A Kent building firm has been fined after a worker was seriously injured when an excavation collapsed on top of him at exclusive girls' school Benenden.

The BBS Construction Ltd employee, who doesn't want to be named, smashed his right hip when he was buried up to his waist in earth and rubble in the incident at the school in on January 18 2011.

He was unable to work for several months.

It came as work was under way to build a new multi-storey science block.

The injured worker, then aged 44, was excavating a basement to support the new building.

But concrete to fix the posts for a supporting wall had been overpoured and the excess had to be chipped away with a manually-operated hydraulic breaker.

It was this work that triggered the collapse.

A quick-thinking excavator driver managed to stem the flow of earth by placing the bucket of his machine into the face of the weakened earth, but his colleague was still caught and trapped. Another worker managed to jump clear.

The Health and Safety Executive (HSE) concluded the risks of manually breaking the excess concrete were not properly assessed by the Tovil-based firm.

“The injured worker was dangerously exposed, and could have been more seriously hurt, or possibly even killed, but for the instinctive action of his colleague in using the excavator to shield him" - HSE inspector Kevin Golding

An inspector also found that earlier in the project a waste water drain had been installed by BBS less than half-a-metre from the face of the basement excavation at a depth of two metres.

Magistrates were told that this may have weakened the earth around the basement and made it more susceptible to collapse.

BBS Construction Ltd, of Church Street, was fined £8,000 and ordered to pay £10,536 in costs after pleading guilty to a single breach of the Construction (Design and Management) Regulations 2007.

After the hearing HSE Inspector Kevin Golding said: "This prosecution demonstrates the need to properly plan all aspects of excavation activity, and to reassess systems and methods of work if a problem arises - as happened here when the concrete for the supporting posts was overpoured.

“The retaining wall system itself was sound, but the decision to manually chip away the excess was flawed.

“The injured worker was dangerously exposed, and could have been more seriously hurt, or possibly even killed, but for the instinctive action of his colleague in using the excavator to shield him.

“BBS Construction Ltd could and should have done more to prevent workers from needing to work so close to the unsupported vertical face of a four metre deep excavation.”