A Union Square building damaged by fire last week may be a total loss, according to a Fire Department official. Reports following the fire at Fiesta Bakery at 314 and 316 Somerville Ave. on Jan. 2 estimated about $35,000 in damage, but that figure is expected to rise, Fire Department Lieutenant Derek Nolan said. “The building may be a total loss,” he said. One firefighter was hospitalized with injuries after the fire, but was discharged a day later and is expected to make a full recovery, Nolan said. The cause of the fire, which started in the basement, is undetermined.