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Revision : 02 Training Division

CONTENTS

Item Title Page1. INTRODUCTION 2

2. DEFINITIONS 3

3. BASIC FORMATION OF EXPLOSION 4

4. BASIC PRINCIPLES OF EXPLOSION PROTECTION 5

5. SAFETY PRINCIPLES 6

6. HAZARDOUS AREA CLASSIFICATION 21

7. EXPLOSION PROTECTION SELECTION FOR INSTRUMENTS 32

8. CERTIFICATION AND TESTING AUTHORITIES 44

9. MARKING 45

10. ATEX 46

11. PROFESSIONAL RESPONSIBILITY 47

ATTACHMENTSNO1. DefinitionsNO2. Limiting Hazardous AreasNO3. Hazardous Area Classification DrawingsNO.4 Intrinsically safe systemNO5. STEP Program

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1- INTRODUCTIONElectrical energy plays an important role in our daily life . Asprofessional electrical and instrument engineers , you are well awareof this and are constantly involved in studying , designing andimplementing installation .This energy which you have made available on a daily basis canbecome a danger to daily life. This can occour when energy is used inany industry or warehouse which processes , manufactures or storesproducts such as ; hydrocarbons , gases , paints , varnishes , glues ,resins , perfumes , cleaning products , rubbers , textiles , plastics ,powders , grains , etc. .There is thus a high explosion risk with serious consequences forpersonnel , equipment and environment .




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2- DEFINITIONS2.1) Inflammable substance : A substance in the form of a gas ,

vapor , liquid , solid or mixture that can react exothermicallywith air when ignited .

2.2) Explosion : Sudden oxidation or coincidental reaction with anincrease in temperature , pressure , or both at the same time .

2.3) Explosive atmosphere : Explosive mixture of gases , vapors ,mists and/or dusts with air and the usual additional substancespresent under atmospheric conditions .

2.4) Explosive mixture : A mixture of gases , vapors with each otheror with mist or dust in which a reaction will spreadautomatically when ignited .

2.5) Hazardous areas : Area in which potentially explosiveatmospheres can form due to the local and operation conditions.

2.6) Hazardous , potentially explosive atmospheres-A mixed quantity is considered hazardous if , when ignited,personal injury or property losses can be expected as a direct orindirect effect of an explosion .

- Hazardous amount >> 10-4 of the room volume- Any cohesive Ex-atmosphere greater than 10I in a closedroom must always be viewed as hazardous.

- The same applies to a compacted 1 mm thick layer of dust.2.7) . . . . . . . . . . . . . . . .

2.8) . . . . . . . . . . . . . . . .

Further Information : For more information ref. to the publicationsand standards of IEC, API, NFPA, ISA, IEEE, …




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3- BASIC FORMATION OF EXPLOSION Three element are required :1. Oxygen in the air .2. An inflammable substance , mixed with air.

This substance can be :- Gas (methane , acetylene , etc. )- Liquid (petrol , solvent , etc.)- Solid (Sulphur , wood dust , etc.)

3. An inflammable (ignition) source :- An electrical arc or a spark with sufficient energy .- and / or rise in temperature .

These three elements together are sufficient to trigger an Explosionwhich may be transferred to the environment .

EXPLOSION




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4- BASIC PRINCIPLES OF EXPLOSION PROTECTIONIn order to reduce the risk of explosion , elimination of one or morecomponents of the “ignition triangle” (Oxygen , Flame , Fuel) isnecessary.In principle , in order to prevent explosion, avoidance of simultaneousappearance of the followings are required :1. Air (oxygen)2. Inflammable substances (gas , vapors , mist or dust)3. Source of ignition (energy in the form of heat or sparks)

…………………………………………………………………………….




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5- SAFETY PRINCIPLESSafety measures are to be taken in the following order :- Avoid the formation of hazardous atmospheres .- Avoid the ignition of hazardous atmospheres .- Reduce the effects of an explosion .

