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WAITING TO HAPPEN
JUNE 2011 MAY be nine years ago now, but the deaths of four workers at Chevron’s Pembrokeshire refinery do not deserve to be forgotten. The UK Health & Safety Executive (HSE) has published a full report on that incident, which highlights the various safety failings and management shortcomings that led inevitably to the fatalities. Shortly after the explosion on 2 June 2011, HSE issued a safety alert to inform industry of the preventative measures required to avert a similar occurrence. “The investigation was complex and we can now share further information about the underlying causes, so that everyone in major hazard industries (not just those involved in tank storage or tank cleaning) can learn from this incident, understand what went wrong, and apply
HSE is quite clear about the causes of the incident. The report states: “The investigation revealed a longstanding and widespread failure to understand and control risks posed by the flammable atmosphere inside the tank. The explosion and the resulting fatalities were therefore avoidable. The incident was not merely the consequence of errors by individual employees, but because of the failure of safety management systems to ensure a safe place and safe systems of work.” TANKS IN QUESTION During what should have been a routine cleaning operation on an atmospheric storage tank within the amine regeneration unit (ARU) of the refinery, an explosion split the tank open, killing four workers on the
The ARU was fitted with two breathable tanks, one used for the separation of waste streams and the second acting as the reservoir for lean diethanolamine, used in the scrubber to strip hydrogen sulphide from petroleum. The stripping process also caused some light hydrocarbons to become entrained in the amine solution; this was designed to be skimmed off in a surge drum. Both storage tanks included a 300-mm blanket of diesel to inhibit oxygen ingress. The HSE report details how changes had been made to the system over the years. Indeed, the two tanks, designed for different purposes, had been used interchangeably. HSE also notes how a proportion of the light hydrocarbons, designed to be skimmed off in the surge drum, accumulated over time in the amine running tank and were taken up by the diesel blanket. This had, over time, expanded in size to 900 mm deep and could no longer be regarded as diesel due to the change in composition. This blanket therefore needed to be siphoned off at intervals. This was not a normal design process and HSE states: “Looking back, HSE believes there were a number of significant events that should have alerted the refinery management team to the presence of light hydrocarbon within the
lessons to their own organisations,” says Jane Lassey, director of HSE’s Chemicals, Explosives and Microbiological Hazards Division, in her introduction to the report. “Although a number of years have elapsed since the incident, the information contained within this report remains highly relevant today.”
spot and severely injuring a fifth; the force of the blast ejected the 5-tonne steel tank roof more than 55 metres through the air. It narrowly missed a pipe rack and landed on a pressurised storage sphere containing butane – luckily the sphere was not punctured.
running tank. These events presented several opportunities to reduce risk and prevent the incident, through the critical review and refreshing of risk assessments, training and maintenance arrangements. Regrettably, the significance of these opportunities went unrecognised.”
ACCIDENT REPORT • SAFETY MANAGEMENT FAILINGS WERE AT THE ROOT OF THE FATAL EXPLOSION AT CHEVRON’S PEMBROKE REFINERY IN JUNE 2011, HSE’S FINAL REPORT CONCLUDES
HCB MONTHLY | JUNE 2020
