likely to have been a generator house in the Northgate car park and the pump house on the HOSL West site. At the time of ignition, the vapour cloud extended to the west almost as far as Boundary Way in the gaps between the 3-Com, Northgate and Fuji buildings; to the north west it extended as far as the nearest corner of Catherine House. It may have extended to the north of the HOSL site as far as British Pipelines Agency (BPA) Tank 12 and may have extended south across part of the HOSL site, but not as far as the tanker filling gantry. To the east it reached the BPA site. The report highlights continuing problems being experienced by local businesses. The report states that Investigation Board members met the Maylands Business Network during April, to listen to views and concerns of the local business community. Some businesses continue to have challenging operating conditions and face difficult decisions about whether to reinstate their premises. Read the report at http://www.buncefieldinvestigation.gov.uk/reports/report3.pdf
•Date: 9th May 2006 • Region: UK • Type: Article •Topic: BC general |
