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Carbon Dioxide
Carbon Dioxide, or CO2, is a gas which occurs naturally in the Earth’s atmosphere as part of animal metabolism (respiration), plant photosynthesis, decomposition, and combustion. The gas is colorless, odorless, tasteless, noncombustible, and soluble in water. CO2 makes up slightly less than 1% of our atmosphere. Though it most commonly appears as a gas, it can also be frozen at extremely low temperatures to form ‘dry ice.’ It is used in industry for such processes as beverage carbonation, welding, and chemical manufacture.

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Primary Sources

Carbon dioxide accumulation inside the home is normally related directly to the number of occupants. Concentration of the gas is usually highest where homeowners (and, if applicable, pets) spend most of their time. Since increasing levels of CO2 encourage plant growth, an unusual flowering or blooming of household plants may indicate an overabundance of carbon dioxide. Also, carbon dioxide by nature is 1.5 times heavier than air, and therefore tends to ’pool’ in low areas such as basements. Carbon dioxide is also the primary gas involved in the “greenhouse effect,” and therefore may be prevalent in an enclosed, windowed area.

Other nonliving sources of the gas may include space heaters, clothes dryers, stoves, or any other unvented gas-burning appliance. The gas may also infiltrate the home from an outdoor source, in which case the cause is most likely to be a large industrial area or any processes which involve the burning of fossil fuels.

Health Effects

Symptoms caused by carbon dioxide are directly related to the fact that increasing carbon dioxide levels cause decreasing oxygen levels in the body, hampering the flow of oxygen to the brain. If the concentration of the gas is still relatively low, common symptoms include headaches, an increasing pulse rate, uncharacteristically high fatigue, and breathing difficulties. When concentration of the gas reaches a high level above 30,000 ppm (parts per million), symptoms can include heavy nausea, dizziness, or vomiting. At these levels asphyxiation or a loss of consciousness can also occur, but this is hardly likely to occur in a common home, where levels of carbon dioxide usually range from 300 to 2,000 ppm.

Exposure Guidelines

Serious health problems relating to carbon dioxide can result from chronic exposure. Acceptable levels have not been determined. 


As with most other gases whose problems arise from long-term accumulation, one of the most effective ways to prevent a buildup of carbon dioxide is to use a balanced, mechanical ventilation system, which will reduce indoor CO2 levels and eliminate many other harmful indoor air contaminants. Other preventative measures in keeping the gas at an acceptable level include ensuring that all gas burning appliances are properly vented, and regularly checking on any and all fuel-burning appliances. Carbon dioxide detectors can also be purchased, which can be calibrated to last as long as two years before needing recalibration (this does not mean you would have to purchase a new detector, just reset it).



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