At room temperature, carbon dioxide (CO2) is a colorless, odorless, faintly acidic-tasting, non-flammable gas. CO2 is the fourth most abundant gas in the earth's atmosphere. Depending on the temperature and pressure, carbon dioxide can also exist as a liquid or a solid. In its solid form, carbon dioxide is called dry ice because it slowly changes from a cold solid directly into a gas.
Where is carbon dioxide found in the environment?
CO2 is a byproduct of normal cell function. It is removed from the body via the lungs in the exhaled air. CO2 is also produced when fossil fuels are burned. Decaying vegetation can also produce CO2. Surface soils can sometimes contain high concentrations of this gas, from decaying vegetation or chemical changes in the bedrock. In its solid form, CO2 is used in fire extinguishers, in laboratories, and in theater and stage productions as dry ice to make fog.
What conditions lead to high carbon dioxide levels indoors?
The amount of carbon dioxide in a building is usually related to how much fresh air is being brought into that building. In general, the higher the CO2 level in the building, the lower the amount of fresh air exchange. Therefore, examining levels of CO2 in indoor air can reveal if the heating, ventilation, and air conditioning (HVAC) systems are operating within guidelines. CO2 levels are usually measured in percent (%) of air or parts per million (ppm). High CO2 levels, generally over 1000 ppm, indicate a potential problem with air circulation and fresh air in a room or building. In general, high CO2 levels indicate the need to examine the HVAC system. High carbon dioxide levels can cause poor air quality and can even extinguish pilot lights on gas-powered appliances.
The use of dry ice in the work place can elevate indoor CO2 if the air is not ventilated.
CDC websites on carbon dioxide
- Building Air Quality: A Guide for Building Owners and Facility Managers (PDF, 2.8 MB)
- Occupational Exposure to Carbon Dioxide (PDF,1.0 MB)
- Biologic Effects of Exposure (PDF, 3.3 MB)
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