According to Wikipedia:
“Carbon monoxide poisoning occurs after enough inhalation of carbon monoxide (CO). Carbon monoxide is a toxic gas, but, being colorless, odorless, tasteless, and initially non-irritating, it is very difficult for people to detect. Carbon monoxide is a product of incomplete combustion of organic matter due to insufficient oxygen supply to enable complete oxidation to carbon dioxide (CO2).
It is often produced in domestic or industrial settings by motor vehicles that run on gasoline, diesel, propane, methane, or other carbon-based fuels and tools, heaters, and cooking equipment that are powered by carbon-based fuels. Exposures at 100 ppm or greater can be dangerous to human health.”