The Span-Wagner (non-polar and polar) equations of state are described in:
Span, R.; Wanger, W. - Equations of State for Technical Applications. I. Simultaneously Optimized Functional Forms for Nonpolar and Polar Fluids. Int. J. Thermophys. 2003, 24(1), 1-39. The two equations differ slightly in their constant parameters.
The specific forms of the NON-POLAR and POLAR equations used in TDE are given in the IUPAC ThermoML data-communication standard.
The article describing the standard is here: Pure Appl. Chem. 2006, 78(3), 541-612.>
The POLAR equation is given on page 71 of the article (page 611 of the Journal).
The NON-POLAR equation is given on page 70 of the article (page 610 of the Journal).
Equation parameters are available in several formats from TDE: Equation Parameters in TDE