Wisconsin –
“…fire departments were called to Cedar Creek Cinema on Sunday after several people fell ill and passed out after leaving the theater…When they got there, they treated five people for suspected carbon monoxide, or CO, poisoning; four of those people then were taken to an area hospital… In theater No. 1, they found levels of 683 parts per million…Officials traced the CO leak to a faulty HVAC system”
No mention of any CO detection onsite.
Carbon monoxide leads to a trip to the hospital in Marathon County | WXPR