ST. CLOUD -- A tool left plugged in is what caused the fire at Apollo High School back in July according to authorities, which ended up causing between $5 and $6-million in damages.

The fire department was called to the school at about 7:00 p.m. on July 11th for an accidental construction-related fire in classroom B635. It was contained, however, several other classrooms and hallways in the building were damaged by smoke.

The tool, an "always-on" type of heating device used for fusing plastic piping together,  had ignited some flammable material on a utility cart in the classroom.  The fire sprinkler system was not operational because it was being worked on when the fire occurred.

Investigators found the fire to be accidental.

The fire caused Apollo students to attend classes on an every other day basis for several weeks, while repairs were made.