Introduction to Inherently Safer Design

Center for Chemical Process Safety

A n I n t r o d u ct ct i o n t o I n h e r e n t l y S a f er e r D es esi g n

Revision # 1, October 19, 2009

© 2008, AIChE, published by Center for Chemical Process Safety

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REVISION LOG Revision No: 1

Reason for Change(s): Original Issue

Date: 10/19/09

Copyright © 2009 by the American American Institute of Chemical Engineers. Engineers. All rights reserved.

Center for Chemical Process Safety of the American Institute of Chemical Engineers 3 Park Avenue New York, New York 10016-5991 ISBN: 978-0-8169-1063-2 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior permission permission of the copyright owner. AIChE and CCPS are trademarks owned by the American Institute of Chemical Chemical Engineers. These trademarks may not be used without the prior express written consent of the American Institute of Chemical Engineers. The use of this product in whole whole or in part for commercial use is prohibited without prior express written consent of the American Institute of Chemical Engineers. To obtain appropriate license license and permission for for such use contact contact CCPS, 646495-1371, [email protected] [email protected]..

It is sincerely hoped that the information presented in this document will lead to an even more impressive safety record for the entire industry; however, neither the American Institute of Chemical Engineers, its consultants, CCPS Technical Steering Committee and Subcommittee members, their employers, their employers’ officers and directors, warrant or represent, expressly or by implication, the correctness or accuracy of the content of the information presented presented in this document. document. As between (1) American American Institute of Chemical Chemical Engineers, its consultants, CCPS Technical Steering Committee and Subcommittee members, their employers, and their employers’ officers and directors, and (2) the user of this document, the user accepts any legal liability or responsibility whatsoever for the consequence of its use or misuse.


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Inherentlysaferdesign(ISD)isaphilosophyforaddressingsafetyissuesinthedesign andoperationofchemicalprocessesandmanufacturingplants.WhenconsideringISD, thedesignertriestomanageprocessriskbyeliminatingorsignificantlyreducing hazards.Often,thetraditionalapproachtomanagingchemicalprocesssafetyhas acceptedtheexistenceandmagnitudeofhazardsinaprocess,andincorporated hardware,procedures,andmanagementsystemstoreduceprocessrisk.Where feasible,ISDprovidesmorerobustandreliableriskmanagement,andhasthepotential tomakethechemicalprocessingtechnologysimplerandmoreeconomicalby eliminatingtheneedforexpensivesafetysystemsandprocedures.However,whenone considersallofthemultiplerisksassociatedwithanytechnology,includingchemical processing,itisunlikelythatanyprocessorplantdesigncaneliminate all hazardsand hazardsand risk.Acombinationofinherent,hardware,procedural,andmanagementsystemswill alwaysberequiredtoadequatelymanageallprocessrisks. ISDaddressestheimmediateimpactofsingleevents(chemicalaccidents)onpeople, theenvironment,property,andbusiness.Inachemicalprocessingplant,thisgenerally meanstheimmediateimpactsoffires,explosions,andthereleaseoftoxicmaterials.In manycases,aninherentlysaferdesignwillalsobebeneficialforothertypesofprocess risk–forexample,environmentalrisk,chronichealthrisk,orrisktoconsumersorusers ofaproduct.Butthisisnotnecessarilytrue–forexample,anon-flammablesolventmay beinherentlysaferfromafireandexplosionriskviewpoint,butitmaybeaserious environmentalcontaminationhazard,oritmaybeachronichealthhazard.While engineersrecognizethepotentialbenefitsofISDinmanagingothertypesofprocess risk,themainintentofISDistoreducethefrequencyandpotentialimpactofchemical plantaccidents–fires,explosions,andacutetoxicexposures.Therefore,theapplication ofISDisoneconsiderationintheselectionofprocessandproducttechnology,butthe decisionaboutwhattechnologyoptionisbestoverallmustconsiderallrisks.

