Fire Marshal Tom Brown said it appeared two children, ages 4 and 5, were playing with matches in a play area on the second floor. "That's not unusual," he said.
Brown said there didn't appear to be any working smoke detectors.
"It certainly would have made a difference," he said.
Brown said the children won't be charged with a crime because they don't meet the state minimum age of seven years.
Brown said in apartments with three units or fewer, it's the responsibility of the tenants to have working fire detectors. Brown said fire companies will install smoke detectors free of charge.
A small white dog with a broken leg named Snoopy was missing from 616 George St. and presumed escaped. The residents in 616 weren't home at the time of the fire.
Betty Socks, who lives in 618 George St., said she, her fiance Hank Shumaker and two friends were in the living room when they heard a neighbor hollering at them to get out of the house.
"If the neighbors hadn't seen it it would have burned down," she said.
Socks said she didn't have any insurance.
Brown said the Red Cross had been contacted to help out the two families dislocated by the fire.
The duplex is owned by Dawn Scibilia.
Firefighters came out of the house drenched with sweat and were cooled down with wet cloths dipped in a mini-swimming pool.
"It was just unbelievably hot up there," Pile said.