Four people were killed in an explosion and fire at an oil refinery in west Wales, Dyfed Powys Police have said.The blast happened at the Chevron refinery at Pembroke Dock on Thursday.Ch Supt Gwyn Thomas said the explosion was in a 730 cubic metre storage tank where maintenance was being carried out. An adjacent tank was also damaged.He said police were informing the victims’ families and an investigation was under way into what appeared to be a “tragic industrial incident”.Milford Haven coastguards reported a “blast large enough to shake the windows” with “black smoke in the air” shortly after 1820 BST.Ch Supt Thomas said: “A police investigation is now under way, with the Health and Safety Executive, and early indications show that this was a tragic industrial incident.”Police officers have secured the scene, and colleagues from Mid and West Wales Fire and Rescue are working to make the site safe to enable a multi-agency investigation into the cause of the explosion to commence.“Assistant Chief Fire Officer Chris Davies said there was no ongoing risk to health to members of the public as a result of the incident.”We can confirm that any material released into the atmosphere as a result of the blast was immediately dispersed. The wind was blowing off shore, away from residential areas,” he said.The Health and Safety Executive said it was too early speculate about the cause of the blast.The Mid and West Wales Fire and Rescue Service sent 10 engines to the scene and brought the incident under control within an hour and a half.Wales Air Ambulance said a man had been airlifted to Morriston Hospital in Swansea with severe burns.Eyewitnesses reported hearing a “massive bang” and saw plumes of black smoke following the blast.Phil Horne was in his back garden in Milford Haven, on the opposite side of the waterway, at the time of the incident.”I heard a large explosion, turned around and saw a large fireball disappearing into the sky,” he said.”It went about halfway up the chimney stack of the refinery.”Liz Herbert, who also lives on the other side of the haven, said: “I heard a massive bang and saw a huge plume of thick black smoke.
“It was really frightening.”In a statement on Thursday evening Chevron said: “Emergency services were called and responded immediately and remain on the scene. The fire has been extinguished.”We are taking appropriate action to respond to the situation. We are still in the process of accounting for all personnel.”Milford Haven Port Authority said it was aware of the incident but it was not affecting any ship movements on the waterway.It said it had two pilot boats on standby if needed but their assistance had not been requested.The refinery was formerly known as Texaco, later rebranded Chevron-Texaco and known as Chevron since around 2005.In March, Chevron confirmed Texan oil company Valero Energy had agreed to buy the refinery for $730m (£446m) and pay a further $1bn (£611m) for the stocks of oil, petrol and other products on site.The site, which can refine 220,000 barrels of crude oil a day into petrol and other products, has yet to change hands. – BBC