TheconceptofISDisnotreallynew,anditisnotreallyuniquetotheprocessindustries. Technologistshavealwaysrecognizedthevalueofeliminatingorreducinghazards. ApplyingISDwithoutca ApplyingISDwithoutcallingitbyth llingitbythatname,t atname,theysimply heysimplyconsidere consideredittobe dittobegood good design.Forexample,whenafamilyofstoneagecavedwellersdecidedtomovetoa cavehigherabovetheriverfollowingaflood,theywerepracticingISDbyeliminatingthe riskofhavingtheirhomeflooded.Theycouldhavestayedintheiroldcaveand managedtheriskinotherways–forexample,bybuildingadikearoundthecavemouth (hardware),orbyassigningafamilymembertomonitortheriverlevelandwarn everybodytomovethemselvesandtheirpossessionstohighergroundwhenaflood wasimminent(procedural). Thespecificterminology“InherentlySaferDesign”cameintouseintheprocess industriesinthe1970s.Followinga1974hydrocarbonvaporcloudexplosionat


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Flixborough,England(Figure1),TrevorKletz,aseniorsafetyadvisorforICI,questioned theneedforsuchlargequantitiesofflammableortoxicmaterialsinamanufacturing plant,andtheneedforprocessingatelevatedtemperature andpressure.Kletzsuggestedthatindustryshouldre-directitsriskmanagementefforts towardeliminationofhazardswherefeasible.Insteadofdevotingextensiveresourcesto safetysystemsandprocedurestomanagetherisksassociated,industrycouldtryto identifyprocessmodificationswhichreduceoreliminatehazards–reducingthequantity ofhazardousmaterial,usingless hazardousmaterials,developing technologywhichoperatesatless severeconditions.Kletzandothers inthechemicalindustryestablished asetofprinciplesforISD,and providedmanyexamplesofits implementation.In1996,theCenter forChemicalProcessSafety (CCPS)publishedalandmarkbook, InherentlySaferChemical , Processes:ALifeCycleApproach , compilinguptodateinformationon industrythinkingonISD.In2009, CCPSpublishedasecondeditionof thisbook,incorporatingthelatest developmentsonISDbasedon morethanadecadeofadditionalindustrialexperience 1 .

Adjective.Existing Adjective.Existingasaness asanessentialcons entialconstituentorc tituentorcharacteris haracteristic;intrinsi tic;intrinsic. c. * FromtheLatin inharens,inhaerent -,presentparticipleof -,presentparticipleof inhaerere,toinhere. Whatdowemeanbyinherentlysaferdesign?Onedictionarydefinitionof“inherent”is “existinginsomethingasapermanentandinseparableelement.”Thismeansthatsafety isbuiltintotheprocess,notaddedon.Hazardsareeliminated,notcontrolled,andthe meansbywhichthehazardsareeliminatedaresofundamentaltothedesignofthe processthattheycannotbechangedordefeatedwithoutchangingtheprocess.Inmany casesthiswillresultinsimplerandcheaperplants.Ifextensivesafetysystemsare requiredtocontrolmajorhazards,theywillintroducecomplexitytoaplant,alongwith cost–bothintheinitialinvestmentforthesafetyequipmentandalsofortheongoing operatingcostformaintenanceandoperationofthesafetysystems.

F ourth Edition * Definition taken from The American Heritage® Dictionary of the English Language, Fourth

Copyright © 2000 by Houghton Mifflin Company.


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BecausethephilosophyofISDistoeliminateorreducethehazardofaprocess,itis importanttounderstandwhatwemeanbytheword“hazard”.TheCenterforChemical ProcessSafety(CCPS)hasdefinedhazardas“aninherentphysicalorchemical characteristicthathasthepotentialforcausingharmtopeople,theenvironment,or property.” 2 Hazardsareintrinsictoamaterialoritsconditionsofuse.Someexamples ofhazardsare: Chlorineistoxicbyinhalation Gasolineisflammable Highpressuresteamcontainsalargeamountofpotentialenergy,bothfromits elevatedtemperatureandalsofromthehighpressure Thesehazardscannotbechanged,exceptbychangingthematerialortheconditionsof use. • • •

Chemicalprocesssafetystrategiescanbegroupedinfourcategories:Inherent, Passive,Active,andProcedural(Figure2).Ingeneral,inherentandpassivestrategies arethemostrobustandreliable,butelementsofallstrategieswillberequiredfora comprehensiveprocesssafetymanagementprogramwhenallhazardsofaprocessand plantareconsidered.

Theinherentapproachtosafetyis,wherefeasible,toeliminateorgreatlyreducethe hazardbychangingtheprocesstousematerialsandconditionswhicharenonhazardousormuchlesshazardous.Thesechangesmustbeintegraltotheprocessor product,andnoteasilydefeatedorchangedwithoutfundamentallychangingthe processorplantdesign.Substitutingwaterforaflammable,andperhapstoxic,solvent asacarrierforapaintorcoating–usingwaterbasedlatexpaintsinsteadofoilbased paints–isanexample.Theeliminationoftheflammableortoxicsolventisaninherent characteristicoftheproductanditsmanufacturingprocess.Thehazardoffireor exposuretotoxicsolventvaporsiseliminated,bothinthemanufacturingprocessand alsothroughoutthemanufacturingsupplychainallthewaytotheproductuser.


