Book extract
Disasters: learning the lessons for a safer
world
by David Eves
£30 softback 256 pages
ISBN 978 0 901357 46 5
The jet fire at Hickson and Welch Limited, Yorkshire,
England, 1992
On 21 September 1992 the HSE’s Area Director
in Leeds telephoned me to report that a catastrophe had just
occurred at a chemical works in Yorkshire, possibly the most
serious incident since Flixborough. We set an investigation in
train immediately.
What happened?
Hickson and Welch Ltd was a chemical manufacturing company of
long standing and a major employer in the Yorkshire town of
Castleford. The company had decided that a batch still that had
been installed in the nitrotoluenes area of the plant in 1961 was
to be cleaned of accumulated residues – the first time this had
been done in 30 years.
A tarry sludge of residue some 14 inches deep had been measured
at the bottom of the still and reported to management, who assumed
it consisted of a thermally stable tar. Neither the sludge nor the
vessel’s atmosphere was analysed. The operators were told to apply
steam to the bottom of the vessel to soften the sludge, and this
was done. The residue could then be raked out manually through a
manhole opening, accessible from a scaffolding platform.
Several men began cleaning the still, working from the scaffold,
using metal rakes. After about an hour the vessel’s temperature
gauge was seen in the control room some distance away to be reading
48º C. The men were told to cut off the steam, and did so.
By around 1.20, during lunchtime, most of the men had left the
raking job and only one man remained on the scaffold. He stopped
raking when he noticed a blue light inside the still, which
immediately turned orange. He leapt for his life from the scaffold
as a jet of flame suddenly roared out of the manhole, wrecking the
scaffold and hurling the manhole cover into the centre of the
control building. Like a giant blowtorch, the horizontal flame
destroyed the control room and played against the wall of the main
office block 55 metres away, setting it on fire. Simultaneously,
burning vapours jetted upwards from the vessel’s rear top vent.
The jet fire is estimated to have lasted one minute before
subsiding from lack of fuel, but by then several other fires had
started. These were extinguished by the local fire brigade, who
attended with 22 appliances and over 100 firefighters.
Sadly, it was discovered that two workers had been killed in the
control room, their escape impeded by an inward opening door. Two
other men who escaped from the room died later from the burn
injuries they had suffered while escaping. In the office block the
body of a woman was found in the lavatories where she had been
overcome by smoke. Fortunately, no one else was in the offices
during lunchtime. Several vehicles in the car park were burnt
out.
Why?
The investigation by the HSE found that a
number of factors had conspired to create this disaster:
- The vessel had not been cleaned for 30 years,
and due to a reorganisation no one present had any knowledge or
experience of the required cleaning operation.
- The sludge and vessel atmosphere were not analysed before
the cleaning operation began.
- The sludge was incorrectly assumed to be thermally stable. In
fact the vapours it gave off were flammable.
- The sludge temperature was inaccurately measured, by the
positioning of the temperature probe.
- The steam supply was at a higher temperature than intended
because of a faulty pressure reducing valve.
- Permit-to-work systems were not properly in place (permits had
been issued for removal of the manhole cover and for blanking off
the inlet at the vessel’s base, but not for the raking out).
- The vessel inlet was not isolated before cleaning began.
- A metal rake was an unsuitable tool for cleaning a vessel
containing flammable materials and vapour.
- The positions of the control room and office block put them at
risk from a fire or explosion in the plant.
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