Safety Instrumented Systems (SIS), Safety Integrity Levels (SIL), IEC61508, and Honeywell Field Instruments.pdfVIP专享VIP免费原创优质

SafetyInstrumentedSystems(SIS),SafetyIntegrityLevels(SIL),IEC61508,andHoneywellFieldInstrumentsHoneywellFieldInstrumentsarereadyforthenewsafetystandardsfortheprocessindustriesBackgroundSafetyInstrumentedSystemsIn1996,theInstrumentSocietyofAmericapublishedstandardANSI/ISAS84.01-1996“Applicationofsafetyinstrumentedsystemsfortheprocessindustries.”ThisstandardwasacceptedbytheAmericanNationalStandardsInstitute(ANSI)inMarchof1997,andthusbecameenforceableunderOSHA’sprocesssafetymanagement(PSM)andtheEPA’sriskmanagementprogram(RMP).Endusers(e.g.,petrochemicalplants)areincreasinglyusingsafetyinstrumentedsystems(SIS)tocomplementtheirprocesscontrolsystems.ASISisutilizedwhentheriskofanaccidentneedstobereduced.SISisdefinedbyISAS84.01andIEC61508as:SISloop:“AnSISisadistinct,reliablesystemusedtosafeguardaprocesstopreventacatastrophicreleaseoftoxic,flammable,orexplosivechemicals.”During1998through2000,theInternationalElectrotechnicalCommission(IEC)publishedtheIEC61508andIEC61511standards.SISloopscope:“Systemcomposedofsensors,logicsolvers,andfinalcontrolelementsforthepurposeoftakingaprocesstoasafestate,whenpredeterminedconditionsareviolated.”TheIEC61508standard,“FunctionalSafetyofElectrical/Electronic/ProgrammableElectronicSafety-relatedSystems,”isforsuppliersofmicroprocessor-basedinstrumentationtotheprocess,medical,andavionicsindustries.EveryelementintheloopispartoftheSIS,andneedstobeconsideredwhendoingananalysisoftheSIS.Thiscouldincludepressureandtemperaturetransmitters,acontrolsystemorstand-alonecontroller,controlvalvesorotherfinalcontroldevices,electricalwiring,processpiping,powersupplies,software,etc.TheIEC61511standard,“FunctionalSafety:SafetyInstrumentedSystemsfortheProcessIndustrySector,”isforendusersandengineeringfirmsdetailingtherequirementsfordesignandimplementationofsafetyinstrumentedsystems(SIS)fortheprocessindustries.ThefunctionoftheSISistomonitortheprocessforpotentiallydangerousconditions(processdemands),andtotakeactionwhenneededtoprotecttheprocess.SafetyIntegrityLevelIECandISAareworkingtogethertostandardizeonIEC61511astheglobalSISstandard,whichwouldmakeIEC61508theglobalstandardformanufacturers.TheSafetyIntegrityLevel(SIL)isastatisticalrepresentationoftheintegrityoftheSISwhenaprocessdemandoccurs.ThepurposeoftheSISistoreducerisk,soSILlevelscanbedefinedintermsoftheriskreductionfactor(RRF).TheinverseoftheRRFistheprobabilityoffailureondemand(PFD),soRRF=1/PFD.IEC61508definesSILlevels1through4,withSILlevel1representingthelowestacceptablerisklevel,andSILlevel4representingthehighestacceptablerisklevel.SafetyIntegrityLevelAvailabilityRequiredProbabilitytoFailonDemand1/PFD(RRF)4>99.99%E-005toE-004100,000to10,000399.90-99.99%E-004toE-00310,000to1,000299.00-99.90%E-003toE-0021,000to100190.00-99.00%E-002toE-001100to10Forexample,theendusercandefineaprocessasaSIL1SIS,acceptingtheriskthattheSISwillbeavailable90%ofthetime(fora10%chanceoffailure).Forinstance,alowwaterlevelonastoragetankwillnormally(90%ofthetime)beexpectedtotripasensor,whichinturnwillcontrolavalvetorefillthetank.10%ofthetime,theSISisexpectedtofail,andthetankwillnotberefilled.IEC61508andHoneywellOneofthestepsrequiredtoachievefunctionalsafetycertificationperIEC61508isaFailureModes,Effects,andDiagnosticAnalysis(FMEDA).CompanieslikeTUVandExidaoffertheirservicestoperformtheFMEDA.Theresultisacertificate,whichcontainsthe...