Lower explosion limit LEL
Definition
Lower limit of the range of the concentration of dust in air, at which the dust/air mixture can be caused to explode.
Determination
The lower explosion limit is determined by the explosion tests described to determine pmax and KSt. In the course of a series of tests, the dust concentrations are varied in a wide range, and the explosion pressure and the rate of explosion pressure rise of the reaction is determined. The concentration, at which ignition of the dust/air mixture no longer occurs is determined by further reduction of the dust concentration according to the same method. By reducing the dust concentration stepwise in the same way, the concentration is determined at which no ignition of the dust/air mixture occurs at least three times. This concentration is by definition regarded as the lower explosion limit of the dust.
The lower explosion limit can also be estimated approximately on the basis of the tests in the modified Hartmann tube.
Remark
Insofar as no values are available from the 1 m3 vessel or from the 20 l sphere (i.e. no data on pmax and KSt are included), the cited value indicates for information purposes the appropriate concentration from tests with the modified Hartmann tube. In some cases the values are calculated.
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