A carbon monoxide leak at a junior hockey game in Lake Delton, Wis., sent 81 people to the hospital Saturday night.
The suspect in question is an ice resurfacing machine.
The employee who operates the propane-fueled machine believed it was performing properly on Saturday.
But Delton fire chief Darren Jorgenson told Associated Press that the machine "wasn't fully combusting the propane," and that the rink's ventilation system wasn't able to negate the issue.
Of the 81 people treated at the hospital for symptoms of dizziness, nausea, vomiting and fainting, some were taken by ambulance and others drove themselves.
"The good thing about this is a lot of people got sick all at once, so it was recognized quickly and the exposure was pretty limited," Matt Lazio, director of St. Clare's emergency department, told WISC-TV in Madison, Wis. "But this is a potentially fatal kind of poisoning."
Both of the rink's resurfacing machines will be inspected Monday.