LYNN – A fire official said investigators think an unextinguished cigarette sparked a fire Sunday night at a group home for disabled persons.Two firefighters also were reported injured in the blaze.Lynn District Fire Chief Arthur Richard said arson investigators believe that a resident’s cigarette may have sparked the two-alarm blaze at 99 North Common St. at around 8 p.m. Sunday. He said a resident reported smoking just before that time in the area where the flames originated.The property is a seven-unit residential home run by Bridgewell, a social-services agency for disabled persons.No residents were reported injured in the blaze, but two firefighters had minor injuries of a strained muscle and debris in an eye, respectively, Richard said.Richard said there was no estimate of the cost of damage to the home.