Carbon monoxide poisoning is a common form of environmental poisoning, caused by inhaling large quantities of incomplete combustion by-products, typically from a gasoline powered engine. However, it can occur wherever wood, oil or natural gas is burned with insufficient oxygen in an area without proper ventilation.
In the blood, hemoglobin binds to oxygen where it is prevalent, and carbon dioxide when it is prevalent. This allows oxygen to be taken from the lungs to the cells and allows carbon dioxide to be taken from the cells to the lungs.
However, carbon monoxide binds to hemoglobin better than both oxygen and carbon dioxide, and when it binds it takes a very high concentration of another gas to dislodge it. Since, for example, cigarette smoke contains carbon monoxide, breathing in the smoke will temporarily disable the hemoglobin. For smokers, the amount of carbon monoxide inhaled is minimal, but in enclosed spaces where combustion is taking place (e.g. a garage), the carbon monoxide builds up to fatal levels rather quickly.
One of the unfortunate effects of carbon monoxide is, unlike other poisonous gases, the symptoms come on imperceptibility and without any respiratory distress. Often, a victim is unaware anything is amiss until concentrations are close to what causes unconsciousness.
Treatment is to put the patient on pure oxygen until their oxygenation level improves. Depending on the dose, this can take hours as the carbon monoxide slowly works its way out of the system.