What is a Gas Flammability Limit? Insight to Understanding Flammable Gas Limits

A Post from the Blog:


Visitors to our websites often search for details on combustible or flammable gases since leaks and exposures of this gas type have created some of the most catastrophic industry events. We will post a series of articles helping to better explain the differences between flammability and combustibility, explosive limits, as well as present a gas tables for reference.

What is a Flammability Limit?

The amount of combustible gas in an air mixture when the mixture is flammable is known as the flammability limit or flammable limit. Gas mixtures that consist of combustible, oxidizing, or inert gases are only flammable under certain conditions. The lower flammability limit (LFL) identifies the smallest mixture able to sustain a flame. The upper flammable limit (UFL) identifies the richest flammable mixture.

A quantifiable difference exists between the flammability limit and explosive limit. In specialized process applications such as combustion engines, achieving the perfect combustible or explosive mixture is important. However, in engineering a gas detection system, the flammable gas cloud is turbulent and the exact mixture can greatly vary. As such, many professionals interchange the term flammability limit (UFL/LFL) and explosive limit (UEL/LEL) depending on their education or geographic location.

Flammable / Combustible / Explosive Gases and Vapors A reference chart of LFL/LEL, EFL/EL, NFPA Classes and their Flash Point

Gases and Vapors
LFL/LEL in %
by volume of air
UFL/UEL in %
by volume of air
NFPA Class
Flash point
Acetaldehyde 4.0 57.0 IA -39°C
Acetic acid (glacial) 4 19.9 II 39°C to 43°C
Acetic anhydride     II 54°C
Acetone 2.6 - 3 12.8 - 13 IB -17°C
Acetonitrile     IB 2°C
Acetyl chloride 7.3 19 IB 5°C
Acetylene 2.5 82 IA -18°C
Acrolein 2.8 31 IB -26°C
Acrylonitrile 3.0 17.0 IB 0°C
Allyl chloride 2.9 11.1 IB -32 °C
Ammonia 15 28 IIIB 11°C
Arsine 4.5 - 5.1 78 IA Flammable gas
Benzene 1.2 7.8 IB -11°C
1,3-Butadiene 2.0 12 IA -85°C
Butane, n-Butane 1.6 8.4 IA -60°C
n-Butyl acetate, Butyl acetate 1 - 1.7 8 - 15 IB 24°C
Butyl alcohol, Butanol 1 11 IC 29°C
n-Butanol 1.4 11.2 IC 35°C
n-Butyl chloride, 1-chlorobutane 1.8 10.1 IB -6°C
n-Butyl mercaptan 1.4 10.2 IB 2°C
Butyl methyl ketone, 2-Hexanone 1 8 IC 25°C
Butylene, 1-Butylene, 1-Butene 1.98 9.65 IA -80°C
Carbon disulfide 1.0 50.0 IB -30°C
Carbon Monoxide 12 75 IA -191°C Flammable gas
Chlorine monoxide     IA Flammable gas
1-Chloro-1,1-difluoroethane 6.2 17.9 IA -65°C Flammable Gas
Cyanogen 6.0 - 6.6 32 - 42.6 IA Flammable gas
Cyclobutane 1.8 11.1 IA -63.9°C[11]
Cyclohexane 1.3 7.8 - 8 IB -18°C - -20°C
Cyclohexanol 1 9 IIIA 68°C
Cyclohexanone 1 - 1.1 9 - 9.4 II 43.9 - 44°C
Cyclopentane 1.5 - 2 9.4 IB - 37 to -38.9°C
Cyclopropane 2.4 10.4 IA -94.4°C
Decane 0.8 5.4 II 46.1°C
Diborane 0.8 88 IA -90°C Flammable gas
o-Dichlorobenzene, 1,2-Dichlorobenzene 2 9 IIIA 65°C
1,1-Dichloroethane 6 11 IB 14°C
1,2-Dichloroethane 6 16 IB 13°C
1,1-Dichloroethene 6.5 15.5 IA -10°C Flammable gas
