03. Basic Concepts on Hazardous Area Classification and Equipment Labelling Method

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TATA CONSULTING ENGINEERS LIMITED

Basic Concepts on Hazardous Area Classification

and Equipment Labelling MethodCOVER SHEET


TCE FORM 329 R4


and Equipment Labelling Method

Date: 18-01-2011

TCE Office Code: DK

Prepared By Assisted By Guided By

Santanu Gain (103566)

Saswata Mandal (103487)

Arun Kumar Maiti

(102608)Sugata Bandyopadhyay (102611)

Amitava Sengupta (104138)


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and Equipment Labelling MethodSHEET : 1 OF 19


TCE FORM 329 R4

SECTIONTITLE

NUMBER

OF PAGES

1.0 Preface 2

2.0 Objective 2

3.0 Explosive Atmosphere 3

4.0 Ignition Triangle 3

5.0 Explosive Mixture Characteristics 4

6.0 Ignition Temperature 5

7.0 Flash-point Temperature 5

8.0 Electrical Safety Standards, Organizations, Testing andCertifying Agencies

6

9.0 Hazardous Locations Classification 8

10.0 The Classification of Hazardous Locations as per US / CanadianStandard: (NEC)

8

10.1 Area Classification 8

10.2 Material Classification 9

1.03 Temperature Classification 10

11.0 The Classification of Hazardous Locations as per EuropeanStandard: (IEC)

12

11.1 Area Classification 12

11.2 Material Classification 13

11.3 Temperature Classification 13

12.0 ATEX Summary 14

13.0 Equipment Labelling Method 15

14.0 Difference between NEC and IEC Practices 17

15.0 Key Installation Points 18

16.0 Conclusion 18

17.0 References 19


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1.0 PREFACE

After World War II, the increased use of oil and its derivatives brought the constructionof a great number of plants for extraction, refining, and transformation of the chemicalsubstances needed for technological and industrial development.

The treatment of dangerous substances, where there exists the risk of explosion orfire that can be caused by an electrical spark or hot surface, requires specificallydefined instrumentation, located in a hazardous location, it also require interfacingsignals coming from hazardous location to be unable to create the necessaryconditions to ignite and propagate an explosion.

This risk of explosions or fire has been the limiting factor when using electricalinstrumentation because energy levels were such that the energy limitation to the

hazardous location was difficult, if not impossible, to obtain. For this reason, thoseparts of the process that were considered risky were controlled with pneumaticinstrumentation.

The introduction of semiconductor devices (transistors first and, subsequently,integrated circuits), along with the capability to reduce the working voltages andenergy levels, made the energy limitation protection technique, called intrinsicsafety, easier to apply when using electronic instrumentation in hazardous locations.Thus, a more economical and more efficient solution to the problem was created.

2.0 OBJECTIVE

The purpose of this document is to explain the concepts of area classification, materialclassification, Temperature classification, national and International standards relatedto hazardous location and its application to anyone who faces the problems relative toselection, design, and installation of electrical equipments in hazardous location.

3.0 EXPLOSIVE ATMOSPHERE

In some process industries, flammable materials such as crude oil and its derivatives,natural gas, alcohols and other hydrocarbons, synthetic, gases, metal dust, carbondust, fibres etc. are handled/ processed. In such plants combustible gases, vapours,dusts may be released into atmosphere either during normal operation of the processor owing to any leakage, spillage or fault. This combustible material, when mixed withthe air (i.e. O2) in correct proportion, produces an explosive medium and hence posesan explosion hazard.

An area which contains explosive concentration of combustible materials, gases,vapours, dusts, fibres etc either during normal operation of the process or owing toany leakage faults is called hazardous area. This is often referred to as explosiveatmosphere.On other hand, safe area is a location where an ignitable concentrationof any combustible material doesnt exist under any condition.

To protect both plant and personnel precaution must be taken to ensure that thisexplosive atmosphere can not be ignited. In order to ascertain whether an electrical


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apparatus is suitable for installation in a hazardous location (i.e. it does not act as asource of ignition) the following aspects have to be considered.

