Florida –
“Firefighters determined a faulty propane-powered floor cleaner was the source of the gas. When turned on, the machine emitted carbon monoxide levels at 1400 parts per million. The U.S. National Ambient Air Quality Standards for outdoor air is 9 parts per million. Average homes are between 0.5 and 5 parts per million.”

Carbon monoxide poisons 7 people at Ocala business (wcjb.com)