LYNN – Fire investigators are not ruling out an electrical malfunction as the cause of the Tuesday midday fire that left 15 West Lynn residents homeless.Fire Lt. David Legere and fellow investigators traced the fire’s origin to a first floor bedroom, but the collapse Wednesday of 9-11 Norton Street’s two upper floors onto the first floor severely hampered attempts to pinpoint the cause.”We could see where it started. One wall was much more damaged than the other,” Legere said, adding the fire’s cause has officially been labeled “undetermined.””We can’t rule out electrical,” he said, adding he will speak with tenants today in an effort to learn more about how the fire started.Firefighters converged on Norton Street at 12:11 p.m. Tuesday and residents alerted by a smoke alarm fled the building unharmed. Two firefighters were slightly injured battling the blaze.The building’s aluminum siding contained heat from the fire and kept it burning an hour after firefighters started fighting it. Legere said damage to the building was so extensive it will have to be torn down.Norton Street was the site of the third major fire since Nov. 2 when firefighters rescued an infant and five adults, including a partially conscious man, from the fire-engulfed third floor of 35 Orchard St.Firefighter Sean Curley pulled a man out of a burning house on Ford Street a day later and Scott Barnard, one of the firefighters involved in the Orchard Street rescue, helped Curley assist the badly burned man.Although no one was killed or seriously injured in Tuesday’s fire, Legere said the blaze left the Norton Street tenants homeless and without possessions days before Thanksgiving.He urged tenants to research the coverage and cost of apartment insurance as a way to potentially recoup some of the loss inflicted by a fire.”Ninety-nine percent of the fires we respond to are apartments,” he said.