Media playback is unsupported on your device Media caption The explosion was caused by flammable gases inside a chemical storage tank

The former owners of an oil refinery in Pembroke have been fined £5m after four contractors were killed in an explosion.

Dennis Riley, Robert Broome, Andrew Jenkins and Julie Jones had been draining a chemical storage tank at the then Chevron refinery in 2011 when flammable gases inside it ignited.

A fifth worker, Andrew Phillips, suffered life-changing burns.

Chevron said it recognised it "did not live up to" its own standards.

Image copyright Family handout Image caption Julie Jones, Dennis Riley, Robert Broome and Andrew Jenkins died in the blast

After the hearing, Health and Safety Executive inspector Andrew Knowles said the accident was "entirely preventable".

Chevron will have to pay the fine andcourt costs of £1m as part of a deal it struck with Valero Energy UK, which bought the site after the disaster.

Specialist cleaning company B&A Contracts, which employed Mr Broome and Mr Jenkins, was fined £120,000 and ordered to pay costs of £40,000 after admitting health and safety breaches.

Sentencing at Swansea Crown Court, Mr Justice Lewis said no fine could "reflect the value of someone's life."

"The tragedy has had a devastating impact on the families of those who died and on Mr Phillips and his family," he said.

"Nothing this court says or does can bring back the four people who lost their lives or minimise the suffering of Andrew Phillips."

Those working for Chevron had failed to "know of or appreciate" the risk of "flammable vapour," which had been