Combustible Gas – LEL and UEL Percentage Levels

LEL Levels and UEL Levels

Combustible gases combine three elements – fuel, oxygen and an ignition source. The primary risk associated with these elements depends on the specific fuel and oxygen mixture.

A combustible gas in a quantity which is either too small or too large will not ignite. The gas levels are measured as a percentage and referred to as the

Lower Explosive Limit – LEL
Upper Explosive Limit – UEL

What are %LEL and %UEL?

Any gas level between the 2 limits will ignite and should be considered explosive with the maximum explosive limit at some mid level point between the upper and lower limits.

Each gas has it’s own LEL and UEL values. The following table gives examples of the LEL and UEL values (although these can vary slightly depending on testing conditions).

Gas LEL % UEL %
Acetone (CH3)2CO 2.15 13.0
Acetylene C2H2 2.5 100
Benzene C6H6 1.2 8.0
Butadiene C4H6 1.1 12.5
Ethane C2H6 3.0 15.5
Ethyl Alcohol CH2H5OH 3.3 19.0
Ethyl Ether (C2H5)2O 1.7 36.0
Ethylene C2H4 2.7 36.0
Hexane C6H14 1.1 7.5
Hydrogen H2 4.0 75.6
IsoButane C4H10 1.8 8.5
Isopropyl Alcohol (IPA) (CH3)2CHOH 2.0 12.7
Methane CH4 5.0 15.0
Methanol CH3OH 6.0 36.0
Pentane C5H12 1.5 7.8
Propylene C3H6 2.0 11.1
Toluene C7H8 1.2 7.0

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