One man has been killed and several wounded following a gas cylinder explosion at the Hertfordshire Data Centre construction site, north of London.
The body of one man was discovered hours after the gas explosion and one other man is described as being in critical condition. One man is in a critical condition in hospital and seven others were described as walking wounded.
The building suffered structural damage.
In an interview with the Welwyn and Hatfield Times, a commander from the local fire service said a cylinder of Argonite caused the fatal blast.
Red Watch commander Paul Enever told the WHT the scene inside the Hertfordshire Data Centre on the Mundells Industrial Estate was "complete devastation."
Mr Enever said Argonite is used as a fire suppressant. He said: "It is usually used in rooms used with computer equipment or data storage. The gas can then be released in the event of a fire. It's not inherently dangerous. But the cylinder yesterday was about 5ft to 6ft tall and made of steel."

He said: "We don't know the details yet but they had been using the cylinders and there has been an accident. It's resulted in one or a number of the cylinders releasing their gas under high pressure. It was complete devastation." Mr Enever used the analogy of a balloon being blown up and then let off to describe the accident. He said the 80kg cylinder would have bounced around the room hitting anything it came into contact with.