“Firefighters were called to the meetinghouse at 650 E. Stadium Ave. in Provo just after 11 a.m. Sunday. They later learned that a boiler problem had sent a buildup of carbon monoxide into the church…Firefighters measured the carbon monoxide in the air at the church at 400 to 500 ppm…Of the 60 people treated, 24 underwent hyperbaric treatment, a therapy where people with carbon monoxide poisoning are put in a chamber filled with pure oxygen”

CO poisoning at Provo church serves as reminder of cold weather risks – Deseret News

https://kutv.com/news/local/at-least-60-sickened-by-carbon-monoxide-at-lds-church-some-may-suffer-long-term