The fire at North Central High School on Wednesday morning has been ruled accidental by Spokane Fire investigators.
Just before 10 a.m., firefighters were called to the school for a report of smoke coming from the roof. Firefighters contained the fire within minutes.
The fire started in the west portion of the school that is currently under construction.
Three construction workers were assisted by EMTs for smoke inhalation. All three were taken to the hospital, one in an ambulance.
Spokane Fire investigators determined the fire was an accident, started by a torch igniting insulation.