Bangor firefighters ventilated smoke from a section of the third floor of the Margaret Chase Smith Federal Building on Friday evening after a transformer malfunctioned.

A fire alarm alerted the fire department to the problem at 7:07 p.m. Part of Harlow Street in front of the federal building was blocked off while firefighters began laying down a water hose and began searching for the cause of the alarm, according to the fire department.

Firefighters entering the third floor first saw a light haze of smoke in the air and then saw more smoke coming from a louver door, said Assistant Fire Chief Vance Tripp. Opening the door, firefighters found they couldn’t see to the other side of the room from all the smoke, Tripp said.

The floor was ventilated with fans and the power on the floor shut off. Investigators found that a transfer box in the electrical room had malfunctioned.