Gas and Vapor Atmospheric Groups | Control Instruments Corporation

Flammable gases and vapors are separated into four different atmospheric groups:

Group A - Atmospheres containing acetylene.
Group B - Atmospheres containing hydrogen, fuel and combustible process gases containing more than 30% hydrogen by volume, or gases or vapors of equivalent hazard (butadiene, ethylene oxide, propylene oxide, and acrolien).
Group C - Atmospheres such as cyclopropane, ethyl ether, ethylene, or gases or vapors of equivalent hazard.
Group D - Atmospheres such as acetone, ammonia, benzene, butane, ethanol, gasoline, hexane, methane, natural gas, naphtha, propane, or gases or vapors of equivalent hazard.

Flammable dusts and debris are separated into three different atmospheric groups:

Group E - Atmospheres containing combustible metals regardless of resistivity, or other combustible dusts of similar hazard characteristics having resistivity of less than 102 ohms per centimeter.
Group F - Atmospheres containing carbon black, charcoal, coal or coke dusts which have more than 8% total volatile material or atmospheres containing these dusts sensitized by other materials so that they present an explosion hazard, and having resistivity greater than 102 ohms per centimeter but equal to or less than 108 ohms per centimeter.
Group G - Atmospheres containing combustible dusts having resistivity greater than or equal to 108 ohms per centimeter.