Unseasonable snow has kept you and your partner huddled in the tent for almost 24 hours. Hunger and thirst led to firing up the stove under the vestibule, but the wind tempted you into moving it inside. Several cups of tea and a freeze-dried dinner later, your mild headache has reached throbbing proportions, and you're thinking your culinary efforts might resurface on the tent floor. Your partner, complaining of head pain earlier, now seems irritable and increasingly confused. Stoves burn inefficiently in an enclosed space with inadequate oxygen.
Higher altitudes increase the chance of poor combustion.
Carbon monoxide is invisible, odorless, and tasteless, and once inhaled, it enters the blood of the victim where it is about 200 times more bondable to the hemoglobin of red blood cells. Hemoglobin normally carries oxygen out to the cells of the body. With CO attached, hemoglobin can't carry as much oxygen and can't release what is attached as efficiently. The brain and heart, the organs most in need of a constant flow of oxygen, begin to deteriorate. CO poisoning accounts for approximately one-half the poison deaths in the United States every year and creates one of the few serious poison threats on wilderness ventures.