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NOTE: This is an unformatted excerpt from our online fire protection training library.

Classification Basics

A Class I, Zone 0 location is a location in which
     (1) Ignitable concentrations of flammable gases or vapors are present continuously, or
     (2) Ignitable concentrations of flammable gases or vapors are present for long periods of time.

     (FPN No. 1):  As a guide in determining when flammable gases or vapors are present continuously or for long periods of time, refer to ANSI/API RP 505-1997, Recommended Practice for Classification of Locations for Electrical Installations of Petroleum Facilities Classified as Class I, Zone 0, Zone 1 or Zone 2; ANSI/ISA-TR 12.24.01-1998 (IEC 60069-10 Mod), Recommended Practice for Classification of Locations for Electrical Installations Classified as Class I, Zone 0, Zone 1, or Zone 2; IEC 60079-10-1995, Electrical Apparatus for Explosive Gas Atmospheres, Classifications of Hazardous Areas; and Area Classification Code for Petroleum Installations, Model Code, Part 15, Institute of Petroleum.

     (FPN No. 2):  This classification includes locations inside vented tanks or vessels that contain volatile flammable liquids; inside inadequately vented spraying or coating enclosures, where volatile flammable solvents are used; between the inner and outer roof sections of a floating roof tank containing volatile flammable liquids; inside open vessels, tanks and pits containing volatile flammable liquids; the interior of an exhaust duct that is used to vent ignitable concentrations of gases or vapors; and inside inadequately ventilated enclosures that contain normally venting instruments utilizing or analyzing flammable fluids and venting to the inside of the enclosures.

     (FPN No. 3):  It is not good practice to install electrical equipment in Zone 0 locations except when the equipment is essential to the process or when other locations are not feasible. [See 505.5(A) FPN No. 2.] If it is necessary to install electrical systems in a Zone 0 location, it is good practice to install intrinsically safe systems as described by Article 504.
NOTE: This is an unformatted excerpt from our online fire protection training library.

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