石油化工企业可燃气体和有毒气体检测报警设计规范

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本英文版为内部资料，仅供参照，以中文版为准。UDCSH中华人民共和国行业原则PSH3063-1999SpecificationsforDesignofCombustibleGasandToxicGasDetectionandAlarmSystemsinPetrochemicalIndustry石油化工企业可燃气体和有毒气体检测报警设计规范Issuedon15Apr.1999Executedsince1Sept.19991999-04-15公布 1999-09-01实行国家石油和化学工业局公布PrefaceTheSpecificationsarerevisedbythiscorporationbasedontheoriginalspecifications“SpecificationsforDesignofCombustibleGasDetectionandAlarmSystemsinPetrochemicalIndustry”SH3063-94accordingtothenotificationofthefile(1996)JBZNo.250issuedbySINOPEC.Thespecificationsconsistofsixchaptersandtwoappendices.Themajorpurposeofthisrevisionistoaddthecontentsonthedesignoftoxicgasdetectionandalarm.Intherevisioncourse,theproblemthattheoriginalspecificationscontainsnocontentonthedesignoftoxicgasdetectionandalarmhasbeengivenbroadlyinvestedandstudied;practicalexperiencesintoxicgasdetectionandalarminpetrochemicalenterprisesinthelastyearshavebeensummarized;suggestionsandopinionsfromrelevantdesign,production,researchanddevelopment,anddetectinginstrumentaspectshavebeencollected;andsomekeyissuesarediscussedmanytimes;finally,thisfinalversionoftheSpecificationsisconfirmed.IfanypartintheSpecificationsisfoundtoreviseorsupplementinitsimplement,pleaseofferyoursuggestionordatatothiscorporationforreferenceinfuturefurtherrevision,Thecontactaddressofthiscorporation:No.27ZhongzhouW.Rd.,Luoyang,Henan,471003.TheSpecificationsiscompiledmainlybyLuoyangPetrochemicalEngineeringCorporation,SINOPEC.UnitsparticipatedthecomplementoftheSpecificationsincludeLanzhouDesignInstitute,SINOPEC,TheInstrumentPlaneofYanshanPetrochemicalCorporation,SINOPEC,ShenzhenAnhuiIndustrialCo.MaindraftersoftheSpecificationsareWangHuaiyi,WangYubin，WangZipinContentsGeneralPrinciples……………3Terminologyandsymbols…………………3Terminology…………3Symbols………………3CommonStipulations………4DeterminationofDetectionPoints…………………5Processinginstallations………………5Storage-transportationFacilities……………………6LocationswhereCombustibleGasesandToxicgasesDiffuseandAccumulate………7DETECTION-alarmSystemsofCombustibleGases

andToxicGases……………………8Systemcompositionandperformance………………8Selectionofthedetectors……………9SelectionofAlarmsorIndicator-alarms……………10InstallationofAlarmsforCombustibleGases

andToxicGases…………………12Installationofthedetector……………12Installationofalarmsorindicator-alarms……………12AppendixA:PropertiesTableofCombustibleGases,ToxicGases,andTheirVapors………………………13Attachment:ElucidationofSomeTermsUsedintheSpecifications…19

1.GeneralPrinciplesTheSpecificationsareformulatedinordertoensurethesafetyproductionand/orpersonalsafetyinpetrochemicalenterprisesbydetectingtheconcentrationofpossiblyleakedcombustiblegasesandtoxicgasesandtimelymakingalarmtopreventfireand/orexplosionhazard.TheSpecificationsareapplicableforthedesignofthedetectionandthealarmofcombustiblegasesandtoxicgasesforpetrochemicalenterprises.1.0.3ThecurrentrelevantmandatorystandardsandspecificationsshouldbemetinadditiontotheSpecifications.TerminologyandSymbolsTerminologyCombustiblegasThecombustiblegasforthepurposeoftheSpecificationsmeansthegasesinClassAwhichlowerexplosivelimitsarebelow10(v/v)%orthedifferencebetweenboththeupperandlowerlimitsaremorethan20(v/v)%,orthecombustiblegasesorthosecontainingsmallamountoftoxicgaseswhichareformedfromliquefiedhydrocarbons,combustibleliquidsinClassesAb,andBabyvaporization.ToxicgasThetoxicgasforthepurposeoftheSpecificationsmeanshydrogensulfide,hydrogencyanide,chlorine,carbonmonoxide,acrylonitrile,epoxyethane,andchlorethylene.AllowablemaximumconcentrationItmeanstheallowablemaximumconcentrationofaorsomehazardoussubstance(s)intheworkshopair,i.e.thefigurewhichisnotallowedtoexceedforthehazardoussubstance(s)inthesirinworkingplacewhereworkersundertaketheirjob.Thefigureisalsocalledasthehighestlimit.Symbols2.2.1LELmeansthelowerexplosivelimit(v/v%)ofacombustiblegas.2.2.2TLVmeanstheallowablemaximumconcentrationofahazardoussubstanceintheworkshopair.CommonStipulations3.0.1InaRegion-2oradditionalRegion-2wherecombustiblegaseswillbeusedorproducedintheprocessinginstallationsorstoragetransportationfacilities(includingthetankfarms,handlingfacilities,andfillingstationsusedforgasesinClassA,liquefiedhydrocarbons,liquidsofClassAb),combustiblegasdetectionandalarminstrumentsshouldbesetinconformitywiththeSpecifications.IntheRegionwheretoxicgaseswillbeusedorproducedintheprocessinginstallationsorstorage-transportationfacilities,toxicgasdetectionandalarminstrumentsshouldbesetinconformitywiththeSpecifications.Foracombustiblegasorthegascontainingatoxicgas,anditmaybecausedfromaleakageeventthattheconcentrationofthecombustiblegasreaches25%ofLFL,andthetoxicgascannotreachtheallowablemaximumconcentration,acombustiblegasdetectingalarminstrumentshouldbeset;Foratoxicgasorthegascontainingacombustiblegas,anditmaybecausedfromaleakageeventthatthetoxicgasreachestheallowablemaximumconcentration,andtheconcentrationofthecombustiblegascannotreach25%ofLFL,atoxicgasdetectingalarminstrumentshouldbeset;Foragaswhichisbothcombustibleandtoxic,onlyonetoxicgasdetectingalarminstrumentneedstobeset;Foraplacewhereareaorsomecombustiblegas(es)andaorsometoxicgas(es),acombustiblegasdetectionandalarminstrumentandatoxicgasdetectingandalarminstructionshouldbesimultaneouslyset.Note:ForthedivisionofRegion-2orAdditionalRegion-2,seethe“SpecificationsforDesignofPowerInstallationsintheEnvironmentswithExplosiveandFireHazard”,GB500Themonitor-alarmofcombustiblegasesandtoxicgasesshouldbethealarmsofClassIorClassI1.Theroutinemonitor-alarmshouldbeClassIalarm.Fortheprocessthatneedsaninterlockingprotectionsystem,ClassIorClassIIalarmshouldbeadopted.AjunctionoutputsignalistransmittedtotheinterlockingprotectionsystematthesameofClassIIalarming.3.0.3Forthehazardousareawherenobodyisallowedtoenterasrequiredforthesakeofaspecialprocessingneed,necessaryrecordingorprintingdeviceshouldbedoneinadditiontoimplementationofthecontinuousdetection,indication,alarmofthereleasingsourceofthecombustiblegasand/orthetoxicgas.3.0.4Thealarmsignalshouldbetransmittedtothecontrolroomoroperationpostswhereareoperatorsconstantlywatchedtheprocessinginstallationsandstorage-transportationfacility.3.0.5Allcombustiblegasdetectionandalarminstrumentsmustbesubjecttocertificationofastate-designatedinstitutionandastate-authorizedinspectionunitinmanufacture,explosion-proofandfire-proofperformancesoftheirmeasuringinstruments.Alltoxicgasdetectionandalarminstrumentsmustbesubjecttocertificationofastate-designatedinstitutionandastate