The blast at the Chevron refinery in Pembrokeshire, which employs 1,400 locally, shattered a 730-cubic metre storage tank killing four and leaving a fifth person with severe burn injuries.

The explosion happened on June 2 during routine maintenance on one of the refinery's 140 storage tanks.

It is believed a single spark ignited gases in the tank, causing a blast which was heard and seen for miles around.

The Chevron refinery in Pembrokeshire, West Wales, can refine 220,000 barrels of crude oil a day into petrol and other products.

The fire was brought under control within two hours and the authorities said there was no risk to the health of members of the public as a result of the incident.

First Minister of Wales Carwyn Jones visited the refinery after the accident to meet emergency workers and staff and thank them for their work in the aftermath of the explosion.