A broken safety gauge was the cause of Europe's biggest peacetime fire, according to an inspectors' report published yesterday.
For more than two hours on 11 December last year, the gauge recorded no change in the volume of fuel in one of the storage tanks at Buncefield oil depot while petrol was being pumped in at a rate of 550 cubic metres an hour. After the tank reached capacity, 300 tons of petrol spilt, forming a vapour cloud which resulted in a series of explosions, injuring 43 people and forcing the evacuation of thousands of residents.
Toxic chemicals used to put out the Buncefield fire have polluted the local water system, prompting the water inspectorate to alter the definition of what constitutes safe drinking water. As reported in The Independent on 4 May, the inspectorate has accepted scientific advice that water is safe to drink if it contains no more than three micrograms per litre of a toxic substance known as PFOS, which was previously considered to be so dangerous that the Government was preparing legislation to ban imports.
Yesterday's report by the Health and Safety Executive (HSE) warned that chemicals from fighting the firehave passed into the water table. Since the fire, inspectors have taken almost 400 water samples from sources around Buncefield, near Hemel Hempstead. They have found traces of PFOS, but below the level said to be safe for human consumption.
Air quality inspectors sought yesterday to allay public fears about the damage done to the atmosphere by a smoke cloud more than 200 miles wide. A separate report published yesterday by the Environment Department, Defra, said: "It is unlikely that pollutants emitted after the Buncefield oil depot explosion had widespread impacts on air quality at ground level."
But experts said that it was because weather conditions allowed the smoke to rise high into the atmosphere, spreading the pollutants over a large distance. Professor Ian Colbeck, director of the Centre for Environment and Society at the University of Essex, said: "If this event occurred in the summer then the corresponding ground level air pollution impacts would have been significant."
Dr Alastair Lewis, of the Department of Chemistry at the University of York, said: "Although air quality was not adversely affected, persistent organic pollutants generated by the fire will not simply have disappeared. They will have ultimately been deposited into the soil or the ocean."
A safety gauge in tank 192 at Buncefield appears to have jammed at about 3am on 11 December, showing the tank two-thirds full. The tank was full by about 5.20am, after which a vapour cloud rose above the tank, visible on CCTV.
The tank was also fitted with an alarm, independent of the faulty gauge, which should have gone off as the petrol reached the maximum level. The alarm should have automatically closed the valves to prevent more fuel being pumped into the tank. But it appears that, like the level gauge, the alarm system was broken. Inspectors may never find out what caused the explosion, because the evidence was destroyed in the fire. It could have been a spark from a nearby fire pump house, or an emergency generator, or a passing car.
The HSE report the third since the fire did not allocate blame for fear of jeopardising a possible court case. But the HSE has been asked whether it is in a position to judge if human error was to blame, because it was responsible for inspecting the site.
Mike Penning, the Conservative MP for Hemel Hempstead, has called for a public inquiry into the fire and said that the progress report moved the inquiry along "only fractionally" and he expressed concern over investigations conducted "behind closed doors".
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