-authorizedinspectionunitinmanufactureoftheirmeasuringinstruments.Alltoxicgasdetectionandalarminstrumentsofflame-prooftypemustbesubjecttocertificationofastate-designatedinstitutionandastate-authorizedinspectionunitinexplosion-proofperformancesoftheirmeasuringinstrumentsinadditiontothatforthecommontype.3.0.6Anyenterprisethatusesthecombustiblegasesandtoxicgasalarminstrumentsshouldbeequippedwiththenecessarystandardizationdeviceandstandardgas.3.0.7Thedetectorshouldbesetonthewindwardsideoftheleastfrequentwinddirectionatthereleasingsourceofthecombustiblegasortoxicgas.3.0.8Theradiusoftheeffectivelydetectablehorizontalplaneofacombustiblegasdetectorshouldbe7.5mforindooruse,or15mforoutdooruse.Usually,onedetectormaybesetfortheeffectivecoverage.Thedistanceofatoxicgasdetectorfromtheleasingsourceispreferablynotmorethan2mforoutdooruse,or1mforindooruse.3.0.9AccordingtothestipulationinfortheSpecifications,thecombustiblegasalarmortoxicgasalarmoffixedtypeshouldbeadoptedfortheplacewherethealarmshouldbeset.Incaseitisimpracticabletosetthealarmoffixedtypeforinsufficientcondition,theportabledetectionandalarminstrumentshouldbeequipped.4.LocationoftheDetectionPoints4.1Processinginstallations4.1.1Detectorsshouldbesetatthefollowingreleasingsourcesofcombustiblegasesortoxicgases:ThecompressorsforgasesofClassAortoxicgases,thepumpsforliquefiedhydrocarbons,andthedynamicsealsofpumpsforliquidsClassAbliquids,orofthemulticellpumpsforliquidsClassBa,andofthepumpsfortheliquidswhichmayvolatilizeouttoxicgases.ThesamplingportfromwhichthegasesofClassA,liquefiedhydrocarbons,orliquidsofClassAb,ortheliquidswhichmayvolatilizeouttoxicgasesmayleakinthecaseofabnormalrunning,andtheliquiddischargeoutletswhichmaydischargeliquidscontainingliquefiedhydrocarbons,liquidsofClassAbortheliquidswhichmayvolatilizeouttoxicgasesinthecaseofabnormalrunning.TheflangeandvalvegrouponequipmentorpipelinesfromwhichgasesofClassA,toxicgases,orliquefiedhydrocarbonsmayleakinthecaseofabnormalrunning.4.1.2ForthosereleasingsourcesstipulatedinClause4.1.1andlocatedinacompletelyorpartiallyopenareaofequipment,ifthedetectionpointsetonthewindwardsideoftheleastfrequentwinddirection.Thedistanceofthedetectionpointfromthereleasingsourceshouldnotbemorethan15mforthecombustiblegasdetection,or2mforthetoxicgasdetection;ifthedetectionpointsetontheleewardsideoftheleastfrequentwinddirection,thedistanceshouldnotbemorethan5mforthecombustiblegasdetection,or1mforthetoxicgasdetection.4.1.3ForthosereleasingsourcesstipulatedinClause4.1.1andlocatedinacompletelyorpartiallyenclosedfactorybuilding,adetectorper15mshouldbeset,andthedistanceofthecombustiblegasdetectorfromanyreleasingsourceisnotbemorethan7.5mpreferably.Thedistancethetoxicgasdetectorfromanyreleasingsourceisnotmorethan1mpreferably.4.1.4Whenequipmentsofdifferentclassesoffirehazardarelocatedinacompletelyorpartiallyenclosedfactorybuilding,thedetectorshouldbesetwithinthescopeof7.5mfromthereleasingsourcestipulatedinClause.1.5FortheleasingsourceofacombustiblegasthatislighterthanairstipulatedinClause4.1.1locatedinacompletelyorpartiallyenclosedfactorybuilding,aormoredetector(s)shouldbesetatthehighestpointeasytoaccumulatethecombustiblegasinadditiontoadetectortobesetabovetheleasingsource.4.2Storage-transportationFacilities4.2.1ForthestoragetankusedforliquefiedhydrocarbonsorliquidsofClassAb,thedetectorsshouldbesetinthefollowingpositions:(1)Adetectorper30mshouldbesetinsidethefirewalloftheliquefiedhydrocarbontankgroup,andthedistancebetweenthedetectorandtheflangeorvalveofthedrainoutletorbottomconnectionpipeofthetankshouldnotbelongerthan15m.