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NFPA 496, Standard for Purged and Pressurized Enclosures for Electrical Equipment

2021 NFPA 496 Standard - Current Edition
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  • Description

    Help mitigate risks by complying with the latest requirements for installing enclosures in Class I and Class II hazardous (classified) locations with NFPA 496.

    Electrical equipment fires, explosions, and other dangers relating to the ignition of a flammable atmosphere pose a significant threat to life and property. Help identify and minimize potentially deadly hazards and better safeguard facilities by referencing and complying with NFPA 496, Standard for Purged and Pressurized Enclosures for Electrical Equipment.

    This critical standard offers protection techniques applicable to Class I and Class II locations. You get comprehensive criteria for designing and operating purged and pressurized electrical equipment enclosures to minimize hazards in the presence of flammable materials.

    This standard applies to purging and pressurizing for the following:

    • Electrical equipment located in areas classified as hazardous by Article 500 or Article 505 of NFPA 70®, National Electrical Code® (NEC®), 2020 edition. Electrical equipment containing sources of flammable vapors or gases that are located in either classified or unclassified areas
    • Control rooms or buildings located in areas classified as hazardous by Article 500 or Article 505 of NFPA 70
    • Analyzer rooms containing sources of flammable vapors or gases that are located in areas classified as hazardous by Article 500 or Article 505 of NFPA 70

    The revised NFPA 496 is updated for consistency with the most current knowledge and NEC, 2020 edition, requirements.

    It is vital electrical designers, installers, and AHJs have the most accurate and complete information for helping to ensure safety at Class I and Class II hazardous locations. This edition of the standard is updated to include significant changes in the Annex sections including:

    • Updates to Annex 4.3.1 to clarify components that complete the enclosure are subject to the same considerations as the enclosure itself
    • Details on methods to prevent the enclosure from excessive protective gas pressure added in A.4.3.1.1
    • Methods provided to prevent the discharge of ignition-capable particles to a Division 1 location in A.4.3.1.2
    • Included Annexes for 4.3.1 and its subsections to correlate with ANSI/ISA-12.04.04-2012, Pressurized Enclosures
    • Added requirements to 4.4.5 for alarms on pressurizing system bypasses and safety measures to prevent their accidental opening,
    • Introduction of French translations of required markings throughout the document
    • New guidance, including a possible test, to confirm that enclosures do not contain trapped flammable gases in A.5.2.3
    • Revisions to A.5.2.6 to indicate that internal components in or through enclosure walls might not be adequately protected by purge/pressurization
    • Addition of A.5.2.6.1 relating to internal components with a small internal volume that might not require protection

    Help ensure you are up to speed on the methods for purging and pressurizing electrical equipment enclosures to prevent the ignition of a flammable atmosphere.

    Be prepared to help protect people, equipment, and facilities by ordering your copy of NFPA 496, Standard for Purged and Pressurized Enclosures for Electrical Equipment, 2021 edition. (Print, 32 pp., 2021)

  • Table of Contents (2021 Current Edition)

    NFPA® 496 Standard for Purged and Pressurized Enclosures for Electrical Equipment, 2021 Edition

    Chapter 1 Administration
    1.1 Scope.
    1.2 Purpose.
    1.3 Application.
    1.4 Equivalency.
    1.5 Units of Measurement.
    1.6 Mandatory Rules, Permissive Rules, and Explanatory Material.
    Chapter 2 Referenced Publications
    2.1 General.
    2.2 NFPA Publications.
    2.3 Other Publications.
    2.4 References for Extracts in Mandatory Sections.
    Chapter 3 Definitions
    3.1 General.
    3.2 NFPA Official Definitions.
    3.3 General Definitions.
    3.4 NEC Extracted Definitions.
    Chapter 4 General Requirements for Pressurized Enclosures
    4.1 Applicability.
    4.2 Suitability of Identified Equipment.
    4.3 Enclosure.
    4.4 Pressurizing System.
    4.5 Protective Gas System.
    4.6 Determination of Temperature Marking.
    4.7 Ventilated Equipment.
    4.8 Power Switching Equipment.
    4.9 Type Z Pressurizing.
    4.10 Type Y Pressurizing.
    4.11 Type X Pressurizing.
    4.12 Markings.
    Chapter 5 Pressurized Enclosures for Class I, or Zone 1, or Zone 2
    5.1 Applicability.
    5.2 General Requirements.
    5.3 Markings.
    5.4 Additional Requirements for Type Y or Type Z Pressurizing.
    5.5 Additional Requirements for Type X Pressurizing.
    Chapter 6 Pressurized Enclosures for Class II
    6.1 Applicability.
    6.2 General Requirements.
    6.3 Markings.
    6.4 Marking Information.
    6.5 Additional Requirements for Type X Pressurizing.
    6.6 Additional Requirements for Ventilated Equipment.
    Chapter 7 Pressurized Control Rooms
    7.1 Applicability.
    7.2 Protective Gas.
    7.3 Considerations Relating to Positive Pressure Ventilation.
    7.4 Requirements for Positive Pressure Air Systems.
    Chapter 8 Pressurized Enclosures Having an Internal Source of Flammable Gas or Vapor
    8.1 Applicability.
    8.2 General Requirements.
    8.3 Specific Requirements.
    Chapter 9 Pressurized Analyzer Rooms Containing a Source of Flammable Gas, Vapor, or Liquid
    9.1 Applicability.
    9.2 General.
    9.3 Specific Requirements.
    Annex A Explanatory Material
    Annex B Informational References
  • 2017 Edition Description

    2017 Edition

    Install electrical equipment in Class I and Class II hazardous (classified) locations to prevent ignition of a flammable atmosphere. The 2017 edition of NFPA 496 helps you protect people, equipment, and facilities from potentially deadly hazards.

    Work with the specialized knowledge you need to head off electrical equipment fires and explosions. Consistent with the 2017 edition of NFPA 70®, National Electrical Code® (NEC®), the 2017 edition of NFPA 496, Standard for Purged and Pressurized Enclosures for Electrical Equipment contains requirements for the design and operation of purged and pressurized electrical equipment enclosures.

    This protection technique is used in Class I and Class II hazardous (classified) locations to reduce or prevent the presence of flammable materials within electrical equipment enclosures as specified by the NEC.

    Electrical designers, installers, and AHJs reference NFPA 496 for vital requirements concerning:

    • General Requirements for Pressurized Enclosures
    • Pressurized Enclosures for Class I
    • Pressurized Enclosures for Class II
    • Pressurized Control Rooms
    • Pressurized Enclosures Having Internal Source of Flammable Gas or Vapor
    • Pressurized Analyzer Rooms Containing a Source of Flammable Gas, Vapor, or Liquid

    To make the Standard more enforceable by states and jurisdictions, changes to the 2017 edition remove unenforceable language such as near, close to, and significant portion, because these terms cannot be quantified in the design or evaluation of an installation designed to NFPA 496 specifications. (Print, 28 pp., 2017)

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