NFPA (Fire) 496

NFPA (Fire) 496 - Standard for Purged and Pressurized Enclosures for Electrical Equipment, 2008 Edition

March, 2008

National Fire Protection Association

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Protect electrical equipment in flammable atmospheres by following the protection techniques outlined in the 2008 NFPA 496.



NFPA 496: 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 NFPA 70™: National Electrical Code®. NFPA 496 also includes chapters covering protection of analyzers and rooms housing analyzers as well as a chapter on pressurized control rooms.



Consistent with the 2008 NEC®, the 2008 NFPA 496 includes the following updates to help control fire hazards: A new requirement to mark purged and pressurized enclosures with an asphyxiation hazard warning where the protective gas is other than air Correlation with the NEC requirements on equipment temperature ratings


Contents
Chapter 1 Administration ............................... 496–5
1.1 Scope ............................................... 496–5
1.2 Purpose ............................................ 496–5
1.3 Application ....................................... 496–5
1.4 Equivalency ....................................... 496–5
1.5 Units of Measurement ......................... 496–5
1.6 Mandatory Rules, Permissive Rules, and
Explanatory Material ........................... 496–5
Chapter 2 Referenced Publications ................... 496–6
2.1 General ............................................ 496–6
2.2 NFPA Publications ............................... 496–6
2.3 Other Publications .............................. 496–6
2.4 References for Extracts in Mandatory
Sections ............................................ 496–6
Chapter 3 Definitions .................................... 496–6
3.1 General ............................................ 496–6
3.2 NFPA Official Definitions ...................... 496–6
3.3 General Definitions ............................. 496–6
3.4 NEC Extracted Definitions .................... 496–6
Chapter 4 General Requirements for
Pressurized Enclosures ..................... 496–7
4.1 Applicability ...................................... 496–7
4.2 Enclosure ......................................... 496–7
4.3 Pressurizing System ............................. 496–8
4.4 Protective Gas System .......................... 496–8
4.5 Determination of Temperature Marking .... 496–8
4.6 Ventilated Equipment .......................... 496–8
4.7 Power Equipment ............................... 496–8
4.8 Type Z Pressurizing ............................. 496–9
4.9 Type Y Pressurizing .............................. 496–9
4.10 Type X Pressurizing ............................. 496–9
4.11 Markings .......................................... 496–9
Chapter 5 Pressurized Enclosures for Class I ...... 496–10
5.1 Applicability ...................................... 496–10
5.2 General Requirements ......................... 496–10
5.3 Markings .......................................... 496–10
5.4 Additional Requirements for Type Y or
Type Z Pressurizing ............................. 496–10
5.5 Additional Requirements for Type X
Pressurizing ....................................... 496–10
Chapter 6 Pressurized Enclosures for Class II ..... 496–11
6.1 Applicability ...................................... 496–11
6.2 General Requirements ......................... 496–11
6.3 Markings ........................................... 496–11
6.4 Marking Information ........................... 496–11
6.5 Additional Requirements for Type X
Pressurizing ....................................... 496–11
6.6 Additional Requirements for Ventilated
Equipment ........................................ 496–11
Chapter 7 Pressurized Control Rooms ............... 496–11
7.1 Applicability ...................................... 496–11
7.2 Protective Gas .................................... 496–11
7.3 Considerations Relating to Positive
Pressure Ventilation ............................. 496–11
7.4 Requirements for Positive Pressure Air
Systems ............................................. 496–11
Chapter 8 Pressurized Enclosures Having an
Internal Source of Flammable
Gas or Vapor .................................. 496–12
8.1 Applicability ...................................... 496–12
8.2 General Requirements ......................... 496–12
8.3 Specific Requirements ......................... 496–12
Chapter 9 Pressurized Analyzer Rooms
Containing a Source of
Flammable Gas, Vapor, or Liquid ........ 496–13
9.1 Applicability ...................................... 496–13
9.2 General ............................................ 496–13
9.3 Specific Requirements ......................... 496–14
Annex A Explanatory Material ......................... 496–14
Annex B Informational References ................... 496–18
Index ........................................................... 496–20
496–4 PURGED AND PRESSURIZED ENCLOSURES FOR ELECTRICAL EQUIPMENT
2008 Edition

Product Referenced By

API RP 500 (R2002) - Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Division I and Division 2 (Edition: 2nd)
IEEE C2-2007 - National Electrical Safety Code (NESC), 2007 Edition
NFPA (Fire) 70 - National Electrical Code, 2008 Edition

Product Replaces

NFPA (Fire) 496 - Standard for Purged and Pressurized Enclosures for Electrical Equipment, 2003 Edition