The Regenstein Library was evacuated at 11 a.m. yesterday when one of the building’s air handling fans overheated and set off smoke alarms.

According to John Pitcher, library facilities manager for the building, the problem occurred on the north end of the second floor reading room inside one of the library’s 12 air handling units, which are used to circulate air throughout the building.

The malfunctioning unit, which supplies air to the second through fifth floors of the north half of the reading rooms, contains two fans that are driven by belts and a motor.

“One of the fan bearings ceased; and the drive belts, continuing to run at full speed, just got hotter and hotter until they started to smell and then to smoke a little,” Pitcher said in an e-mail sent to library staff explaining the incident. “The [air unit’s] smoke detector…picked up the smoke.”

Pitcher added that the malfunction could have been caused by usual equipment wear or a lack of lubrication.

Fire department officials responded to the alarms as students and staff evacuated the building at around 11 a.m.

Using the library’s enunciator panel, which displays parts of the building where smoke has been detected, fire officials spent approximately 20 minutes inspecting the problem before allowing people back into the building, according to Pitcher.

“There was no sign of any problems at first,” Pitcher said, adding that a slight burning smell lingered in the affected areas for some time after the fire department left.

Although the affected air unit’s second fan continues to function normally, Pitcher said that plans to repair the defective fan are yet to be determined.

“I do not yet know what the timetable may be on repairs to the immobilized fan,” Pitcher said. “Fortunately, the second fan [on the south end of the reading room] is still functional, so approximately half of the normal air can still be provided.”