North American Hazardous (Classified) Locations
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North American Hazardous (Classified) Locations

Area Classification

Area classification is the division of a facility into a two or three-dimensional hazardous location, a non hazardous location and the sub-division of the hazardous location into ‘Divisions’ or ‘Zones’.

In the United States of America, hazardous (classified) locations may be sub-divided as follows:

Class I, Flammable Gases, Vapours Or Liquids Class I, Flammable Gases, Vapours Or Liquids
Division 1:
Where ignitable concentrations of flammable gases, vapours or liquids can exist all or some of the time under normal operating conditions.
Zone 0:
Where ignitable concentrations of flammable gases, vapours or liquids can exist all of the time or for long periods at a time under normal operating conditions.

Zone 1:
Where ignitable concentrations of flammable gases, vapours or liquids can exist some of the time under normal operating conditions.
Division 2:
Where ignitable concentrations of flammable gases, vapours or liquids are not likely to exist under normal operating conditions.
Zone 2:
Where ignitable concentrations of flammable gases, vapours or liquids are not likely to exist under normal operating conditions.
Class II, Combustible Dusts
Division 1:
Where ignitable concentrations of combustible dusts can exist all or some of the time under normal operating conditions.
Division 2:
Where ignitable concentrations of combustible dusts are not likely to exist under normal operating conditions.
Class III, Ignitable Fibres And Flyings
Division 1:
Where ignitable concentrations of fibres and flyings can exist all or some of the time under normal operating conditions.
Division 2:
Where ignitable concentrations of fibres and flyings are not likely to exist under normal operating conditions.

There is no Zone classification for dusts, fibres or flyings at present in the NEC.

For further information on the classification of hazardous (classified) locations see:

NEC, NFPA 70 - National Electric Code, NFPA 70.

NFPA 30 - Flammable and Combustible Liquids Code.

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

NFPA 499 - Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas.

ANSI/API RP500 - Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Division 1 and Division 2.

ANSI/API RP 505 - Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Zone 0, Zone 1 or Zone 2.

Apparatus for use in Class 1, Division 1
  • Explosion-proof.
  • Intrinsically safe.
  • Purged / pressurised (type X or Y).
Apparatus for use in Class 1, Division 2
  • Any Class I, Division 1 method.
  • Non-incendive.
  • Non-sparking device.
  • Purged / pressurised (type Z).
  • Hermetically sealed.
  • Oil immersion.
Apparatus for use in Class 1, Zone 0
  • Intrinsic safety AEx ia.
  • Class I, Division 1 intrinsically safe.
Apparatus for use in Class 1, Zone 1
  • Any Class I, Zone 0 method.
  • Any Class 1, Division 1 method.
  • Flameproof, AEx d.
  • Increased safety, AEx e.
  • Intrinsic safety, AEx ib.
  • Purged pressurised, AEx p.
  • Powder filling, AEx q.
  • Oil immersion, AEx o.
  • Encapsulation, AEx m.
Apparatus for use in Class 1, Zone 2
  • Any Class 1, Zone 0 method.
  • Any Class 1, Division 1 method.
  • Type of protection AEx n.

Apparatus selection according to Class 1

Intrinsically safe equipment listed for use in Class I, Division 1 locations for the same gas, or as permitted by Section 505.8 of the NEC, and with suitable temperature rating is permitted in Class I, Zone 0 locations.

Equipment approved for use in Class I, Division 1 or listed for use in Class I, Zone 0 locations for the same gas, or as permitted by Section 505.8 of the NEC, and with a suitable temperature rating is permitted in Class I, Zone 1 locations.

Equipment approved for use in Class I, Division 1 or Division 2 locations for the same gas, or as permitted by Section 505.8 of the NEC, and with a suitable temperature rating is permitted in Class I, Zone 2 locations.

Equipment listed as classified for use in Class I locations is not necessarily acceptable for Class II locations as it may not be dust-tight or operate at a safe temperature with a dust covering.

