What is LEL?
LEL stands for Lower Explosive Level and expresses the concentration value of the gas below which it cannot explode. Why is it important to know this value? Gas detectors normally use a scale from 0 to 100, where 100 equals the LEL precisely because their action is carried out below the explosion limit.
This is why you can find the wording “alarm threshold 10% LEL” in the detector data sheets.
Let’s have a look at how we can interpret this measurement.
Methane LEL is 4.4% volume-per-volume, which means that if the concentration of methane in 1 cubic metre of air exceeds 4.4%, the mixture will explode. If the alarm goes off at 10% LEL, it means that the detector will calculate 10% of 4.4%, being 0.44% of the cubic metre of air.
Some final clarifications
The measuring range of gas detectors can be expressed in % LEL or ppm.
In the case of commercial environments or thermal units, the field is usually 50% LEL, as higher concentrations are unlikely to be reached. 100% LEL is used in industrial or processing plants, often even in ATEX classified zones. 500 ppm is rather the standard measuring range for toxic gases such as carbon monoxide.