HAZARDOUS AREA CLASSIFICATION & SELECTION OF ELECTRICAL EQUIPMENT FOR FLAMMABLE ATMOSPHERES

It is clear from the fire triangle that fire/ explosion/ combustion can be eliminated or avoided if any one component of the triangle is eliminated. Electrical spark is one of major ignition source. By proper selection of electrical equipment at the design stage, it is possible to avoid this major source of ignition. This would help in avoiding or reducing the accident due to electrical sparks in hazardous area.
Hazardous Areas-Definitions
          Petroleum Rules, 1976
          An area  shall be deemed to be a hazardous area, where:
         petroleum having FP below 65 deg C or any inflammable gas or  vapour in concentration capable of ignition is likely to be present
        petroleum or any inflammable liquid having FP above is likely to be refined, blended or stored at or above its FP
          IS 5572
        Hazardous area is an area in which an explosive gas atmosphere is present, or likely to be present, in quantities such as to require special precautions for the construction, installation and use of electrical apparatus.
Why Area Classification?
          HAC is a method of analyzing and classifying the environment where explosive gas atmospheres may occur to allow the proper selection of electrical apparatus to be installed in that environment.
          Ignition sources not considered
        ESD
        Sparks
        Lightning
        Flames/Fires
        Hot surfaces
          IS 5572
        HAs are classified in zones based on the frequency of the appearance and the duration of an explosive gas atmosphere.
Why Zoning?
          Leak Potential & Presence of Ignition Sources
          Hazardous properties of hydrocarbons
          Safe selection (& optimization) of Electrical Equipment
Zone 0 -Typical areas
(Continous grade)
          An area in which an explosive gas atmosphere is present continuously or is present for long periods.
          Vapour space above:
         closed process vessels,
        storage tanks
        closed containers,
        areas containing open tanks of volatile, flammable liquid
How to identify  Zone 1 areas (IS 5572) ?
          Flammable gas or vapour concentration is likely to exist in the air under normal operating conditions
          Flammable atmospheric concentration is likely to occur frequently because of maintenance, repairs or leakage
          Flammable liquid or vapour piping system (containing valves, meters, or screwed or flanged fittings) is in an inadequately ventilated area
          The area below the surrounding elevation or grade is such that flammable liquids or vapours may accumulate therein
Zone 1 -Typical areas
          Imperfectly fitting peripheral seals on floating roof tanks
          Inadequately ventilated pump rooms for flammable gas or for volatile, flammable liquids
          Oily waste water sewer / basins
          Loading / unloading gantries of hazardous products
          Production blocks, Tank form areas in API units
Typical  Zone 2 areas (IS 5572) ?
(Secondary grade)
          An area in which an explosive gas atmosphere is not likely to occur in   normal operation and if does occur it will exist for a short period only.
          Normal Operation The situation when the plant equipment is operating within its designed parameters. 
          Minor releases of flammable material may be part of normal operation. For example, releases from seals which rely on wetting of fluid being pumped are considered to be minor release. 
          Failures (such as the breakdown of pump seals, flange gaskets or spillages caused by accidents) which involve repair or shut-down are not considered to be part of normal operation
Safe Areas -Typical areas
The following locations are considered safe from the point of view of electrical installation:
          Areas where the piping system is without valves, fittings, flanges or similar appurtenances
          Areas where flammable liquids or vapours are transported only in suitable containers or vessels
          Areas where permanent ignition sources area present like area where combustion gases are present, for example flare pits, tips, other open flames & hot surfaces
          DG shed room / shed having adequate ventilation
For Zone – 1 & 2:
        The coverage is 8 Mtrs above the source and 16 Mtrs horizontally in all directions.
        If there is possibility of large release of volatile products, the Zone 2 area may be further extended to 32 Mtrs with height of 0.63 Mtrs.
        In case of petroleum carrying pipelines in well ventilated area the extent of Zone 2 area is 4 Mtrs. in all directions.
        All areas below ground level are considered as Zone 1 area.
        If source of hazard gives rise to a hazardous atmosphere under normal operating conditions then the area described above as Zone 2 shall be considered as Zone 1.

        In the event of an enclosed premises not containing the source of hazard but situated within Zone 1 or Zone 2 area, the inside of the premises shall be classified as Zone 1 unless separated from outside hazardous area by a fire wall.

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