A series of safety failings led to a devastating explosion at an oil refinery which claimed the lives of four workers, a court has heard.
Dennis Riley, aged 52, Robert Broome, aged 48, Julie Jones, aged 54, and 33-year-old Andrew Jenkins died when a storage tank exploded at the Chevron plant in Pembroke in June 2011.
A fifth worker Andrew Phillips suffered life-changing injuries.
The blast was so powerful it blew the roof of the tank more an 150ft feet across the site and sent it crashing into a bupane gas tank, which fortunately did not rupture.
Swansea Crown Court heard details of a catalogue of errors and failings that contributed to the fatal incident and which, taken together, meant that the Pembrokeshire plant had become 'fundamentally unsafe".
The terrible day a massive explosion killed four oil refinery workers
Oil company Chevron - now Valero Energy UK - and local firm B&A Contracts had each previously pleaded guilty to breaches of health and safety rules when they appeared in court for sentencing.
The court heard that on the day of the explosion workers were emptying a tank at the plant's amine recovery unit (ARU), the part of the refinery where substances used to clean or "scrub" the crude oil were processed and recycled.
Andrew Langdon QC, for the prosecution, said contractors B&A were tasked with pumping out sludge from the bottom of tank 302 to prepare it for cleaning and maintenance.
The decision was taken to carry out the work by lowering a hose into the tank from an access point on the roof to enable the contents to be pumped into a waiting bowser.
The court heard the hose was not earthed, as it should have been.
Some 10 minutes into the operation the contents of the tank suddenly ignited, causing a massive explosion and fire ball.
The barrister said there were two possible sources of ignition - static electricity generated in the hose, or pyrophoric substances in the tank, that is substances that spontaneously combust on contact with air.
He said it was not not possible to determine to the legal burden of proof which of the two possible methods had caused the blast, but that it was the prosecution case that the an electrostatic spark was the "overwhelmingly likely" cause.
The barrister said little or no consideration seemed to have been given to the prospect of the atmosphere in the tank being contaminated with highly flammable light hydrocarbons such as methane, ethane and hexane - a mistake that was to prove fatal.
He said the risk of hydrocarbon vapours in the storage vessel "should have been foreseen, and acted upon".
Mr Langdon listed five broad areas of failures which contributed to the explosion.
- A lack of proper working practices or procedures for the task being undertaken, and such procedures as were in place not being followed.
- Weaknesses in the system for issuing on-site permits for carrying out jobs.
- Problems with the way contractors were managed and monitored.
- Inadequacies in risk assessments carried out by Chevron.
- Inadequate gathering and recording of safety information and data.
Mr Landgon described the five areas as "overlapping systemic failures".
He said: "It is unusual to find so many parallel systemic failures, each of which had a direct causation.
"These are manifest failings which paint a picture of a workplace which had become, over time, fundamentally unsafe."
The refinery was being operated by Chevron at the time of the blast, but a few months later ownership was transferred to Valero Energy UK, and it is under this name that the legal action has been brought.
Companies admit health and safety failings over oil refinery explosion that killed four
The barrister said it was the prosecution case that B&A had been using a hose with a metal scaffold pole gaffer-taped to the end to pump out the sludge - a length of such poling was subsequently found by a police forensic investigator in the charred ruins of the tank.
The court heard the contractors did not accept this in its basis of plea.
The prosecutor said the pumping method selected should never have been used had the presence of flammable vapours in the tank been known.
All five people who were killed or injured in the incident had been near the storage tank when it exploded.
The court heard a tanker lorry driver on the site who witnessed the explosion reported seeing the sides of the storage tank "rippling" before a "massive blast" blew its top off.
Another reported hearing a noise like "thunder" and feeling the vibrations of the explosion.
Mr Langdon said the resultant blaze had been "large and ferocious" and there were initial fears that nearby tanks and pipes could catch fire in a "domino effect".
Auxilliary firefighters from the plant tackled the fire before 10 engines from Mid and West Wales Fire and Rescue Service arrived on the scene.
The court also heard details of victim impact statements from the families of the deceased, as well as one from the survivor Mr Phillips who suffered horrific burns in the incident
In his statement, Mr Phillips said the flammable vapours in the tank should have been removed before he and his team set to work that day.
He added if he had known they were present, he would not have allowed the work to go ahead.
He described feeling guilty at surviving the explosion while his colleagues had died and said he had wished he had swapped places with Miss Jones that day.
Mr Phillips said following the blast he received a card from the widow of Mr Riley, at which point he realised the other families did not blame him for the disaster.
He said the card "saved my life".
The sentencing hearing is expected to last until Friday.
