A STEEL company has admitted failing to make a suitable risk assessment after two engineers were killed in an explosion in the basement of a factory.

Peter O'Brien, 51, from Llanishen, Cardiff, and Mark Sim, 41, from Caldicot, died at the Celsa steelworks in Cardiff.

Celsa Manufacturing Ltd was being prosecuted by the Health and Safety Executive for breaching health and safety laws relating to the equipment involved in the blast on November 18, 2015.

The firm are facing a potential fine of £1.5 million.

Judge Neil Bidder QC addressed jury members before the start of the trial, telling them Mr O'Brien and Mr Sim were employees at the factory where scrap metal was turned into steel used to reinforce concrete.

Judge Bidder said: "You're going to be hearing about a serious accident which occurred there in 2015.

"In the basement of that factory was a large metal container which contained lubricated oil, a back-up for oil sent to lubricate rollers which rolled hot steel.

"Two men in that basement were employees of the company doing work on an accumulator. While working there was an explosion, and the two men were tragically killed and another employee seriously injured.

"The Health and Safety Executive, the prosecution in this case, are prosecuting the defendant company for what they alleged to be a breach of health and safety law."

But before the prosecutor Simon Morgan was due to open the case to the jury, the company pleaded guilty to a new charge of failing to make a suitable assessment of risk.

A third man, Darren Wood, was injured in the blast.

After Celsa admitted the charge through defence barrister Richard Matthews QC, Judge Bidder said: “The oil ignited and reached flash point … it caused a terrible explosion.

"The company has pleaded guilty to having failed to make suitable risk assessments. Had they made the assessments this accident would not have occurred.

“Two men were tragically killed. They went out to work one day and never came back, and another man was very seriously injured.”

After Mr O'Brien and Mr Sim's deaths their families released tributes to them.

A statement from Mr O'Brien's wife Marie and their six children said: "Dad was a kind, gentle and funny man who loved the simple things in life - the outdoors, camping, burning things on the barbecue and of course spending time with his loving family.

"He took a major role as a member of the church and local community, through the 27 years of marriage he and Mum have spent time running Christ the King Junior Club, he was involved in rugby coaching at his children's primary school for many years and loved his role as Confirmation Catechist at Christ the King parish church.

"He loved playing sport and was a keen gymnast in his youth, as well as being a respected rugby player and award-winning bowls player for St Peters well into his adult life.

"We'll always remember his huge appetite and insistence on having Classic FM on in the car as well his cheesy jokes and big smile. Rest in peace, thanks for everything, we'll miss you."

Mr Sim's wife Samantha said in her tribute: "Mark was dedicated to his job and would always do it to the best of his ability and was always willing to help others.

"He was dedicated to his home life as much as work. He had two families, Celsa and home.

"I will cherish time we had together, the laughs and parties, because Mark loved a good party - always the last one to leave. He help coached the local under 14s football team.

"Mark will leave a big hole in our hearts and a great void in the lives of his daughter Georgia and son Jackson and to everyone's lives that he touched.

"I would like to thank all our friends and family for their continued support at this difficult time."

The jury was discharged and Celsa will be sentenced on October 4.

A second charge of breaching health and safety regulations, relating to the machinery which caused the blast, would lie on file.