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The Buncefield Incident:
Investigation Board Report
In 2005, a
release of gasoline resulted in a number of Vapour Cloud Explosions (VCE)
at the Buncefield oil storage depot in Hemel Hempstead, Hertfordshire, UK. This resulted in
significant damage to the surrounding area, and the subsequent fires
burned for several days.
During a standard product transfer to
the site, one of the storage tanks was overfilled. Some of the fuel flowed off the roof of
the tank and was channelled onto the tank wall while the rest flowed over
the top of the deflector plates and is understood to have dispersed into
droplets. Most of the fuel flowing
down the tank wall hit a wind girder, creating a second cascade of
droplets. This promoted the rapid
formation of a rich fuel/air mixture.
There was more than one explosion, and
several potential ignition sources were identified, both on and off
site. The explosions generated
much higher overpressures than would have been predicted based on
previous understanding of this type of scenario, and the investigation
into the mechanism behind this is ongoing.
It is estimated that over 700,000
litres of foam concentrate and 68 million litres of water were used in
the fire fighting response.
Source:
http://www.buncefieldinvestigation.gov.uk/index.htm
In 2007, the Buncefield Major Incident Investigation Board (MIIB)
made various recommendations to reduce the risk of this scenario
occurring at other installations, including:
•
Assessing
safety integrity levels;
•
Protecting
against loss of primary containment;
•
Engineering
to protect against escalation following loss of containment;
•
Engineering
against loss of secondary and tertiary containment.
In July 2008,
the Board provided details of how a more comprehensive risk assessment
might be conducted. However, a
number of areas of uncertainty remained in relation to the mechanism of
cloud formation and in calculating the impacts associated with ignition
of an unconfined vapour cloud.
In December 2008, the UK authorities commenced proceedings to prosecute five
companies involved for their failure to prevent this accident from
occurring at the site.
Also in December 2008, the MIIB issued
its final report into the incident.
This document consolidates the work from all the previous reports
and includes a high-level risk assessment, comparing the costs of
implementing the additional protective measures recommended by the MIIB
with the benefits of reducing the probability of a similar scenario occurring
again in the future.
Although this is the final report of the MIIB, it does not conclude the
investigation into the incident.
The Board has set up the first phase of a technical programme to
promote further research into the mechanism behind the explosion. It was anticipated in December 2008
that Phase 1 of this investigation would be completed in the first
quarter of 2009, though it has not been published to date.
At Byrne Ó Cléirigh, we can assist
operators of oil storage installations to assess the risk of this
scenario occurring at their sites and to ensure that all necessary
measures are in place to minimise risk.
We have modified our consequence
modelling procedure in light of the Buncefield
reports and have conducted analyses for several clients in the petroleum
storage industry. We continue to
monitor the investigation for any new developments and to ensure that our
risk assessment and consequence modelling procedures are up-to-date.
This article is taken from the
presentation “Fire Safety in Oil
Storage Installations”, presented by Thomas Leonard of Byrne Ó
Cléirigh to the Institution of Engineers of Ireland. The full
presentation can be viewed by clicking here.
If you are interested in the content of
this article, and would like to discuss it further, please contact
Mr. Thomas Leonard on +353-1-474 1533
or email Tom.Leonard@boc.ie.
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