Class I—Locations in which flammable gases or vapors may or may not be insufficient quantities to produce explosive or ignitable mixtures.
Group D—Atmospheres containing a flammable gas, flammable liquid-produced vapour, or combustible liquid-produced vapour whose MESG is greater than 0.75 mm or MIC ration is greater than 0.80. Typical gases include acetone, ammonia, benzene, butane, ethanol, gasoline, methane, natural gas, naphtha, and propane.