Electrical+Classification.ppt

ElectricalClassification-TrainingObjective,ProvideabasicunderstandingofwhatiselectricalclassificationShowhowtodeterminetheelectricalclassificationofageneralareaDoesnotequipparticipantstodetermineextentoftheclassifiedarea.,ElectricalClassification-Definitions,AutoignitionTemperature(AIT).Theminimumtemperaturerequiredtoinitiateorcauseself-sustainedcombustionofasolid,liquid,orgasindependentlyoftheheatingorheatedelement.ClassI,Division1Area.Alocationwhere(1)ignitableconcentrationsofflammablegasesorvaporsexistundernormaloperatingconditions;or(2)ignitableconcentrationsofsuchgasesorvaporsmayexistfrequentlybecauseofrepairormaintenanceoperationsorbecauseofleakage;or(3)breakdownorfaultyoperationofequipmentorprocessesmightreleaseignitableconcentrationsofflammablegasesorvaporsandmightalsocausesimultaneousfailureofelectricalequipment.,ElectricalClassification-Definitions,ClassI,Division2Area.Alocation(1)inwhichvolatileflammableliquidsorflammablegasesarehandled,processed,orused,butinwhichtheliquids,vapors,orgaseswillnormallybeconfinedwithinclosedcontainersorclosedsystemsfromwhichtheycanescapeonlyincaseofaccidentalruptureorbreakdownofsuchcontainersorsystems,orincaseofabnormaloperationofequipment;or(2)inwhichignitableconcentrationsofgasesorvaporsarenormallypreventedbypositivemechanicalventilation,andwhichmightbecomehazardousthroughfailureorabnormaloperationoftheventilatingequipment;or(3)thatisadjacenttoaClassI,Division1location,andtowhichignitableconcentrationsofgasesorvaporsmightoccasionallybecommunicatedunlesssuchcommunicationispreventedbyadequatepositive-pressureventilationfromasourceofcleanairandeffectivesafeguardsagainstventilationfailureareprovided.,ElectricalClassification-Definitions,CombustibleLiquid.Aliquidhavingaflashpointatorabove100F(37.8C).Combustibleliquidsaresubdividedasfollows:ClassIIliquidsarethosehavingflashpointsatorabove100F(37.8C)andbelow140F(60C).ClassIIIliquidsarethosehavingflashpointsatorabove140F(60C),andaresubdividedasfollows:ClassIIIAliquidsarethosehavingflashpointsatorabove140F(60C)andbelow200F(93.4C).ClassIIIBliquidsarethosehavingflashpointsatorabove200F(93.4C).,ElectricalClassification-Definitions,CombustibleMaterial.*Agenerictermusedtodescribeaflammablegas,flammableliquidproducedvapor,orcombustibleliquidproducedvapormixedwithairthatmayburnorexplode.FlammableLiquid.AliquiddesignatedasClassI,havingaflashpointbelow100F(37.8C)andhavingavaporpressurenotexceeding40psiaat100F(37.8C).ClassIliquidscanbefurthersubdivided.FlashPoint.Theminimumtemperatureatwhichaliquidgivesoffvaporinsufficientconcentrationtoformanignitablemixturewithairnearthesurfaceoftheliquid,asspecifiedbytest.,ElectricalClassification-ClassificationofHazardousAreas,Article500oftheNECdesignatesashazardous(classified)anyareainwhichacombustiblematerialisormaybepresentintheatmosphereinsufficientconcentrationtoproduceanignitablemixture.Article500designatesthreemajorcategoriesofhazardousareas:ClassI,ClassII,andClassIII.InaClassIhazardousarea,thematerialpresentisaflammablegasorvapor.InaClassIIhazardousarea,thematerialpresentisacombustibledust.InaClassIIIhazardousarea,thematerialpresentisanignitablefiberorflying.,ElectricalClassification-ClassificationofHazardousAreas,TheClassIcategoryisfurthersubdividedintoeitherClassI,Division1orDivision2asfollows:ClassI,Division1inwhichthecombustiblematerialispresentnormallyorfrequentlyClassI,Division2inwhichthecombustiblematerialispresentasaresultofinfrequentfailureofequipmentorcontainersAreasnotclassifiedeitherasClassI,Division1orDivision2,are“unclassified”areas,ElectricalClassification-BehaviorofGases/Vapors,Lighter-than-Air(VaporDensityLessthan1.0)Gases.Thesegasestendtodissipaterapidlyintheatmosphere.Theywillnotaffectasgreatanareaasheavier-than-airgasesorvapors.Exceptinenclosedspaces,suchgasesseldomaccumulatetoformanignitablemixtureneargradelevel,wheremostelectricalinstallationsarelocated.Heavier-than-Air(VaporDensityGreaterthan1.0)Gases.Thesegasestendtofalltogradelevelwhenreleased.Thegasmayremainforasignificantperiodoftime,unlessdispersedbynaturalorforcedventilation.,ElectricalClassification-BehaviorofLiquids,FlammableLiquids.Whenreleasedinappreciablequantity,aClassIliquidwillbegintoevaporateataratethatdependsonitsvolatility:thelowertheflashpoint,thegreaterthevolatility;hence,thefastertheevaporation.ThevaporsofClassIliquidsformignitablemixtureswithairatambienttemperaturesmoreorlessreadily.Evenwhenevolvedrapidly,thevaporstendtodisperserapidly,becomingdilutedtoaconcentrationbelowthelowerflammablelimit.Untilthisdispersiontakesplace,however,thesevaporswillbehavelikeheavier-than-airgases.ClassIliquidsnormallywillproduceignitablemixturesthatwilltravelsomefinitedistancefromthepointoforigin;thus,theywillnormallyrequireareaclassificationforproperelectricalsystemdesignCombustibleLiquids.Acombustibleliquidwillformanignitablemixtureonlywhenheatedaboveitsflashpoint.,ElectricalClassification-BehaviorofLiquids,WithClassIIliquids,thedegreeofhazardislowerbecausethevaporreleaserateislowatthenormalhandlingandstoragetemperatures.Ingeneral,theseliquidswillnotformignitablemixtureswithairatambienttemperaturesunlessheatedabovetheirflashpoints.Also,thevaporswillnottravelasfarbecausetheytendtocondenseastheyarecooledbyambientair.ClassIIliquidsshouldbeconsideredcapableofproducinganignitablemixturenearthepointofreleasewhenhandled,processed,orstoredunderconditionswheretheliquidmayexceeditsflashpoint.ClassIIIAliquidshaveflashpointsatorabove140F(60C)butbelow200F(93.4C).Theseliquidsdonotformignitablemixtureswithairatambienttemperaturesunlessheatedabovetheirflashpoints.Furthermore,thevaporscoolrapidlyinairandcondense.Hence,theextentofthearearequiringelectricalclassificationwillbeverysmallornonexistent.ClassIIIBliquidshaveflashpointsatorabove200F(93.4C).Theseliquidsseldomevolveenoughvaporstoformignitablemixturesevenwhenheated,andtheyareseldomignitedbyproperlyinstalledandmaintainedgeneralpurposeelectricalequipment.AClassIIIBliquidwillcoolbelowitsflashpointveryquicklywhenreleased.Therefore,areaclassificationisseldomneeded.,ElectricalClassification-ConditionsNecessaryforIgnition,InaClassIarea,thefollowingthreeconditionsmustbesatisfiedforthecombustiblematerialtobeignitedbytheelectricalinstallation:Acombustiblematerialmustbepresent.Itmustbemixedwithairintheproportionsrequiredtoproduceanignitablemixture.Theremustbeareleaseofsufficientenergytoignitethemixture,ElectricalClassification-Division1ClassifiedAreas,AconditionforDivision1iswhethertheareaislikelytohaveanignitablemixturepresentundernormalconditions.Forinstance,thepresenceofacombustiblematerialintheimmediatevicinityofanopendiptankisnormalandrequiresaDivision1classification.Normaldoesnotnecessarilymeanthesituationthatprevailswheneverythingisworkingproperly.Forinstance,theremaybecasesinwhichfrequentmaintenanceandrepairarenecessary.Theseareviewedasnormaland,ifquantitiesofaflammableliquidoracombustiblematerialarereleasedasaresultofthemaintenance,theareaisDivision1.However,ifrepairsarenotusuallyrequiredbetweenturnarounds,theneedforrepairworkisconsideredabnormal.Inanyevent,theclassificationofthearea,asrelatedtoequipmentmaintenance,isinfluencedbythemaintenanceproceduresandfrequencyofmaintenance.,ElectricalClassification-Division2ClassifiedAreas,ThecriterionforaDivision2areaiswhethertheareaislikelytohaveignitablemixturespresentonlyunderabnormalconditions.Theterm“abnormal”isusedhereinalimitedsenseanddoesnotincludeamajorcatastrophe.Asanexample,consideravesselcontainingliquidhydrocarbons(thesource)thatreleasescombustiblematerialonlyunderabnormalconditions.Inthiscase,thereisnoDivision1areabecausethevesselisnormallytight.Toreleasevapor,thevesselwouldhavetoleak,andthatwouldnotbenormal.Thus,thevesselissurroundedbyaDivision2area.,ElectricalClassification-RelativeMagnitude,RelativeMagnitudesofProcessEquipmentandPipingHandlingCombustibleMaterials:,ElectricalClassification-ProcedureforClassifyingAreas,StepOneDeterminingNeedforClassification.Theareashouldbeclassifiedifacombustiblematerialisprocessed,handled,orstoredthere.StepTwoGatheringInformation.ProposedFacilityInformation:foraproposedfacilitythatexistsonlyindrawings,apreliminaryareaclassificationcanbedonesothatsuitableelectricalequipmentandinstrumentationcanbepurchased.Plantsarerarelybuiltexactlyasthedrawingsportraythem,sotheareaclassificationshouldbemodifiedlaterbasedupontheactualfacility.,ElectricalClassification-ProcedureforClassifyingAreas,StepTwoGatheringInformation(cont.)Foranexistingfacility:theindividualplantexperienceisextremelyimportantinclassifyingareaswithintheplant.Bothoperationandmaintenancepersonnelintheactualplantshouldbeaskedthefollowingquestions:Havetherebeeninstancesofleaks?Doleaksoccurfrequently?Doleaksoccurduringnormalorabnormaloperation?Istheequipmentingoodcondition,questionablecondition,orinneedofrepair?Domaintenancepracticesresultintheformationofignitablemixtures?Doesroutineflushingofprocesslines,changingoffilters,openingofequipment,andsoforth,resultintheformationofignitablemixtures?,ElectricalClassification-ProcedureforClassifyingAreas,StepTwoGatheringInformation(cont.)ProcessFlowDiagram:aprocessflowdiagramshowingthepressure,temperature,flowrates,compositionandquantitiesofvariousmaterials(i.e.,massflowbalancesheets)passingthroughtheprocessisneeded.PlotPlan:aplotplan(orsimilardrawing)isneededshowingallvessels,tanks,trenches,lagoons,sumps,buildingstructures,dikes,partitions,levees,ditches,andsimilaritemsthatwouldaffectdispersionofanyliquid,gas,orvapor.Theplotplanshouldincludetheprevailingwinddirection.FireHazardPropertiesofCombustibleMaterial(e.g.flashpoint,AIT,%LFL,%UFL,vapordensity,vaporpressure,etc.),ElectricalClassification-ProcedureforClassifyingAreas,StepThreeSelectingtheAppropriateClassificationDiagram.Reviewthequantities,pressures,flowratestodeterminerelativemagnitudeofequipmentSelectappropriateclassificationdiagram(s).StepFourDeterminingtheExtentoftheClassifiedArea.Theextent/boundariesoftheclassifiedareamaybedeterminedbyusingsoundengineeringjudgmenttoapplythemethodsgivenandthediagramsgiveninNFP