MESG Maximum Experimental Safe pressure dependence

The maximum gap of a combustible substance/air mixture is the gap width at which an ignition through the gap does not occur just any more. The lowest value of all maximum gaps of a substance that was determined under atmospheric pressure in dependence on the substance concentration is the Afaximum Experimental Safe Gap (MESG). The appertaining combustible substance mixture is designated as the most readily ignitable mixture. The gap width depends on the temperature and the pressure. A rise in pressure and temperature leads to a reduction of the gap width. 

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