DULUTH  — High carbon monoxide levels sickened several people and caused an evacuation at an ice arena in Duluth.

Fire officials continue to investigate the source of what they say were “dangerously high” CO levels at the Fryberger Arena Wednesday night. Emergency responders evacuated about 30 people. Elevated blood levels of carbon monoxide were found in eight people who complained of headaches and nausea. Only one person was taken to the hospital.

Duluth fire officials said early today that the suspected causes of the carbon monoxide are the aging heating system and propane-powered Zamboni, which resurfaces the ice.

Hockey teams that had played earlier in the evening were notified of the problem and urged to go to the hospital if they experienced any symptoms. One person was transported to the ER from his home by ambulance.