Air, Breathing and the Environment
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Air and Breathing
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The Way of Breath
Air Quality
Cars and Trucks
Car Exhaust Pollutants
Air Pollution
Climate Change
Airborne Diseases
Air Quality Inside Buildings
The Environment
Airborne Fungi and Disease
Airborne Viruses
Fibrosis & Sarcoidosis
Food and Lung Disease
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Indoor Air Quality --- Carbon monoxide (CO)

Carbon monoxide (CO) is a colorless, odourless, poisonous gas. Deaths are usually caused by carbon monoxide poisoning from combustion in poorly ventilated enclosures. The symptoms of carbon monoxide poisoning are: headache, nausea, shortness of breath, dizziness and confusion. The severity of symptoms depends on the concentration of gas. High concentrations quickly cause death. Low level exposure produces flu-like symptoms and is usually not recognized.

Carbon monoxide gas is produced when fossil fuel burns incompletely because of insufficient oxygen. During incomplete combustion, the carbon and hydrogen combine to form carbon dioxide, water, heat, and carbon monoxide. In properly installed and maintained appliances, the fuel burns cleanly and produces only small amounts of carbon monoxide. Anything that interferes with the burning process or results in a shortage of oxygen can increase carbon monoxide production. Wood, coal, and charcoal fires always produce carbon monoxide, as do gasoline engines. Exposures in parts per million (PPM)

30 PPM Permissible Averaged over 8 hours
200 PPM Maximum for acute exposure
800 PPM Lethal < 2 hour exposure

Sources: Combustion - furnaces, boilers, space-heaters, stove tops, hot water heaters ( gas), clothes dryers (gas), wood stoves, fireplaces, BBQ's, tobacco smoking, combustion engines, candles, incense, kerosene lanterns, propane appliances. Official recommendation: concentration levels should be below 30 PPM average exposure.

Our recommendation: safe concentration levels are 0 (zero), the hazard increases dramatically above 30 PPM. Average occupational exposures above 10PPM (sustained through the work day) are unacceptable if your goal is normal function and good health long term. Smokers provide their own personal supply of carbon monoxide and will often have exposure levels above safe limits when their personal CO exposure is added to ambient air exposure.


  1. Stain indicator tubes are useful for screening industrial environments.
  2. electronic devices for continuous monitoring
  3. electrochemical devices - accuracy +/- 5%


When Carbon Monoxide is inhaled, the CO combines with the hemoglobin to form carboxyhemoglobin  (COHb). CO displaces oxygen attached to the carrier molecule, hemoglobin. The COHb bond is over 200 times stronger than oxygen's bond with hemoglobin. The strong COHb bond makes it difficult for the body to eliminate CO  from the blood.

Carbon Monoxide can poison slowly over a period of several hours, even in low concentrations. Sensitive organs such as the brain, heart, and lungs suffer the most from a lack of oxygen. Unfortunately, the symptoms of CO poisoning are easily mistaken for other common illnesses and low level CO poisonings are often misdiagnosed. Symptoms such as headaches, dizziness and fatigue are common to a number of illnesses such as the flu or the common cold. These symptoms can occur with a COHb blood saturation levels of 10-30%.

At 30-50% COHb symptoms are nausea, severe headaches, dizziness, and increased pulse and respiration. COHb levels over 50% cause progressive symptoms proceeding to loss of consciousness, collapse, convulsions, coma, and finally death.

How much is dangerous? High concentrations of carbon monoxide kill in less than five minutes. At low concentrations it will require a longer period of time to affect the body. Exceeding the EPA concentration in air of 9 ppm for more than 8 hours will have adverse health affects. The U.S. Occupational Health and Safety limit for healthy workers is 50 ppm in inhaled air.

