Firefighters investigated small fire in the ventilation system at Fibercorr Mills, LLC Friday morning on the city’s northwest side. Firefighters arrived shortly after 6:30 a.m. to the corrugated paper mill at 670 17th St. NW. The fire was extinguished by the company’s sprinkler system prior to their arrival. Capt. Chris Schweier said the fire was still smouldering and firefighters checked the building for hot spots. Paper making is a messy process that generates a lot of dust and paper particles, he said. The dust collected in the ventilation system and caught fire after being exposed to heat. No injuries were reported, Schweier said.