An explosion at Chevron’s Pembroke oil refinery has killed four workers.

An investigation is said to be underway over the blast that happened at around 6pm yesterday.

The four workers who died were contractors. A fifth worker is receiving treatment in hospital for serious injuries.

Greg Hanggi, refinery General Manager said: “This news is utterly devastating. The loss of our co-workers has come as a huge shock to us all. Our thoughts and deepest sympathy go out to their families. We will ensure that all employees and contractors are fully supported throughout this difficult time.”

“We will take every step possible to determine the series of events that led to this tragic incident and ensure that any lessons learnt from it will be integrated into the business and shared with our industry partners.

The Welsh plant processes crude mainly from the North Sea into fuels including diesel, gasoline and jet fuel and is said to be fully operational now.

The Health and Safety Executive said that due to the nature of the case, they would be investigating the accident alongside the police and wouldn’t be able to comment until a police enquiry was complete.

The UK Petroleum Industry Association, which represents the nine main oil refining and marketing companies in the UK, said it could not comment either.