Definition: A halon is an organic compound containing one or two carbon atoms and halogen atoms.
Halons are numbered by a numbering scheme that follows the pattern:
a is the number of carbon atoms
b is the number of fluorine atoms
c is the number of chlorine atoms
d is the number of bromine atoms.
e is the number of iodine atoms.
Halon numbers with less than five digits are assumed to have values of zero at the end of the number.
For example, halon 1011 is bromochloromethane (CH2BrCl): 1 carbon, 0 fluorine, 1 chlorine and 1 bromine atom.