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’. Hazardous (classified) locations may be sub-divided as follows:
In the United States of America, hazardous (classified) locations are sub-divided into three Zones or two Divisions, as follows:
| Class I, Flammable Gases, Vapors Or Liquids | Class I, Flammable Gases, Vapors Or Liquids |
|---|---|
| Division 1: Where ignitable concentrations of flammable gases, vapors or liquids can exist all of the time or some time under normal operating conditions. |
Zone 0: Where ignitable concentrations of flammable gases, vapors or liquids can exist all of the time or for long periods at time under normal operation conditions. Zone 1: Where ignitable concentrations of flammable gases, vapors or liquids can exist some of the time under normal operating conditions. |
| Division 2: Where ignitable concentrations of flammable gases, vapors or liquids are not likely to exist under normal operating conditions. |
Zone 2: Where ignitable concentrations of flammable gases, vapors or liquids are not likely to exist under normal operating conditions. |
| Class II, Combustible Dusts |
|---|
| Division 1: Where ignitable concentrations of flammable gases, vapors or liquids can exist all of the time or some 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 ignitable fibres and flyings can exist all of the time or some of the time under normal operating conditions. |
| Division 2: Where ignitable concentrations of ignitable 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 Vapors 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.
North American Hazardous (Classified) Locations
Apparatus selection according to Class 1
| Apparatus for use in Class 1, Division 1 |
|---|
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| Apparatus for use in Class 1, Division 2 |
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| Apparatus for use in Class 1, Zone 0 |
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| Apparatus for use in Class 1, Zone 1 |
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| Apparatus for use in Class 1, Zone 0 |
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Intrinsically safe equipment listed for use in Class I, Division 1, locations for the same gas or a permitted by Section 505-7(d) 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 505-7(d) 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 505-7(d) 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.
North American Hazardous (Classified) Locations
Apparatus selection according to the ignition temperature of the gas or vapor
The equipment must be selected so that its maximum surface temperature will not reach the ignition temperature of any gas or vapor that may be present.
| Temperature Class Of Electrical Apparatus | Maximum Surface Temperature Of Electrical Apparatus | Ignition Temperature Of Gas Or Vapor |
|---|---|---|
| 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 vapors, 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 vapors are classified into categories A, B, C and D.
| Gas / Vapor 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). |
North American Hazardous (Classified) Locations
Apparatus Construction Standards
ANSI / UL 1203 - Explosion-proof and Dust-ignition Proof Electrical Equipment for use in Hazardous (Classified) Locations.
ANSI / ISA - S12.12 - 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 - Metal-Clad Cables and Cable-Sealing 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 2279 - Electrical Equipment for use in Class I, Zone 0, 1 and 2 Hazardous (Classified) Locations.
ISA S12.0.01 - Electrical Apparatus for use in Class I, Zone 0, 1 Hazardous (Classified) Locations, General Requirements.
ISA S12.22.01 - Electrical Apparatus for use in Class I, Zone 1 and 2 Hazardous (Classified) Locations, Type of Protection - Flameproof ‘d’
ISA S12.16.01 - Electrical Apparatus for use in Class I, Zone 1 and 2 Hazardous (Classified) Locations, Type of Protection - 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 14FZ - 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.
