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The Chevron Pembroke refinery was rocked by a blast in 2011. Image courtesy of ODN/Youtube.

Chevron will not face any criminal charges for a 2011 refinery blast in the UK that killed four workers and severely injured another.

According to the BBC, the Crown Prosecution Service has determined after a four year investigation that there is not enough evidence to pursue corporate manslaughter charges against Chevron, who operated the refinery at the time of the accident.

A portion of the refinery, located in Pembrokeshire in South West Wales, caught fire on June 2, 2011 after a 160,578 gallon storage tank exploded and damaged a neighboring tank.

According to the UK Health and Safety Executive, the blast happened during tank cleaning operations within the amine recovery unit at the refinery site.

Andrew Jenkins, 33, Dennis Riley, 52, Julie Schmitz, 54, and Robert Broome, 48, were killed during the accident.

Although Chevron was operating the refinery at the time of the incident the company had already reached a deal to sell the refinery to Valero.

The UK Health and Safety Executive told the BBC it will continue its own probe into the blast.