Carbon dioxide is the result of animal respiration. Carbon monoxide is the result of using combustion equipment, such as heaters and gas-operated power washers, in a confined area. This equipment produces more carbon monoxide when engines don't burn cleanly.
At high concentrations, carbon dioxide and carbon monoxide can cause respiratory distress and headaches. At prolonged high exposures, these gases can be fatal. Federal standards set maximum concentrations at 5,000 parts per million (ppm), about 0.5 percent, for carbon dioxide; and 50 ppm, about 0.005 percent, for carbon monoxide.
Solution: These gases usually aren't a problem under normal conditions with proper ventilation. However, it's important to maintain some ventilation at all times, even when animals are not present.
(Source: ISU Extension publication #: Pm-1518k )
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