In popular jargon, a vapor/air mixture below the lower flammable limit is too "lean" to burn or explode, and a mixture above the upper flammable limit is too "rich" to burn or explode. The LFL is also known as the lower explosive limit (LEL). The UFL is also referred to as the upper explosive limit (UEL). No attempt is made to differentiate between the terms flammable and explosive as applied to the lower and upper limits of flammability.