What does the measurement range of combustible gas detector 0-100%LEL mean?
"LEL" refers to lower explosive limit. The lowest concentration of flammable gas that explodes when encountering an open fire in the air is called the lower explosion limit—abbreviated as %LEL. English: Lower ExplosionLimited.
The highest concentration of flammable gas that explodes when encountering an open fire in the air is called the upper limit of explosion—abbreviated as %UEL. English: UpperExplosion Limited.
So what is the lower explosive limit?
There is no danger if the concentration of flammable gas is too low or too high. It will burn or explode only when it is mixed with air to form a mixture, or more precisely, when it encounters oxygen to form a mixture of a certain proportion. Combustion is a violent oxidation reaction accompanied by light and heat. It must have three elements: a. combustible material (gas); b. combustion aid (oxygen); c. ignition source (temperature). The combustion of combustible gas can be divided into two categories. One is diffusion combustion, that is, the combustible gas that volatilizes or ejects or leaks from the equipment mixes and burns when it encounters an ignition source. Another type of combustion is when combustible gas and air are mixed and ignite. This kind of combustion reaction is intense and fast, and generally produces huge pressure and sound, which is also called an explosion. There is no strict distinction between combustion and explosion.
Relevant authoritative departments and experts have conducted combustion and explosion analysis of the currently discovered combustible gases and formulated the explosion limits of flammable gases, which are divided into upper explosion limits (UEL, abbreviation for upper explosion limit in English) and lower explosion limits (abbreviation for lower explosion limit, in English). LEL?). Below the lower explosion limit, the combustible gas content in the mixed gas is insufficient to cause combustion or explosion; above the upper limit, the oxygen content in the mixed gas is insufficient to cause combustion or explosion. In addition, the combustion and explosion of combustible gas are also related to factors such as gas pressure, temperature, and ignition energy. Explosion limits are generally expressed in terms of volume percentage concentration.
The explosion limit is a general term for the lower explosion limit and the upper explosion limit. An explosion will occur only when the concentration of flammable gas in the air is between the lower explosion limit and the upper explosion limit. There will be no explosion below the lower explosion limit or above the upper explosion limit. Therefore, when conducting explosion measurements, the alarm concentration is generally set below 25% LEL of the lower explosion limit.
Fixed combustible gas detectors usually have two alarm points (related to the model of the alarm host): 10% LEL is an alarm, and 25% LEL is a secondary alarm.
Portable combustible gas detectors usually have an alarm point: 25% LEL is the alarm point.
For example, the lower explosion limit of methane is 5% volume ratio. That is to say, divide this 5% volume ratio into one hundred equal parts and let 5% volume ratio correspond to 100% LEL. That is to say, when the detector value reaches 10 At the %LEL alarm point, it is equivalent to the methane content at this time being 0.5% volume ratio. When the detector value reaches the 25% LEL alarm point, it is equivalent to the methane content at this time being 1.25% volume ratio.
Therefore, you don’t have to worry about whether there will be danger at any time after the alarm. This is a reminder to you to take corresponding measures immediately, such as turning on the exhaust fan or cutting off some valves, etc., which is far from the lower limit of explosion where danger may actually occur. There is still a big gap, so that it can serve as an alarm reminder.
