LLanwern : Steelmaking finished here earlier this year

That year also saw the last major explosion at a Welsh steel plant when a cannister of propane gas was lowered onto molten metal at the Llanwern workers near Newport.

Twelve workers were seriously injured. Again, the courts took a dim view and fined Corus �175,000.

What's unusual about this latest tragedy is that it involves Corus's own employees and took place during routine operations.

The blast furnaces are the very epicentre of the works, where raw iron is produced before being tapped off in a molten state and moved elsewhere on the site to be converted into steel.

Port Talbot has two furnaces, the only remaining ones in Wales following the end of steelmaking at Llanwern earlier this year.

Each furnace is lined with heat resistant bricks which eventually have to be replaced.

This tragedy involved Corus's own staff

Number Five furnace, the scene of Thursday's accident, was last relined back in 1989.

In contrast the larger Number Four was completely rebuilt and relined in 1992.

Alun Cairns, the Conservative Assembly Member for South West Wales who has relatives working in the plant, said he has heard concern expressed that the company was taking Number Five beyond its normal lifespan.

A spokesman for Corus said the position was recently subject to a "thorough review", which concluded that number five was "in a sound condition and able to produce quality iron until 2005".

He added that the Corus executives who took that decision would not take either the financial or the safety risks of running an unsafe furnace.

It will now be for the Health and Safety executive to determine what caused the explosion.