Electrical code classified areas

At all intakes for fresh air or HVAC systems to buildings in an electrically classified area according to the National Electrical Code (NEC) or subject to ingestion of combustible vapors. Especially if they are considered inhabited, critical or of a high value. Typically control rooms, critical electrical switchgear, or main process area power sources are provided with gas detection. 

Classified Area - Any area that is electrically classified following the guidelines of a nationally recognized electrical code such as the requirements of the NEC, Article 500 or API RP 500. 

Once a hazardous location has been classified, appropriate electrical equipment must be chosen for that area. In general, equipment must be approved for use in that hazardous classified area. Testing labs such as UL test, label, list, or approve equipment suitable for installation in accordance with their legislated code. 

Articles 500 and 505 of the National Electrical Code (NFPA 70) define classified areas in which flammable materials may be present at high enough concentrations to be ignitable. In a Class I location, the ignitable material is a gas or vapor. Class I locations are further divided into either Divisions or Zones as follows ... 

When electrically driven equipment is to be operated in an XP and/or an electrically classified area (meaning flammable vapors are, or could be, present), it must be rated to operate in that environment. This means that the ignition source associated with the electricity used to power the equipment must be sealed to prevent the flammable vapors from infiltrating the housing (usually done by the manufacturer). The robustness and the integrity of these seals dictate whether the equipment can be operated in an environment where flammable vapors are always present [National Electric Code (NEC) Class 1 Division 1 area] or where flammable vapors could be present (NEC Class 1 Division 2). 

The National Electrical Code (NEC) classifies hazardous areas of various types and states what sort of equipment is safe for use in each. Refineries and petrochemical plants are most concerned with those areas which the NEC calls Class I. Class I locations are those in which flammable gases or vapors are or may be present in the air in amounts large enough to produce ignitable or explosive mixtures. 

An area or a zone defined as a three-dimensional space in which a flammable atmosphere is or may be expected to be present in such frequencies as to require special precautions and restrictions for the construction and use of electrical apparatus and hot surface exposures (e.g., lights) that act as an ignition source. Classified areas have specific restrictions based on the equipment involved, the gases encountered, and the probability of leakage. Several national and industry institutions have guidelines and codes for the classification of areas, e.g., defined in the United States by the National... 

Electrical Classification. In those areas of the plant where a hazardous quantity of dust accumulates or is suspended in the air, the area should be classified and all electrical equipment and installations in those areas should comply with Article 502 or Article 503 of NFPA 70, the National Electrical Code,... 

The process designer and project engineer should classify the various areas of a plant following NEPA-70, Article 50528.29 order to advise the electrical and other project team members of the degree of electrical hazards anticipated. The appropriate equipment (motors, instruments, conduit, wiring, etc.) should be specified according to NEPA-70, Article 500 and others as applicable, the ASME Code and the API Code as appropriate. See NEPA-497A and... 

NFPA Code 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, 1997 Edition. 

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