Celsa steelworks: Peter O'Brien and Mark Sim died in blast
Two workers who died in an explosion at a Cardiff steelworks have been named as Peter O'Brien and Mark Sim.
South Wales Police said father-of-six Mr O'Brien, 51, was from Llanishen, Cardiff, and Mr Sim, 41, from Caldicot, Monmouthshire.
Emergency services are working to recover their bodies after the blast, which happened in the basement of the rod and bar mill at Celsa Steel UK on Wednesday.
Five men were also injured.
Police said of the four people taken to hospital, three have now been discharged. Another man was treated at the plant in Splott.
Celsa Steel UK chief executive Luis Sanz said Wednesday was "a tragic day for all in our Celsa family."
Speaking outside the steelworks at Thursday lunchtime, Mr Sanz said Celsa's deepest sympathies were with the families of those who died.
He said the firm was "incredibly grateful to the local community for their support and solidarity at such a difficult time".
"In memory of our colleagues, we will strive to avoid another day like yesterday," he added.
The company is working with the Health and Safety Executive and police who are leading the investigation to determine the cause of the blast.
Flowers have been left at the site, many with tributes to those who died.
Speaking to BBC Wales, Mr O'Brien's brother Kevin said "he was the true embodiment of a rock" who "loved life at the works".
"My brother was a family man," he said.
"Husband to Marie and father of Keiran, Hannah, Sean, Rachel, Martha and Dominic; son of Sheila and Bart; brother of Bernard, Kevin and Catherine. He will be sadly missed."
He said Mr O'Brien joined Celsa - which was then Allied Steel and Wire - as a 16-year-old apprentice and was named Welsh Apprentice of the Year aged 19.
After leaving school with one O-level, he continued his education at night school and eventually achieved a first class honours degree.
After working at various firms including the Royal Mint in Llantrisant and Kingsmill Bakery in Cardiff, he returned to the firm where he began his career as an engineer.
St Peter's RFC in Roath posted a tribute on its website to Mr O'Brien, who had represented the club in baseball and rugby and was well known to the 90 players in the various squads.
He was also the founder and current club champion of St Peter's Bowls Club.
The club said he was "a well loved and exceptionally popular member" and a "family man" who would be "sadly missed".
His colleague Mr Sim, who was originally from Newcastle upon Tyne, was married to Sam and had a young son and daughter.
He was a Newcastle United football fan and played for a local darts team in the Caldicot area.
Unions will meet Celsa HR staff and senior management to discuss how best to support staff following the deaths.