Prof Venart is an expert in steel furnace explosions

James Venart, a professor in Canada, said the "super-heating" of water at Corus' furnace number five in Port Talbot probably caused the blast.

He said he thought the water had been released onto molten metals when some furnace coolers burned out.

Stephen Galsworthy, 25, Len Radford, 53, and Andrew Hutin, 20, were killed.

Twelve other workers were seriously injured by showers of molten metal and super-heated gas during the incident on 8 November, 2001.

One kilogram of water super-heated released more energy than if you were to explode 1kg of TNT Professor James Venart

Professor emeritus in engineering at the University of New Brunswick, Professor Venart extensive experience of dealing with steel plant explosions in the United States and Canada.

He told the inquest at Swansea's Guildhall that of the four possible causes of the explosion he had come up with, his favoured option was the one involving the released of water.

He said a chain reaction would have followed, causing an initial explosion, which led to the release of 88lbs (40kg) of water into the furnace from a damaged cooler.

Stephen Galsworthy, Andrew Hutin, and Len Radford died

"One kilogram of water super-heated released more energy than if you were to explode 1kg of TNT," Prof Venart added.

Hugh Carlisle, the lawyer for Corus, did not ask Prof Venart questions after his evidence, saying the academic himself had admitted his explanation was an interpretation.

The inquest, which has been running for a month, had previously heard that hydrogen levels had been high in the furnace in the hours before the explosion, indicating water was leaking into it.

Senior managers had believed the problems had been resolved when levels dropped back.

Area technician David Humphrey had said the water may have been "slagged up", causing the gas level to drop but with the problem actually still remaining.