(i) Degree of hazard associated with a location. This is referred to as area

classification. Area classification indicates the probability of a mixture of a

combustible gas/ vapour/ dust and air being present in a particular area.

(ii) The nature of the combustible material present in the hazardous area and its

ignition energy requirements. This is referred to as Material Classification.

Material classification involves the grouping of gases and dusts based on their

ignition energy requirements.

(iii) An explosive mixture can be ignited by contact with hot surface. Hence all

electrical apparatus used in a hazardous area should be classified according

to their maximum surface temperature. This is referred to as Temperature

Classification. An electrical apparatus installed in a hazardous area must be

so designed that its maximum surface temperature never exceeds the ignition

temperature of the combustible mixture present in the hazardous area.

4.0 IGNITION TRIANGLE

From a chemical point of view, oxidation, combustion, and explosion are all exothermicreactions with different reaction speeds. For such reactions to take place, it isessential that the following three components be present simultaneously in suitable

proportions.

Fuel: flammable vapours, liquids or gases, or combustible dust or fibres in an

ignitable concentration

Oxidizer : generally air or oxygen;

Ignition Energy: electrical or thermal.

These three ingredients necessary for an explosion to occur in the correct proportion.By eliminating those conditions an explosion is impossible.

These three components are identified in the ignition triangle displayed in Figure 1.1.

Figure-1.1 : Ignition Triangle


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Once that reaction is ignited, depending on how the exothermic energy is released,the results can be a controlled combustion, flame wave, or explosion.

All protection methods used today are based on eliminating one or more of the trianglecomponents in order to reduce the risk of explosion to an acceptable level. In aproperly designed safety system, it is generally acceptable that two or moreindependent faults must occur, each one of low probability, before a potentialexplosion can occur.

5.0 EXPLOSIVE MIXTURE CHARACTERISTICS

The risk of an ignition of an air/gas mixture depends on the probability of thesimultaneous presence of the following two conditions:

1. Formation of flammable or explosive vapours, liquids or gases, or combustibledusts or fibres with atmosphere or accumulation of explosive or flammable

material;

2. Presence of an energy source electrical spark, arc, or surface temperature

that is capable of igniting the explosive atmosphere present.

It is possible to draw an ignition characteristic for each type of fuel. The characteristiccurves of hydrogen and propane are illustrated in figure-1.2.

Figure-1.2: Ignition energy in relation to hydrogen

and propane air/gas concentration


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CONCEPT OF MIE, LEL & UEL

MIE - A minimum ignition energy (MIE) exists for every fuel that represents the idealratio of fuel to air. At this ratio, the mixture is most easily ignited. Below the MIE,ignition is impossible for any concentration.

LEL - For a concentration lower than the one corresponding to the MIE, the quantity ofenergy required to ignite the mixture increases until a concentration value isreached below which the mixture cannot be ignited due to the lower quantity offuel. This value is called the lower explosive limit (LEL).

UEL- In the same way, when increasing the concentration the energy requirementincreases, and a concentration value is identified above which ignition cannotoccur due to the low quantity of an oxidizer. This value is called the upper

explosive limit (UEL).

For example, the following table lists the explosive characteristics of hydrogen andpropane.

MIE LEL UEL

Hydrogen 20 micro-Joules 4% 75%

Propane 180 micro-Joules 2% 9.5%

Table 1.1

For a practical point of view, LEL is more important and significant than UEL because

it establishes, percentage-wise, the minimum quantity of gas needed to create anexplosive mixture. This data is important when classifying hazardous locations.

The MIE (minimum energy required to ignite an air/gas mixture in the most favourableconcentration) is the factor upon which the intrinsic safety technique is based. Withthis technique, the energy released by an electrical circuit, even under fault conditions,is limited to a value lower than the MIE.

