Stephen Galsworthy, Andrew Hutin, and Len Radford died

But managers who could have stopped people from working in the danger area at Port Talbot's Corus plant were not aware of the dangerous circumstances.

David Humphrey, area technician, told the Swansea inquest how gas levels then appeared to drop, masking the problem.

Len Radford, 53, from Maesteg, and Stephen Galsworthy, 25, and Andrew Hutin, 20, both from Port Talbot, died.

The jury heard that hydrogen levels in the blast furnace had been excessively high for a prolonged period, three hours, on the afternoon of the explosion in November 2001.

But the problem, a sign that water was leaking into the furnace, was not fully known to managers who had held an urgent meeting an hour before the blast, Mr Humphrey told the inquest.

Twelve other workers were injured when the furnace exploded

Earlier this week, the jury heard that a decision had been made at that meeting to forge ahead with efforts to repair the blast furnace.

Mr Humphrey said that he had ordered workers to locate and repair a water leak which the team had become aware of on that day.

But by the time the team met to discuss problems with the furnace, the hydrogen level had dropped again, disguising what may have been a fatal problem.

Lloyd Williams, representing the three families of the steel men killed in the explosion, suggested to Mr Humphrey that that the water leak may not have been repaired because it appeared to have gone away.

He went on to suggest that the water may have been "slagged up", leading the hydrogen level to drop when, in reality, the problem was left unresolved.

Mr Williams asked Mr Humphrey: "If someone had said that to you and the decision had been yours, would you have closed down the furnace?"

Mr Humphrey replied: "I would have, yes."

'Ball of gas'

Mr Williams: "So if there had been an explosion there would not have been anyone there?" .

"That is right," Mr Humphrey answered. He also explained to the jury how he had been caught up in the blast.

"I was turning on the ball of my foot and I caught something out of the corner of my eye," he said.

"Stephen Galsworthy was standing next to me. Then I got lifted off my feet in what I believe was the ball of gas that was emitted from the furnace.

"I remember going up and coming back down. I was told by other people that I was spinning through the air." He said that he managed to crawl to safety.

Explosion

Earlier in the week, the inquest heard that maintenance had been carried out on the furnace the day before the explosion.

On the day of the blast, water was found to be flowing into the furnace and, at a meeting, it was a decided to discover the source of the leak.

It was later decided to close the furnace down until the problem had been solved. The explosion happened about one hour, 15 minutes later.