An analysis of experimental data for some compounds suggests occurrence of a physico-chemical transformation of the compound at the front of strong shock waves and is attended by a significant change in density (~20%) and compressibility of medium. Therefore the thermodynamic properties of such substances are described by separate equations of state for the material prior to (low pressure EOS) and after (high pressure EOS) transformation.
You can learn more about the model of KEOS2K equation of state by downloading the file in pdf format.