LEL (Lower
Explosive Limit)
This is the minimum concentration of a flammable gas or
vapor that will propagate flame when exposed to a source of ignition. LEL also
called LFL (Lower Flammable Limit), a mixture below this concentration level is
too “lean” to burn.
UEL (Upper
Explosive Limit)
The maximum concentration of a gas or vapor in air that will
combust. Above this level, the mixture is too “rich” to burn. Also called UFL
(Upper Flammable limit).
Explosive Range
The range between the LEL and UEL is known as the Explosive
(flammable) range for that gas or vapor. This includes all concentration of gas
or vapor in air that will propagate flame when exposed to a source of ignition.
LEL and UEL
Concentration Level for some Common Gases
NAME
|
FORMULA
|
LEL
|
UEL
|
Acetone
|
(CH3)2CO
|
2.5%
|
13.0%
|
Ammonia
|
NH3
|
15.0%
|
28.0%
|
Acetylene
|
C2H2
|
2.5%
|
100%
|
Benzene
|
C6H6
|
1.2%
|
7.8%
|
Isobutene
|
C4H10
|
1.8%
|
8.4%
|
Ethane
|
C2H6
|
3.0%
|
12.5%
|
Ethyl Alcohol
|
CH2H5OH
|
3.3%
|
19.0%
|
Ethyl Ether
|
C2H5OC2H5
|
1.9%
|
36.0%
|
Ethylene
|
C2H4
|
2.7%
|
36.0%
|
Hexane
|
C6H14
|
1.1%
|
7.5%
|
Hydrogen
|
H2
|
4.0%
|
75.6%
|
Isopropyl Alcohol
|
(CH3)2CHOH
|
2.0%
|
12.7%
|
Methane
|
CH4
|
5.0%
|
15.0%
|
Methyl Alcohol
|
CH3OH
|
6.0%
|
36.0%
|
Pentane
|
C5H12
|
1.5%
|
7.8%
|
Propylene
|
C3H6
|
2.0%
|
11.1%
|
Propane
|
C3H8
|
2.1%
|
9.5%
|
Toluene
|
C7H8
|
1.1%
|
7.1%
|
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