ATEX Zones - Hazardous Area Classification

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.

Dust and gas Ex zones

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.

• Zone 0/20: A potentially explosive atmosphere occurs continuously, over long periods or frequently.
• Zone 1/21: A potentially explosive atmosphere occurs occasionally during normal operation.
• Zone 2/22: A potentially explosive atmosphere does not or only briefly occur during normal operation.

Equipment groups and categories

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:

• Device Group I is for hazardous areas in mining applications. The hazard arises from mining gas and/or dust. Included here are the categories M1 and M2:
  
  • Category M1 indicates a very high level of safety, even on occurrence of two independent errors.
  • Category M2 indicates a high level of safety. The equipment shuts itself off on occurrence of explosive atmospheres.
• Device Group II is for hazardous areas in applications above ground. The hazard arises from liquids or gases. Included here are equipment categories 1, 2 and 3:
  • Equipment category 1 indicates a very high level of safety.
    The degree of protection is very high in the case of rare malfunctions and the occurrence of two independent errors.
  • Equipment category 2 indicates a high level of safety.
    The degree of protection is high in the event of an expected malfunction and one error.
  • Equipment category 3 indicates an increased level of safety.
    The degree of protection is normal under standard operation.
• Device Group III is for hazardous areas in applications above ground. The hazard arises from finely suspended solids (dust).

Marking of dedusting systems

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:

• CE marking, number of the notified body and the EX marking
• Group and equipment category withing the meaning of 2014/34/EU
• Protection principle, e.g. Exh=constructive safety
• Gas or dust group:
  • The gas group IIB includes the IIB and IIA groups, but not IIC.
  • Dust group IIIA defines combustible lint; dust group IIIB defines non-conductive dusts, and dust group IIIC defines conductive dusts
• Temperature range in which the system may be operated. The definition is made via the process temperature.
  • Class: Allowable surface temperature / max. process temperature
    T1: 450°C/360°C ; T2: 300°C/240°C ; T3: 200°C/ 160°C ;
    T4: 135°C/108°C ; T5: 100°C/80°C ; T6: 85°C/68°C
• Equipment protection level: Indication of the equipment protection level required for the equipment category.
  • Zone 2 resp. 22: Prevention of ignition sources in regular operation.
    Marking: Gc resp. Dc.
    Zone 1 resp. 21: Prevention of ignition sources also under common operational malfunctions.
    Marking: Gb resp. Db.
    Zone 0 resp. Zone 20: Prevention of ignition sources also under rare operational malfunctions.
    Marking: Ga resp. Da.
• Field for certification (if no use, then "/")
• Applicational range of the equipment
  • --: The equipment can be used without restriction.
  • X: There are specific application conditions that must be described in more detail in the documentation.
  • U: Incomplete machine, without CE marking

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:

Summary

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.