Cal Poly students were evacuated from Muir Hall after a mattress caught fire Wednesday night.
The fire was first reported at 9:18 p.m.
Fire officials say they found a mattress on fire on the 2nd floor.
Three floors were evacuated due to the fire.
Cal Poly police used a fire extinguisher to put out the fire and used fans to clear out smoke from the building.
Students were let back into the hall soon after.
There is no word on how many students have been displaced.
The cause of the fire is under investigation.