Hazardous Area Classification

ATEX hazardous area classifications analyse and classify the environment where explosive atmospheres may occur in order to aid the correct selection, installation and usage of equipment.

Flammable and/or combustible substances are materials which may form an explosive atmosphere either through being flammable themselves, or through being capable of producing a flammable gas, vapour or mist.

A “source of release” is a point or location from which a flammable gas, vapour or liquid may be released into the atmosphere in such a way that an explosive gas atmosphere could be formed. The basic elements for establishing the classification of ATEX zones are the identification of the source of release and the determination of the grade of release.

  • Continuous – release which is continuous or is expected to occur frequently or for long periods;
  • Primary – release which can be expected to occur periodically or occasionally during normal operation*;
  • Secondary – release which is not expected to occur in normal operation and, if it does occur, is likely to do so infrequently and for short periods.

(* Normal operation is defined as a situation when the equipment is operating within its design parameters.)

The extent of the hazardous area is based on the estimated or calculated distance over which an explosive atmosphere exists before it disperses to a concentration in air below its lower explosive limit.

Hazardous locations are then divided into two categories based on material type and are classified in terms of zones on the basis of the frequency and duration of the occurrences of an explosive atmosphere. The two categories are: (1) Gases, vapours and mists, and (2) Dusts.

Gases, Vapours and Mists:

EX-logoATEX Zone 0 – A place in which an explosive atmosphere, consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is present continuously, for long periods or frequently.

EX-logoATEX Zone 1 – A place in which an explosive atmosphere, consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is likely to occur in normal operation.

EX-logoATEX Zone 2 – A place in which an explosive atmosphere, consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is not likely to occur in normal operation, but if it does occur, will persist for a short period only.

 Dusts

EX-logoATEX Zone 20 – A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, for long periods or frequently. These areas may include the inside parts of equipment, such as mixers, silos, filters, mills, transfer pipes and closed conveyors.

EX-logoATEX Zone 21 – A place in which an explosive atmosphere in the form of a cloud of combustible dust in the air is likely to occur in normal operation occasionally. This may include areas such as: emptying areas, places where dust accumulates and where the formation of air-dust mixtures is high.

EX-logoATEX Zone 22 – A place where an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur but, will persist for a short period only. Areas may include storage facilities of closed packages, outlet sides of air filters and the surroundings of rarely opened equipment.

The ATEX framework defines equipment categories and the corresponding hazardous area classifications in which the explosion proof equipment can be used – click here for more information on ATEX equipment.

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