title: Maximum experimental safe gap
text: # Maximum experimental safe gap
  
  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 electrical equipment in hazardous areas, and flame arrestor devices. The National Electric Code classifies Class I hazardous locations into different groups depending on the respective MESG's of gases in the area.
  
  ## Examples
  
  NEC Class I Group and Gas MESG :
  
  | NEC Class I Group | Gas MESG | Example Gas |
  | - | - | - |
  | Group A | 0.25 mm | Acetylene |
  | Group B | ≤0.45 mm (Except acetylene) | Hydrogen |
  | Group C | 0.45 mm < x ≤ 0.75 mm | Ethylene |
  | Group D | > 0.75 mm | Propane |
  