6.0 IGNITION TEMPERATURE

The minimum ignition temperature of an air/gas mixture is the temperature at whichthe explosive atmosphere ignites without electrical energy being supplied.

This parameter is important because it establishes the maximum surface temperatureallowed for devices located in a hazardous location, under both normal and faultconditions. This must always be lower than the ignition temperature of the gaspresent.

7.0 FLASH-POINT TEMPERATURE

The flash-point temperature is a characteristic of a volatile liquid, and it is defined asthe lowest temperature at which the liquid releases sufficient vapors that can beignited by an energy source.

Since a liquid above its flash point constitutes a source of danger, this parameter must

be considered when classifying locations.


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8.0 ELECTRICAL SAFETY STANDARDS, ORGANIZATIONS, TESTING AND

CERTIFYING AGENCIES

Over the past several decades, the increased use of electrical instrumentation inchemical plants and Refineries throughout North America & Europe has brought aboutan increase in the magnitude of safety problems and the need for safety standardsrelating to the requirements of equipments in hazardous locations.

During the 1950s, there were no industry-accepted safety standards. Up until thattime, rules and regulations were created by individuals (designers, engineers,government agencies etc.) trying to be safe. However, with the increase in demand formore and more complex electronic equipment for use in hazardous locations, amovement began toward the standardization of safety requirements.

Many organizations, including BASEEFA, CENELEC, CSA, FM, IEC, ISA, NEC,NEMA, NFPA, PTB, and UL, perform different function in ensuring the safety ofindustrial plants and refineries.

UNITED STATES PRACTICE

NEC (National Electrical Code)

Electrical installation practices in the United States are based on the NationalElectrical Code (NEC). The National Fire Protection Association (NFPA) has acted asa sponsor of the NEC since 1911. The NFPA has given the authority for maintainingand revising the NEC to the National Electrical Committee.

The 1993 edition of the NEC recognized the importance of the use of intrinsic safetyas a protection method by the significant expansion of Article 504, intrinsically safesystems. A further expansion of the NEC occurred in 1991 when Article 505 wasadded. The importance of this section is based on the fact that it included the so calledzone method for classifying hazardous locations.

The International Society of Automation (ISA) has been very active in the developmentof hazardous location standards including safety.

FM (Factory Mutual) and UL (Underwriters Laboratories)

Both of them are famous organization and they are the two major standardization and

approval authorities in the USA. They formulate their own standards which covers awide variety of subjects including the topic of explosion prevention in hazardouslocations. They also acts as a testing and certification authority i.e. they testequipment submitted by manufacturers to determine whether they meet therequirements laid down in the standard and if approved, they issue certificate ofconformity to the relevant FM/UL Standard.

CANADIAN PRACTICE

In Canada, the Canadian Electrical Code (CEC) is similar to the National ElectricalCode and is the standard for electrical equipment installations. The CanadianStandard Association (CSA) is also recognized by OSHA (Occupational Safety and

Health Administration) as a Nationally Recognized Testing Laboratory.


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EUROPEAN PRACTICE

IEC (International Electro technical Commission)

It is an international organisation responsible for electro technical standardization. Ithas developed standards that relate to the various aspects of the subject of explosionprevention in hazardous locations.

CENELEC

(In English, the form translates to European Committee for Electro technicalStandardization) Most European countries are members of CENELEC and theCENELEC standards are given the status of national standard by its membercountries. (For example, in UK which is a member of CENELEC, the CENELEC

Standards would be accepted as British Standard).

BASEEFA

(British approval service for Electrical Equipment in flammable areas).This is anagency which develops the British Standards that related to explosion prevention inhazardous locations and is the British national testing, approval and certifying authorityfor electrical equipment used in hazardous locations. This standards providesguidelines as to how equipments are to be designed so that they are safe forinstallation in hazardous areas, and also gives guidance on safe installationprocedures.

