Zones 0, 1 and 2: Atmospheres with explosive gases and vapours (AS2380; AS/NZS/IEC 60079)
The definition according to IEC60079-10-1 is “an area in which an explosive gas atmosphere is present continuously or for long periods or frequently”. As a guide for Zone 0, this can be defined as over 1,000 hours/year or >10% of the time. A potential few examples of this are:
The definition according to IEC60079-10-1 is “an area in which an explosive gas atmosphere is likely to occur in normal operation occasionally”. This includes areas in which the explosive mixture may exist frequently because of leakage. As a guide for Zone 1, this can be defined as 10–1000 hours/year or 0.1–10% of the time. A few potential zone 1 examples are:
The definition according to IEC60079-10-1 is “an area in which an explosive gas atmosphere is not likely to occur in normal operation but, if it does occur it will exist for a short period only”. As a general guide for Zone 2, unwanted substances should only be present under 10 hours/year or 0–0.1% of the time. A few examples of this kind of zone 2 are:
Zones 20, 21 & 22: Hazardous Areas due to the presence of combustible dusts, fibres or flyings (AS/NZS/IEC 60079-31)
Some historically associated standards that have been superseded include AS 2236 and AS/NZS 61241. These standards relate to flammable dusts which, when suspended in air can explode. Some every dry powders such as flour, cocoa powder and baby formula powder can explode violently when suspended in the air and ignited. Typically dusts are not an explosive hazard when they are settled, however wherever there’s dust which is settled there’s dust suspended in a cloud. If the dust which is suspended ignites it can set off a chain reaction which will cause the settled dust to lift off and disperse which in turn adds fuel to the explosion.
An area in which combustible dust, as a cloud, is present continuously or frequently during normal operation in sufficient quantity to be capable of producing an explosive concentration of combustible dust mixed with air, and/or where layers of dust of uncontrollable and excessive thickness can be formed.
An area not classified as zone 20 in which combustible dust, as a cloud, is likely to occur during normal operation in sufficient quantities to be capable of producing an explosive concentration of dust mixed with air.
Areas not classified as zone 21 in which combustible dust clouds may occur infrequently and persist for only short periods, or in which accumulations or layers of combustible dust may be present under abnormal conditions and give rise to combustible mixtures of dust in air. Where, following an abnormal condition, the removal of dust accumulations or layers cannot be assured, then the area is to be classified zone 21.
