Ex zones at a glance: Classification and hazardous areas

Industrial plants often have hazardous areas, such as chemical plants where flammable gases or vapors can be released, or grain silos where combustible dusts can accumulate. In Europe, hazard analyses must be carried out in order to identify such potential hazards and take appropriate safety measures.

Potentially explosive areas are divided into Ex zones. There are six Ex zones in total; three for gases and vapors (Ex zones 0, 1, and 2) and three for dusts (Ex zones 20, 21, and 22). The classification into the respective zone is determined by the frequency and duration with which the hazardous substance is present in dangerous, i.e. explosive, concentrations.

Zone 0 (gases and vapors) or Zone 20 (dust)
Constant or frequent occurrence of an explosive atmosphere, i.e. over 50 percent of the operating time.

Example Zone 0: The inside of a gasoline tank in a refinery, where flammable vapors are almost constantly present in a dangerous concentration

Example Zone 20: The inside of a grain silo, where fine grain dust is constantly present in the air, which could ignite and explode in the event of an ignition source.

Zone 1 (gases and vapors) or Zone 21 (dust)
Occasional occurrence of an explosive atmosphere, i.e. usually one to 10 percent of the operating time, in any case less than 50 percent.

Example Zone 1: The area around a filling station in a chemical plant where vapors are occasionally released during the transfer of flammable liquids such as ethanol, which can form an explosive atmosphere.

Example Zone 21: A flour mill where fine dust is regularly, but not constantly, whirled up during the processing of flour, which could cause an explosion in contact with an ignition source.

Zone 2 (gases and vapors) or Zone 22 (dust)
As a rule, an explosive atmosphere does not occur during normal operation. However, this is possible rarely and for short periods, usually less than 30 minutes per year.

Example Zone 2: The area around a gas vent where gas only escapes briefly in the event of a leak.

Example zone 22: The area under a conveyor belt in a sugar factory. Normally there is no dust in dangerous quantities, but if the conveyor belt breaks down for a short time or something is spilled, a small amount of sugar dust could accumulate, which would be explosive if an ignition source were present.

Note: There is no binding definition for the terms “frequent”, “occasional” and “rare”. The actual frequency of occurrence of an explosive atmosphere is also often disputed. In case of doubt, the less favorable case should always be chosen.

Vanessa Bartsch