Fluidyne Standards for Maximum Experimental Safe Gap (MESG) is a standardized measurement of how easily a gas flame will pass through a narrow gap bordered by heat-absorbing metal. MESG is used to classify flammable gases for the design and/or selection of flame arrestors The National Electric Code classifies Class I hazardous locations into different groups depending on the respective MESG's of gases in the area. The flame bank design selected conforms to the area classifications and requirements of MESG.