Columbus Fire investigators don't know yet what started the fire yesterday morning at a north side apartment building. Dozens of residents were forced to evacuate. Ten were taken to area hospitals. Battalion Chief David Ringley says the fire began inside of a second floor apartment. A resident who lives there noticed smoke and when he came back inside to get some belongings, he left his door open to the hallway. Ringley says some fire doors in the hallway were also propped open. "The doors, the smoke barriers and fire doors that lead from the corridor into the stair tower, had been blocked open prior to the fire and that also allowed the fire and smoke to travel immediately into the stairwell, up that stairwell, got into the attic," explains Ringley. Ringley says the building which is more than 35 years old did not have to have a sprinkler system which he believes could have stopped the fire before it damaged the entire structure.