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Gases - Explosion and Flammability Concentration Limits

Flame and explosion limits for gases - propane, methane, butane, acetylene and more

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The Flammable Range (also called Explosive Range) is the concentration range of a gas or vapor that will burn (or explode) if an ignition source is introduced.

Three basic requirements must be met for explosion to take place:

  1. flammable substance - fuel
  2. oxidizer - oxygen or air
  3. source of ignition - spark or high heat

Below the explosive or flammable range the mixture is too lean to burn and above the upper explosive or flammable limit the mixture is too rich to burn. The limits are commonly called the "Lower Explosive or Flammable Limit" (LEL/LFL) and the "Upper Explosive or Flammable Limit" (UEL/UFL).

The lower and upper explosion concentration limits for some commonly used gases are indicated in the table below. Some of the gases are commonly used as fuel in combustion processes.

Fuel Gas"Lower Explosive or Flammable Limit"
(LEL/LFL)
(% by volume of air)
"Upper Explosive or Flammable Limit"
(UEL/UFL)
(% by volume of air)
Acetaldehyde 4 60
Acetic acid 4 19.9
Acetone 2.6 12.8
Acetonitrile 3 16
Acetyl chloride 7.3 19
Acetylene 2.5 100
Acrolein 2.8 31
Acrylic acid 2.4 8
Acrylonitrile 3.0 17
Allyl chloride 2.9 11.1
Allyll alcohol 2.5 18
Alyllamine 2.2 22
Ammonia 15 28
Aniline 1.3 11
Arsine 5.1 78
Benzene 1.2 7.8
Biphenyl 0.6 5.8
Bromobuthane (1-Bromobuthane) 2.6 6.6
Bromoethane 6.8 8
Bromoethene 9 15
Butadiene (1,3-Butadiene) 2.0 12
Butanal 1.9 12.5
Butane (n-Butane) 1.86 8.41
Butanoic acid 2 10
Butyl acetate 1.7 7.6
Butyl alcohol, Butanol 1 11
Butyl formate 1.7 8.2
Butyl methyl ketone 1 8
Butylamine 1.7 9.8
Butylbenzene 0.5 5.8
Butylene 1.98 9.65
Butyll acrylate 1.9 9.9
Carbon disulfide 1.3 50
Carbon monoxide 12 75
Carbon oxysulfide 12 29
Chlorobenzene 1.3 9.6
Chloroethane 3.8 15.4
Cyanogen 6.0 42.6
Cyclobutane 1.8 11.1
Cycloheptane 1.1 6.7
Cyclohexane 1.3 8
Cyclohexanol 1 9
Cyclohexanone 1 9
Cyclopropane 2.4 10.4
Decane 0.8 5.4
Diacetone alcohol 1.8 6.9
Diborane 0.8 88
Dibutylamine 1.1 6
Dichloroethane (1,1-Dichloroethane) 6 11
Diesel fuel 0.6 7.5
Diethanolamine 2 13
Diethyl ether 1.9 36
Diethylamine 2 13
Diethylether 1.9 48
Diisobutyl ketone 1 6
Diisopropyl ether 1 21
Dimethyl sulphoxide 3 42
Epichlorohydrin 4 21
Ethane 3 12.4
Ethyl acetate 2 12
Ethyl acrylate 1.4 14
Ethyl alcohol, Ethanol 3.3 19
Ethyl chloride 3.8 15.4
Ethyl nitrite 4 50
Ethyl propyl ether 1.7 9
Ethyl vinyl ether 1.7 28
Ethylamine 3.5 14
Ethylbenzene 1.0 7.1
Ethylcyclobutane 1.2 7.7
Ethylene 2.75 28.6
Ethylene oxide 3 100
Etylene glycol 3 22
Fluoroethene 2.6 21.7
Formaldehyde 7 73
Formic acid 18 57
Fuel Oil - No.1 0.7 5
Furan 2 14
Furfural 2 19
Gasoline 1.4 7.6
Glycerol 3 19
Heptane 1.0 6.7
Heptane (n-Heptane) 1.0 6.0
Hexane 1.1 7.5
Hexane (n-Hexane) 1.25 7.0
Hydrazine 5 100
Hydrogen 4 75
Hydrogen 6 40
Hydrogen sulfide 4.3 46
Isobutanal 1.6 10.6
Isobutane 1.80 8.44
Isobutene 1.8 9.0
Isobutyl alcohol 2 11
Isooctane 0.79 5.94
Isopentane 1.32 9.16
Isophorone 1 4
Isopropyl alcohol, Isopropanol 2 12
Isopropylbenzene 0.9 6.5
Kerosene Jet A-1 0.7 5
Mesityl oxide 1.4 7.2
Methacrylic acid 1.6 8.8
Methane 4.4 16.4
Methylamine 4.9 20.7
Methyl acetate 3 16
Methyl alcohol, Methanol 6.7 36
Methyl acrylate 2.8 25
Methyl chloride 10.7 17.4
Methyl ethyl Ketone 1.8 10
Methyl formate 4.5 23
Methylhydrazine 2.5 92
Methyl isocyanate 5.3 26
Mineral spirits 0.7 6.5
Naphtalene 0.9 5.9
Naphthalene 0.9 5.9
Neohexane 1.19 7.58
Neopentane 1.38 7.22
Nitrobenzene 2 9
Nitroethane 3.4 17
Nitromethane 7.3 22.2
Nonane 0.8 2.9
Octane (n-Octane) 1.0 7
Oxirane 3 100
Paraformaldehyde 7 73
Pentane (n-Pentane) 1.4 7.8
Pentene (n-Pentene) 1.65 7.7
Pentyl acetat 1.1 7.5
Pentylamine 2.2 22
Phenol 1.8 8.6
Piperidine 1 10
Propane 2.1 10.1
Propanoic acid 2.9 12.1
Propene 2 11.1
Propyl acetate 2 8
Propylamine 2 10.4
Propylbenzene 0.8 6
Propyl nitrate 2 100
Propylene 2.0 11.1
Propylene oxide 2.3 36
Propyne 2.1 12.5
Pyridine 2 12
Silane 1.5 98
Styrene 1.1 6.1
Tetrafluoroethene 10 50
Tetrahydrofuran 2 12
Toluene 1.1 7.1
Trichloroethylene 13 90
Triethylene glycol 0.9 9.2
Triptane 1.08 6.69
Trimethylamine 2 11.6
Turpentine 0.8
Vinyl acetate 2.6 13.4
Vinyl butanoate 1.4 8.8
Vinyl chloride 3.6 33
o-Xylene 0.9 6.7
m-Xylene 1.1 7
p-Xylene 1.1 7

Note! The limits indicated are for gas and air at 20oC and atmospheric pressure.

It is important that areas that store flammable gases are well ventilated. When designing ventilation systems be aware of the specific gravity of the actual gas. The gas mixture from a leakage will not be homogeneous and lighter gases concentrates along the ceiling. Heavy gases concentrates along the floor.

Ventilation, natural or mechanical, must be sufficient to limit the concentration of flammable gases or vapors to a maximum level of 25% of their "Lower Explosive or Flammable Limit" (LEL/LFL).

  • Minimum ventilation required: 1 cfm/ft2 (20 m3/h m2)
  • Recommended ventilation: 2 cfm/ft2 (40 m3/h m2) or 12 air changes per hour - half the air supplied and exhausted near the ceiling and half the air supplied and exhausted near the floor
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