A Harvard Square bank was evacuated for 25 minutes Monday afternoon while Cambridge firefighters searched for the source of smoke seeping from a ventilator.

Officials determined that the building was not ablaze and that the smoke resulted from dust being circulated through the heating, ventilation and air conditioning ducts, said Cambridge Fire Department Deputy Joel Reardon.

Workers within the Cambridge Savings Bank pulled a fire alarm at 2:42 p.m., alerting the Cambridge Fire Department dispatch center on Broadway St., according to fire officials.

After arriving at the scene, firefighters evacuated the three-story building, Reardon said.

Maintenance employees had been working in the ducts earlier this week and had not completely sealed the system's gaskets, officials said.

"Dust was introduced into the duct work," said a fire department official, speaking on condition of anonymity.

"It was then sprayed throughout the building, giving the appearance of smoke in the duct work," the official said.

This was the first time that the Cambridge Savings Bank has ever alerted the fire department to a suspected blaze, employees said. After the alarm, the bank resumed normal business.

Bank employees said they waited outside while firefighters conducted a search of the building, which suffered no structural damages.

"It's standard procedure to evacuate [buildings] when we receive calls of distress," Reardon said.