TWO army officers have been quietly awarded the George Medal for helping to avert an explosion at one of Britain's biggest nuclear and chemical research facilities.

 Managers at the Atomic Energy Authority (AEA) plant at Harwell, Oxfordshire, are now facing charges under health and safety legislation over the incident, which required the two bomb disposal experts to risk their lives.

 Local schoolchildren were removed from the area and a blast perimeter was set up after an experiment went wrong inside a laboratory codenamed Building 220 at the secure plant in September 1999.

 Unstable "silver compounds" built up in the lab, which is close to partially decommissioned nuclear reactors, radiochemical laboratories and waste stores.

 Senior managers at the government-owned AEA called in army bomb experts. Captains Justin Priestley and Richard Baker, of the Royal Logistic Corps, spent 36 hours making the building safe.

 Their citation in December reveals that the explosive material was "an unstable explosive compound, liable to spontaneously detonate or explode if subjected to movement of any kind".

 To reduce the risk of explosion, nitric acid was introduced "very gradually" into the tank where silver compounds had formed. The citation notes the men's "great nerve, courage and total professionalism".

 The AEA called in the army because safety experts on the site advised bosses that the building could not "certainly" be made safe using the facilities provided at Harwell. After a detailed 18-month investigation, the Health and Safety Executive issued a prosecution against Atomic Energy Authority Technology, part of the AEA, which is also in court as the safety authority for the Harwell site.

 Last night a spokesman for the AEA expressed its "disappointment" that charges had been brought after 18 months. "We are still looking at the large bundles of evidence they have sent us and will proceed from there," she said. There was no nuclear material inside Building 220 at the time.

 At the time the AEA said little about the dangers of the explosion, other than to apologise to local people who were evacuated. In a brief statement, it promised: "For the moment, we will still retain prudent control over the facility, which has been of concern. The events of the past two days will be studied carefully and any lessons learnt will be fed into future plans."

 One Royal Logistic Corps officer said yesterday: "Everyone is very proud of what Justin and Richard did. They were working in a difficult place and would have been in deep trouble had there been an explosion. We understand there's a court case, which we don't know too much about, but clearly it's our job to make these things safe regardless."

 Harwell occupies about 500 acres behind a perimeter fence guarded by the site's own police force.

 About 2,000 people work on what are described as "science and engineering" experiments for customers around the world.