Upper Flammable Limit 02


Upper Flammable Limit 02 : Limits: (1) Lower Explosive Limit: Lower Explosive Limit (LEL): The lowest concentration (percentage) of a gas or a vapor in air capable of producing a flash of fire in presence of an ignition source (arc, flame, heat). The term is considered to be the same as the lower flammable limit (LFL). At a concentration in air lower than the LEL, gas mixtures are "too lean" to burn. Methane gas has a LEL of 5%. If the atmosphere has less than 5% methane, an explosion cannot occur even if a source of ignition is present. Percentage reading on combustible air monitors should not be confused with the LEL concentrations. Explosimeters designed and calibrated to a specific gas may show the relative concentration of the atmosphere to the LELthe LEL being 100%. A 5% displayed LEL reading for methane, for example, would be equivalent to 5. 1% multiplied by 5%, or approximately 0. 25% methane by volume at 20 degrees C. Control of the explosion hazard is usually achieved by sufficient natural or mechanical ventilation, to limit the concentration of flammable gases or vapors to a maximum level of 25% of their lower explosive or flammable limit
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