Authorities say a pool heater is to blame for a carbon monoxide leak that sickened eight people in southeast Missouri.

The leak happened Tuesday at Ozark Fitness in Poplar Bluff. The Poplar Bluff Daily American Republic reports that firefighters found dangerously high carbon monoxide levels at the business.

None of the illnesses were serious. The business was closed for about five hours while ventilation fans helped clear the building of carbon monoxide.