Students safely were evacuated when a fire broke out Monday afternoon inside Upper Perkiomen High School in Montgomery County.
At about 1:45 p.m., an electric motor overheated in the high school's shop area, setting off smoke detectors and fire alarms.
Heavy smoke was reported inside the school.
Students were evaluated to the school's stadium, then dismissed for the day.
School officials said school buses were running about 45 minutes late.
The high school is at Walt Road and Montgomery Avenue in Red Hill.
Firefighters from numerous departments responded to what was reported as a two-alarm fire.
The school was declared safe and has reopened, but all Monday after-school activities were canceled.
High school students should report to school at regular time Tuesday morning.