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May 21, 2006

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Safety-system failure implicated in Buncefield blast

Safety mechanisms which should have warned operators at Buncefield that a storage tank at the fuel depot was becoming dangerously overfilled and automatically shut down the system failed to operate in the early hours of 11 December 2005, leading to the catastrophic explosion that wrecked the Hertfordshire site.

The third progress report of the ongoing investigation into the incident states that although Tank 912 in Bund A, which was being filled with unleaded petrol on the morning of the explosion, reached capacity at around 5.20am evidence shows that the protection system that would have automatically closed the valves to prevent overfilling did not deploy. Some 40 minutes later, the thick cloud of hydrocarbon-rich vapour that had formed as a result of the overflow of 300 tonnes of fuel ignited, causing a blast so powerful it was heard up to 200 miles away and was detected by seismic recording equipment.

As yet, the joint HSE/Environment Agency investigation team does not know why the safety systems did not work. Simulation exercises and tests on the alarms and control panels have proved that they worked normally but the report does state that when the override switch was tested, it did inhibit the alarm/trip signals. Further tests will need to be carried out on the ultimate high-level safety switch, which suffered significant damage in the blast and has yet to be retrieved.

Because the investigation is incomplete and ongoing the necessarily stark statements about the failure of the protection systems and the override switch have led to speculation about the role of human error in the incident. Following publication of the third progress report the national press focused on the failure by control room staff to notice either the faulty equipment or the gathering vapour cloud which eventually ignited and caused the blast.

The HSE, when contacted by SHP, would not be drawn on the subject, stating that the investigation is currently at “a difficult stage”. A criminal investigation is also currently underway, at the conclusion of which it will be up to the HSE and the Environment Agency to decide whether there are grounds for prosecuting any company or individual involved. Consequently, the investigation Board has to be careful about the information it publishes in order to avoid prejudicing any future legal proceedings.

In the meantime, the Board has emphasised the need for operators of similar sites to continue to act on the advice of the HSE issued after the first progress report (see News, SHP April). A spokesperson for the Executive told SHP that it is currently analysing the response of operators to this safety alert, with a view to producing a report later this month.

The Chemical Industries Association welcomed the urgency with which the issue is being addressed. Said its chief executive, Steve Elliott: “There is plenty for our members to consider regarding the protection of their own storage tanks against overfilling. We look forward to playing our part in putting measures in place to minimise the risk of repetition.”

The Buncefield Investigation: Third Progress Report is available to download from


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