STILLWATER, Okla. (AP) _ Fire damaged the Gallagher-Iba Arena on the Oklahoma State University campus today.

The blaze began around 9:30 a.m. in a first floor electrical and mechanical room and spread to the second floor, where offices are located, Stillwater Fire Chief Larry Mullikin said. No one was injured.

The blaze did not reach the arena floor and did not affect the building's structural integrity, he said.

``We had quite a bit of heavy smoke inside, but we were able to confine the fire,'' Mullikin said.

The damage occurred in the southwest corner of the arena, which is undergoing a $40 million expansion. Mullikin said the sprinkler system had been disconnected during the construction without notification to fire officials.

``When we charged the sprinkler system, it just flooded the basement,'' he said.

Mullikin did not have damage estimates and said the state fire marshal's office is investigating.