Carbon monoxide poisoning kills over 5,000 people per year in the US, mostly from suicide. CO is a colorless, odorless gas produced by incomplete combustion of carbon-containing fuels like gasoline. It is deadly because it binds to hemoglobin in red blood cells over 200 times more strongly than oxygen, preventing oxygen from being delivered to tissues. Symptoms range from headache and nausea at low levels to confusion, coma and death at high levels. Treatment focuses on removing the victim from the source of CO and administering high-concentration oxygen therapy to accelerate removal of CO from the bloodstream.