A man was killed today by an explosion at a water treatment plant which propelled a storage tank through a roof and 200ft in the air.
Two workmen were injured in the blast at the waterworks close to the village of Eglinton near Derry.
At the height of the alert, people were urged to stay indoors because of fears of dangerous gases leaking.
Roads were also blocked off as up to 40 firefighters were called in to search for casualties and examine the damage.
Staff at Altnagelvin Hospital in Londonderry put an emergency plan into operation but ambulance officials confirmed that injuries to the two men were not life-threatening.
One of the men is being treated for leg injuries while the other is suffering from chest pains.
Politicians praised the response of the emergency services but Sinn Fein tonight called for a full and open inquiry into the accident.
Eyewitnesses described how the 10ft by 12ft storage tank shot into the air before landing in a nearby field.
Jeff Ennis, 32, who works at a Land Rover Centre 150 yards from the plant, said: “There was a loud explosion. I was just heading outside and I saw the storage tank 200ft in the air.
“It was at its full height and there was debris floating after it.
“I was shocked. You don’t expect to see something that size flying through the air.”
The service manager, from Coleraine, added: “Police closed off the roads and told us there was acid in the tank.”
William Buchanan, 59, a former security guard at the site and whose home is 200 yards from the entrance, said: “The tank blew through the roof and landed in a field 50 metres away.
“It’s terrible somebody has lost their life. We’ve never had any trouble with the water treatment works in the 40 or 50 years it’s been here.”
The dead man had been working on the site just off the main Limavady Road and was believed to be close to the tank at the time of the accidental explosion.
It is understood an outside construction team was involved in work and it is thought the tank contained a large amount of sodium chloride and a mix of other chemicals.
An ambulance crew specialising in infection control was sent to the scene as a precaution, but their services were not required.
Sinn Féin MLA Mitchel McLaughlin called for a full inquiry into the accident.
SDLP leader Mark Durkan praised the professionalism of the emergency services.
The Foyle MP said: “This was obviously a very shocking and serious incident.”