Gases - Explosion and Flammability Concentration Limits
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:
- flammable substance - fuel
- oxidizer - oxygen or air
- 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.
Note! The limits indicated are for gas and air at 20oC and atmospheric pressure.
| 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 |
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
Related Topics
• Combustion
Boiler house topics, fuels like oil, gas, coal, wood - chimneys, safety valves, tanks - combustion efficiency.
• Gases and Compressed Air
Air, LNG, LPG and other common gas properties, pipeline capacities, sizing of relief valves.
Related Documents
Acetone - Thermophysical Properties
Chemical, physical and thermal properties of acetone, also called 2-propanone, dimethyl ketone and pyroacetic acid. Phase diagram included.
Acetylene - Thermophysical Properties
Chemical, Physical and Thermal Properties of Acetylene.
Air Contaminants - Exposure Limits
Exposure limits for various air contaminants.
Butane - Thermophysical Properties
Chemical, physical and thermal properties of n-Butane.
Carbon Monoxide - CO - Thermophysical Properties
Chemical, Physical and Thermal Properties of Carbon Monoxide - CO.
Dust Explosions - Substances, Critical Temperatures and Concentrations
Critical temperatures and concentration parameters for substances like coal, zinc, uranium and more.
Ethane Gas - Specific Heat vs. Temperature
Specific heat of Ethane Gas - C2H6 - for temperatures ranging 250 - 900 K.
Ethane Liquid - Thermal Properties
Density, specific heat and more of liquid ethane.
Flash Points - Liquids
The flash points for some common liquids and fuels.
Fuels and Chemicals - Autoignition Temperatures
Autoignition points for fuels and chemicals like butane, coke, hydrogen, petroleum and more.
Gases - Dangerous Concentration Levels
Dangerous vs. tolerable concentration levels for some industrial gases.
Gases - Densities
Densities and molecular weights of common gases like acetylene, air, methane, nitrogen, oxygen and others.
Gases - Gross and Net Heat Values
Gross heat and net heat values for gases like hydrogen, methane and more.
Gases Solved in Water - Diffusion Coefficients
Diffusion flux [kg/m2s] tells how fast a substanse solved in another substance flows due to concentration gradients. Diffusion constants [m2/s] for several gases in water.
Gasoline - Density, Specific Heat, Viscosity and Thermal Conductivity vs. Temperature
Density, specific heat, dynamic and kinematic viscosity and thermal conductivity of gasoline vs. temperature
Hazardous Areas - European Classification Standard
European hazardous area classification with zones, protection types, temperature codes and codes.
Hazardous Areas - North America Classification
North American hazardous locations classification with classes, divisions and groups
Hydrocarbons - Autoignition Temperatures and Flash Points
Autoignition temperatures and flash points (°C and °F) of different types of hydrocarbons with varying carbon numbers up to C12.
Hydrogen - Thermophysical Properties
Chemical, Physical and Thermal Properties of Hydrogen - H2.
Methane - Dynamic and Kinematic Viscosity vs. Temperature and Pressure
Online calculator, figures and tables showing dynamic and kinematic viscosity of methane, CH4, at varying temperature and pressure - Imperial and SI Units.
Methane - Thermophysical Properties
Chemical, Physical and Thermal Properties of Methane - CH4. Phase diagram included.
Molecular Weight of Substances
Definition and molecular weight (molar mass) of some common substances.
Octane Liquid - Thermal Properties
Density, specific heat, thermal conductivity and more.
Oxygen - Thermophysical properties
Chemical, Physical and Thermal Properties of Oxygen - O2.
Propane - Thermophysical properties
Chemical, physical and thermal properties of propane gas - C3H8.
Propane - Vapor Pressure vs. Temperature
Vapor pressure vs. temperature.
Propane Butane Mixture - Evaporation Pressure
Evaporation pressure of propane butane mixture vs. temperature.
Propane Gas Piping - Capacity vs. Size
Sizing of propane gas pipe lines with pressures above 5 psig (35 kPa).
Toluene - Density and Specific Weight vs. Teemperature and Pressure
Density and specific weight of liquid toluene.
Toluene Liquid - Thermal Properties vs. Temperature
Density, specific heat, thermal conductivity and more.
Water Sprinkler - Protection Area vs. Classification
Maximum fire sprinkler protection area vs. classification and construction.