Lower Explosive (Flammable) Limit
Minimum concentration of combustible gas or vapor in air (expressed in percent of gas or vapor in air by volume) below which propagation of flame does not occur on contact with an ignition source.
NOTE Lower flammable limit (LFL) is synonymous with lower explosive limit (LEL.
Source: API RP 98, Personal Protective Equipment Selection for Oil Spill Responders, First Edition, August 2013. Global Standards