5.1 Avoiding the formation of hazardous atmospheres5.1.1 Avoid / limit the use of flammable substances

• Replace flammable substance with safe materials• Reduce the amount of flammable substances• Use substances with the highest flash point

5.1.2 Prevent the formation of hazardous atmospheres inside ofequipment

• Selecting concentrations outside of the explosion limits .• Addition of inert substances (nitrogen , carbon dioxide)• When using a vacuum : Reduction of the explosion pressure and

increase in the minimum ignition energy .• Note all start up and shutdown conditions.




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5.1.3 Preventing the formation of hazardous Atmospheres nearequipment

● Planning of enclosed plants and equipment● Tightness of seals on equipment

●● Also take interactions and corrosion into account●● Maintenance and monitoring

● Reduction in the amount of flammable substances emitted whenrefilling , taking samples , draining

● Check equipment to ensure there are no leaks●● prior to its first commissioning and regularly after longershutdown periods.

● Ventilation measures●● Natural ventilation●● Technical ventilation (room ventilation)P Monitoring requiredP Note the intake and exhaust air clearance areasP Gases and vapors near the floorP Obstacles in the room

●● Suctioning in of objects




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5.2. Avoiding the ignition of hazardous atmospheres5.2.1 Classify the area into zones● ZONE 0An area in which a hazardous , explosive atmosphere consisting of amixture of air with flammable substances in the form of gas , vaporor mist is present continuously for long periods or frequently .

● ZONE 1An area in which a hazardous , explosive atmosphere consisting of amixture of air with flammable substances in the form of gas , vaporor mist is likely to occur occasionally in normal operation .

● ZONE 2An area in which a hazardous , explosive atmosphere consisting of amixture of air with flammable substances in the form of gas , vaporor mist is not likely to occur in normal operation but , if it doesoccur, will persist for a short period only .




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• Probability of occurrence of explosive atmospheresZone potentially explosive

atmosphere presentZone 0 >1000 hours / yearZone 1 10-1000 hours / yearZone 2 <10 hours / yearNon-Ex <1 hours / year(Unclassified)

• Example of classification into zones( For further example refer to figures 1 to 106 of API 505 )




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Classification of Zones

Zone 2

Zone 1

Zone 0




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unclassified




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● ZONE 20An area in which a hazardous , explosive atmosphere in the form ofa cloud of combustible dust in the air is present continuously , forlong periods or frequently .

● ZONE 21An area in which a hazardous , explosive atmosphere in the form ofa cloud of combustible dust in the air is likely to occur occasionallyin normal operation .

● ZONE 22An area in which a hazardous , explosive atmosphere in the form ofa cloud of combustible dust in the air is not likely to occur in normaloperation but , if it does occur, will persist for a short period only .




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Classification of Zones (Dusts)

Zone 22

Zone 21

Zone 20




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5.2.2 Ignition sources● Electrical sources● ● Electrical sparks● ● Electrical arcs● ● Stray electrical currents● ● Static charges● ● Electromagnetic waves● ● Ionizing radiation

● Non-electric sources● ● Flames and hot gases● ● Hot surfaces● ● Mechanically generated sparks● ● Radiation in the form of optic rays● ● Lightning● ● Chemical sources of ignition● ● Adiabatic pressures● ● Ultrasound

5.3 Reducing the effects of an explosion5.3.1 Explosion – resistant construction5.3.2 Explosion pressure relief5.3.3 Explosion suppression5.3.4 Prevention of subsequent explosions




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6. Hazardous area classification• In many industrial processes where flammable materials are handled ,

any leakage or spillage may give rise to an explosive atmosphere,these areas at risk known as Hazardous Areas.As said before , one of the recommendations to reduce such risks is toclassify the areas into Zones .

• In a project , this is the responsibity of the electrical department todetermine which area of a plant is hazardous or non-hazardous(unclassified) and also in which class is each hazardous areaclassified based on the specification of the materials being processed.

