A fire destroyed one classroom and damaged two others at Isabella High School this weekend.

Principal Ricky Porter said an air-conditioning unit caught fire in the K-3 building, creating smoke and soot damage throughout the structure.

He said a custodian discovered the thick black soot covering the rooms early Monday at approximately 7 a.m.

Porter said a teacher went to the school Saturday evening and discovered the high school’s smoke alarms sounding off. The teacher called a custodian who then came to the school to turn off the alarms after the two did not see or smell any signs of a fire in the high school.

“We don’t know exactly when it happened,” Porter said. “We are extremely lucky it was contained within two classrooms and an adjoining bathroom. It could have been really bad.”

The air-conditioning unit was plugged into the wall but was not turned on.

Porter said the school’s reading resource room was “completely charred.”

Wayne Howell, the IHS maintenance supervisor, will oversee the cleanup after an insurance company inspects the damage.

The fire apparently burned itself out in the room, according to Porter. The unit was under a window, which did not bust open. Porter said had the window broken and allowed more oxygen into the room, the fire could have spread and damaged the rest of the building.

The air-conditioner that caught fire was a new unit that had been installed this past school year.

Porter said the school will not have to rebuild any rooms, but the reading resource and the adjoining bathroom will be gutted and renovated.

“Not one book in it can be saved,” he said.

IHS suffered another fire in the mid-1980s that burned the entire school down when it was a wooden structure. That was also an electrical fire due to an air conditioner malfunction.