Group D : Atmospheres such as acetone, alcohol, ammonia, benzine, benzol, butane, gasoline, hexane, lacquer solvent vapors, methane, naphtha, natural gas, propane, or gases or vapors of equivalent hazard
EESiFlo North America, Terminology and Glossary: Explosion Proof & Hazardous Areas, Pennsylvania, USA 2002, flowmeterdirectory.com/flowmeter_terminology, (Mrtm/ Explo Proof and Haz Areas - Amer) {561}