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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