A large banner was lit on fire and the smoke triggered the sprinkler system, Central Pierce Fire & Rescue spokesman Brian Levings said. A wrestling match was evacuated, Puyallup School District spokesman Brian Fox said.
Water from the sprinkler system was the primary concern, Levings said.
School will go on as scheduled, Fox said.
The extent of the damage from the fire and the water used to extinguish it is unknown.