BUNCEFIELD UPDATE
Although the actual
cause of the December
11 incident in
Hertfordshire, UK, is still to be
determined, the failures of the
bunds to cope with fire and
hydraulic pressures were such
that in the report's
accompanying statement, the
MIIB has urged storage site
operators to “consider the
adequacy of existing bunds on
their sites”.
The 26-page second
progress report reiterates the
initial findings: that the
explosion and fire were due to
an escape of fuel. How the
fuel escaped and why it
vaporised so quickly are
questions which have yet to
be answered, although at
time of writing, the MIIB was
hoping to publish its findings
by mid May. The UK Health
and Safety Laboratory is
working to discover the
nature and composition of the
flammable mixture in the
hope that this will explain why
an explosion should occur in
an unconfined vapour cloud.
Secondary containment
There were a number of
different types of bund at
Buncefield, ranging from
earth banks with earth bases
to concrete walls with
concrete bases. The majority
of the bunds affected by the
fire were concrete, although
some were concrete with
clay bases.
Unlike the pumping station,
the bunds survived the
explosion largely intact. But
their ability to contain fuel
and fire waters was lost due
to the explosion itself and the
subsequent fires. A particular
area of concern is apparent
loss or damage to joint
sealant across the site. In
some cases the explosion
caused the concrete walls to
heave, allowing fuel and fire
water to escape onto the site.
Five months after the
incident there were safety
concerns, including residue
fuel in pipes, which meant the
investigating team had still
not been able to examine all
of the bunds affected by the
explosion. Buncefield
investigation manager Taf
Powell said: “Bund
performance during the
incident forms an important
but as yet inconclusive aspect
of the investigation.” The MIIB
has not ruled out future work
on reviewing the resilience of
bunds, including their design
and construction.
Martyn Lyons, chairman of
the Tank Storage Association,
said the second update raised
almost as many questions as
it answered, not least about
the type of sealant used and
what happened to it, plus
why gaps around the pipes
pictured in the report are
so big.
