Zones 0, 1 & 2: Atmospheres with explosive gases & vapours (AS2380; AS/NZS 60079)
Zones 20, 21 & 22: Hazardous Areas due to the presence of combustible dusts, fibres or flyings (AS2236; AS/NZS 61241)
In a mine, or industrial plant such as a refinery or chemical process plant, handling of large quantities of flammable liquids and gases creates a risk of leaks. In some cases the gas, ignitable vapor or dust is present all the time or for long periods. Other areas would have a dangerous concentration of flammable substances only during process upsets, equipment deterioration between maintenance periods, or during an incident. Refineries and chemical plants are then divided into areas of risk of release of gas, vapor or dust known as divisions or zones.
The process of determining the type and size of these hazardous areas is called area classification. Guidance on assessing the extent of the hazardous gas zones is given in the current edition of IEC 60079-10-1. For hazardous dusts, the guiding standard is IEC 60079-10-2.