Apparatus selection according to the ignition temperature of the gas or vapour

The equipment must be selected so that its maximum surface temperature will not reach the ignition temperature of any gas or vapour that may be present.

Temperature Class Of Electrical Apparatus Maximum Surface Temperature Of Electrical Apparatus Ignition Temperature Of Gas Or Vapour
T1 450°C > 450°C
T2 300°C > 300°C
T2A 280°C > 280°C
T2B 260°C > 260°C
T2C 230°C > 230°C
T2D 215°C > 215°C
T3 200°C > 200°C
T3A 180°C > 180°C
T3B 165°C > 165°C
T3C 160°C > 160°C
T4 135°C > 135°C
T4A 120°C > 120°C
T5 100°C > 100°C
T6 85°C > 85°C

Low ambient conditions require special consideration. Explosion proof or dust ignition proof equipment may not be suitable for use at temperatures lower than -25°C (-13°F) unless they are identified for low temperature service. Unless the equipment is marked otherwise, it is for use only in an ambient temperature range of -25°C (-13°F) to +40°C (+104°F).

Equipment that is approved for Class I and Class II should be marked with the maximum safe operating temperature.

For information regarding data for flammable gases and vapours, see NFPA 497 and NFPA 325.

Apparatus selection according to the ignition temperature of the dust

The equipment must be selected so that its maximum surface temperature will be less than the ignition temperature of the specific dust. For information regarding data for dusts, see NFPA 499.

Apparatus selection according to apparatus grouping

Equipment that is approved for Class I and Class II should be marked with the maximum safe operating temperature.

The grouping of Class I gases and vapours are classified into categories A, B, C and D.

Gas / Vapour Group
A (typical gas - acetylene).
B (typical gas - hydrogen).
C (typical gas - ethylene).
D (typical gas - propane).

The grouping of Class II dusts are classified into categories E, F, and G.

Dust Group
E (typical atmospheres containing combustible metal dusts).
F (typical atmospheres containing coal dusts).
G (typical atmospheres containing grain dusts).

Apparatus Construction Standards

ANSI / UL 1203 - Explosion-proof and Dust-ignition Proof Electrical Equipment for use in Hazardous (Classified) Locations.

ANSI / ISA - 12.12.01-2007 - Non-incendive Electrical Equipment for use in Class I and II, Division 2 and Class III, Divisions 1 and 2 Hazardous (Classified) Locations.

ANSI / NFPA 496 - Standard for Purged and Pressurised Enclosures for Electrical Equipment.

ANSI / UL 913 - Intrinsically Safe Apparatus and Associated Apparatus for use in Class I, II and III, Division 1, Hazardous Locations.

ANSI / UL 698 - Industrial Control Equipment for use in Hazardous (Classified) Locations.

ANSI / UL 2225 - Cables and Cable-Fittings for use in Hazardous (Classified) Locations.

UL 1604 - Electrical Equipment for use in Class I and II, Division 2 and Class III Hazardous (Classified) Locations.

ANSI/UL 60079 - Electrical Equipment for use in Class I, Zone 0, 1 and 2 Hazardous (Classified) Locations.

ISA 60079-0 - Electrical Apparatus for Gas Atmospheres – Part 0: General Requirements.

ISA 60079-1 - Explosive Atmospheres – Part 1: Equipment Protection by Flameproof Enclosures ‘d’.

ISA 60079-7 - Explosive Atmospheres – Part 7: Equipment Protection by Increased Safety ‘e’.

Installation Standards and Codes

NEC, NFPA 70 - National Electrical Code (NEC).

USCG 46 CFR Parts 110 - 113 - Shipping, Sub-Chapter J, Electrical Engineering.

ANSI / API RP 14F - Recommended Practice for Design and Installation of Electrical Systems for Fixed and Floating Offshore Petroleum Facilities for Unclassified and Class I, Division 1 and Division 2 Locations

API RP 14RZ - Recommended Practice for Design and Installation of Electrical Systems for fixed and floating offshore petroleum facilities for Unclassified and Class I, Zone 0, Zone 1, and Zone 2 Locations.