A senior citizen was killed in a fire that broke out in the air-conditioner at his home in Madambakkam past midnight on Thursday. Police said 76-year old Balasubramaniam and his relatives were sleeping on the ground floor of their home on Shantiniketan Colony Second Street, when the fire broke out from the AC. It engulfed the bedroom damaging electronic gadgets and while the rest of the relatives rushed out, Balasubramaniam entered the house again to fetch the car keys. He fell unconscious and was rushed to a private hospital, where he was declared dead due to suffocation, police said. Selaiyur police are investigating.