Other: Carbon Monoxide Poisoning

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Other: Carbon Monoxide Poisoning

Causes and Symptoms
The Future
For more information


Carbon monoxide (CO) poisoning is a potentially fatal condition caused by breathing carbon monoxide, which is a colorless and odorless gas produced by the incomplete burning of natural gas, propane, gasoline, kerosene, coal, wood, smoking tobacco, other plant matter, or any other fuel containing carbon. It can also result from breathing the vapors of methylene chloride, a chemical found in paint thinners, degreasers, and solvents.


Carbon monoxide (CO) is a substance that has always been present in Earth's atmosphere in low concentrations; it can be produced by natural processes as well as by human activity. Most of the naturally occurring CO in the atmosphere comes from volcanic eruptions; however, some is also generated by wildfires. The human body itself produces small quantities of CO as a byproduct of certain metabolic processes.

Carbon monoxide poisoning occurs when fuels or other materials containing carbon are burned without adequate ventilation. The gas is hard to detect without special equipment because it is colorless, odorless, and tasteless. People may not realize they have been exposed until they begin to feel dizzy or headachy, or have trouble breathing.

At concentrations of CO as low as 100 parts per million (ppm), people who are otherwise healthy will feel fatigued, and people with heart conditions will experience chest pains. At higher concentrations, people begin to experience disturbances of vision, loss of memory, nausea, vomiting, confusion, and eventually loss of consciousness and death.

Carbon monoxide has a history as a method of deliberate killing; it was used by the Nazis before and during World War II (1939–1945) to kill people with mental and physical disabilities and some concentration camp prisoners. As of 2008, Illinois, North Carolina, and some other states still permit the use of carbon monoxide chambers to kill unwanted pets.

The Environmental Protection Agency (EPA) stipulates that outdoor concentrations of CO should be no higher than 9 parts per million

(ppm) for periods of eight hours or longer, or 35 parts per million for one hour. There are no official standards for indoor air. For purposes of comparison, here are some typical levels of carbon monoxide in various locations:

  • 0.1 ppm: Normal level of CO in Earth's atmosphere.
  • 0.5–5 ppm: Average level in homes without gas stoves.
  • 5–15 ppm: Average level in homes with properly installed gas stoves.
  • 200 ppm: Average level of automobile exhaust in downtown Mexico City.
  • 5,000 ppm: Concentration in the chimney of a fireplace when a wood fire is burning.
  • 7,000 ppm: Undiluted exhaust from an automobile without a catalytic converter.
  • 30,000 ppm: Undiluted cigarette smoke.


The CDC estimates that there are about 2,500 deaths each year in the United States attributed to CO poisoning. About 2,000 of these are suicides, a few are murders, and 500 are unintentional. The highest rates of unintentional poisonings are in cold or mountainous parts of the

country. Many of the unintentional deaths involve automobile exhaust; other leading causes of unintentional deaths are coal, wood, or kerosene stoves and fireplaces; burning of natural gas leaking from a pipeline; combustion of gasoline, acetylene, or utility gas; and industrial sources.

Some people are more susceptible to CO poisoning than others. They include:

  • People with asthma, bronchitis, or other lung disorders
  • Smokers
  • People with chronic heart conditions
  • Unborn babies
  • Elderly people, particularly those over seventy-five

Causes and Symptoms

The basic cause of CO poisoning is loss of oxygen to body tissues. When a person breathes in carbon monoxide, the gas binds to hemoglobin, the red pigment in red blood cells that transports oxygen to body tissues. When the hemoglobin becomes filled with CO, it cannot carry oxygen to other parts of the body. The heart and the central nervous system are particularly vulnerable to loss of their oxygen supply. If the person goes away from the source of the carbon monoxide, it will take about three hours to get rid of half the CO remaining in the body through the lungs. Giving supplemental oxygen cuts the time to thirty minutes to an hour.

Safety Tips

The Environmental Protection Agency (EPA) recommends the following safety measures to reduce the risk of exposure to carbon monoxide:

  • Keep stoves and other gas appliances properly adjusted and regularly serviced.
  • Have a trained technician inspect, clean, and tune up furnaces, flues, and chimneys every year.
  • Repair any leaks promptly.
  • Be sure that kerosene heaters are operated with the correct fuel.
  • Do not idle cars or trucks inside a garage, even with the doors open.
  • Do not use charcoal grills or hibachis indoors or in an enclosed garage.
  • Install a carbon monoxide detector with a battery backup and test it once a month. If possible, install a detector on each level of the house and especially near bedrooms. CO detectors should not, however, be installed in kitchens. If the CO detector's alarm sounds, leave the house at once and call the fire department or local utility company from a nearby phone.

People who notice the early symptoms of CO poisoning—headache, dizziness, nausea, vomiting, chest pain, confusion, disorientation—should move outside into fresh air and call for emergency medical care.

Common sources of CO include:

  • Fuel-burning space heaters.
  • Charcoal grills and hibachis.
  • Gas cooking ranges and water heaters.
  • Fireplaces.
  • Portable generators.
  • Car and truck exhaust. Children riding in the back of enclosed pickup trucks are particularly vulnerable to exhaust fumes.
  • Motorboat engines. Swimmers have been overcome by CO when swimming behind motorboats.

The most common symptoms of CO poisoning have already been described. Some people also develop a sunburn-like skin rash. Firefighters or workers who are employed in certain industries such as pulp mills or metal foundries sometimes develop memory problems or psychiatric symptoms as a result of chronic exposure to CO.


