Area Classification

Zone 0 An area in which a flammable atmosphere, or is present for long periods. This classifications are applicable only where he hazard will exist continuously in the petroleum industry such a condition is rarely encountered except in confined spaces. Such as the vapour space of closed process vessels, storage tanks or closed containers. In Zone 0, any arc or spark would almost certainly lead to fire or explosion. Any electrical apparatus must afford a degree of protection as near as practicable to absolute. It is recommanded to avoid installing electical equipment in zone 0 areas to the extent possible.
Zone 1 An area in which a flammable atmosphere is likely to be present periodically during normal operation. In Zone 1, the hazard is likely to occur at any time requiring fullest practicable application of measures.
Zone 2 An area in which a flammable atmosphere is likely to occure in normal operation and it if does occur it will exist for a short time only. Zone 2 is applicable to areas where hazard is unlikely and may be caused only by the highly improbale and simultaneous occurrence of an arc or spark together with a hazardous atmosphere arising out of failure of conditions of control. It presupposes that any abnormal occurrance is rapidly dispersed so that possible contact with electrical apparatus iis of minimum duration.
Note:1 Earlier, classified areas were called divisions.
Note:2 This area classification deals only with risk due to combustible gases and vapours and combustible mistd. It does not deal with dusts since these material can be quiescent for long period of time until they are disturbed into suspension by a suitable mechanism.
Note:3 By implication, an area not classified as Zone 0, Zone 1, or Zone 2, is deemed non-hazardous or safe and special precautions are necessary.