ATTLEBORO - Several city workers were sent home early Thursday after elevated levels of carbon monoxide were detected in their office, Mayor Kevin Dumas said.

A malfunctioning furnace was responsible, he said.

The workers, employees of the building inspection department housed in the basement of the old post office, were permitted to leave their jobs in the early afternoon because of the odorless and potentially deadly gas. No one was reported to be injured or ill.

Building Inspector Doug Semple said the draft plate in the exhaust damper of the building's boiler got stuck, causing carbon monoxide to build up in the work area.

He said the gas did not reach dangerous levels and the problem was fixed. The fire department detected the higher than normal carbon monoxide level when it was called for an odor problem that was also related to the furnace.

The source of the bad odor was not dangerous, officials said.

The office was ventilated with fans.

Dumas said the office will be open as usual today. "Everything will be back to normal," he said.