The Coast Guard is investigating a tug fire that occurred yesterday south of Demopolis, Ala. on the Tombigbee Waterway. The Alabama Marine Police notified the coast guard Monday morning when the tug, Nonnie, pushing six empty hopper barges had caught on fire and was drifting south on the Tombigbee Waterway. The Coast Guard Cutter, Wedge, from Demopolis, an HU-25 Falcon jet from Aviation Training Center Mobile, and pollution response and investigation teams from Marine Safety Office Mobile were immediately dispatched to the scene. The vessel, owned and operated by Equipment Chartering Company inc. in bay St. Louis, Miss., was en route with the barges to a quarry on the Tennessee River from Back Bay Biloxi, Miss.