A fire at a major hospital in Northern Ireland did not reach areas containing patients, the health minister has said.
Most of the disruption at Altnagelvin Hospital was caused after water pipes were melted by the heat of the blaze at a roof-top plant room, Edwin Poots added.
Seven wards were evacuated on Friday night.
Mr Poots said: "All indications would suggest that the cause of the fire was accidental and not related to the fabric of the building itself. The site of the fire was in a small plant room and at no time did the fire itself penetrate the roof into areas accommodating patients or staff.
"The majority of the disruption was caused by very significant water ingress emanating from pipes adjacent to the fire in the plant room which had melted with the heat of the fire."
He told MLAs the emergency plans of the Western Health Trust proved hugely effective and the evacuation of patients and staff was managed in a professional manner without injury to anyone.
SDLP MLA Pat Ramsey has called for an immediate inspection. Mr Ramsey also claimed repeated warnings about health and safety at the building may not have been acted upon. "It is imperative, absolutely essential, that the department of health or other bodies who have a jurisdiction in this - health and safety - carry out an inspection of the tower block as it is commonly known," he said.
The minister and senior health service managers have said the hospital is safe. Up to 120 patients had to be moved from affected wards on Friday night. The operation was treated as a major incident by the hospital and Northern Ireland Ambulance Service. Almost 50 firefighters in 11 appliances battled the blaze.
The latest incident followed an electrical fire on November 6 which led to 20 patients being moved to other areas of the hospital.
Some surgeries have been cancelled but some went ahead. An investigation into the cause of the blaze has been launched.