An employee arriving to work at a warehouse discovered a fire inside the building this morning. Firefighters were called to Heavy Duty Manufacturing at 4317 Clubview Drive, west of Engle Road, just before 6 a.m. Crews found the sprinkler system was holding the fire in check in the warehouse area of the building, the Fort Wayne Fire Department said. Firefighters extinguished the flames in about 20 minutes, the fire department said. The building was damaged by smoke and water and the fire mostly damaged items inside the building, the department said. No one was hurt fighting the fire. The blaze is under investigation.