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.[1] The National Electric Code classifies Class I hazardous locations into different groups depending on the respective MESG's of gases in the area.[2]
Examples
| 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 |
References
- Enardo Flame Arrestor Technology. "Flame Arrestor Technology" (PDF).
- Class I: Flammable gases, vapors or liquids
http://site.ul.com/global/documents/offerings/services/hazardouslocations/CI_groups.pdf%5B%5D
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