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Basic Knowledge on Gases

Combustible Gas

Combustible gas is a gas that can burn in the air or in Oxygen. Examples of combustible gases are Hydrogen, Methane, Propane, Iso-butane. Mixture of a certain amount of combustible gas and Oxygen will explode in the presence of an ignition source. Combustible gas is a typical cause of gas explosion accidents.

■Explosive range of combustible gases

The lowest concentration of combustible gas mixed with air that can explode when ignited is called Lower Explosion Limit (LEL), and Upper Explosion Limit (UEL) for the highest concentration of combustible gas in air. A combustible gas detector should be designed to trigger an alarm for shutting off the gas supply and activating ventilations before combustible gas concentration level exceeds the LEL in the area where a gas detector is installed.

Combustible gas concentration

*1 Alarm setting level is in accordance with:
Inspection Standard for Gas Alarm intended for City Gas JIA E 001-15

Gas LEL(vol%) UEL(vol%)
Hydrogen(H2) 4.0 75.6
Methane(CH4) 5.0 15.0
Propane(C3H8) 2.1 9.5
Iso-butane(C4H10) 1.8 8.4
Ethylene(C2H4) 2.7 34
Toluene(C6H5CH3) 1.2 7.0
Methanol(CH3OH) 5.5 44
Ethanol(C2H5OH) 3.5 19