The diagnosis of CO poisoning is not always obvious because some of the early symptoms resemble those of the flu or other illnesses caused by viruses. If the person shows signs of smoke inhalation from a fire or can give a history that suggests recent exposure to CO, the doctor will take a sample of blood to be tested for carbon monoxide levels. In some cases memory loss, confusion, impaired judgment, or other psychiatric symptoms are useful diagnostic clues.


Emergency treatment of CO poisoning involves removing the person from the source of the carbon monoxide as quickly as possible and administering 100 percent oxygen through a face mask. If necessary, the person may also be put on an artificial respirator to help them breathe. In severe cases, the patient may be moved to a hyperbaric oxygen (HBO) chamber. Hyperbaric means that the oxygen in the chamber is at twice or three times normal atmospheric pressure. Treatment in an HBO speeds up the removal of CO from the body, sometimes bringing it down is as little as fifteen to twenty minutes.


The prognosis of CO poisoning depends on a number of factors, including the patient's age, presence of heart or lung disorders, smoking habits, length of exposure to the carbon monoxide, and the concentration of the carbon monoxide that was inhaled. Most people recover completely with proper treatment; however, some suffer lifelong memory loss, difficulty thinking, or other neurological or psychiatric problems.

In general, patients who have gone into coma or whose heart has stopped temporarily have poorer outcomes.


CO poisoning can be prevented by following the safety tips outlined in the sidebar.

The Future

Better public education about the dangers of CO poisoning is part of the Centers for Disease Control and Prevention's plan for the future. According to the National Fire Protection Association, 93 percent of American homes have smoke detectors, but only about 15 percent have carbon monoxide detectors. In addition, the CDC believes that most people are unaware of the dangers of CO poisoning while boating or camping. In terms of treatment, a new portable HBO chamber is presently being evaluated for use by firefighters and other emergency personnel. It has been shown to be safe and effective in laboratory conditions, and was being tested in the field as of early 2008.

SEE ALSO Asthma; Smoke inhalation; Smoking


Hemoglobin: The substance in red blood cells that transports oxygen to the cells of the body.

Hyperbaric oxygen: Oxygen that is delivered to a patient in a special chamber at two to three times normal atmospheric pressure.

For more information


Deboo, Ana. Safety around the House. Chicago, IL: Heinemann Library, 2008.

Penney, David G., ed. Carbon Monoxide Poisoning. Boca Raton, FL: CRC Press, 2008.


Associated Press. “Proposed Bill Would Ban Carbon Monoxide in PetEuthanasia.” Chicago Daily Herald, February 11, 2008. Available online at http://www.dailyherald.com/story/?id=132581&src=109 (accessed May 26, 2008).

Centers for Disease Control and Prevention (CDC). “Carbon Monoxide Poisonings after Two Major Hurricanes—Alabama and Texas, August-October 2005.” Morbidity and Mortality Weekly Report 55 (March 10, 2006): 236-239. Available online at http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5509a4.htm (accessed May 26, 2008).

Levit, Fred, MD. “Cases: The Sunless Sunburn Mystery.” New York Times, November 4, 2003. Available online at http://query.nytimes.com/gst/fullpage.html?res=940DE5DF1530F937A35752C1A9659C8B63&sec=&spon=&pagewanted=all (accessed May 26, 2008). This is a case study of a woman who developed a sunburn-like skin rash as a symptom of carbon monoxide poisoning.


American Industrial Hygiene Association (AIHA). “Carbon Monoxide—The Silent, Cold Weather Killer.” Available online at http://www.aiha.org/Content/AccessInfo/consumer/carbonmonoxide.htm (updated November 2, 2007; accessed May 27, 2008).

Centers for Disease Control and Prevention (CDC). “Avoiding Carbon Monoxide Poisoning after Severe Weather.” Available online at http://www.bt.cdc.gov/disasters/hurricanes/psa/video/co.asp (updated May 14, 2007; accessed May 26, 2008). This is a general-information video with voiceover about CO poisoning; it takes about a minute and a half to play.

Centers for Disease Control and Prevention (CDC). “Carbon Monoxide Poisoning: Home.” Available online at http://www.cdc.gov/co/default.htm (accessed May 27, 2008). This is the home page of the CDC'swebsite on CO poisoning. It includes information about product recalls and research as well as general information and prevention guidelines.

Environmental Protection Agency (EPA). “Carbon Monoxide: Basic Information.” Available online at http://www.epa.gov/iaq/co.html (updated April 1, 2008; accessed May 26, 2008). Web page contains numerous links to information about specific types of appliances, vehicles, and other sources of CO.

National Aeronautics and Space Administration (NASA)/Goddard Space Flight Center. “Global Map of Carbon Monoxide.” Available online at http://www.nasa.gov/mpeg/60034main_global.mpeg (updated November 30, 2007; accessed May 26, 2008).This is an animation of the movement of carbon monoxide around Earth from March through December of an average year.

National Library of Medicine (NLM). “Tox Town.” Available online at http://www.toxtown.nlm.nih.gov/text_version/chemicals.php (accessed May 27, 2008). Tox Town is an interactive website that allows viewers to click on a list of chemicals as well as a choice of five neighborhoods (town, city, farm, port, and the United States/Mexico border) to find out where a specific chemical might be found in that type of neighborhood and how it might affect health.

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