The upper flame limit (UFL) (or upper explosion limit (UEL)) is the maximum concentration of substance in air that will exhibit flame propagation (generally measured in volume % in air). The lower flame limit (LFL) can depend on the test apparatus and criteria used; the actual method used to determine each value should be identified. Well-established testing methodologies (e.g., ASTM E681 for flammable limits) should be employed where possible.
