Characteristics of Carbon Dioxide (CO2)
Despite the fact that we breathe out carbon dioxide and that it is present in the atmosphere (about 400 ppm), its maximum safe level is 5000 ppm (0.5% by volume). It is a product of complete combustion and is dangerous it is heavier than air and collects at low levels. There is some degree of risk in crowded, badly ventilated places, and an oxygen deficient atmosphere often accompanies this problem. Carbon dioxide odorless, colorless and difficult to measure in ppm levels, making infrared absorption the usual technique.
Source: Dangerous Properties of Industrial Materials (Sixth Edition) by N. Irving Sax
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