The explosion and fires at the Texaco Refinery, Milford Haven. 24th July
The series of events that led to the accident started on the morning of
Sunday 24 July 1994. A severe electrical storm caused plant disturbances
that affected the vacuum distillation, alkylation and butamer units as well
as the fluidised catalytic cracking unit (FCCU). The crude distillation unit
that provided feed to the Pembroke Cracking Company (PCC) units was shut
down as a result of a fire, which had been started by a lightning strike.
During the course of the morning all PCC units except the FCCU were shut
However the direct cause of the explosion that occurred some five hours
later was a combination of failures in management, equipment and control
systems during the plant upset. These led to a release of about 20 tonnes of
flammable hydrocarbons from the outlet pipe of the flare knock out drum of
The explosion was caused by flammable hydrocarbon liquid being
continuously pumped into a process vessel that, due to a valve malfunction,
had its outlet closed. The only means of escape for this hydrocarbon once
the vessel was full was through the pressure relief system and then to the
flare line. The flare system was not designed to cope with this excursion
from normal operation and due to liquid breakthrough at the FCCU flare knock
out drum, a failure occurred in the outlet pipe.
A total of 20 tonnes of a mixture of hydrocarbon liquid and vapour was
released, which found a source of ignition about 110 m from the flare drum
and subsequently exploded. This caused a major hydrocarbon fire at the flare
drum outlet itself and a number of secondary fires. The fires were
effectively contained and escalation prevented by cooling nearby vessels
that contained flammable liquids. As the explosion had incapacitated the
flare relief system, the safest course of action was to allow the fires to
continue to burn which they did, finally being extinguished on the evening
of Tuesday 26 July 1994.
Failures in technical measures
- A control valve being shut when the control system indicated it was
open. Inadequate maintenance of plant and instrumentation.
- Control Systems: actuator/valve,
- Maintenance Procedures: maintenance
- Modification of the plant which had been carried out without an
assessment of the potential consequences.
- Plant Modification / Change Procedures:
- Control panel graphics did not provide necessary process overviews.
Excessive number of alarms in emergency situation reduced effectiveness
of operator response.
- Control Room Design: plant layout,
human factors/ergonomic issues
- Attempts to keep the unit running when it should have been shut down.
- Emergency Response / Spill Control:
emergency operating procedures/training
Health and Safety Executive, ‘The explosion and fires at the Texaco
Refinery, Milford Haven, 24 July 1994: A report of the investigation by the
Health and Safety Executive into the explosion and fires on the Pembroke
Cracking Company Plant at the Texaco Refinery, Milford Haven on 24 July
1994’, ISBN 0 7176 1413 1, 1997.