A carbon monoxide leak coming from a furnace at the Howard Johnson Hotel in South Portland sickened one guest and led to the building’s evacuation Monday afternoon, authorities said.

Rescue crews were first called to the hotel at 675 Main Street about noon Monday, where one person became ill, said South Portland Fire Department spokesman Lt. Robb Couture.

Inside the building, EMTs found a man who was found unconscious and vomiting in a stairwell. He was transported to an area hospital. Couture did not know the man’s condition.

Couture said emergency medical staff who first entered the building were alerted to the high levels of carbon monoxide by small portable detectors attached to the medical bag that each EMT carries.

The man who was sickened had been staying in a room directly above the hotel’s furnace room, Couture said, where the highest concentrations were detected.

At their peak, carbon monoxide levels in the building reached 400 parts-per-million, which can become life-threatening after about three hours of exposure.

By comparison, the federal Occupational Safety and Health Administration prohibits workers from being exposed to more than 50 parts-per-million during a eight-hour workday.

Couture said the hotel was equipped with carbon monoxide detectors but he didn’t know whether they had gone off.

A housekeeper at the hotel entered the man’s room and found a heavy toxic smell present, Barlow said.

Carbon monoxide by itself does not have a detectable odor, but other fumes that contain carbon monoxide can be detected by smell, such as vehicle exhaust or other byproducts of burning fossil fuels.

As of about 2:30 p.m., the hotel was still evacuated as crews attempted to control the source of the gas. Couture did not know how many people were displaced by the evacuation.

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