Refrigerants are classified by ASHRAE under latest standard 34 as either class 1, 2, 2L or 3 for their flammability characteristics, and class A or B for non-toxic or toxic characteristic respectively. The specific classification is based on their respective flammability variables such as flame velocity, Lower Flammability Limit (LFL) and heat of combustion. Flame velocity is the variable used to classify refrigerants between class 2 and class 2L. Figure 16 below shows the flame velocity of the various refrigerants (including R32 and the HFOs) relative to each other. All refrigerants with a flame velocity below 10 cm/s were recently classified as “2L” by ASHRAE 34, thus introducing two new categories of refrigerants, A2L and B2L (Figure 17).