• Reference documents , in a project, are as follow :Document Title Department

● ● Instrument projects Instrumentengineering specifications

● ● Area classification ElectricalDrawings

• The classification of zone is a complex problem but the main factorsto consider are :● ● The probability of the presence of gas● ● The quantity and duration● ● The amount of ventilation● ● The nature of gas : lighter or heavier than air




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• In this course , it is not planned to practice the classification methodsbut only to review the area classification drawings of some of theprojects .

• Further information : for more information on classification ofLocations, refer to API recommended practice 505, 500, . . . & IEC79

• To easier understand the subject matter and related drawings anddocuments ,one should review the “Definitions” . For this purpose ,some of them are discussed below , some are enclosed as perAttachment No. 1 , but the reader is suggested , for furtherinformation, to refer to the publications and standards of API , NFPA,IEC, ISA, . . . , etc. .

• Class I Location :In this course, classification of class I locations are reviewed wherethere may be a risk of ignition due to the presence of flammable gasor vapor mixed with air under normal atmospheric conditions .

• Flash Point :The minimum temperature of a liquid at which sufficient vapor isgiven off to form an ignitable mixture with air, near the surface of theliquid or within the vessel used, as determined by the test procedureand apparatus specified in NFPA 30 .




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• Ignition (Auto ignition) Temperature :The lowest temperature of a heated surface at which , under specifiedconditions , the ignition of a flammable substance in the form of a gasor vapor mixture with air will occur .

• Lower Explosion Limit (LEL) :The lower explosion limit is the lowest concentration of a mixturethat is potentially explosive (mixture is too thin).

• Upper Explosion Limit (EEL) :The upper explosion limit is the highest concentration of a mixturethat is potentially explosive (mixture is too thick).




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● ● LEL & UEL Graphical Presentation :

UEL

LEL




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● ● LEL & UEL For Hydrogen :




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● ● LEL & UEL For Some Substances :




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• Defining hazardous area for gas and vapors :The International Electrotechnical Commission (IEC 79) makes adistinction between the following hazardous zones :

• ZONE 0Explosive atmospheres present frequently or continuously for longperiods .

Typically More than 1000 hrs/yearExample : Space above flammable liquid in a tank

• ZONE 1Explosive atmospheres are likely to occur under normal operatingconditions .

Typically between 10 and 1000 hrs/year

Example :a) Around the openings of tank lorries or load tankers drums andtanks etc. when they contain flammable liquid.

b) At the moment of drawing off a flammable product, or around theoutlet of a safety valve when the safety valve is discharging anexplosive gas .

c) Pit in which gas accumulates , located near a place where there is apossibility of explosive gas leakage .




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• ZONE 2

Explosive atmospheres are not likely to occur under normal operatingconditions or present only infrequently and for a short period.

Typically less than 10 hrs/yearExample :a) Area in which a dangerous concentration of gas is produced by theleakage of flammable gas brought about by the failure of a vesseldue to corrosion etc.

b) Area in which explosive gas is likely to be discharged by mis-operation or a leak caused by an abnormal reaction .

c) A room into which explosive gas is likely to intrude adjacent to oraround a zone 1 area .




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Gas / vapor area zones




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• In summary , 3 types of Zones can be distinguished:

• These Zones are geographical , yet the frontiers between each ofthem are not easily defined. In fact, a zone may shift for variousreasons:● ● Temperature rise of products● ● Defective ventilation of the area● ● Climatic variations● ● Operating error● ● Movement of air

• For further clarification refer to Attachment No. 2• For familiarization with hazardous area classification drawings refer

to Attachment No. 3

Zone 0

Explosive Atmosphere is continuously present

Zone 1

Explosive Atmosphere is often present

Zone 2

Explosive Atmosphere may accidentally be

present




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● Hazardous Area Classification/Various Nation Codes




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7. Explosion Protection Selection For Instruments• The instrument engineer by referring to the area classification

drawings (prepared by electrical engineer/ department) should nowselect the appropriate instruments for different zones .

