The Edgartown town hall was closed Friday afternoon and through yesterday after carbon monoxide was detected in the building.

The town hall was promptly closed at 2 p.m. Friday after fire department chief Peter Shemeth discovered the noxious fumes. The building was ventilated over the weekend and remained closed yesterday to town employees, though no carbon monoxide showed up on tests Monday morning.

The leak of the poisonous, odorless gas was discovered on a fluke, town administrator Pamela Dolby said.

“On Friday someone noticed a funny smell in the town hall and when fire chief came over with his detectors he detected CO,” she said.

Representatives from Nauset Environmental Services flew in yesterday morning to check levels and will prepare a checklist for the town administrator. But for now, Mrs. Dolby said, no one knows the cause of Friday’s leak. She added that a common cause for such a leak can be a backfired furnace, but the town hall boiler is not turned on during the summer months.

And the origin of the odor that prompted the call to Mr. Shemeth also has not been determined. “The smell was unrelated, we don’t know what that was. We don’t know a lot of things at the moment,” Mrs. Dolby said.

Meanwhile six carbon monoxide detectors have been installed and staff are expected to be back in the town hall today.

The leak is the latest in a string of mishaps to do with the building. For much of the spring the selectmen’s meeting room was taken over by library staff running a makeshift operation out of the ground floor room, escaping oily vapor damage in their own building following a furnace puff-back incident.

Shortly after the library vacated the premises a little over two months ago, chunks of the third floor town hall ceiling began falling down. The 100-year-old horsehair plaster had decayed with age, and equipment and staff were evacuated from the top floors. Since then many departments have been working in makeshift office space and without natural light. Engineers have determined the ceiling needs to be replaced; no completion date is currently available for the repairs.

“We have had a bad run,” Mrs. Dolby said yesterday. “We hope eventually to be on an uphill trend.”