ATEX

The two European Community (EC) regulations that fundamentally changed thehazardous location landscape in Europe are Directive 94/9/EC (ATEX 95) andDirective 1999/92/EC (ATEX 137). ATEX 95 is focused mainly at manufacturers ofelectrical equipment for hazardous areas while ATEX 137 is centred primarily onoperators of systems within hazardous locations.

Most other countries in Europe as well as many other countries such as the USA,Canada, Japan, Australia etc have similar agencies in their countries, some of whichhave been listed below:

Serial No. Country Agency

1. USA FM & UL

2. Canada CSA

3. Germany PTB

4. France LCIE

5. UK BASEEFA

Table 1.2

Finally it is to be noted that countries which do not have their own national standardsand a national testing and certifying agency, accept the IEC or the Americanstandards and accept equipments/ systems certified by European / American approvalagencies.


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9.0 HAZARDOUS LOCATIONS CLASSIFICATION

The identification of hazardous (classified) locations in a plant is normally carried outby experts or highly qualified personnel, such as process or chemical engineers. Thepossibility of presence of the hazardous atmosphere, in what condition and for howlong, must be established. The most common dangerous areas are located where thepossibility of a leakage of flammable gas is present. The leakage can occur during anormal or fault condition, or due to the deterioration of the components operating inthe process. Depending on the type of leakage continuous or intermittent (ifintermittent, with what frequency) the classification of the hazardous location isdetermined.

The area surrounding the location identified as hazardous is extended to a distancewhere the flammable substance becomes so diluted with air that ignition is no longer

possible. This distance is related to a number of factors, such as the nature andquantity of the gas, degree of ventilation, etc.

Although many areas are classified as hazardous due to the presence of gas,combustible dust hazards are equally important due to the potential for explosion. Acombustible dust explosion hazard can exist in a variety of industries, including food(e.g. candy, starch, flour, feed), Plastics, wood, rubber, furniture, textiles, pesticides,pharmaceuticals, dyes, coal, metals (e.g., aluminium, chromium, iron, magnesium,and zinc), and fossil fuel power generation.

10.0 THE CLASSIFICATION OF HAZARDOUS LOCATIONS AS PER US / CANADIAN

STANDARD: (NEC)

In the United States, the classification of hazardous locations is based on the NationalElectrical Code, NFPA 70, Articles 500 through 505.

In Canada, C22.1, Part I of the Canadian Electrical Code applies. Similar to the UnitedStates.

In North American installations, hazardous areas are defined by divisions, classes,and groups to classify the level of safety required for equipment installed in theselocations.

Divisions define the probability of the presence of the hazard being present duringnormal or abnormal conditions.

Classes define the type of hazard in terms of whether it is a gas or vapour, acombustible or conductive dust or an ignitable fibre or flying.

Groups classify the exact type and nature of the hazardous substance.

10.1 AREA CLASSIFICATION FOR NEC

Hazardous Area Classification identifies those areas in the premises where flammableatmospheres can be found. Flammable atmospheres are generally mixtures of air withflammable gas, Vapour, Dust or aerosol (Mist). This Area classification also provides


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an estimate as to how often these flammable atmospheres may be found dependingon the type of leakage continuous or intermittent (if intermittent with what

frequency). The hazardous area is divided according to the level of risk present. Ingeneral, the divisions are as follows:

Division 1Danger can be present during normal functioning, duringrepair or maintenance, or where a fault may cause thesimultaneous failure of electrical equipment.

Division 2Combustible material is present but confined to a closedcontainer or system, is normally vented or is in an areaadjacent to a Division 1 location

Table 1.3

10.2 MATERIAL CLASSIFICATION FOR NEC

A hazardous area may contain flammable gases or vapour, combustible dusts orignitable fibres or flying (material classification involves the grouping of combustiblematerials on the basic of their ignition energy requirement.)

In both countries (United States and Canada), hazardous locations are categorizedinto the following three classes, depending on the type of flammable substancespresent:

Class IHazardous due to the presence of flammable substancessuch as gases or vapours.

Class II Hazardous due to the presence of flammable substancessuch as dusts or powders.

