IE was washing the slope at the 2200'. EE had the fire hose on top of shoulder and was transitioning it to under EE's arm. The fire nozzle caught EE's bibs or hit EE's hip causing it to turn on. The IE lost balance and fell to the ground striking EE's head on the floor. Witness thought EE was knocked unconscious but IE didn't believe EE was. IE was diagnosed with a concussion.