The concentration of flammable gas is too low or too high it is not dangerous, it is only mixed with air to form a mixed gas, or more precisely meet a certain proportion of oxygen mixed gas combustion or explosion will occur.
Combustion is an oxidation reaction accompanied by intense heat and light, it must have three elements:
a. Combustible (gas);
b. Comburent (oxygen);
c. Ignition Source (temperature)
"LEL" refers to the lower explosive limit.
In case of combustible gas in the air next lowest concentration of fire explosion, known as the lower explosive limit - Shorthand:% LEL.EN：Lower Explosion Limited。
In case of combustible gas in the air next highest concentration of fire explosion, known as the higher explosive limit - in short %UEL.EN：Upper Explosion Limited。
Combustible gas combustion can be divided into two categories, one is the diffusion combustion, which volatilize or ejected from the device, a gas leak may encounter an ignition source mixed combustion.
The other type of combustion, is a mixture of gas and air combustion, the combustion reaction is intense and fast, will produce a huge pressure and sound, but also known as the explosion. There is no strict distinction between combustion and explosion.
Relevant authorities and experts were burning combustible gas explosion analysis, reach conclusion of a combustible gas explosion limit, it is divided into upper explosive limit(Shorthand:UEL)and lower explosive limit(Shorthand:LEL).
Below the lower explosive limit,The content of combustible gas in the mixed gas is insufficient,can not cause combustion or explosion;Above the upper explosive limit,insufficient oxygen content in mixed gas,it can not cause combustion and explosion.
The combustion and explosion of combustible gas It is also related to the pressure, temperature and ignition energy of the gas ,and other factors. Explosive limit is generally represented by volume percentage concentration.
Combustible gas concentration in the air only in the explosion limit will occur explosion .Below the lower explosive limit or above the upper explosive limit the explosion will not happen.Therefore, when the explosion measured, the alarm concentration is generally set at less than 25%LEL of the lower explosive limit .
The measuring range of combustible gas detector is 0-100%LEL.Fixed type combustible gas detector is usually equipped with two alarm points (model of the alarm host):10%LEL for the first level alarm, 25%LEL for the two level.