Class IIIHazardous due to the presence of flammable substancesin a fibre or flying state.

Table 1.4

Class I (Gas or Vapours)

Class I hazardous locations are subdivided into the following four groups, dependingon the type of flammable gases or vapours present:

Group A Atmospheres containing acetylene

Group B

Atmospheres containing hydrogen, fuel and combustibleprocess gases containing more than 30 percent by volume,or gases or vapours of equivalent hazard such asbutadiene, ethylene oxide, propelling oxide and, acrolein.

Group C

Atmosphere such as ethyl ether, ethylene, or gases orvapours of equivalent hazard.

Group D

Atmospheres such as acetone, ammonia, benzene,butane, cyclopropane, ethanol, gasoline, hexane,methanol, methane, natural gas, naphtha, propane, orgases or vapours of equivalent hazard.

Table 1.5


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Class II (Combustible Dusts or Powders)

Class II hazardous locations are subdivided into the following three groups, dependingon the type of combustible dusts or powders present:

Group E

Atmospheres containing combustible metal dusts, includingaluminium, magnesium and their commercial alloys, orother combustible dusts whose particle size, abrasivenessand conductivity present similar in the use of electricalequipment.

Group F

Atmospheres containing combustible carbonaceous dusts,including carbon black, charcoal, coke dust that have morethan 8 percent total entrapped volatiles, or dusts that havebeen sensitized by other materials so that they present an

explosion hazard.

Group G

Atmospheres containing combustible carbonaceous dustsnot included in Group E or Group F, including flour, grainwood, plastic, and chemicals.

Table 1.6

Class III (Easily Ignitable Fibres or Flyings)

Class III hazardous locations are those that are hazardous because of the presence ofeasily ignitable fibres or flyings, but in which such fibres or flyings are not likely to be insuspension in the air in quantities sufficient to produce ignitable mixtures.

Class III, Division 1 locations are those in which easily ignitable fibres materialsproducing combustible flyings are handled, manufactured, or used.

Class III, Division 2 locations are those in which easily ignitable fibres are stored orhandled.

Locations belonging in this class usually include parts of textile mills, cotton gins, flax-processing plants, clothing manufacturing plants, woodworking plants, etc.

Easily ignitable fibres and flying include rayon, cotton, sisal, hemp, cocoa fibre, kapok,Spanish moss, excelsior, etc.

Class III locations are not further subdivided.

10.3 SURFACE TEMPERATURE CLASSIFICATION FOR NEC

An apparatus directly located in a hazardous location must also be classified for themaximum surface temperature that can be generated by the instrument, either duringnormal functioning or under a fault condition.

The maximum surface temperature must be lower than the minimum ignitiontemperature of the gas present.


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In the United States and Canada, temperature classifications are divided into sixclasses- T1 through T6. Classes T2, T3 and T4 are further subdivided, as shown in

the following table.

Maximum Temperature

Degree C

North American

Temperature Classification

450 T1

300 T2

280 T2 A

260 T2 B

230 T2 C

215 T2 D

200 T3

180 T3 A165 T3 B

160 T3 C

135 T4

120 T4 A

100 T5

85 T6

Table 1.7

Surface temperature classifications in North America

Each gas is associated with a temperature class based on its ignition temperature. It is

important to note that there is no correlation, for any specific mixture, between ignitionenergy and ignition temperature.

For example, hydrogen has minimum ignition energy of 20 J and an ignitiontemperature of 560C, while acetaldehyde has ignition energy greater than 180 J andan ignition temperature of 140C.

Maximum surface temperature, calculated or measured under the worst conditions, isnot to be confused with the maximum working temperature of the apparatus. Forexample, an electrical apparatus designed to work with a maximum temperature of70C, even under the worst conditions of the expected temperature range, must nothave a temperature rise greater than the safety margin specified by the applicable

standards.

An apparatus classified for a specific temperature class can be used in the presenceof all gases with an ignition temperature higher than the temperature class of thespecific instrument. For example, an apparatus classified as T5 can be used with theall gases having an ignition temperature greater than 100C.

