2.6.4.2. In the case of mixtures containing known flammable liquids in defined concentrations, although they may contain non-volatile components e.g. polymers, additives, the flash point need not be determined experimentally if the calculated flash point of the mixture, using the method given in 2.6.4.3 below, is at least 5°C greater than the relevant classification criterion and provided that:
(a) The composition of the mixture is accurately known (if the material has a specified range of composition, the composition with the lowest calculated flash point shall be selected for assessment);
(b) The flash point (closed-cup as given in 2.6.4.4 below) of each component is known (an appropriate correlation has to be applied when these data are extrapolated to other temperatures than test conditions);
(c) The activity coefficient is known for each component as present in the mixture including the temperature dependence;
(d) The liquid phase is homogeneous.