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Passivesafetyfeaturesminimizehazardsusingprocessorequipmentdesignfeatures whichreduceeitherthefrequencyorconsequenceofanincidentwithouttheactive functioningofanydevice.Forexample,ifachemicalreactionwhichhasamaximum possiblepressureof5barincaseofarunawayreactionisdoneinareactordesignedto containapressureupto10bar,themaximumreactionpressurewillbecontainedwithin thereactorvessel.Thereactorcontainsthepressurebecauseofitsdesignand construction–thethicknessandstrengthofthemetalfromwhichitisfabricated,the strengthofthegasketsandboltswhichholdittogether,andit’sotherphysical components.Thiscontainmentisveryrobustandreliable–thereactordoesnotneedto sensehighpressureandtakeanyactiontocontainthepressure,andnomovingparts arerequiredtocontainthepressure.Butthehazard(5barpressure)stillexists,sothere issomeriskthatanincidentwilloccur,andthepassivestrategywouldbeconsidered lessrobustthananinherentstrategywhichwouldeliminateorreducethepressure.The reactormaybedamaged,corroded,improperlyconstructed,orcontainafaultygasket, forexample,anditispossiblethatitwouldfailtocontainthepressurefromtherunaway reaction.

Activesafetysyst Activesafetysystemsinclude emsincludeprocess processcontrols controlsystems,sa ystems,safetyinstr fetyinstrumenteds umentedsystems ystems (SIS),andautomaticincidentmitigationsystemssuchassprinklersystemstoextinguish afire.Theseactivesystemsaredesignedtosenseahazardousconditionandtakean appropriateaction.Activesystemsmaybedesignedtopreventanincident,orto minimizetheconsequencesofanincident.Forexample,atankmighthaveahighlevel interlockwhichshutsoffapumpfeedingthetankandclosesallfeedvalves–this systemisdesignedtopreventatankoverflow.Afiresprinklersystemisanactive systemdesignedtominimizetheconsequencesofafire–itdoesnotpreventthefire, andmaynotevenbeactivatedunlessafireisdetected.

Proceduralsafetyfeaturesincludestandardoperatingprocedures,safetyrulesand procedures,operatortraining,emergencyresponseprocedures,andmanagement systems.Forexample,anoperatormaybetrainedtoobservethetemperatureinthe reactorandapplyemergencycoolingifitexceedsaspecifiedcriticalvalue.Ingeneral, forahighhazardsystem,proceduralriskmanagementsystemsdonot,bythemselves, provideadequateriskmanagement.Humanreliabilityisnothighenough,andpeople oftencannotdiagnoseaproblem,determinetheappropriateaction,andtakethataction quicklyenough.However,proceduralsafetysystemswillalwaysbeapartofa comprehensiveriskmanagementprogram–ataminimumtheywillberequiredto ensureongoingmaintenanceandmanagementofactiveandpassivesafetysystems.


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CCPShascategorizedstrategiesfordesigninginherentlysaferprocessesintofour groups: Substitute–uselesshazardousmaterials,chemistry,andprocesses Examples:analternatesynthesischemistryforamoleculeuseslesstoxic o rawmaterials;waterbasedlatexpaintseliminatefire,toxicity,and environmentalhazardsassociatedwithsolventbasedpaints Minimize–usesmallquantitiesofhazardousmaterials,reducethesizeof equipmentoperatingunderhazardousconditionsuchashightemperatureor pressure Examples:nitroglycerinecanbemadeinacontinuouspipereactorwitha o fewkilogramsofinventoryinsteadofalargebatchreactorwithseveral thousandkilogramsofinventory Moderate–reducehazardsbydilution,refrigeration,processalternativeswhich operateatlesshazardousconditions Example:acombustiblesolidwashandledasapelletinsteadofafine o powder,reducingthedustexplosionhazard Simplify–eliminateunnecessarycomplexity,design“userfriendly”plants o Example:Oldpipingwhichwasnolongerneededbecauseofprocess modificationswasremovedfromaplant,makingitimpossibletoaccidently transfermaterialintoareactorthroughthatpipingbyoperatingerroror leakingvalves •

