Altnagelvin Hospital fire report released
The fire service has released its preliminary report on the fire at Londonderry's Altnagelvin Hospital.
More than 100 patients were moved from their wards when the blaze was found on the roof of the tower block on Friday.
The investigation has indicated the fire started accidentally in a small room on the roof containing electrical equipment, near water storage tanks.
The fire service said the blaze "did not start in the fabric of the main building".
It added that it "was not caused by the fabric of the main building".
"We would like to thank like to thank the Western Trust for its cooperation which has enabled the fire investigators to produce their preliminary findings in such a short period of time," the report added.
On Tuesday, the Royal College of Nursing (RCN) said some staff at the hospital were concerned about the safety of the tower block where the fire broke out.
Three wards on the top floors of the unit are to be closed following the fire.
Seven wards at the hospital were evacuated on Friday night after a fire started.
It was the second fire at the premises in just over a fortnight.