page_title: Buncefield fire
section_title: Causes
hierarchical_section_title: Buncefield fire / Causes
caption_attribution_description: The smoke plume from the Buncefield fire, seen from 3.75 miles (6 km) away, the day after the explosion
context_page_description: The Buncefield fire was a major fire at an oil storage facility on 11 December 2005 at the Hertfordshire Oil Storage Terminal, located near the M1 motorway, Hemel Hempstead, in Hertfordshire, England. The terminal was the fifth largest oil-products storage depot in the United Kingdom, with a capacity of about 60 million Imperial gallons of fuel. The terminal is owned by TOTAL UK Limited and Texaco.
  The first and largest explosion occurred at 06:01 UTC near tank 912, which led to further explosions which eventually overwhelmed 20 large storage tanks.
  The emergency services announced a major emergency at 06:08 and a firefighting effort began. The cause of the explosion was a fuel-air explosion in a vapour cloud of evaporated leaking fuel. The British Geological Survey monitored the event, which measured 2.4 on the Richter scale.
  News reports described the incident as the biggest of its kind in peacetime Europe and certainly the biggest such explosion in the United Kingdom since the 1974 Flixborough disaster. The flames had been extinguished by the afternoon of 13 December 2005.
context_section_description: The final report of the Major Incident Investigation Board (MIIB) was written in 2008 and released in February 2011. The investigation found that Tank 912 at the Buncefield oil storage depot was being filled with petrol. The tank had a level gauge that employees used to monitor the level manually, and an independent high-level switch which would shut off inflow if the level got above a certain setpoint. On Tank 912, the manual gauge was stuck and the independent shut-off switch was inoperative, meaning that the tank was being "filled blind" with petrol (i.e., being filled without a clear indication of the level). Eventually Tank 912 filled up completely, the petrol overflowed through vents at the top, and formed a vapour cloud near ground level, which ignited and exploded. The fires from the explosion then lasted for five days.
  The investigation found that the level gauge had stuck at random times after a tank service in August 2005, but it did not concern maintenance contractors or site management. The independent shut-off switch was not fitted with a critical padlock to allow its check lever to work. Secondary containment (meant to trap the petrol in a retaining wall around the tank) failed and allowed petrol to flow out. Tertiary containment (drains and catchment areas to prevent release of spilled chemicals to the environment) also failed, and fuel and firefighting foam entered groundwater supplies. The investigation found secondary and tertiary containment to be inadequately designed and poorly maintained.
  Wider management failings were found by the investigation to have contributed to the explosion: management safety checks at the site were found to be deficient and not properly followed. Site staff did not have control over the flow rates and timing of two of the three inlet sources, meaning that they did not have enough information to properly manage the storage of incoming fuel. Further, overall throughput had increased, reducing wait times further and shifting the emphasis to process operations instead of process safety.
caption: The smoke plume from 3.75 miles (6 km) away, the day after the explosion
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