According to FM 3610 and UL 913, all temperature data shall be referred to a baseambient temperature of 40C. Tests to be based on an ambient temperature within therange of 20-40C. The difference between the ambient temperature at which the testwas conducted and 40C shall then be added to the temperature measured.


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11.0 THE CLASSIFICATION OF HAZARDOUS LOCATIONS AS PER EUROPEAN

STANDARD: (IEC)

11.1 AREA CLASSIFICATION FOR IEC

Area classification involves the subdivision of hazardous areas on the basis of theprobability of flammable mixture being present and the length of time for which it islikely to exist. In Europe as well as major portion of the rest of the world, the presentpractises is to categorize hazardous areas according to the relevant IEC standard(IEC-International Electrical Commission). However, USA and Canada follow adifferent standard for area classification as define by NEC (National Electrical Code) inthe USA. In India, we follow both, possibly with a greater tilt towards the IECstandards.

In Europe, the tendency is to follow the recommendation of IEC 60079-10, based onwhich any place where the probability of the presence of a flammable gas exists mustbe classified according to the subdivision in one of the following zones:

Zone 0An area in which an explosive air/gas mixture iscontinuously present for long periods

Zone 1An area in which an explosive air/gas mixture is likely tooccur in normal operation

Zone 2An area in which an explosive air/gas mixture is unlikely tooccur; but, if it does, only for short periods of time

Table 1.8

However, if the combustible material is in the form of a dust, no IEC standard existsfor area classification. In such cases, European countries follow the CENELECstandards wherein hazardous areas containing dusts are classified into Zone 20, Zone21 and Zone 22

Zone 20An area in which a combustible dust cloud is part of the airpermanently, over long periods of time or frequently

Zone 21An area in which a combustible dust cloud in air is likely tooccur in normal operation

Zone 22

An area in which a combustible dust cloud in air may occurbriefly or during abnormal operation

Table 1.9

Any other plant location that is not classified as a hazardous location is to beconsidered a nonhazardous location.

Finally it is to be noted that the IEC/ NEC definitions merely provide guidelines forclassifying a specific hazardous location but do not specify any concise rules or aquantitative method for deciding whether a location is Zone 0, 1 or 2. Interpretation ofarea classification varies and trying to categorize a specific location into one of thethree Zones (or two Divisions) is a difficult job and a wide variety of factors needs tobe considered such as:


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i) The probability of the presence of a combustible material in the atmosphere

ii) The quantity of combustible material present

iii) The degree of ventilation

iv) The nature of the combustible gas (whether heavier or lighter than air)

v) The topography of the site (for exampleif in a particular location the wind velocityis larger, then any combustible gas/ vapour released tends to be flushed out(swept away) by air resulting in relatively lower degree of hazard.

11.2 MATERIAL CLASSIFICATION FOR IEC

European standard EN60079-0:2006 requires that apparatus be subdivided into twogroups:

Group IApparatus to be used in mines where the danger isrepresented by methane gas and coal dust

Group II

Apparatus to be used in surface industries where thedanger is represented by gas and vapor that has beensubdivided into three groups: A,B and C. Thesesubdivisions are based on the maximum experimental safegap (MESG) for an explosion proof enclosure or theminimum ignition current (MIC) for intrinsically safeelectrical apparatus.

Group II A Propane, Carbon di Sulphide

Group II B Ethylene

Group II C Acetylene, Hydrogen

Table 1.10

The groups indicate the types of danger for which the apparatus has been designed.Since Group I is intended for mines. The apparatus in Group II can be used in an areawhere gases or vapours are present (Class I hazardous location).

11.3 SURFACE TEMPERATURE CLASSIFICATION FOR IEC

An explosive mixture may be ignited by contact with hot surfaces (whose temperatureis greater than or equal to the ignition temperature of the mixture). Hence all electricalapparatus installed in the hazardous area must be classified according to its maximumsurface temperature classification indicates the maximum surface temperature of anelectrical apparatus (both under normal operating condition as well as faultconditions).

