As crews were finishing up with todays training, Milton was alerted for possible CO in a structure, at the Allen Harim Food Plant in Harbeson. Engine 85-4, Rescue 85, and Ambulance 85 responded within a minute of dispatch. Engine 4 arrived first and met with plant officials to investigate the complaint. Rescue 85 arrived and their crews assisted the crew of Engine 4 with the investigation. Crews checked the entire plant and turned the scene over to plant officials. Units cleared and returned. Units responding, Engine 85-4, Rescue 85, A-85, Engine 85-5, DSFP.