King Middle School in Portland was evacuated and the students were sent home Friday morning after smoke from a rooftop ventilation unit entered the school through ductwork.

Principal Mike McCarthy said a squirrel climbed into a transformer just behind the school and caused it to blow, WCSH-TV reported. When Central Maine Power crews restored power, it caused a power surge in the school’s gym. Two electrical motors caught fire and smoke poured out of the ducts, according to the Portland TV station.

Students were led out of the Deering Avenue school into Deering Oaks park while the Fire Department made sure the school was safe. Students were allowed in to get their belongings and then sent home on school buses before lunch.

There were no reports of injuries.