Hazardous Areas Classification - North America North American hazardous locations classification in classes, divisions and groups

Sponsored Links Electrical devices used in hazardous areas need to be certified for use according the requirements specified for the area. In North America certification is provided by Factory Mutual - An approval agency primarily concerned with insurance underwriting. Underwriters Laboratories - An independent, not-for-profit product safety testing and

certification organization. Canadian Standards Association - A not-for-profit membership-based association serving business, industry, government and consumers in Canada developing standards addressing public safety and health.

The types of protection required depends on the risk involved in the area. In general hazardous locations in North America are separated by classes, divisions, and groups to define the level of safety required for equipment installed in these locations. Classes The classes defines the general nature of hazardous material in the surrounding atmosphere.

Class Hazardous Material in Surrounding Atmosphere

Class I Hazardous because flammable gases or vapors are present in the air in quantities sufficient to produce explosive or ignitable mixtures.

Class II Hazardous because combustible or conductive dusts are present.

Class III Hazardous because ignitable fibers or flying's are present, but not likely to be in suspension

in sufficient quantities to produce ignitable mixtures. (Group classifications are not applied to this class.)

Divisions The division defines the probability of hazardous material being present in an ignitable concentration in the surrounding atmosphere.

Division Presence of Hazardous Material

Division 1 The substance referred to by class is present during normal conditions.

Division 2 The substance referred to by class is present

only in abnormal conditions, such as a container failure or system breakdown.

Groups The group defines the hazardous material in the surrounding atmosphere.

Group Hazardous Material in Surrounding Atmosphere

Group A Acetylene

Group B Hydrogen, fuel and combustible process

gases containing more than 30% hydrogen by volume or gases of equivalent hazard

such as butadiene, ethylene, oxide, propylene oxide and acrolein.

Group C Ethyl and ethylene or gases of equivalent hazard.

Group D Gasoline, acetone, ammonia, benzene, butane, cyclopropane, ethanol, hexane,

methanol, methane, natural gas, naphtha, propane or gases of equivalent hazard.

Group E

Combustible metal dusts, including aluminum, magnesium and their commercial

alloys or other combustible dusts whose particle size, abrasiveness and conductivity present similar hazards in connection with electrical equipment.

Group F Carbonaceous dusts, coal black, charcoal, coal or coke dusts that have more than 8% total entrapped volatiles or dusts that have

been sesitized by other material so they present an explosion hazard.

Group G Flour dust, grain, wood, plastic and chemicals.

The specific hazardous materials within each group and their automatic ignition temperatures can be found in Article 500 of the National Electrical Code and in NFPA 497. Group A, B, C and D apply to class I locations. Group E, F and G apply to class II locations. Temperature Code A mixture of hazardous gases and air may ignite in contact with a hot surface. The condition for ignition depends on several factors as surface area, temperature and concentration of gas. Equipment approved receives a temperature code indicating the maximum surface temperature of the equipment.

Temperature Code Maximum Surface Temperature

oF oC

T1 842 450

T2 572 300

T2A 536 280

T2B 500 260

T2C 446 230

T2D 419 215

T3 392 200

T3A 356 180

T3B 329 165

T3C 320 160

T4 275 135

T4A 248 120

T5 212 100

T6 185 85

Equipment that not exceed a maximum surface temperature of 212 oF (104 oF ambient temperature) is not required to be marked with a temperature code (NEC). Recommended reading for this topic: National Electrical Code, NFPA 70, Chapter 5, Article 500 29 CFR 1910 Subpart S, Electrical 1910.307 NFPA 497, "Classification of Gases, Vapors, and Dusts for Electrical Equipment in Hazardous

Classified Locations" NFPA Handbook, "Electrical Installations in Hazardous Locations, " by P. J. Schram and M. W. Earley NFPA 70E, Chapter 5, "Hazardous (Classified) Locations" NFPA 325, "Fire Hazard Properties of Flammable Liquids, Gases, and Volatile Solids" ANSI/UL 913, "Intrinsically Safe Apparatus" NFPA 496, "Purged and Pressurized Enclosure for Electrical Equipment in Hazardous Locations."

Hazardous Areas Classification - Europe European hazardous areas classifications in zones, protection types, temperature codes and codes

Sponsored Links Hazardous areas outside North America are classified by gas groups and zones. Zones are used to define the probability of the presence of flammable materials. Groups classify the exact flammable nature of the material. Protection Types are used to denote the level of safety for the device. Equipment approved receives a temperature code indicating the maximum surface temperature of the equipment. Zones The zone defines the probability of hazardous material being present in an ignitable concentration in the surrounding atmosphere.

