LEWISTON — Spontaneous combustion caused the late-night fire Wednesday inside a Hill Mill business, a fire investigator said Thursday.

Fire Inspector Paul Ouellette said oily rags left stuffed in a bin caused a chemical reaction and burst into flames shortly before 11 p.m.

Fire crews went to the section of mill near Chestnut and Canal streets after smoke was reported pouring from the second floor of the building. When firefighters got inside, the fire was out, doused by an overhead sprinkler system.

Fire damage was limited to the area around the bin and an 8-foot section of wall, Ouellette said. However, water damage was extensive to the first and second floors as well as the basement.

“There’s more water damage than fire damage,” Ouellette said.

Only one sprinkler head activated but the volume of water was heavy. It soaked the floor on the second story and flooded the floors below.

All of the affected space is used by Action Screen Printing. Ouellette said a lot of the water damage was to products soaked on the first floor and in the basement. There was also damage to the electrical system and to an office on the first floor, Ouellette said.

When the blaze was first reported, firefighters came from all directions, fearful that the long mill building along the canal might go up in flames.

“Just hearing word of smoke pouring from a mill …” Ouellette said. “It could have been worse.”