Firefighters were called to a freak outbreak at Menzieshill High School in Dundee.
A neighbour contacted the emergency service after seeing smoke billowing from the roof of the building in Yarrow Terrace at about 3.30pm yesterday.
It was first thought the cause may be suspicious in that a culprit had scaled scaffolding erected around sections of the three-storey building which is undergoing roof repairs.
Work on the project had been suspended for some time owing to the bad weather and no workmen had any reason to be in the vicinity over the weekend.
Once they reached the affected section, firefighters saw that the outbreak had been caused by unusual circumstances.
Station manager Ron Massie explained that an extractor fan set in a window had malfunctioned and caught fire and had ignited roofing materials leaning against it on the other side.
“That part of the building is on different levels and there is a classroom that looks out on to a section of roof,” he explained.
“The extractor fan had gone on fire, but there was roofing felt and insulation material stacked against the window outside, and the fire spread to it. It was an unusual way for a fire to happen.
“At first we thought someone had got on to the roof and maybe started it deliberately but that wasn’t the case at all.”
Mr Massie said the outbreak was quickly extinguished by two units from the Macalpine Road fire station.
One was a resident unit and the other was on stand-by from Forfar as the Macalpine station had units dealing with flooding elsewhere in Tayside.
The classroom was smoke-logged but the outbreak was otherwise contained.
He said the incident would not prevent Menzieshill High from opening today.