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