(2)InsidethefirewalloftheliquidsofClassAb,aormoredetector(s)shouldbeset,andthedistancebetweenthedetectorandtheflangeorvalveofthetankdrainoutlet,samplingport,orbottom(side)connectionpipeshouldnotbelongerthan15m.4.2.2ForthehandlingfacilitiesusedforliquefiedhydrocarbonsortheliquidsofClassAb,aormoredetector(s)shouldbesetatthefollowingpositions:(1)Fortherailroadplatformequippedwithsmallfillingrisers,adetectorissetforeverytankwagonlengthpreferably,andthehorizontaldistancebetweenthedetectorandtheinletofthewagonshouldnotbelongerthan15m;(2)Fortherailroadplatformequippedwithbigfillingrisers,adetectorissetpreferably;(3)Thehorizontaldistancebetweenthepositionfillingtankcarandthefillingriserinanautomobilehandlingstationshouldnotbelongerthan15m.ThedetectorshouldbelocatedinaccordancewiththestipulationinforClause4.1.2oftheSpecificationswhenthereisasurgetankintheautomobilehandlingstation.4.2.3DetectorsforthepumpsandcompressorsofthehandlingfacilitiesshouldbesetinaccordancewiththestipulationsinforClauses4.1.1through4.1.3oftheSpecifications.4.2.4Detectorsinthefillingstationofliquefiedhydrocarbonsshouldbesetinaccordancewiththefollowingrequirements:(1)Forcompletelyorpartiallyclosedcylinder-fillingworkshop,thedistancebetweenthefillingportandthedetectorshouldbewithintherangeof5-7.5m;(2)ThecompletelyorpartiallyclosedcylinderwarehouseshouldaccordwiththestipulationsinforClause4.1.3oftheSpecifications.Aroundthewarehousepartiallyintheopenair,adetectorshouldbesetper15-30ml;onedetectorshouldbesetwhenthecircumferenceislongerthan15m;(3)Thedistancebetweenthedetectorandthedrainoutletorvalvegroupofthesurgetankshouldbewithintherangeof5-7.5m.4.2.5Forthecompletelyorpartiallyenclosedworkshoptofillhydrogencylinders,thedetectorsshouldbesetinthehighestpointabovethefillingport,wherethegaseasilystaysindoor.4.2.6Forthedockstohandleliquefiedhydrocarbons,liquidsofClassesAbandBa,adetectorshouldbesetinthehorizontalareaof15mradiusfromthetransferringarm.Whenthedetectorcannotbesetso,thedetectionofthecombustiblegasesshouldaccordwiththestipulationsinforClause3.0.9oftheSpecifications.ToxicgasdetectorsusedfortoxicgasstorageandtransportationfacilitiesshouldbesetinaccordancewiththestipulationsinforClauses4.1.2and.3LocationswhereCombustibleGasesandToxicGasesDiffuseandAccumulate4.3.1Thedetectorordetectorsshouldbesetinapoint5mfromthefiredheateroroutsidethefirewallbetweentheheaterandtheequipmentforthegasesofClassAandliquefiedhydrocarbonsoraprobablereleasingsourcesinthecaseofabnormalrunning.4.3.2Adetectorshouldbesetinthecontrolroom,andpowerdistributionroom,aswellasplaceswithin30mfromtheprocessingequipmentsetorstorage-transportationforthegasesClassA,toxicgases,liquefiedhydrocarbons,andtheliquidsofClassAbmeetingthefollowingconditions:(1)Thedoororwindowoftheroomfacestheprocessingequipmentsetorstorage–transportationfacilities;(2)Thecontrolroomorpowerdistributionroomwheretheovergroundpowercabletroughsortubesandpipelinesfortheinstrumententer.4.3.3Adetectorshouldbesetinthenon-explosion-proofonlineinstrumentcubiclelocatedwithinRegion-2.Fordetectionofthecombustiblegaslighterthanair,thedetectorshouldbesetthehighestpointwherethecombustiblegaseseasilyaccumulateintheinstrumentcubicle.4.3.4Detectorsshouldbesetonthosespotsoutoftheeffectivelydetectablecoverageofthedetector:(1)Thelowestgroundofpitand/orsewageditch,wherethecombustiblegasesand/ortoxicgasmayaccumulate,intheareaoftheprocessingunitorstorage-transportationfacilitieswhichuseorgenerateliquefiedhydrocarbons,and/ortoxicgases.(2)ThecornerpocketswherethegasesofClassA,toxicgaseseasilyaccumulate.5.DETECTION-ALARMSYSTEMSOFCOMBUSTIBLEGASESANDTOXICGASES5.1SystemCompositionandPerformance5.1.1Suchasystemshouldbeacombustiblegasalertinstrumentconsistingeitherofadetectorandanalarmofcombustiblegasortoxicgas,orofadetectorandaindicator-alarmofcombustiblegasortoxicgasasitsessentialpart.Besides,italsomaybeadetectionandalarmsystemconsistingofaspecialdata-acquisitionsystemandadetector.5.1.2Thesystemcompositionshouldmeetthefollowingrequirements:ForthedetectorthatadoptsmVsignal,frequencysignal,or4~20mAsignalasitsoutput,itisrecommendedtouseanindicator-alarmasitsspecialalarmcontroller;aalarmconsistingofasignalsetterandaflashalarmunitalsomaybeused;thesignaltotheinterlockingprotectionsystemandthealarmrecorderpreferablycomesfromthealarmcontrollerorthesignalsetter.Forthedetectoradoptingcontactoutputmode,itisrecommendedtoconnectthealarmsignaltotheflashalarmsystemortheinterlockingprotectionsystem,andoutputofthesignaltothealarmrecordermayberealizedbytheflashalarmsystemortheinterlockingprotectionsystem.Itisrecommendedtoadoptaspecialdata-acquisitionunitordeviceasthedata-acquisitionsystemofacombustiblegasand/oratoxicgas,anditisunsuitabletoconnectadetectorusedforacombustiblegasand/oratoxictosomeothersignal–acquisitionunitordevice,consequently,mutualsubstitutionbetweenboththeacquisitionunitsordevicesmustbeavoided.Whenthesignalsetterandthealarmcontrollerareadopted,thealarmrecordershouldbesetinaccordancewiththestipulationinforClause3.0.3oftheSpecifications,andthealarmrecordershouldhavebothalarmprintingandhistorydatastoringfunctions.ThealarmrecordermaybeaDCSorsomeotherdata-acquisitionsystem,oraselectedspecialindustrialmicrocomputerorsystem.Technicalperformancesofdetectors,indicator-alarms,oralarmsshouldaccordwiththerelevantstipulationsinthecurrentnationalstandard“GasdetectionandAlarmforWorkplaceAtmosphereGeneralTechnicalRequirements”,GB12358.5.2TheSelectionofDetectors5.2.1Theselectionofcombustiblegasdetectorsshouldaccordwiththefollowingstipulations:Thedetectorofcatalyticcombustiontypeispreferablyadopted,andthedetectorofsomeothertypealsoissuitable;Forthelocationwheresmallamountofthemedium,suchassulfur-,phosphor-,arsenic-,orhalogen-containingcompounds,whichmaypoisonthecatalyticburntdetectingelement,adetectorofantitoxiccatalyticcombustiontypeorsemiconductivetypeshouldbeadopted.Thedetectorofelectrochemicaltypeorconductivetypeshouldbeadoptedfordetectinghydrogen.Thesuitabletypeofatoxicgasdetectormaybeselecteddependingontheconcretecharacteristicofthetoxicgastobedetected:Adetectorofconstant-potentialelectrolytictype,orsemiconductivetypemaybeadoptedfordetectinghydrogensulfide,orcarbonmonoxide;Adetectorofdiaphragmelectrodetype,catalyticcombustiontype,orsemiconductivetypemaybeadoptedfordetectingchlorine;Adetectorofgelelectrolytic(electriccell)type,diaphragmelectrodetype,orconstant-potentialelectrolytictypemaybeadoptedfordetectinghydrogencyanide;Adetectorofsemiconductivetype,orconstant-potentialelectrolytictypemaybeadoptedforethyleneepoxide,oracrylonitrile;Adetectorofsemiconductivetype,orphotonelectrolytictypemaybeadoptedfordetectinggasofchloroethylene.Mutualaffectionbetweenthetoxicgastobedetectedandotherpossiblegas(es)intheenvironmentwhereatoxicgasdetectorissetshouldbetakenintoaccountwhenselectingasuitabletoxicgasdetector.Selectionofasuitableexplosion-prooftypedetectorshouldaccordwiththefollowingstipulations:Asuitableexplosion-prooftypeofadetectorshouldbeselecteddependingonClassofexplosivedangerouszonethedetectedplacefalls;Theexplosion-proofclassandgroupofadetectorshouldbeselecteddependingonthecategory,class,andgroupofthecombustiblegastobedetected;Adetectorofcatalyticcombustiontypepreferablyisadetectorofframe-prooftype;Foradetectorofelectrochemicaltypeorsemiconductivetype,itpreferablyisadetectorofframe-prooftypeorintrinsicallysafeexplosive-prooftype;Aframe-proofstructureshouldbeadoptedforanelectricsuctionsampler.Samplingmodeofadetectorshouldbeselecteddependingondifferentsiteswherethedetectorissetasperthefollowingstipulations:Itisgenerallyrecommendedtoadoptadetectorofdiffusiontype.Adetectorofsingle-spotormulti-spotsuctiontypeispreferablyadoptedinthefollowingcases:Asitewhereevensmallamountofleakagemaycauseseriousconsequence;Asitewhereadetectorofdiffusiontypeisdifficulttobeusedbecauseofitsmountingand/ortheenvironmentalrestriction;Theleasingsourceofa(extremelyhazardous)gasofGradeI;Asitewhereareleasingsourcesoftoxicgasesconcentrated.Whenatoxicgasdetectorofsuctiontypeisusedfordetectingacombustibletoxicgas,itispreferabletoselectasamplingsystemofpneumaticsuctiontype.5.3SelectionofAlarmsorIndicator-alarms5.3.1Thealarmorindicator-alarmshouldhavethefollowingfunctions,respectively:Canpoweracombustiblegasortoxicgasdetectorandsomeotherpartconnectingtoit.Candirectlyorindirectlyreceivethealarmsignalcomingfromthecombustiblegasand/ortoxicgasdetectorandotheralarmtriggers,giveoutanauraland/oropticalsignal,andkeepit.Theaudiosignalshouldbeabletobemanuallyeliminated,andcangiveoutalarmasanotheralarmsignalisinputted.Thedetectionconcentrationrangesfordifferentcombustiblegasesarewithin0-100%oftheirrespectiveLEL’s;thedetectionconcentrationrangesfordifferenttoxicgasespreferablyare0~3oftheirrespectiveILV’s.Withintheabove-saiddetectionrange,theindicator-alarmshouldbeabletogivedefiniteindication;whenanalarmthathasnomeasuredvalueindicationfunction,thestipulationinClause3.0.3oftheSpecificationsshouldbefollowed,ananalogsignalshouldbeputintoamultipointsignaldatalogger,DCS,orsomeotherinstrumenttoindicate.signaldatalogger,DCS,orsomeotherinstrumenttoindicate.Theindicator-alarm(alarmcontroller)shouldhavethefunctiontooutputaswitchingvalueforafire-fightingfacilityorinterlockingprotection.Themultipointindicator-alarmoralarmshouldhavethealarmfunctionswithrelativeindependence,andwithoutmutualinfluence,andshouldbeabletodistinguishandidentifytheitemnumberofthealarmedplace.Afteranalarmisgivenout,evenifthegasconcentrationhaschangedinthecircumstance,thealarmstillcontinuesanddoesnotstopuntilthechangeisconfirmedandthecorrespondingmeasureistaken.Inthefollowingconditions,theindicator-alarmshouldbeabletogiveoutanauraland/oropticaltroublesignalobviouslydistinguishingfromthealarmsignalforcombustiblegasesortoxicgases:Disconnectionbetweentheindicator-alarmandthedetector;Anelementinthedetectordoesnotwork;Undervoltagewiththepowersupplyoftheindicator-alarm.Analarmrecordershouldhavethefollowingfunctions:Recordingalarmtimeforcombustiblegasesandtoxicgases,andthedailytimingerrorofthetimershouldnotexceed30s;Showingthecurrenttotalnumberofalarmedplaces;Distinguishingtheearliestalarmedplace;Retrospectivelyshowingthealarmedplaceswithinatleastoneweekanddistinguishingtheearliestalarmedplace.5.3.2Thesettingvalueofthealarmshouldbedeterminedinconformitywiththefollowingstipulations:(1)TheselectionofClass-IorClass-IIalarmisbasedonthestipulationsinforClause3.0.2oftheSpecifications;(2)ForClass-Ialarm(Highlimit)forcombustiblegases,thevalueissetat25%LELorlower;(3)Class-Ialarm(Highhigh-limit)forcombustiblegases,thevalueissetat50%LELorlower;(4)Thealarmsettingvaluefortoxicgasespreferablyislessthanorequalto1TLV,orbelow2TLVifitisdifficulttoconfecttheteststandardgas.5.3.3Theindicatingerrorandthealarmerrorshouldaccordwiththefollowingstipulations:Theindicatingerrorforcombustiblegases:±5%LELastheindicatingrangeiswithintherange0~100%LEL.Theindicatingerrorfortoxicgases:±10%oftheindicatedvalueastheindicatingrangeiswithintherange0~3TLV;or±10%ofthemeasurablerangevalueastheindicatingrangeisover3TLV.Thealarmerrorforcombustiblegases:within±25%ofthesettingvalue.Thealarmerrorfortoxicgases:within±25%ofthesettingvalue.Neitherindicatingnoralarmaccuracyisallowedtodropasvoltagechangeofthepowersupplyislessthanorequalto10%.Theresponsetimetodetect-alarmshouldaccordwiththefollowingstipulations:Theresponsetimedetect-alarmforcombustiblegases: lessthan30sforthediffusiontype; lessthan20sforthesuctiontype.Theresponsetimedetect-alarmfortoxicgases: lessthan60sforthediffusiontype; lessthan30sforthesuctiontype.6.Installationofdetectionandalarminstruments6.1InstallationofDetectors6.1.1Forthosecombustiblegasesortoxicgassesheavierthanair,thedetectorshouldbeset0.3-0.6mhigherthanthegroundorfloorlevel.Note:Thosegaseswithadensitygreaterthan0.97kg/m3(underthestandardcondition)areconsideredasgasesheavierthanair,thosegaseswithadensitylessthan0.97kg/m3(underthestandardcondition)areconsideredasgaseslighterthanair.Forthosecombustiblegasesortoxicgasseslighterthanair,thedetectorshouldbeset0.5-2mhigherthanthereleasingsource.6.1.3Thedetectorpreferablyissetinaplacewithouttheinterferenceofimpactingorvibrationorhighintensitymagneticfield,andthereshouldbeleftanetclearancenotlessthan0.3maroundthedetector.6.1.4Theinstallationandwiringofthedetectorshouldbeconductedinconformitywiththerequirementsstipulatedbythemanufacturer,andtherelevantstipulationsforinstallationandwiringofexplosion-proofinstruments.6.2InstallationofAlarmorIndicator-alarm6.2.1Forthoseprocessingunitsandstorage-transportationfacilitieswithcentralcontrolrooms,thealarmsorindicator-alarmsshouldbesetintheircentralcontrolroo