Authorities have determined that a fire that killed one resident at a Philadelphia boardinghouse and seriously injured two early yesterday was deliberately set by a resident.

Flames forced the evacuation of 11 residents from the Pace Personal Care Boarding Home, a four-story brownstone in the 1800 block of Green Street in the Spring Garden section. It housed physically and mentally challenged residents.

A resident set the fire at 4 a.m. after arguing with another resident, Philadelphia Fire Commissioner Lloyd Ayers said. Homicide detectives are investigating, he said.

"I'm not sure what she'll be charged with, but we do expect there will be charges," Ayers said, declining to identify the suspect.

A neighbor and a Red Cross official identified the deceased as Charles Johnson. The two injured residents were taken to Temple and Hahnemann University Hospitals. Officials there would not release their names or conditions.

The blaze, which was brought under control within a half-hour, started on the second floor and trapped several people on the third floor, including Johnson, Ayers said.

The home had no obvious housing or fire-code violations, he said, adding that officials from the city's Department of Licenses and Inspections would conduct a more thorough evaluation this week.

"I saw the alarm system, which worked. They did have signs and a fire escape," Ayers said. "It's just a sad thing."

On a visit to his fire-damaged property yesterday, owner Nathanial Pace declined to be interviewed, saying: "I have to take care of my people."

The brownstone, which he owns with his mother, Mattie, has a prominent "For Sale" sign on it. Yesterday, the once-handsome building, which features marble columns and elaborate stonework around the windows, was ringed by yellow police tape. Charred bedsprings, clothes and broken furniture littered the sidewalk.

At Fairmount Pharmacy, across from the boardinghouse, owner Bob Woltjen recalled Johnson as a friendly, daily visitor.

"He used to sit in the store and drink a soda every day," Woltjen said. "He was a nice guy."

The eight displaced residents were given food and clothing at a Salvation Army facility on Brown Street. The Red Cross, working with Pace, found new shelters for them. Five were placed at three boardinghouses in Philadelphia, and three were taken to an assisted-living facility in Reading that Pace owns, Red Cross volunteer Marjorie Nightingale said.