Lindsay Thurber Comprehensive High School in Red Deer was evacauted on Monday, after what RCMP believe was pepper spray was in the ventilation system.
Red Deer fire crews responded to the high school at 2 p.m. after reports of oleoresin capsicum, the primary ingredient used in tear gas, was being sprayed into a bathroom vent.
Students were dismissed early while crews worked to clear the ventilation system.
RCMP say the investigation is still ongoing. People who have any information can call the Red Deer RCMP at 403-406-2200.