Carbon monoxide detectors, which are designed to protect against high concentration of carbon monoxide are required to sound an alarm when concentrations are greater than 100 ppm. Continued exposure to carbon monoxide can cause permanent brain, nerve, or heart damage. Some people require years to recover while others might never fully recover. The time of exposure, the concentration of CO, the activity level of the person breathing the CO, and the person's age, sex, and general health all affect the danger level. Exposure to Co at a concentration of 400 ppm will cause headaches in 1 to 2 hours; in 3 to 5 hours the same concentration can lead to unconsciousness and death. Physical exertion, with an accompanying increase in respiration rate, shortens the time to critical levels by 2 or 3 fold. Respiratory capacity decreases and the risk of heart attack increases at levels well below 50 ppm.

Low Level CO poisoning should be suspected when

  • Entire family is sick at the same time.
  • Flu-like symptoms decrease while away from the house.
  • Illness is present when gas appliances are in use.
  • Excess moisture on the interior of windows.

Urgent treatment- CO poisoning

Move immediately into fresh air; administer oxygen if available. go to hospital for treatment. In severe cases, patients are treated in a hyperbaric chamber which forces carbon monoxide from the body.  The half-life of carboxyhemoglobin in fresh air is approximately 4 hours - complete flushing takes 12 to 24 hours. Oxygen and hyperbaric chambers, can reduce CO damage, speed recovery, and reduce brain damage.

Loss of consciousness suggests high levels of carbon monoxide poisoning. Death is imminent unless the victim is rescued and treated in a well equipped emergency room.

Even patients who recover have symptoms for several weeks. They will suffer from headache, fatigue, loss of memory, difficulty in thinking clearly, irrational behavior, and irritability. Recover can be slow and frustrating. Some individuals suffer permanent brain and organ damage. Victims may be highly sensitive to CO for the rest of their lives.

A breath test can determine carbon monoxide levels. Medical laboratories can measure carboxyhemoglobin levels in the blood. Carboxyhemoglogin levels in the blood drop after the victim is removed from the carbon monoxide source Because the effects of carbon monoxide poisoning may last for months, normal carboxyhemoglobin levels in the blood 24 or more hours after exposure are not relevant.

Protection from the dangers of carbon monoxide poisoning

Do not use combustible fuel devices in closed spaces.

Purchase and use carbon monoxide detector(s).

Check heating appliances by a qualified heating contractor.

Replace open heating units - space heaters, wood stoves and fireplaces with direct-vent, sealed combustion units.

Auto Emissions of CO

In  cities, about  two-thirds of the carbon monoxide emissions come from transportation sources, with the largest contribution coming from highway motor vehicles. In urban areas, the motor vehicle contribution to carbon monoxide pollution can exceed 90 percent. In 1992, carbon monoxide levels exceeded the Federal air quality standard in 20 U.S. cities, home to more than 14 million people.

Carbon monoxide results from incomplete combustion of fuel and is emitted directly from vehicle tailpipes. Incomplete combustion is most likely to occur at low air-to-fuel ratios in the engine. These conditions are common during vehicle starting when air supply is restricted ("choked"), when cars are not tuned properly, and at altitudes where "thin" air reduces the amount of oxygen available for combustion (except in cars that are designed or adjusted to compensate for altitude).

By 1975, most new cars were equipped with catalytic converters that convert carbon monoxide to carbon dioxide.  In the 1980's, automakers improved CO conversion with computers and oxygen sensors that increased the efficiency of  catalytic converters. Carbon monoxide emissions from automobiles increase in cold weather because cars need more fuel to start at cold temperatures, and because some emission control devices (such as oxygen sensors and catalytic converters) operate less efficiently when they are cold.


Discussions of Environmental Science and Human Ecology were developed by Environmed Research Inc. Sechelt, B.C. Canada. Online Topics were developed from the book, Air and Breathing. This book helps you understand air quality issues, normal breathing and the causes of breathing disorders. You will find detailed information about the atmosphere, air pollution, climate change, airborne infection, air quality and airborne hazards at home.

Stephen J. Gislason MD. Air and Breathing available as a Printed book and Digital eBook Edition for Download

Not all respiratory diseases are caused by airborne pathogens. If asthma, bronchitis and/or nose sinus congestion is chronic or attacks occur frequently in all seasons and are not related to airborne exposure, then consider delayed pattern food allergy as the cause and do diet revision using the Alpha Nutrition Program.

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