Zone Class Safety

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Sales Bul le t in No. 06/2005

Hazardous Area Classi f ic at ions

Dated: 09.06.2005

Hazardous Areas are locations where the potential for fire or explosion exists because ofgases, dust, or easily ignitable fibers or flyings in the atmosphere.

In North America, hazardous areas are separated by classes, divisions, and groups to definethe level of safety required for equipment installed in these locations. Classes define thegeneral form of the flammable materials in the atmosphere. Divisions define the probability

of the presence of flammable materials. Groups classify the exact flammable nature of thematerial.

In Europe and countries outside of North America, classification of hazardous areas isaccomplished differently. Zones are used to define the probability of the presence offlammable materials. Protection Types denote the level of safety for the device. Groupsclassify the exact flammable nature of the material. These groups are separated differentlythan North American Groups. Temperature Identifications convey the maximum surfacetemperature of the apparatus based on 104° F (40° C) ambient. These temperature codesare selected carefully not to exceed the ignition temperature of the specific gas or vapor to

be encountered in the application.

Some classifications are not shown here. For further detailed information, see specificstandards published by approval organizations.





Classifications Inside North America

Classes

Ignitable fibers or flyings are present, but not likely to be in suspension insufficient quantities to produce ignitable mixtures. (Group classifications arenot applied to this class.)

Class III

Combustible or conductive dusts are present.Class II

Flammable gases or vapors are present in the air in quantities sufficient to

produce explosive or ignitable mixtures.

Class I

Division

The substance referred to by class is present only in abnormal conditions,such as a container failure or system breakdown.

Division 2

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

Groups

Grain DustGroup G

Coal DustGroup F

Metal DustGroup E

Gasoline (or gases of equivalent hazard)Group DEthylene (or gases of equivalent hazard)Group C

Hydrogen (or gases of equivalent hazard)Group B

AcetyleneGroup A





Protection Types

2Normally Nonsparking and/or Nonincendive Circuits)n

1,2Encapsulationm

2Powder Filling (Sand Filling)q

1,2Pressurized Apparatus (Purged Apparatus)p

2Oil Immersiono

1,2Intrinsic Safetyib

0,1,2Intrinsic Safetyia

1,2Increased Safetye

1,2Flameproof (Explosion proof) EnclosuredZone

Temperature Codes

85185T6

100212T5

135275T4

200392T3

300572T2

450842T1

° C° F

Classifications Outside North America

Zones

Area in which an explosive gas-air mixture is not likely to occur, and if itoccurs it will only exist for a short time.

Zone 2

Area in which an explosive gas-air mixture is likely to occur in normaloperation.

Zone 1

Area in which an explosive gas-air mixture is continuously present or

present for long periods.

Zone 0





Groups

For application in above ground installations where hazards due tohydrogen or acetylene may exist. This group most closely matches theNorth American Groups A and B.

Group IIC

For application in above ground installations where hazards due toethylene may exist. This group most closely matches the NorthAmerican Group C.

Group IIB

For application in above ground installation where hazards due to

propane may exist. This group most closely matches the North AmericanGroup D.

Group IIA

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

Group I

Hazardous-Area Classification and equipment

The term hazardous location once meant a place within a petrochemical or some other equally

volatile plant. Today, hazardous manufacturing processes include coatings, adhesives andflammable liquids in parts-cleaning tanks and dry-cleaning plants. Even flood processing and otheragricultural-related industries are becoming familiar with hazardous designations by the nature of the

processes involved, such as grain elevators or flour and feed mills. Textile mills and any plant thatcreates sawdust also fall into the hazardous category.

Selecting equipment that may be used in such locations requires an understanding of how hazardsare classified. The NEMA, Underwriters’ Laboratories , and the National Fire Protection Association

have categorized hazardous environments by the following classes with divisions similar toEuropean zones.

The division defines the probability of an explosive mixture being present:

Division 1 locations are areas where the hazardous concentration exists

continuously, intermittently or periodically under normal operating conditions. Division 2 locations are those where the hazardous vapors are present only in

case of accidental rupture or breakdown of equipment.

Classification of hazardous areas varies slightly between the United States and other countries. TheEuropean classification of hazardous areas generally follows that of the International

Electrotechnical Commission (IEC) and is affiliated with the International Organisation forStandardisation (ISO), as its electrotechnical division. The IEC classifications are as follows. Ahazardous area is divided into zones:

Zone 0: Where an explosive gas-air mixture is continuously present for long

periods Zone 1: Where an explosive gas-air mixture is likely to occur in normal operation

Zone2: Where an explosive gas-air mixture is not likely to occur, and if it occurs, itwill only exist for a short time.





The following table shows the zone and division cross reference used in IEC countries andNorth America.

Division 2Division 1United States

Zone 2Zone 1Zone 0IEC

The responsibility for the area classification of a plant rests jointly with the engineering,process, safety, and any other departments involved in its design and operation. Factors tobe considered include:

1. The probability that the hazardous gas is present2. The quantity of hazardous gas3. The nature of the gas (e.g. is it heavier than air?)4. The extent of ventilation5. The consequences of an explosion

Product ClassificationTwo other safety aspects are commonly included in the classification of devices for use inhazardous areas-gas groupings and temperature classification. The gas grouping takesaccount of the maximum amount of energy which can be released under operating or faultconditions, whereas the temperature classification is concerned with the maximumtemperature which can be attained by the external surface of the device.

Temperature classificationGas–air mixtures can be ignited by contact with a hot surface, and consequently all electricalequipment used in hazardous atmospheres must be classified according to its maximumsurface temperature: Table 11.2 shows the ignition temperature to be taken into considerationin Europe (IEC) and the United States (NEC) for the gases and vapors stipulated there. Alltemperature classifications, unless otherwise specified, are assessed with reference to amaximum ambient temperature of 400C (1040F). If the equipment is used in a temperaturehigher than this, then its temperature classification should be reassessed.