Zone 0 Area in which an explosive gas-air mixture is continuously present or present for long periods.

Zone 1 Combustible or conductive dusts are present. Area in which an explosive gas-air mixture is likely to occur for short periods in

normal operation.

Zone 2 Area in which an explosive gas-air mixture is not likely to occur,

and if it occurs it will only exist for a very short time due to an abnormal condition.

Protection Types Different protection techniques are used to address the hazardous zones.

Zone

Ex d Flameproof (Explosion proof) Enclosure 1, 2

Ex e Increased Safety 1, 2

Ex ia Intrinsically Safe 0, 1, 2

Ex ib Intrinsically Safe 1, 2

Ex o Oil Immersion 2

Ex p Pressurized Apparatus (Purged Apparatus) 1, 2

Ex q Powder Filling (Sand Filling) 2

Ex m Encapsulation 1, 2

Ex n or Ex N Non incentive or/and normally no sparking circuits 2

Flameproof (Explosion proof) Enclosure All electrical circuits are enclosed in a house strong enough to contain any explosion or fire that may take place on the inside. Increased Safety Electrical circuits incorporates special measures to reduce the probability of excessive temperatures and the occurrence of arcs and sparks in normal service. Intrinsically Safety

The electrical energy available in circuits and equipment, is limited to a level to low to ignite the most easily ignitable mixtures in a hazardous area. Intrinsically safe barriers, as Zener, are installed in the circuit to limit current and voltage in the hazardous areas to avoid sparks or hot spots under fault conditions.

Hazardous Area Types of Protection

Temperature Codes A mixture of air and hazardous gases may ignite by coming in contact with a hot surface. An ignition depends on surface area, temperature and the concentration of the gas. Certified equipment are tested for maximum temperature ratings by approval agencies. Equipment for Group II receives a temperature code indicating the maximum surface temperature.

Temperature Code oF oC

T1 842 450

T2 572 300

T3 392 200

T4 275 135

T5 212 100

T6 185 85

The coding is based on a 104 oF (40 oC) ambient temperature. The automatic ignition temperature can be found in IEC 79-4.

Critical Temperature Parameters For Dust Explosions

Groups Electrical equipment are divided into two groups where Group I covers equipment used in mines and Group II covers all other applications. Group II is subdivided into three subgroups where the specific hazardous materials within each group can be found in CENELEC EN 50014.

Group I For application in below ground installations (mines) where methane (firedamp) and coal dust may be present.

Group IIA For application in above ground installation where hazards due to propane may exist.

Group IIB For application in above ground installations where hazards due to ethylene may exist.

Group IIC For application in above ground installations where hazards due to hydrogen or acetylene may exist.

Hazardous Areas Classification Hazardous areas are classified (North America) Class I - Spaces and areas with flammable gases or vapors. Subdivided in Division 1 - where

the substance referred to by class is present during normal conditions, and Division 2 - where the substance referred to by class is present only in abnormal conditions, such as a container failure or system breakdown. Class II - Spaces and areas with combustible dusts Class III - Spaces and areas with easily ignitable fibers or flyings

More about Hazardous classification in North America here! and Hazardous classification in Europe here! Protection Techniques in Hazardous Areas Common protection techniques in hazardous areas are: Dust-ignitionproof equipment - excludes dust, will not permit arcs, sparks or heat to ignite

exterior dust in the enclosure Explosionproof equipment - withstands an internal explosion without igniting the external atmosphere Hermetically sealed equipment - sealed against the external atmosphere to prevent the entry of hazardous gases or vapors Intrinsically safe systems - electrical circuits designed not to release sufficient energy to ignite or explosive the atmosphere Nonicendive circuits and components - designed to prevent any arc or thermal effect

Oil immersed equipment - arc producing components are immersed in oil, an arc will never reach the surface of the oil Purged and pressurized systems - spaces and equipment are pressurized above the external atmosphere, hazardous gases and vapors are not able to enter from the enclosure

Appropriate Protection Techniques

Protection Technique

Hazardous Area

Class I Class II Class II

Division 1 Division 2

Dust-ignitionproof equipment

2) 2) 1) 1)

Explosionproof equipment 1) 1) 1) 1)

Hermetically sealed

equipment 2) 1) 1) 1)

Intrinsically safe systems 1) 1) 1) 1)

Nonicendive circuits and components

2) 1) 1) 1)

Oil immersed equipment 2) 1) 1) 1)

Purged and pressurized systems

1) 1) 1) 1)

1) The protection technique is appropriate to the classification 2) The protection technique is not acceptable for the classification

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