Maximum experimental safe gap


Maximum experimental safe gap 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 Electrical Code classifies Class I hazardous locations into different groups depending on the respective MESG's of gases in the area.

Examples

NEC Class I GroupGas MESGExample Gas
Group A0.25 mmAcetylene
Group B≤0.45 mm Hydrogen
Group C0.45 mm < x ≤ 0.75 mmEthylene
Group D> 0.75 mmPropane