The materials in these four groups is based on the ignition temperature of the material, the explosion pressure of the material generated during an explosion; and other flammable characteristics.
In simple terms, the materials are rated by how easily they will ignite. And – with some materials there can be more than a fire. When ignited, they can explode, which creates a blast or shockwave (technically called explosion pressure). So, there can be different types of explosions, each with a different level of explosion pressure, and these are used to categorize the gasses and vapors in the four Class I Groups.
The only substance in Group A is Acetylene, which makes up only a very small percentage of all hazardous locations. Acetylene is a gas with an extremely high explosion pressure.
is another relatively small percentage of all hazardous classification areas. This group includes Hydrogen and other gases with similar characteristics.
Groups C & D
are by far the most common of the Class I Groups, with the highest percentage of hazardous locations. Present in Group D are the most common flammable gases and vapors, including Butane, Gasoline, Natural Gas and Propane.
List of Groups and their materials: