An oil worker remained in hospital in a critical condition today after an explosion that killed four of his colleagues.
The man is being treated for severe burns at Morriston Hospital in Swansea following yesterday's blast at the Chevron Refinery, Pembroke Dock, south Wales.
A joint police and Health and Safety Executive investigation is being carried out into the explosion, which is believed to have been a "tragic industrial accident".
Maintenance work had been carried out on a 730 cubic metre storage tank which exploded around 6.20pm yesterday, damaging an adjacent vessel.
Sources said that three of those who died were male painters while the fourth was a woman on fire-watch duties.
Investigators are being urged to find out what caused the deadly explosion as quickly as they can.
David Urpeth, national head of workplace injuries at legal firm Irwin Mitchell said: "Major industrial accidents like this have a devastating impact on both workers and the local community and everyone in Pembroke will undoubtedly be seeking answers as to how this terrible and tragic incident came to occur.
"It is absolutely vital that Chevron, HSE and other authorities work swiftly to determine what caused the explosion and subsequent fire and, more importantly, how it could have been prevented."
Local Tory MP Simon Hart, who represents Carmarthen West and South Pembrokeshire, said he was "assured that a full investigation will be taking place".
He added: "We live alongside these industrial giants that provide so much work for the county, and few of us think of the risks that come with working there."
Welsh Secretary Cheryl Gillan said: "It is essential to understand how this tragedy occurred."
The refinery and a nearby construction site, where a new power station is being built for npower, were closed today as a mark of respect.
The police divisional commander for Pembrokeshire and Ceredigion said: "Early indications suggest that this is a tragic industrial incident.
"Sadly four people have lost their lives, and a fifth person remains in hospital, critically ill.
"We are not currently in a position to release the names of the victims, as they have not yet been formally identified, and this process may take some time."
Locals expressed shock at what had happened but said a certain level of risk was inevitable at an industrial site.
A former welder at the site, Tony Spicer, 75, of Gwyther Street, Pembroke Dock, said: "At a refinery you are working within a time-bomb and at any time something can go wrong.
"It is terrible when something like this happens. The lives of four people is a great loss. But this is not the first accident.
"I think that an accident and loss of life is inevitable from time to time. It's not always human error, it is just something that can happen."
Pembroke Dock shopper Bronwen Lewis, 63, said there would never be a guarantee that accidents would not happen.
"There will always be accidents wherever you have a big place like this.
"These places have got to be there at the end of the day and accidents will occasionally happen, no matter what anyone does. Unfortunately, in this case, lives have been lost."
Chevron is carrying out its own investigation into what happened.
The latest statement from the company said: "Chevron is hugely saddened by the death of four of its contractor colleagues in the incident yesterday evening and our thoughts go out to their families at this very difficult time.
"One contractor colleague remains in hospital where he is still receiving treatment. Pembroke Refinery is a very close family and this tragedy has been a great shock to everyone. The welfare of our employees is our key priority and we are providing counselling support to all our staff and their families."
Unite, which has more than 400 members at the site, expressed its "deep sympathy" at the death of the four contractors.
Regional officer Allan Card said: "Unite would like to express its deepest sympathy and sincere condolences to the families of those who died and the contractor who was seriously injured. It will be a devastating blow to the communities in which they lived.
"Unite regards health and safety in the workplace as the highest priority and we will fully co-operate with the investigation which is under way. It is premature for any conclusions to be drawn."Reuse content