Dichlorofluoromethane   54.7   Non flammable, -36.1°C
Dichloromethane, Methylene chloride 16 66   Non flammable
Dichlorosilane 4 - 4.7 96 IA -28 °C
Diesel fuel 0.6 7.5 IIIA >62°C (143°F)
Diethanolamine 2 13 IB 169°C
Diethylamine 1.8 10.1 IB -23°C to -26°C
Diethyl disulfide 1.2   II 38.9°C
Diethyl ether 1.9 - 2 36 - 48 IA -45°C
Diethyl sulfide     IB -10°C
1,1-Difluoroethane 3.7 18 IA -81.1°C
1,1-Difluoroethylene 5.5 21.3   -126.1°C
Diisobutyl ketone 1 6   49°C
Diisopropyl ether 1 21 IB -28°C
Dimethylamine 2.8 14.4 IA Flammable gas
1,1-Dimethyl hydrazine     IB  
Dimethyl sulfide     IA -49°C
Dimethyl sulfoxide 2.6 - 3 42 IIIB 88 - 95°C
1,4-Dioxane 2 22 IB 12°C
Epichlorohydrin 4 21   31°C
Ethane 3 12 - 12.4 IA Flammable gas -135 °C
Ethanol, Ethyl Alcohol 3 - 3.3 19 IB 12.8°C (55°F)
2-Ethoxyethanol 3 18   43°C
2-Ethoxyethyl acetate 2 8   56°C
Ethyl acetate 2 12 IA -4°C
Ethylamine 3.5 14 IA -17 °C
Ethylbenzene 1.0 7.1   15-20 °C
Ethylene 2.7 36 IA  
Ethylene glycol 3 22   111°C
Ethylene oxide 3 100 IA −20 °C
Ethyl Chloride 3.8 15.4 IA −50°C
Ethyl Mercaptan     IA  
Fuel oil No.1 0.7 5    
Furan 2 14 IA -36°C
Gasoline (100 Octane) 1.4 7.6 IB < −40°C (−40°F)
Glycerol 3 19   199°C
Heptane, n-Heptane 1.05 6.7   -4°C
Hexane, n-Hexane 1.1 7.5   -22°C
Hydrogen, dihydrogen, molecular H with two protons together 4 75 IA Flammable gas
Hydrogen sulfide 4.3 46 IA Flammable gas
Isobutane 1.8 9.6 IA Flammable gas
Isobutyl alcohol 2 11   28°C
Isophorone 1 4   84°C
Isopropyl alcohol, Isopropanol 2 12 IB 12°C
Isopropyl chloride     IA  
Kerosene Jet A-1 0.6 - 0.7 4.9 - 5 II >38°C (100°F) as jet fuel
Lithium Hydride     IA  
2-Mercaptoethanol     IIIA  
Methane (Natural Gas) 4.4 - 5 15 - 17 IA Flammable gas
Methyl acetate 3 16   -10°C
Methyl Alcohol, Methanol 6 - 6.7 36 IB 11°C
Methylamine     IA 8°C
Methyl Chloride 10.7 17.4 IA -46 °C
Methyl ether     IA −41 °C
Methyl ethyl ether     IA  
Methyl ethyl ketone 1.8 10 IB -6°C
Methyl formate     IA  
Methyl mercaptan 3.9 21.8 IA -53°C
Mineral spirits 0.7 6.5   38-43°C
Morpholine 1.8 10.8 IC 31 - 37.7°C
Naphthalene 0.9 5.9 IIIA 79 - 87 °C
Neohexane 1.19 7.58   −29 °C
Nickel tetracarbonyl 2 34   4 °C
Nitrobenzene 2 9 IIIA 88°C
Nitromethane 7.3 22.2   35°C
Octane 1 7   13°C
iso-Octane 0.79 5.94    
Pentane 1.5 7.8 IA -40 to -49°C
n-Pentane 1.4 7.8 IA  
iso-Pentane 1.32 9.16 IA  
Phosphine     IA  
Propane 2.1 9.5 - 10.1 IA Flammable gas
Propyl acetate 2 8   13°C
Propylene 2.0 11.1 IA -108°C
Propylene Oxide 2.3 36 IA  
Pyridine 2 12   20
Silane 1.5 98 IA  
Styrene 1.1 6.1 IB 31 - 32.2°C
Tetrafluoroethylene     IA  
Tetrahydrofuran 2 12 IB -14°C
Toluene 1.2 -1.27 6.75 - 7.1 IB 4.4°C
Triethylborane       -20°C
Trimethylamine     IA Flammable gas
Trinitrobenzene     IA  
Turpentine 0.8   IC 35°C
Vegetable oil     IIIB 327°C (620°F)
Vinyl acetate 2.6 13.4   −8 °C
Vinyl chloride 3.6 33    
Xylenes 0.9 - 1.0 6.7 - 7.0 IC 27 - 32°C
m-Xylene 1.1 7 IC 25°C
o-Xylene     IC 17 °C
p-Xylene 1.0 6.0 IC 27.2°C
Gases and Vapors
LFL/LEL in %
by volume of air
UFL/UEL in %
by volume of air
NFPA Class
Flash point

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