Safe levels of carbon monoxide are less than 70 parts per million, or 70 ppm, as identified by the U.S. Consumer Product Safety Commission. At levels between 70 and 150 ppm, people can experience fatigue, headache and nausea. Exposure to higher levels can cause unconsciousness and death.
The Centers for Disease Control and Prevention warns that unintentional carbon monoxide poisoning causes more than 20,000 emergency department visits, 4,000 hospitalizations and 400 deaths annually. People aged 65 and older, people with respiratory problems or heart disease, unborn babies and infants have the greatest risk of succumbing to the effects of carbon monoxide.