• Responsibilities : Responsibilities for determining the type of hazardprotection of instruments in each project are as follows :● ● Preparation : Engineer● ● Checking : Head Engineer● ● Approval : Lead Engineer

7.1 Standards throughout the worldThe worldwide electrotechnical standard for electrical equipment forexplosive atmosphere is covered by two major “Standards” :

• CENELEC / IEC = *(CENELEC = European Committee of Electrotechnical Standards)* In some literature this is referred to CEC

• NEC(NEC = National Electrical Code of America)Products which conform to CEC or NEC standards have identicalprotection , even though they are designed differently to meet specificinstallation regulations .




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7.2 Classification of locations

CLASS INFLAMMABLE MATERIAL

I Gases & vapors AcetyleneHydrogenPropylene OxideEthyl OxideButadieneCyclocpropane

Ethyl etherEthyleneAcetoneBenzeneButanePropaneHexanePaint SolventsNatural Gas

II Combustible DustsMagnesiumAluminiumAu MetalicDustwithR≤ 10 5 ohms * Cm

III Fibers and dustsRayonCottonLinenWoodHempFlax bastTowCoconut fiber




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7.3 Equipment GroupGroup I MinesGroup II Surface Industries

7.4 Category Of EquipmentGroup I (Mines) Group II (Surface Industries)

Subdivided into categories Category Subdivided into ZoneM1 Equipment remains 1G (Gas) Equipment with a very 0(gas)

functional with an explosive 1D (dust) high level of protection 20(dust)atmosphere present

2G (Gas) Equipment with a 1(gas)2D (dust) high level of protection 21(dust)

M2 Equipment to bede-energized in the event of an 3G (Gas) Equipment with a 2(gas)explosive atmosphere 3D (dust) normal level of protection 22(dust)

7.5 Gas Group Classification7.5.1 Group I : A term used (by IEC 79-10) to describe atmospheres containing

firedamp (a mixture of gases, composed mostly of methane, foundunderground, usually in mines) .

7.5.2 Group II : The group used to describe gases found aboveground and issubdivided into IIA, IIB and IIC, as some of them are tabulatedbelow as representative gases.




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7.5.3 Apparatus ClassificationIn some technical documents “Apparatus Group” is used in the following form :

Apparatus Group = Equipment Group + Gas / Dust Group

GAS GROUP CLASSIFICATIONNEC

Typical GasCEC

Class I Gases & Vapors

Group II Gases & Vapors

Group DPropaneASub Group

Group CEthyleneB

Group BHydrogenC

Group AAcetylene

Apparatus ClassificationIgnition EnergyNECCENELE

CHazard Categories

Class I , Group DGroup IMines (Methane)

< 20 µJClass I , Group AGroup II, C

Acetylene

< 20 µJClass I , Group BGroup II, C

Hydrogen

< 60 µJClass I , Group CGroup II, B

Ethylene

< 180 µJClass I , Group DGroup II, A

Propane

MoreClass II , Group EGroup IIMetal dust

easilyClass II , Group FGroup IICoal Dust

ignitableClass II , Group GGroup IIGrain dust

Class IIIFiber




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7.6 Temperature ClassificationThe IEC has defined a temperature classification for equipment used inhazardous areas .Following this , CEC and NEC have also been modified to include atemperature classifications . This temperature table is as follows :

ClassificationTemperatureTemp.Max. Surface

NECCECF°C°

T1T1842450

T2

T2

572300

T2 A536280

T2 B500260

T2 C446230

T2 D419215

T3

T3

392200

T3356180

T3329165

T3320160

T4T4

275135

T4 A248120

T5T5212100

T6T618585




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7.7 Protection Methods (Modes)Basically there are three methods of protection :

7.7.1 Explosion Containment :This method allows the explosion to occur but confines it in a well defined

place and avoids the propagation to the surrounding atmosphere .

- Explosionproof EEx d

7.7.2 Segregation :This technique attempts to physically separate or isolate the electrical parts

or hot surfaces from the explosive mixture, this method includes various techniquesas pressurization, encapsulation etc.

