Hazardous areas are divided into appropriate zones - depending on the frequency and duration of the occurrence of hazardous explosive atmospheres. The specification of the zone for the operation of the system is the responsibility of the system operator. The specification of the zone for the system is the responsibility of the manufacturer. In the end, the system operator decides on the zone classification.
Zone classification as well as marking and categorization are considered in more detail in this article.
The basis for the classification into zones is the duration of the presence of the potentially explosive atmosphere: The longer it is present, the more critical the zone. A differentiation is made between gas Ex zones and dust Ex zones: Gas Ex zones are 0/1/2 and dust Ex zones are 20/21/22. As to the classification, they are the same.
In addition to the classification of the areas, there is also a classification of the equipment that can be used according to the necessary safety requirements. The classification results from the risk assessment: The manufacturer of equipment with a potential ignition source must relate the protection measures for explosion protection to the probability of the occurrence of potentially explosive atmospheres.
For standard systems, testing of a model type is possible, provided that it remains with this design and no modifications are made to the model type. For all other systems, a separate inspection is required (either by a notified body or a service technician trained for this purpose).
According to Directive 2014/34/EU (ATEX), the classification is made into the following equipment groups and categories:
|Combustible medium||Duration of the presence of explosive atmosphere||Ex zone||Classification
|Gases, vapors, mists (G)
||Constantly, continuously||Zone 0||II||
|Dust (D)||Constantly, continuously||Zone 20||II||
The marking of dedusting systems subject to 2014/34/EU takes place
according to EN 80079-36. The marking of a deduster in an explosive atmosphere respectively in operation with explosive dusts or gases must be placed clearly and non-erasable on the equipment, e.g. in the form of a type plate. The marking must include the following information:
The marking must be indicated separately for dust Ex as well as gas Ex. This means that for hybrid mixtures, two markings are required to be on the equipment.
An example marking for dedusting systems may look as shown below:
|Gases/Vapor:||CE 0588||II 2/-G||Exh||IIB||T6...T5||Gb /||-|
|Dust:||CE 0588||II 2/-D||Exh||IIIA||T85°...T100°C||Db /||-|
The classification of hazard as well as the division into equipment categories means that different safety concepts apply for the equipment and systems deployed. The requirements can be found in the relevant standards. It is important that the processes and substances must be known in order to make the right choice and thus protect the safety of people and the environment.