MORE ABOUT HAC
Hazardous areas are classified into zones based on an assessment of the frequency of the occurrence and duration of an explosive gas atmosphere, as follows:

• Zone 0: An area in which an explosive gas atmosphere is present continuously or for long periods;

• Zone 1: An area in which an explosive gas atmosphere is likely to occur in normal operation;

• Zone 2: An area in which an explosive gas atmosphere is not likely to occur in normal operation and, if it occurs, will only exist for a short time.

When the hazardous areas of a plant have been classified, the remainder will be defined as non-hazardous, sometimes referred to as ‘safe areas’.

An area extent and classification study involves due consideration of the following:

• The flammable materials that may be present;

• The physical properties and characteristics of each of the flammable materials;

• The source of potential releases;

• Prevailing operating temperatures and pressures;

• Presence, degree and availability of ventilation (forced and natural);

• Dispersion of released vapours to below flammable limits;

• The probability of each release scenario.

These factors enable appropriate selection of a grouping, temperature class, zone type and zone extent.

This information may be summarised in Hazardous Area Classification data sheets, supported by appropriate reference drawings.

The zone so designated is a three-dimensional area of space, and thus will extend above and below the plant item under consideration (if appropriate), as well as horizontally.

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