- Pressurizing EEx p

- Encapsulation EEx m

- Oil Immersion EEx o

- Powder Filling EEx q




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7.7.3 PreventionThis method tries to limit the energy both thermal and electric to safelevels even in un favorable circumstances. Intrinsically safety methodis the most representative technique of this method .A) Refined Mechanical Design

- Increased Safety EExe- Non-Incendive EExn( Non-sparking)

B) Energy Limiting- Intrinsically Safe EExi

Further Information : For more information on Intrinsically Safe Systemrefer to Attachment No. 4

Hazardous Area

Safe Area

ia / ib

Certified Interface




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7.8 Protection IndexesThe degree (Index) of protection is determined by the abbreviation IP(coming from Ingress Protection) followed by three digits (example IP657) .The third digit is not necessary to be stated except for the cases where theinstrument may be exposed to mechanical shocks or vibration .Protection degrees specified by these figures are given below .




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3RD FIGURE : MECHANICAL PROTECTION

FIGURE DEFINITION TESTS0 No protection

1 Impact energy 0.225 joule



5 Impact energy 2.00 joules






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7.9 Hazardous Areas Vs. Protection Methods(The following table is only a recommendation!)

Protection ModesHazardous Areas

iaZone / Division 0

ia , ib , d , p , e, oZone / Division 1

ia , ib , d , p , e, oZone / Division 2




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7.11 ProcedureStep 1: For each individual instrument fed by electrical power and

also for junction boxes, the instrument engineer shoulddetermine the area classification in which that instrumentis going to be installed (by referring to the areaclassification drawings) .

Step 2: The instruments located in un-classified area , need not tobe protected and ordinary instruments with generalpurpose enclosures shall be ordered .

Step 3: If the instrument is located in hazardous area the instrumentengineer should refer to the area zone . If the location isspecified as zone 0 the instrument must be protectedintrinsically safe (using barriers, isolators, etc.) .If thelocation is specified as zone 1 or zone 2 the instrumentengineer should refer to the project engineeringspecification and see whether explosion proof method isapproved for this area or intrinsically safe; and designrespectively .

Step 4: In both protection methods it is necessary for theinstruments to be certified by one of international ornational certifying authorities .

Step 5: In addition to the above , it is needed to check theequipment for the protection against atmosphericenvironments .

Step 6: While finalizing the equipment selection, the installationrequirements of the main equipment & accessories shouldbe checked as per the methods accepted by the authoritiesof the country .




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8. CERTIFICATION AND TESTING AUTHORITIES




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9. MARKING9.1 CE

If the respective requirements of a standard is stipulated (forexample within the European union) , the equipmentmanufacturer can add the CE mark to the respective device.Any violation in this regard is a punishable offence .According to the ATEX guideline , the number of the notifiedcenter that carried out the QA system acceptance test is added tothis mark when referring to explosion protection .

9.2 ATEX 137Directive 99/92/EC

Warning sign for places where explosive atmosphere may occur.

9.3 ATEX 95Directive 94/9/EC

Explosion Protection Marking used for the equipment which maybe used in potentially explosive atmospheres .

EX

EX




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10. ATEXATEX is named after French “ATmosphere EXplosive” , andcommonly given to the framework for controlling explosiveatmospheres and standards of equipment and protective systemsused in them . It is based on the requirements of two EuropeanDirectives .

10.1 Directive 99/92/EC(Also known as “ATEX 137”, or the “ATEX Workplace Directive”)on minimum requirements for improving the health and safetyprotection workers potentially at risk from explosive atmospheres .

The text of the Directive and the supporting EU producedguidelines are available on the EU – website .




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10.2 Directive 94/9/ECThis Directive provides the technical requirements to be applied toequipment intended for use in potentially explosive atmospheres.This Directive has been mandatory from 1st July 2003 .Manufacturers who apply its provisions and affix the CE markingare able to sell their equipment anywhere in Europe without furtherrequirements being applied with respect to the risks covered beingapplied .

11. PROFESSIONAL RESPONSIBILITYAs an always- to-remember point , we as professional engineersshould bear in mind, is to improve the industries environmental,health and safety performance .It is recommended to refer to the STEP program, enclosed asAttachment No. 5




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