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Buncefield disaster exposes blast engineering flaws

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GOVERNMENT ENGINEERS this week said they had exposed flaws in the understanding of blast dynamics following an analysis of the explosion of the Buncefield oil depot near Hemel Hempsted.

They are expected to recommend that worst case scenarios for oil depot fires are upgraded.

It is possible their findings could affect the future location of oil storage depots.

Health & Safety Laboratory's (HSL) principal fire engineer Graham Atkins said the vapour explosion was thousands of times stronger than anyone thought possible.

It was initially thought to have been caused by the ignition of vapour in an empty petrol storage tank.

But CCTV footage and information from the depot control room's computers have confirmed the vapour cloud was not in a confined space.

Atkins was charged with calculating the size of the blast wave generated by the explosion. To do this he attempted to replicate damage done to cars parked close to the site under laboratory conditions. This involved causing gas explosions inside a steel tank containing cars and examining the resulting damage.

The explosions increased air pressure inside the tank, but still failed to replicate damage caused by the depot blast.

At Buncefield, petrol spilling from the top of an overfilled storage tank created a fine spray which mixed with the air to form a highly explosive mist.

This was then ignited by an unknown source.

The resulting explosion tore through a nearby industrial estate and residential area causing widespread damage.

Investigators discovered that the gauge that monitored petrol levels in the pipe-fed tank had become stuck. They also found and that the alarm which should have been triggered when the tank was full was not functioning. It is undertstood that the alarm had been disconnected for a routine check.

Buncefield Investigation Board investigation manager Taf Powell said the worst scenario planned for at the site was a 100m 2 pool fire caused by a tank splitting. He agreed that this would have to be upgraded following the Buncefield investigation.

'There are 108 other depots in the UK in similar situations; Buncefield is one of the largest.

It is not sustainable to base planning on these sites on a pool fire because this is obviously not correct.' HSE lead inspector Christine Marshall said industry has been asked to review its understanding of blasts because current thinking underestimates the power of vapour explosions.

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