DESIGN OF oil storage tanks at the Buncefield oil depot exacerbated the spread of the fire, a report into the incident published by the Buncefield Major Incident Investigation Board said last week.
The report also states that a faulty safety device on a single tank triggered the disaster near Hemel Hempstead (NCE 15/29 December 2005).
Report authors included senior members of the Environment Agency and the Health and Safety Executive (HSE). They concluded that on 11 December at 5.20am a faulty switch failed to close the inlet valve for tank 912, causing unleaded petrol to spill over.
Rather than collecting directly into bunded areas the fuel sprayed into the air as it hit the side of a 'deflector plate' at the top of the storage tank. It then fell onto a ridge created by the tank's structural bracing and dispersed further into the air (see diagram).
As the spray mixed with air it vaporised and rose, coming into contact with nearby industrial equipment, such as electrical generators, causing explosions and fires across the fuel depot.
The report also said that bunded areas around the tanks were inadequate and some collapsed when fires broke out.
This also allowed water used in firefighting, known as 'firewater' to escape from the site.
The report calls for further research into the cause of the fires that were of greater severity than current thinking predicts.
'The public health implications of potential vapour cloud explosions must be considered in both on-site and off-site emergency plans. Although the public health impact of Buncefield appears to have been minimal, this may not necessarily have been the case under different conditions, ' the report says.
The board also advised planning authorities to reconsider siting commercial and residential developments near similar fuel depots. The HSE is producing a report on this in the autumn.
To read the report, Buncefield Major Incident Investigation, visit www. nceplus. co. uk.
The Environment Agency is still investigating how to treat the firewater used to tackle the blaze, being stored at Maple Lodge sewage treatment works.