A STEEL firm has been ordered to pay nearly £2m in fines and costs after two engineers were killed in a plant explosion.

Father-of-two Mark Sim from Caldicot and colleague Peter O’Brien died in the blast at the Celsa steel mill in Cardiff on November 18, 2015.

Cardiff Crown Court heard that Celsa had failed to carry out a risk assesment on an oil heating machine which was being drained, but was still turned on.

Outside the court after the sentencing, Mr Sim’s wife Samantha described the mechanical engineer’s death as “the most traumatic experience I have ever dealt with.”

“He has left a huge void in our hearts and our lives, a void people say heals in time but I believe it never truly heals, we just learn to live our lives differently,” she said.

Mr Sim, a coach at Caldicot Youth FC who moved to the area from Tyneside when he was based at Beachley Barracks with the Royal Engineers, was working in the basement of the scrap metal plant’s rod and bar mill when oil ignited causing the blast.

The explosion killed the 41- year-old and his 51-year-old colleague, a father-of-six from Llanishen in Cardiff, and injured five others, one seriously.

A Health and Safety Executive investigation found the blast would have come without warning to the employees.

Cardiff Crown Court was told that a flammable atmosphere developed in an accumulator vessel, and was suddenly ignited by an electric heater, with devastating results.

An HSE spokesperson said: “The company failed to assess the risks to which its employees were exposed when draining lubrication oil from the accumulator.

“Manually draining hydraulic lubrication oil from the accumulator by a procedure referred as a ‘blow down’ had developed through the company employees’ local custom and practice.

“This “procedure” was not fully understood or consistently carried out by the company’s employees, exposing them to the risk of explosion.”

Celsa Manufacturing (UK) Ltd of East Moors Road, Car- diff, pleaded guilty to breaching Regulation 3 of the Management of Health and Safety at Work Regulations 1999.

It was fined £1.8m and ordered to pay costs of £145,771 and a £120 surcharge.

Speaking after the hearing, HSE inspector Lee Schilling said: “This incident, which had devastating consequences for all of those involved, was entirely preventable.

“The company failed to assess the risks of the maintenance work and identify suitable control measures to prevent an explosion.”

Judge Neil Bidder told the court the accident scene looked like “a bomb site”, and the risk of the explosion “could and should have been recognised”.

The company apologised “for the shortcomings which contributed to the most tragic event in our history.”

A Celsa spokesman said after the hearing: “Whilst nothing we can do will ever bring Mark and Peter back, our thoughts and deepest sympathies remain with those closest to them.

“The loss of two friends and colleagues will always be felt deeply by the whole Celsa family. We have left no stone unturned to ensure that nothing like this could ever happen again.”

Mr Sim, a father of two teenage children, played darts for Caldicot FC and loved karaoke. A lifelong Newcastle United fan, mourners at his funeral at Cinderford Crematorium wore the club’s black and white in tribute to him.