A water treatment works where a welder was killed in a massive explosion should have been shut down at the time, an inquest heard today.
Water Service had no effective risk assessment in place and had not adequately warned the contractors about volatile gas which sent a storage tank 200ft into the air when a spark ignited it.
Drew Stevenson (51) died and a colleague was seriously injured in the blast at the site near Derry in June 2005.
The married father-of-six was using an angle grinder on the roof of the waterworks when the container flew through the roof beneath his feet.
Health and Safety Executive inspector William Burns told the Derry hearing: "The system should have been shut down and verified as safe before starting up again.
"Even if this installation was completed and Mr (Peter) Thompson and Mr Stevenson had done what they were proposing to do, the system would have been left in a situation which was less safe than it was to begin with."
Mr Stevenson, from Main Street, Killen, Castlederg, was replacing a roof vent on the building, at Carmoney Water Treatment Works, Eglinton, which contained hydrogen produced during water treatment.
The inspector said the new vents would not have been adequate to prevent a future explosion and added up to three people could have died in the accident.
Mr Burns also criticised Water Service for not having a risk assessment in place for that specific job, for allowing the two men onto the site without a written permit to work warning, for inadequate warning signage and for not properly signing in.
PA