A numbering system describing chlorofluorocarbons (CFCs), which are Class I ODSs, and hydrochlorofluorocarbons (HCFCs), which are Class II ODSs, has been developed to simply and systematically name each compound. The numbering system for both classes of compounds is the same (except for a slightly different numbering system used to describe the Halons and also the prefix before each number, which is simply CFC- or HCFC-, depending on the class to which that particular compound belongs). For CFCs and HCFCs, the one's digit (last) indicates the number of fluorine atoms in each molecule, the ten's digit represents the number of hydrogen atoms in each molecule plus one, and the hundred's digit represents the number of carbon atoms in each molecule minus one. For example, trichlorotrifluoroethane is a CFC that has three fluorine atoms, no hydrogen atoms, and two carbon atoms in each molecule; hence, the designation CFC-113. Since two carbon atoms and thus six sites are available for halogens (chlorine or fluorine only, no bromine) and hydrogens, the number of chlorine atoms is determined by the difference between the total number of sites available and the sum of the hydrogen and fluorine atoms. In this case, 6 - (0+3) = 3, or the number of chlorine atoms.

The Halon numbering system uses four digits. It is similar, but also a bit simpler, since the Halons, like the CFCs, are totally halogenated, lacking any hydrogen atoms. The numbering system uses a simple count of the number of atoms of each element in the molecule from the one's digit to the thousand's digit: bromine (Br), chlorine (Cl), fluorine (F), and carbon (C), respectively. For example, the bromochlorodifluoromethane molecule has one bromine atom, one chlorine atom, two fluorine atoms, and one carbon atom; hence, the designation Halon 1211 or CF₂ClBr.

The common name or chemical formula can be derived for most of these compounds since the numbered names have a lowercase letter following the one's digit. This letter indicates a particular isomer or arrangement of the molecule, but no other specific information to further establish the compound’s exact identity.

For refrigerants, a more complete discussion of the numbering system can be found in ASHRAE/ANSI Standard 34 (Number Designation and Safety Classification of Refrigerants). To obtain a copy of ASHRAE/ANSI 34, contact:

American Society of Heating Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE)
1791 Tullie Circle, NE
Atlanta, GA 30329
Phone: 800-527-4723 or (404) 636-8400
Fax: (404) 321-5478
E-mail: ashrae@ashrae.org
URL: http://www.ashrae.org/

Du Pont Fluorochemical Products Information
Halon Division
1006 Market St.
Wilmington, DE   19898
Phone: (800) 235-7882