Fire erupted in a small condominium complex on Brentwood Avenue Tuesday morning, inflicting serious damage to the upper floor and attic of one unit.

Flames were visible at the rear of the structure when the blaze was reported about 9:45 a.m. to Fairfield firefighters by an off-duty Bridgeport mounted police officer, who was passing by the complex at 157 Brentwood Ave. The units in the four-unit complex were unoccupied at the time, except for some pets that were uninjured, firefighters told the Fairfield Citizen.

Firefighters quickly brought the fire under control; there were no reported injuries among the fire crews although one firefighter was transported to Bridgeport Hospital for treatment of dehydration.

"The initial attack of the first company was critical in saving most of the condo," said Fire Chief Richard Felner, who was on the scene. "Our personnel did an outstanding job."

The fire damage was confined to the third floor and attic area of an end unit, although there was residual smoke damage in a neighboring unit.

Fire Marshal William Kessler said the fire is under investigation, but appears to have started on the third floor in a rear room used as an office.