We are working with our partners to try to understand exactly what happened in the incident

Brian James, South Durham Health Care NHS Trust

Bosses at South Durham Health Care NHS Trust say the workers were discharged shortly after the incident, but the planned 8 April opening of the outpatient department has been delayed while safety checks are carried out.

The HSE investigation is the latest setback for the �67m Bishop Auckland project.

Even before its completion a merger with the new University Hospital of North Durham, also a PFI hospital, was considered amid fears the future health needs of the area could not be met.

Electrical system

Director of Planning and Operations for the Trust, Brian James, says it is not safe to open any part of the hospital until it is clear what went wrong.

He said: "Obviously until we get the Health and Safety Executive report we are not in a position to fully understand the nature of what caused the incident.

"Until we have established that, we would clearly be unhappy without further reassurance about the safety of the hospital's electrical distribution system.

University Hospital Durham: Also under fire

"We are working with our partners to try to understand exactly what happened in the incident and to make sure the electricity supply system is safe and robust for the future.

"Until we understand how that is going to be achieved, clearly this is going to cause a slight delay to opening."

Head of health for the public sector union Unison, Liz Twist, said: "Yet again we have another example of a hospital built under PFI showing problems right from the start."

Trust chief executive John Saxby said the cause of incident, which happened in March, but has only now come to light, would not be known until HSE inspectors had completed their report.

Risk assessment

He said this was only the second incident to have hit the project.

He said the first potentially-harmful accident was when a piece of wood fell and pierced a ceiling. No-one was injured.

Managers are now waiting for a risk assessment to be carried out by Criterion Healthcare, a consortium of private companies in charge of the PFI scheme.

The country's first PFI hospital in Cumbria has also come in for criticism after a cancer specialist claimed crowded wards were a danger to patients.

Dy Paul Dyson said it was too difficult to wheel in resuscitation equipment because the beds at the Cumberland Infirmary in Carlisle are too close together.