Fond du Lac Fire/Rescue says the cause of a Monday morning duplex fire is under investigation, but doesn’t appear to be suspicious. At 7:12 a.m., crews were called to 220 6th St. They found fire in a second floor ceiling. The fire was contained and crews continued with salvage and overhaul. Fond du Lac Fire Chief Peter O’Leary says the fire caused “moderate damage” to the unit. O’Leary says the unit is uninhabitable. No one was hurt.