Four people were treated for carbon monoxide poisoning Sunday morning after the heating, ventilation and air conditioning system at a fitness center in Scarborough apparently malfunctioned.

Deputy Fire Chief Wes Merritt said the firefighters were called at 7:20 a.m. to the Lifestyle Fitness Center on Pleasant Hill Road to investigate an odor in the building and reports of people feeling ill.

The fire department measured carbon monoxide levels at approximately 600 parts per million, according to Merritt. The HVAC system is the suspected cause, he said.

According to the Occupational Safety and Health Administration, carbon monoxide levels in the workplace are considered dangerous when levels average 50 parts per million over an eight-hour period.

Carbon monoxide is an odorless, colorless gas that can kill a person if levels are high enough.

Four people were treated at the scene Sunday and one of them was taken to Maine Medical Center for further treatment. The fire department shut down the building’s ventilation systems and ventilated the building. Another person who had gone home from the gym unaware of a problem sought medical help later, a police dispatcher said.

Lori Gaudreau, a front desk assistant at the gym, said the problem was discovered when several people complained of feeling lightheaded and sat down on the exercise equipment they were using. About 30 people were using the gym at the time.

Gaudreau said the building was evacuated and would remain closed for the day. Lifestyle Fitness Center will reopen on Monday at its regular hours, according to a message posted on its website.