European standard EN60079-0:2006 requires that the maximum surface temperaturebe subdivided into six classes from T1 to T6, assuming a reference ambient

temperature of 40C.


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Maximum Surface

Temperature(Deg C)

European Temperature

Classification(IEC)

Better Apparatus

450 T1

300 T2

200 T3

135 T4

100 T5

85 T6Table 1.11

Surface temperature classification in Europe

Note that the maximum temperature of an electrical apparatus produced as aconsequence of power dissipation within the device, depends on the ambienttemperature. When electrical power is dissipated within an apparatus heat isgenerated which caused the temperature of the device to rise relative to itssurrounding [Heat generated (owing to power dissipated in the device) = Mass XSpecific heat X (TdeviceTambient)]. Large the amount of power dissipated; greater isthe temperature rise of the device. For a given dissipation, the surface temperature

produce depends on the ambient temperature. Tdevice = [Heat / (Mass X SpecificHeat)] + Tambient.

Hence it is important to specify the ambient temperature, while indicating thetemperature classification of an electrical apparatus. For higher ambient temperature(>40C) the temperature classification given above should be regarded as atemperature rise assessment. Thus if an apparatus has a temperature classificationof T6 (i.e. maximum surface temperature = 85C) corresponding to an ambienttemperature of 40C (i.e. a temperature rise of 45C= (85C - 40C) over ambient),then for ambient temperature of 55C and 80C the maximum surface temperaturemay be assume to be (55C ambient + 45C temperature rise) = 100C and (80C+45C) = 135C respectively. Hence a device which has a temperature classification ofT6 (40C ambient) would have a temperature classification T5 and T6 at ambienttemperature of 55C and 80C.

12.0 ATEX SUMMARY

With the introduction of the ATEX requirements, a new marking program took affecton all products for use within the EC. The intent of the marking requirements is basedon uniformity. The CE conformity mark on the product is an indication that all relevantdirectives (i.e., ATEX, Low Voltage-2006/95/EC, Machinery-2006/42/EC) have beensatisfied and that the product is suitable for use according to the manufacturesinstructions. For hazardous area products, the following chart applies:


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Device

Group

Device

Category

Type of

Atmosphere

Protection to

be Ensured

Hazardous Area

Characteristics

Zone

Comparison

I (mining)

M1

-----

Very High

Presentcontinuously

equipmentcannot be de-

energized

-

M2 High

Presentcontinuouslyequipment can

be de-energized

-

II (allareasexceptmining)

1G

(gas, vapour,mist)

D(dust)

Very HighPresentcontinuously,

for long periodsor frequently

Zone 0Zone 20

2 High

Likely to occurin normal

operation andfor short

periods of time

Zone 1Zone 21

3 Normal

Not likely tooccur in normal

operation or

infrequently

Zone 2Zone 22

Table 1.12

13.0 EQUIPMENT LABELLING METHOD

All equipment certified for use in hazardous areas must be labelled to show the typeand level of protection applied. The following example identifies the key elements ofthe equipment marking:

II (1) G D [Ex ia] IIC PTB 00 ATEX 2080

Symbol identifies the product for hazardouslocations

II Device GroupNon-mining application

1Device Category- Can be used in Zone 0 and/orZone 20-() indicates only part of the device meetsthe requirements of the category

ATEX GAtmosphere TypeCan be used in/for areas withflammable gas

Portion DAtmosphere TypeCan be used in/for areas with

flammable dust

Ex

Ex


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[]Associated apparatus that supplies safety into the

hazardous area.

