Lower Explosive Limit (LEL)

Definition - What does Lower Explosive Limit (LEL) mean?

Lower explosive limit (LEL) refers to the lowest concentration of gas/fumes/vapors required to produce fire in the presence of an ignition source like flame or heat. In the United States, the Occupational Safety and Health Administration (OSHA) provides guideline limits for the presence of explosive and flammable liquids in the air as well as the for the safe storage of these materials to prevent fire and explosion.

The lower explosive limit is also known as the lower flammable limit (LFL).

Safeopedia explains Lower Explosive Limit (LEL)

When the vapors of a flammable or combustible liquid are mixed with air in the right proportion, it can lead to explosion or combustion if heat or some form of ignition are applied. Generally, there is a minimum concentration of gas below which a flammable or combustible gas will not ignite and an upper concentration above which the air will be "too rich" to ignite. These boundary lines are known as the upper and lower explosive limits. They are usually expressed as a percentage.

There is slight confusion between the percentage reading on combustible air monitors and lower explosive limit. Explosimeters are designed and calibrated to a specific gas and may show a relative concentration of gas in the atmosphere. Lower explosive limit, on the other hand, generally deals with the volume or quantity of combustible gas present in the air that can get ignited in the presence of a source like a flame or spark.

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