We've come a long way since the turn of the 20th century, when your refrigerator could prove fatal. In those days, toxic gases (specifically, ammonia, methyl chloride and sulfur dioxide) were used as refrigerants. After leaking methyl chloride caused a series of deaths, three American corporations began a search for a less toxic substitute.

What they came up with was a synthesis of chlorofluorocarbons (CFCs). CFCs are nontoxic, nonflammable chemicals containing atoms of carbon, chlorine and fluorine. By 1935, these corporations had sold over 8 million new refrigerators in the United States using Freon-12 (CFC-12).

Unfortunately, although they serve well as refrigerants, CFCs are considered by the EPA to be an environmental hazard. Safe to use in most applications and inert in the lower atmosphere, they undergo significant reaction in the upper atmosphere or stratosphere. There, the chlorine released by CFCs destroys the ozone at the rate of 100,000 molecules of ozone per chlorine atom.

Proceed through this section of the EVC to learn some best practices related to refrigeration units and CFCs. Regulatory requirements related to CFCs are not included in the EVC; but CFCs are regulated under the Clean Air Act. For the complete text of the regulations related to CFCs, click here: