Flammability refers to the ability of a fuel to burn and encompasses three variables: ignitability, combustibility and sustainability (Trabaud 1976): Ignitability indicates how easily a fuel burns when exposed to a heat source. Combustibility refers to the ease with which the fuel burns, releasing enough energy to consume itself and ignite surrounding fuel. Sustainability describes the stability of burning rate, that is, the extent to which a  fuel continues to burnover time. It can be restricted to the flame duration or can also include the smoldering phase. Combustion rate can be quantified as the mass weight loss during combustion.