LEL and UEL in relation with the Minimum Ignition Energy
LEL: The Lower Explosive Limit (LEL) is the lowest concentration of a gas, vapor or dust that will burn in air.
UEL: The Upper Explosion Limit (UEL) is the highest concentration of a gas, vapor or dust, that will burn in air.
These values for gases and vapors are mostly expressed as a volume-% (vol%) in air. For dust mostly as the mass-concentration in air in gr/m3. When the concentration of the substance in air is between these values there is an explosive atmos[here. When the concentration is beneath the LEL, the mixture is too lean and when the concentration of above the UEL the mixture is too rich to ignite.
![What means the LEL and UEL of substances? 1 lel uel graph tekengebied 1](https://hazcalconline.com/img/272d68c9-ef4d-4efb-b70f-9fded0dad2bf/lel-uel-graph-tekengebied-1.jpg?fm=png&q=80&fit=max&crop=1686%2C1080%2C0%2C0)
Within this figure it is shown that always a Minimum Ignition Energy is needed for combustion. More energy is needed when a mixture is getting quite lean or quite rich. Below the LEL or above the UEL no combustion is possible.
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