Method of analyzing and classifying the environment where and classifying the environment where explosive gas atmospheres may occur so as to facilitate the proper selection and installation of equipment to be used safely in explosive atmosphere. Allows preparation of safety procedures for plant operation and maintenance. The area classification process reduces the overall installation risk level through design improvements.
ZONE 0, 20 : to be used instrument category : 1
ZONE 1, 21 : to be used instrument category : 2
ZONE 2, 22 : to be used instrument category : 3
Gas
ZONE 0: Flammable atmosphere highly likely to be present - may be present for long periods or even continuously. Locations such as the inside of the containers of explosives, the inside of the explosive processing apparatus (evaporators, reaction vessels) are available in this group.
ZONE 1: Flammable atmosphere possible but unlikely to be present for long periods. More than 95% of the existing explosive atmosphere is in this group. Instruments to a second category can be used in Zone 1 according to ATEX 100a. Almost all ex-certified devices fall into this category.
Zone 2: Flammable atmosphere unlikely to be present except for short periods of time - typically as a result of a process fault condition. Instruments to a third category can be used in Zone 2 according to ATEX 100a.
Dust
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 than normal, a factor of safety is applied to the layer ignition temperature.
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 periodIn Zone system, explosive gases and powders is shown with the letter G and D.
