Updated: 10/14/10 4:58 p.m.

CHICAGO (CBS) – A Wednesday night fire in the rectory of an abandoned church in the South Side Grand Crossing neighborhood which left a firefighter injured was caused by an open flame, fire officials said Thursday.

The fire started about 7:45 p.m. in the Imani House, the rectory for the unoccupied St. Laurence Church at 1300 E. 72nd St., Fire Media Affairs Director Larry Langford said.

The blaze, which was elevated to a second alarm, was contained to the second floor and attic area of the large 2 1/2-story brick building, Langford said. The brick building is connected to the church through a breezeway, but the blaze did not travel through the walkway and the abandoned church is unaffected by the fire.

About 80 firefighters were called to the scene under a 2-11 alarm for the fire, in part to ensure the fire did not spread to the church building.The fire was extinguished at 9:40 p.m., Langford said.

One firefighter was taken in good condition to Mercy Hospital and Medical Center with lacerations, Langford said.

Officials on Thursday determined the cause of the fire was “incendiary” in nature, meaning it was caused by an open flame source, Fire Media Affairs Director Larry Langford said.

There was nobody in the rectory, which appeared to be abandoned and had a “No Trespassing” sign, and nobody else was injured.

Jacqueline Childers lived in the rectory with her stepfather as caretakers until they moved out three weeks ago. She speculated there was criminal activity going on when the blaze began.

“Probably somebody in there doing drugs (or) set a garbage can on fire to keep warm,” she told CBS 2’s Mike Parker.

Police on Thursday said the fire is being investigated as non-criminal in nature, although the investigation continues.

St. Laurence Church was closed by the Archdiocese of Chicago in 2002; both it and the rectory were built in 1911, according to the Landmarks Preservation Council of Illinois.

The Sun-Times Media Wire contributed to this report.

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