Northampton, MA – Firefighters evacuated a 16-unit apartment building at 180 Earle St. after detecting high levels of carbon monoxide Tuesday night.

The Fire Department was called to the building after its carbon monoxide detectors were activated about 8:20 p.m. Firefighters had natural gas shut off while emergency responders investigated and ventilated the building.

The building containing single-room occupancy units is owned by HAP Inc., which is based in Springfield. Many of the tenants stood outside in the cold waiting to get back into their units.

Northampton Deputy Fire Chief David Gagne said firefighters had a reading of 50 parts per million of carbon monoxide when they entered the building, a figure that dropped to 8 or 9 parts per million by about 8:40 p.m. Tenants were allowed back into the building around 8:55 p.m. when carbon monoxide levels dropped to about 2 parts per million, Gagne said.

He added that firefighters were checking appliances in the building, the heating system and dryer vents to determine the source of the carbon monoxide. “Could be a chimney blockage,” Gagne said at the scene.

He said Columbia Gas of Massachusetts was called to the scene as firefighters continued to check rooms and determined that no tenants showed any symptoms of carbon monoxide exposure.

“We left it with the gas company to try to figure out where the issue was,” Gagne said.