Bostock Library was evacuated twice early Thursday afternoon after a fifth-floor air handling unit overheated and began emitting smoke.
No one was hurt in the incident, and no books or property were damaged, said Ashley Jackson, building manager for Perkins Library.
Phyllis Cooper, police major for the Duke University Police Department, added that nobody was ever in danger of being hurt.
Library workers said they smelled smoke in the basement of the building, which just opened in October 2005.
When the alarm went off the first time, Jackson said police and fire officials believed the smoke was coming from an electrical short in the elevator mechanical room.
After finding no fire, people were allowed to return into the building, Jackson said.
Cooper said about 20 minutes later the smoke detector alarms were tripped for a second time.
After inspecting the building again, the source of the smoke was determined to be a belt in a fifth-floor air handling unit.
Smoke spread through the building in the airshafts and concentrated in the elevator electrical room in the basement.
Jackson said the belts in the units are not standard across campus and that this kind of event is rare.
The Durham Fire Department responded to the call with at least three fire trucks and about a dozen officers. Fire Department official T. W. Reams said the division was responding to a call for a construction fire.
"Normally Duke police come and check the building," Jackson said, noting that a large majority of fire alarms turn out to be false alarms. "Somehow the alarm was turned off, and [the belt] didn't get checked."
Cooper said officers first look on the fire panel to locate the area that is in trouble. Officials then check the area in question for the source of what triggered the fire alarm.
"There's a lot of times when the fire alarms will go off and they look and they can't find anything," Cooper said. "If there isn't any smoke or fire or anything obvious to show the officers what's going on, the fire department will clear."
The air handling units bring in fresh air and discharge stale air. Jackson said Bostock has four units and was designed to operate with one or two functioning units.
"The air doesn't circulate as quickly, but it does circulate and move," he said, adding that the broken unit should be fixed Friday.
Cindy Shurling, a second-year graduate student in the Nicholas School of Earth and Ocean Sciences, was one of about 75 people waiting outside for the building to reopen.
"I am a little bored," she said. "I imagine some people were working on things that were time-sensitive."
Lenore Ramm, an applications specialist for the Center for Instructional Technology, said she could smell the smoke in the stairwell.
Ramm, who was in a wheelchair, said she had to wait on the second floor for help before evacuating the building.
She was eventually evacuated with help from her CIT co-workers through a connection to Perkins Library.
"I wasn't really scared because Bostock is full of sprinklers," she said. "According to Fire Safety, nobody has ever died in a building with sprinklers. As long as I could see a sprinkler, I was probably in good shape."
"At least it's nice out," she added. "Better being evacuated when it's 70 degrees outside."
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