Table 11.2 Temperature Classes

>8518585T685T6

>100212100

T5100T5

>120248120

T4A

>135275135

T4135T4

>160320160

T3C

>165329165

T3B

>180356180

T3A

>200392200

T3200T3

>215419215

T2D

>230446230

T2C

>260500260

T2B

>280536280

T2A

>300573300

T2300T2

>450842450

T1450T1

F°C°

Ignitiontemp. ofgases or

vapors, C°

Max surfacetemperature

Temperatureidentification

number

Max. surfacetemperature

C°

Temperatureclass

NECIEC





Table 11.3 Gas Groupings for IEC*

BA

IICIIC

HydrogenCarbon disulfideAcetylene (with special material limitations)

CIIBNatural GasHydrocarbons such as ethylene propyleneOxygen compounds such as ethyl, ether, aldehydesHydrogen sulfide

DIIAHydrocarbons such as alkenes, including propane,benzenoids, alkenes, gasolineOxygen compounds such as carbon monoxide, alcoholsand phenols, some aldehydes, ketones, estersHalogensNitrogen compounds such as ammonia, amines,amides

NorthAmerica(group)

IECExample of gases

*NOTE: These are approximate correlations.





Pneumatic SystemsPneumatic Systems are, by their nature, a safe means of control because they are poweredby air. Pneumatic systems are generally clean and easy to service, but the number ofcontrol operations performed by pneumatic sequencers is limited. This can be augmented byan electropneumatic interface which enables pneumatics to be controlled by aProgrammable Logic Controller.The drawbacks to pneumatic systems are in distance and reaction time. Where installationsare spread over a wide area, the slow reaction time of pneumatic systems increases controlreaction time. The length of control circuits in a total pneumatic system must be limited forthe control cycle time to remain short.

Explosion-proof housingsExplosion-proof housings provides a simple means to adapt electric and electromechanical

and electropneumatic controls to hazardous locations. Explosion-proof housings aredesigned to withstand the explosion of a mixture inside the enclosure and to prevent thespread of the flame to the outside. These enclosure are effective, especially for interruptinghigh currents to motors using limit switches. However, this methods lacks flexibility in theuse of sensing techniques because of the size of the devices. In addition to the spacerequired for explosion-proof devices, material and labour costs for installation and servicemay be high.

Gas or Apparatus GroupingThe same gas groupings are used for flameproof and intrinsically safe equipment, andtables are available showing the equipment classification which can be used with particulargroups of gases. Table 11.3 gives some examples with the IEC and North Americanclassifications, Gas groups E, F, and 0 are concerned with hazards associated with the

presence of dust.The overall term used in Europe covering all methods of protection is explosion-proof, andthe symbol Ex is used. In the United States engineers tend to use the term explosion-proofas being synonymous with the European term flameproof and this often causes confusion.

Methods of Safe ControlUnderstanding design methods for operating equipment in hazardous areas starts with thecombustion triangle. Fuel, Oxygen and a source of ignition (spark or temperature) must bepresent at the same time (and in the necessary proportions) for combustion to occur.

One approach to creating a safe environment for hazardous areas is confinement, isolatingthe area reduces the possibility of accidents. Isolation involves removing or confining anypossible element which could create a spark and ignite an explosion. There are threecommon methods of providing safety within a hazardous location, categorized by the powertechnology used: (1) pneumatic, (2) explosion-proof, and (3) intrinsically safe systems.




Meets applications requirements class II of National Electrical Code, conforms withspecifications of Underwriters´ Laboratories Inc. used for atmosphere containing metal

dust, carbon black, coal or coke dust, flour, starch or grain dusts.

IX. Hazardouslocations

(combustibledust)

Type 9 enclosures are for use in indoor locations classified as class II, groups E, F, andG as defined in the National Electrical Code.

Type 9enclosure(hazardouslocations, dust-ignition proof)

Type 8 enclosures are for indoor or outdoor use in locations classified as class I, GroupsA, B, C, or fl as defined in the National Electrical Code.

Type 8enclosure (VIII.

Hazardouslocations, oil-

immersed)

Meets applications requirements class I of National Electrical Code, conforms with

specifications of Underwriters´ Laboratories Inc. used for atmosphere containinggasoline, hexane, naphtha, benzene, butane, propane, acetone, benzol, lacquer-solventvapors, and natural gas.

VII. Hazardous

location(explosive gas orvapor)

Design depends on specified conditions of pressure and time, used for submersion inwater, as in quarries, mines, and man holes.

VI. Submersible

Provided with gaskets or equivalent to exclude dust, used in steel mills and cement

plants.

V. Dusttight

Must exclude at least 65 gal/mm (247 L/m) of water from 1-in (25-mm) nozzle deliveredfrom a distance of not less than 10 ft (3m) for 5mm. Used outdoors on ship docks, indairies, and in breweries.

IV. Waterlight(weatherproof)

Protects against weather hazards such as rain and sleet, used outdoors on ship docks,for construction work, and in tunnels and subways.

III. Weatherresistant

Similar to type I, with addition of drip shields or equivalent, used where condensation maybe severe as in cooling rooms and laundries.

II. Driptight

Project against indirect splashing of dust and light but is not dusttight, primarily preventscontact with live parts, used indoors and under normal atmospheric conditions.

I. Generalpurpose

NEMA classifications.The NEMA classifies electrical equipment and enclosures for industrial applications as follows:

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Zone Class Safety