RIVERDALE (WBBM NEWSRADIO) -- Residents of five apartment units were displaced this morning by an extra alarm fire in south suburban Riverdale.According to Fire Chief Mick Smith, firefighters were called about 5 a.m. to a burning building at 14137 Tracy Ave. The fire began in an abandoned three-story building and spread to two next-door buildings.Smith said as many as 11 neighboring departments helped put out the fire and no one was injured in the blaze.He said damage to the next-door buildings was mostly the result of firefighters making holes in the roofs and breaking windows in order to determine how much the fire had spread. The chief said the fire only spread to the exteriors of the building.He said the cause is under investigation by the Mutual Aid Box Alarm System (MABAS) 24 investigations unit. He said the fire was extinguished by 9 a.m.