Buncefield Fire - Inquiry

Inquiry

A government inquiry held jointly by the Health and Safety Executive (HSE) and the Environment Agency was started, but calls for a full public enquiry were declined. The Board included Lord Newton of Braintree; Prof Dougal Drysdale, an authority on fire safety; and Dr Peter Baxter, a medical expert. Environment Agency and HSE staff were also on the board. Its aim was to identify the immediate causes of the explosion, rather than consider who was to blame for any deficiencies, so as not to prejudice further legal proceedings.

An initial progress report by the Major Incident Investigation Board on 21 February 2006 did not go into the causes of the explosion, but summed up the event and the immediate reaction from the emergency services. A second progress report, published on 11 April 2006, looked at the environmental impact.

A further announcement was made on 9 May 2006 about the sequence of events which caused the explosion. Starting at 19:00 on the evening of 10 December 2005, Tank 912, towards the north west of the main depot, was filled with unleaded petrol—from the Coryton Refinery located in Essex, England. At midnight the terminal closed, and a check was made of the contents of tanks, which found everything normal. Normally the gauges monitor the level of the fuel in the tank as it fills from the particular pipeline. From about 03:00 the level gauge for Tank 912 began to indicate an unchanging level reading, despite it being filled at 550 cubic metres (19,423 cu ft) per hour.

Calculations show that the tank would have begun to overflow at about 05:20. There is evidence suggesting that a high-level switch, which should have detected that the tank was full and shut off the supply, failed to operate. The switch failure should have triggered an alarm, but it too appears to have failed. Forty-one minutes later, an estimated 300 tonnes of petrol would have spilled down the side of the tank through the roof vents onto the ground inside a bund wall—a semi-enclosed compound surrounding several tanks.

An overflow such as this results in the rapid formation of a rich fuel and air vapour. CCTV footage showed such a vapour flowing out the bund wall from around 05:38. By 05:50 the vapour started flowing off the site, near the junction of Cherry Tree and Buncefield Lane. Around 05:50 the rate at which fuel was being pumped into the tank increased dramatically. Initially the fuel was pumped in at 550 cubic metres (19,423 cu ft) per hour, but it increased to about 890 cubic metres (31,430 cu ft) per hour. By 06:01, when the first explosion occurred, the cloud which was initially about 1 metre (3 ft) deep, thickened to 2 metres (7 ft) and had spread beyond the boundaries of the site.

The extent of the damage meant it was not possible to determine the exact source of ignition, but possibilities include an emergency generator and the depot's fire pump system. The investigators did not believe that it was caused either by the driver of a fuel tanker, as had been speculated, or by anyone using a mobile phone. It was felt unlikely that the explosion had a widespread effect on air quality at ground level.