Lower and Upper Explosive
Limits for Flammable Gases and Vapors (LEL/UEL)
Before a fire or explosion can occur, three conditions
must be met simultaneously. A fuel (ie. combustible
gas) and oxygen (air) must exist in certain proportions,
along with an ignition source, such as a spark or flame.
The ratio of fuel and oxygen that is required varies
with each combustible gas or vapor.
The minimum concentration of a particular combustible
gas or vapor necessary to support its combustion in
air is defined as the Lower Explosive Limit (LEL) for
that gas. Below this level, the mixture is too "lean"
to burn. The maximum concentration of a gas or vapor
that will burn in air is defined as the Upper Explosive
Limit (UEL). Above this level, the mixture is too "rich"
to burn. The range between the LEL and UEL is known
as the flammable range for that gas or vapor.
The values shown in this table are valid only for
the conditions under which they were determined (usually
room temperature and atmospheric pressure using a 2
inch tube with spark ignition). The flammability range
of most materials expands as temperature, pressure and
container diameter increase. All concentrations in percent
by volume.
Gas |
LEL |
UEL |
Acetone |
2.6 |
13.0 |
Acetylene |
2.5 |
100.0 |
Acrylonitrile |
3.0 |
ĘC |
Allene |
1.5 |
11.5 |
Ammonia |
15.0 |
28.0 |
Benzene |
1.3 |
7.9 |
1,3-Butadiene |
2.0 |
12.0 |
Butane |
1.8 |
8.4 |
n-Butanol |
1.7 |
12.0 |
1-Butene |
1.6 |
10.0 |
Cis-2-Butene |
1.7 |
9.7 |
Trans-2-Butene |
1.7 |
9.7 |
Butyl Acetate |
1.4 |
8.0 |
Carbon Monoxide |
12.5 |
74.0 |
Carbonyl Sulfide |
12.0 |
29.0 |
Chlorotrifluoroethylene |
8.4 |
38.7 |
Cumene |
0.9 |
6.5 |
Cyanogen |
6.6 |
32.0 |
Cyclohexane |
1.3 |
7.8 |
Cyclopropane |
2.4 |
10.4 |
Deuterium |
4.9 |
75.0 |
Diborane |
0.8 |
88.0 |
Dichlorosilane |
4.1 |
98.8 |
Diethylbenzene |
0.8 |
ĘC |
1,1-Difluoro-1-Chloroethane |
9.0 |
14.8 |
1,1-Difluoroethane |
5.1 |
17.1 |
1,1-Difluoroethylene |
5.5 |
21.3 |
Dimethylamine |
2.8 |
14.4 |
Dimethyl Ether |
3.4 |
27.0 |
2,2-Dimethylpropane |
1.4 |
7.5 |
Ethane |
3.0 |
12.4 |
Ethanol |
3.3 |
19.0 |
Ethyl Acetate |
2.2 |
11.0 |
Ethyl Benzene |
1.0 |
6.7 |
Ethyl Chloride |
3.8 |
15.4 |
Ethylene |
2.7 |
36.0 |
Ethylene Oxide |
3.6 |
100.0 |
Gasoline |
1.2 |
7.1 |
Heptane |
1.1 |
6.7 |
Hexane |
1.2 |
7.4 |
Hydrogen |
4.0 |
75.0 |
Hydrogen Cyanide |
5.6 |
40.0 |
Hydrogen Sulfide |
4.0 |
44.0 |
Isobutane |
1.8 |
8.4 |
Isobutylene |
1.8 |
9.6 |
Isopropanol |
2.2 |
ĘC |
Methane |
5.0 |
15.0 |
Methanol |
6.7 |
36.0 |
Methylacetylene |
1.7 |
11.7 |
Methyl Bromide |
10.0 |
15.0 |
3-Methyl-1-Butene |
1.5 |
9.1 |
Methyl Cellosolve |
2.5 |
20.0 |
Methyl Chloride |
7.0 |
17.4 |
Methyl Ethyl Ketone |
1.9 |
10.0 |
Methyl Mercaptan |
3.9 |
21.8 |
Methyl Vinyl Ether |
2.6 |
39.0 |
Monoethylamine |
3.5 |
14.0 |
Monomethylamine |
4.9 |
20.7 |
Nickel Carbonyl |
2.0 |
- |
Pentane |
1.4 |
7.8 |
Picoline |
1.4 |
ĘC |
Propane |
2.1 |
9.5 |
Propylene |
2.4 |
11.0 |
Propylene Oxide |
2.8 |
37.0 |
Styrene |
1.1 |
ĘC |
Tetrafluoroethylene |
4.0 |
43.0 |
Tetrahydrofuran |
2.0 |
ĘC |
Toluene |
1.2 |
7.1 |
Trichloroethylene |
12.0 |
40.0 |
Trimethylamine |
2.0 |
12.0 |
Turpentine |
0.7 |
ĘC |
Vinyl Acetate |
2.6 |
ĘC |
Vinyl Bromide |
9.0 |
14.0 |
Vinyl Chloride |
4.0 |
22.0 |
Vinyl Fluoride |
2.6 |
21.7 |
Xylene |
1.1 |
6.6 |
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