Emergency responders were called to a South Asheville, N.C., strip mall around 9 p.m. Monday after multiple detectors sounded an alarm warning of high carbon monoxide levels.
Upon arrival, the Asheville Fire Department followed the increasing levels of the gas through the building to an Anytime Fitness, which is believed to be the source of the gas.
While there were no recorded injuries, 12 people were evacuated from the gym.
One patron told ABC News, "It's usually quiet. Don't know what to think about it. Really. Usually, I come over here and there's nothing going on. So, I pull in and see all these red lights. So, I guess I'm going home.”
The cause of the unsafe carbon monoxide levels is still under investigation by local authorities.