CENELEC/IEC Ex Product TypeExplosion protection

Portion ia Protection TypeIntrinsic safety

IIC Equipment GroupIIC is most hazardous area

PTB Certifying Test Agency

Certificate 00 Test Year

Details ATEX Compliance with Directive 94/9/EC

2080 Running Number

Table 1.13

The following badge represents a typical example of equipment labelling

Figure-1.3: Typicalexample of equipment labelling


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14.0 DIFFERENCE BETWEEN NEC AND IEC PRACTICES

The following table shows the differences between the North American (NEC) andEurope (IEC) practices, regarding the classification of hazardous locations.

Organisation MethodContinuous

Hazard

Intermittent

Hazard

Abnormal-

condition

Hazard

NEC Division Division 1 Division 2

IEC Zone Zone 0/20 Zone 1/21 Zone 2/22

Table 1.14

It is evident from the above table that Zone 2/22 (IEC/EUROPE) and Division 2 (NorthAmerica) are most equivalent, while Division 1 includes the corresponding Zone 0/20and Zone 1/21. An instrument designed for Zone 1/21 cannot necessarily be directlyused in Division 1. In the stated definition from the cited standard, no quantification ofthe expressions long period time for Zone 0/20, can be present for Zone 1/21 andDivision 1, and not normally present for Zone 2/22, is given.

The main difference between the North American and the European classification ofhazardous locations is that there is currently no direct equivalent to the European

Zone 0 in the North American system.

Zone 0 is, therefore, the most dangerous. An instrument designed for Zone 0 must beincapable of generating or accumulating sufficient energy to ignite the fuel mixture.

In Europe, the apparatus are certified on the basis of design and constructioncharacteristics. From a practical point of view, the two systems are equivalent even ifthere are minor differences, as shown in the following table:

Hazard Categories Apparatus Classification Ignition Energy

Europe (IEC) North America (NEC)

Methane Group I (mines) Class I, Group D

Acetylene

Hydrogen

Ethylene

Propane

Group IIC

Group IIC

Group IIB

Group IIA

Class I, Group A

Class I, Group B

Class I, Group C

Class I, Group D

> 20 Joules

> 20 Joules

> 60 Joules

>180 Joules


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Conductive (Metal)

Dust

Nonconductive(Coal) Dust

Grain Dust

Group IIIC

Group IIIB

Group IIIA

Class II, Group E

Class II, Group F

Class II, Group G

More easilyignited

Combustible Flying Class III

Table 1.15

Apparatus classification in North America and Europe

Each subgroup of Group II and of Class I is associated with a certain number of gaseshaving an ignition energy included in the value reported and is represented by the gasreference in the above table that is used in certification tests.

Group IIC and Class I, Group A and B are the most dangerous because they requirethe lowest level of ignition energy. An apparatus designed for these groups must beincapable of igniting, by electrical means, any potentially explosive air/gas mixture.

The current IEC 60079-0 standard now contains dust protection requirements and

defines dust atmospheres as Group IIIC, IIIB, and IIIA.

15.0 KEY INSTALLATION POINTS:

1. The nature of the hazardous atmosphere: (Based on Gas / Liquid / DustClassification(Material Classification))

2. Ignition Temperature (Material Classification)

3. The probability that the hazardous atmosphere will be present(based on AreaClassification)

4. The maximum spark energy it can produce (Apparatus Group)

16.0 CONCLUSION

In order to avoid hazard in a chemical process plant it is important to know the natureof chemical being handled and depending upon the nature of chemical, the type ofelectrical items to be used in that area of plant is determined. Finally to make thematter more clear, various sections of process plant and storage are classifieddepending upon the severity of hazard in taking decision regarding type of electricalitems to be provided. This document is helpful in general for hazardous classificationand selection of electrical items suitable for use in process industries (Chemical,Petrochemical, fertiliser etc.)


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17.0 REFERENCES

(TCE.M10-PCS-01): Guide for Hazardous Area Classification for Chemical andIndustrial Plants.

Interface Technology Engineers Guide (PEPPERL&FUCHS)

www.wikipedia.org
http://www.wikipedia.org/http://www.wikipedia.org/

Documents

03. Basic Concepts on Hazardous Area Classification and Equipment Labelling Method