| Definition: | lower flammable limit (LFL) and upper flammable limit (UFL), stated in percent by volume or in g/m3 of gas in a gas-air mixture, between which a flammable mixture is formed Note 1 to entry: In the past, "flammable" and "explosive" have been used interchangeably in many texts, but the trend is to avoid the confusion that this causes. The term "flammable" relates to the properties of the material that determine its ability to produce self-sustaining flame propagation in any direction (upwards, sideways or downwards). The term "explosive" relates to flame propagation that is accompanied by pressure and temperature rise and noise (usually higher-speed propagation) and is significantly affected by (non-material related) test chamber conditions (geometry, degree of confinement…). LFL concentrations are typically lower than LEL concentrations for the same material and UFL concentrations are typically higher than UEL concentrations for the same material.
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