Division 2 and / or Zone 2: An area, location, or atmosphere, which is known not to contain any concentrations of ignitable or flammable vapor, gas, liquid, and / or dust during normal operation and if it should occur will exist only during short periods, such as equipment failure, breakdown, or service and maintenance.

Division 1 and / or Zone 1: An area, location, or atmosphere, which is known to contain concentrations of ignitable or flammable vapor, gas, liquid, and / or dust during normal operation and will exist frequently because of equipment failure, breakdown, or service and maintenance.

Division 1 and / or Zone 0: An area, location, or atmosphere, which is known to contain concentrations of ignitable or flammable vapor, gas, liquid, and / or dust, which is present continuously or for long periods of time.