Halogen, including five elements: F (Fluorine), Cl (Chlorine), Br (Bromine), iodine (Iodine), astatine (Astatine). Element symbols are F, Cl, Br, I, At. And astatine is radioactive element, it is often said that the halogen means fluorine, chlorine, bromine and iodine. The halogen free referred to Chlorine and Bromine.

Halogen compounds have caused more concern because of the below reasons:
1, many of the compounds harmful to the environment and human, such as: persistent organic pollutants;
2, some halogen compounds are ozone depleting substances ODS, or greenhouse material GHG itself;
3, Combustion of organic halogen compounds can release dioxins, harmful to human health. 

Halogen that contained in plastic materials are mainly BFRs, CFRs, chlorine plasticizers, other organic bromine and organic chlorine compounds such as pigments, refrigerants, fire extinguishing agents, cleaning agents, blowing agents, etching agents are mainly the halogen compounds that constituent with F, Cl, Br.

Standards and Regulations

Halogen free requirements:
IEC61249-2-21, PCB board substrate requirements:
Br≤900ppm （0.09%w/w)
Cl≤900ppm （0.09%w/w)
(Br+Cl)≤1500ppm （0.15%w/w)

Tests：
EN14582, IEC61189-2, JPCA-ES-01, ASTM D7359, GB/T 9872
The material is added to oxygen bomb, combustion of the halide ions can absorpted with specials solutions, then using ion chromatography IC to test;
XRF can be used to determine Br, Cl can be determined by preliminary XRF, but the uncertainty is too large.