ATEX Zones – Hazardous Area Classification

Potentially explosive atmospheres are divided into corresponding zones – depending on the frequency and duration of the occurrence of hazardous explosive atmospheres. The definition of the zone for the operation of the plant is the responsibility of the plant operator. The manufacturer is responsible for determining the zone for the equipment. Finally, the plant operator decides on the zoning.

Zoning and labeling and categorization are considered in more detail in this paper.

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 this is present, the more critical the zone becomes. A distinction 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. In terms of classification, they are the same.

• Zone 0/20: An explosive atmosphere occurs continuously, for long periods or frequently.
• Zone 1/21: An explosive atmosphere occurs occasionallyduring normal operation.
• Zone 2/22: An explosive atmosphere does not occur or is likely to occur in the short term during normal operation.

Device 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 protective measures for explosion protection to the probability of the occurrence of explosive atmospheres.

For standard plants, testing of a type is possible, provided that it remains with this design and no modifications are made to the type. For all other equipment, a separate inspection is required (either by a notified body or a trained service technician).

According to Directive 2014/34/EU (ATEX), the classification is made into the following equipment groups and categories:

• Equipment group I covers potentially explosive atmospheres below ground. The hazard arises from mine gas and/or dust. This includes the categories M1 and M2:
  • The M1 category testifies to a very high level of safety, even when two independent faults occur.
  • The M2 category testifies to a high level of safety. The devices switch themselves off when explosive atmospheres occur.

• Equipment group II covers potentially explosive atmospheres above ground. The hazard arises from liquids or gases. This includes the device categories 1,2 and 3:
  • Device category 1 testifies to a very high level of safety.
    The degree of protection is very high for rare faults and for the occurrence of two independent faults.
  • Equipment category 2 testifies to a high level of safety.
    The degree of protection is high in the event of an expected malfunction and a fault.
  • Equipment category 3 testifies to an increased level of safety.
    The degree of protection is normal in normal operation.

• Equipment group III covers potentially explosive atmospheres above ground. The hazard arises from finely dispersed solids (dust).

Assignment of the device categories to the Ex zones

Dust collector markings

The marking of dust collectors subject to 2014/34/EU is carried out
in accordance with EN 80079-36. The marking of a dust extractor in a potentially explosive atmosphere or in operation of potentially explosive dusts or gases must be clearly and indelibly placed on the system, e.g. in the form of a type plate. The labeling must include the following information:

• CE marking, number of the notified body and the EX mark
• Group and the device category within the meaning of the 2014/34/EU
• Protection principle, e.g. Exh=constructive safety

• Gas or dust group:
  • Gas group IIB contains groups IIB and IIA, but not IIC.
  • Dust group IIIA defines combustible fluff, dust group IIIB does not.
    conductive dusts and the dust group IIIC conductive dusts

• Temperature range in which the equipment may be used. The definition is made via the process temperature.
  • Class: perm. 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

• Device protection level: indication of the device protection level required for the device category.
  • Zone 2 or 22 : Avoidance of ignition sources in normal operation.
    Marking: Gc or Dc.
  • Zone 1 or 21: Avoidance of ignition sources even in the event of normal operating faults.
    Marking: Gb or Db.
  • Zone 0 or Zone 20: Avoidance of ignition sources even in the event of infrequent operating faults.
    Marking: Ga or Da.

• Field for acceptances (if not used, then “/”)

• Range of application of the device
  • –: the device can be used without restriction.
  • X: there are specific conditions of use, which are described in more detail in the documentation.
    must be described.
  • 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 labels must be present on the equipment.

An example labeling for dust collection equipment may look like this:

Gases/vapors:	CE 0588		II 2/-G	Exh	IIB	T6...T5	Gb /	-
Dust:	CE 0588		II 2/-D	Exh	IIIA	T85°...T100°C	Db /	-

Conclusion

The classification of hazards and the division into equipment categories means that different safety concepts are applied to the equipment and systems used. 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 maintain the safety of people and the environment.