Classification of Areas

When electrical equipment is used in, around, or near an atmosphere that has flammable gases or vapours, flammable liquids, combustible dusts, ignitable fibres or flying, there is always a possibility or risk that a fire or explosion might occur. Those areas of classification are where the possibility or risk of fire or explosion might occur due to an explosive atmosphere and/or mixture is often called a hazardous (or classified) location/area.

Examples of These Areas:

Pharmaceutical & Medical Industry:

Hospitals
Clinics
Veterinary Clinics

Chemical & Finishing Processes:

Flammable / Chemical Stores & Warehouses
Laboratories

Petrochemical:

Filling Stations
Depots
Refineries

Agricultural & Manufacturing Plants:

Silos
Sawmills
Manufacturing

Mining & Extractive:

Gold & Coal Mines
Process Plants

Oil & Gas:

Storage Depots
Utility Installations
Furnace Installations

Automotive:

Spray & Paint Booths
Workshops and Assembly Lines

Hazardous Area Zones

Hazardous Areas are defined by three main criteria

-The type of hazard

-The likelihood of the hazard being present in flammable concentrations

-The (auto) ignition temperature of the hazardous material

The type of hazard (groups)

The hazard will be in the form of gas, vapour, dust or fibre.

The likelihood of the hazard being present in flammable concentrations (Zones)

The likelihood of the hazard being present in flammable concentrations will vary from place to place. A location very close to an open source of hazard will have a high likelihood of a flammable atmosphere. On the other hand, outside a flanged pipe containing a flammable liquid, the likelihood of a flammable atmosphere being present is much lower since it will only occur if the flange leaks. Rather than work with an infinite range of possibilities, three zones are defined

Gases and Vapours

There are three zones for gases and vapours:

Zone 0 Flammable atmosphere highly likely to be present – may be present for long periods or even continuously

Zone 1 Flammable atmosphere possible but unlikely to be present for long periods

Zone 2 Flammable atmosphere unlikely to be present except for short periods of time – typically as a result of a process fault condition.

Zone zero is the most severe zone (the highest probability of flammable atmosphere presence). Equipment for this zone needs to be very well protected against providing a source of ignition.

Dusts

There are three zones for dusts:

Zone 20 Dust cloud likely to be present continuously or for long periods

Zone 21 Dust cloud likely to be present occasionally in normal operation

Zone 22 Dust cloud unlikely to occur in normal operation, but if it does, will only exist for a short period

(The presence of dust layers does not automatically lead to the dust zone. The likelihood of the dust layer being disturbed to create a cloud needs to be considered. Dust layers also need careful consideration in terms of ignition temperature. Because the dust layer can make the equipment under it hotter then normal, a factor of safety is applied to the layer ignition temperature.)