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Processdesignstartswiththe selectionofabasictechnologyfora processoperation.Asthetechnology progressesthroughprocess development,conceptualplant design,scaleup,engineeringand detailedplantdesign,plant construction,startup,andongoing operationandfuturemodification, differentkindsofchoicesand decisionsarerequiredbychemists, engineers,andothertechnologists (Figure3).ThephilosophyofISD appliesatallstages,buttheavailable optionschange.Thebest opportunitiesforimplementationof inherentlysaferdesignareearlyin productorprocessresearchand development.Atthispoint,therehas notbeenanycommitmenttoa particulartechnology,resourceshavenotbeenexpendedonresearchanddevelopment whichwouldhavetobedoneoveragain,potentialcustomershavenotcommittedto usingproductsproducedbyacertaintechnologyanddevelopedtheirprocessestofit thisproduct,andcapitalhasnotbeencommittedtobuildaplanttoimplementa particulartechnology.Astheprocessmovesthroughthelifecycle,itbecomesmore difficulttochangethebasictechnology.However,itisnevertoolatetoconsiderISD– butoptionsforimplementationmaybemorelimitedinanexistingplant.Toillustratehow ISDcanbeappliedatvariouslevelsofprocessdevelopmentanddesign,disinfectionof drinkingwaterwillbeusedasanexampleprocess.

Therearemanywaystodisinfectwater–forexample,chlorination,ozone,ultraviolet light,radiation,andothers.ThesevarioustechnologieshavedifferingISD characteristicsrelativetodifferenthazardsofconcern.Forexample,chlorineistoxic andmayproducehazardouschlorinatedorganicmaterialsinwatercontainingcertain organicprecursors.Ozoneandultravioletlightprovidedisinfectionatthepointof treatment,butdonothaveresidualactivityshouldthewaterbecontaminated downstreamofthetreatmentplant.ToconsiderISDforbasictechnologyselection,the decisionmakermustunderstandallhazardsofconcernandtheinherentsafety characteristicsoftheavailableprocessoptionsrelativetothosehazards.


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Oncethebasictechnologyhasbeenselected,theremaybemanyoptionsavailablefor actualimplementationofthattechnology.Usingthewatertreatmentexample,assume thatchlorinationtechnologyhasbeenselected.Nowtheprocessdesignerhastodecide howchlorinationwillbeimplemented.Someoptionshemightconsiderinclude elementalchlorinegas,sodiumhypochlorite,orsolidchlorinatingagents.Eachoption hasspecificISDcharacteristicsrelativetovarioushazardsofconcern.Thedesigner mustalsoconsiderotherfactorssuchaseconomics,feasibilityofthetechnology,state ofdevelopment(proventechnology,anewprocesswhichhasneverbeenused,or somewhereinbetween),andotherriskconcerns(environmental,chronichealth,etc.).

Atthispointinthep Atthispointintheprocesslif rocesslifecycle,th ecycle,thedesigne edesignermustcon rmustconsiderISD siderISDforaspe foraspecificplant cificplant design.Factorsmightinclude: Locationoftheplantrelativetosurroundingpopulation,in-plantoccupiedareas, sensitiveenvironmentalareas,etc. generallayoutoftheequipmentontheselectedplantsite numberofparallelsystemsandsizeofthosesystems(onebigplant,ortwoor moresmallerplants,forexample) •

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Ifweassumethatthedesignersofthisparticularwatertreatmentsystemhavedecided thatdisinfectionusinggaseouschlorineistheoptimumprocess,ISDshouldbe consideredwhendeterminingwherethefacilityislocatedinthecommunity,wherethe chlorineisstoredandhandledonthesiteoncethesitehasbeenselected,thenumber andsizeofthewaterchlorinationsystems,etc.

ThedesignershouldconsiderISDinthedetaileddesignofeachpieceofequipmentin theplant.Therearemanyoptionsinthedesignequipmentsuchasheatexchangers, chlorinevaporizers,andotherdevicesthatmightbeincludedinthewatertreatment plant.DifferentequipmentdesignswillhavedifferentISDcharacteristics–forexample, theinventoryofhazardousmaterialintheequipment.Also,thedetailedlayoutofthe equipmentwillimpactthingssuchasthelengthanddiameterofpipingcontaining hazardousmaterials.Considerationofhumanfactorsinthedesignofequipment,to minimizethepotentialformis-operationandhumanerror,willalsoresultinaninherently saferplant.


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Onceaplantisbuilt,ISDshouldbeconsideredinthedevelopmentofoperating proceduresandmaintenanceprocedures.Thesemustbeclear,logical,andconsistent withactualhumanbehavior.Also,theplantshouldconsiderISDoptionsthroughoutthe operationallifetime,particularlywhenmodificationsaremade,orifnewtechnology becomesavailable.

ISDisnotamagicbu ISDisnotamagicbulletwhichwillma lletwhichwillmakeallpote keallpotentialriskas ntialriskassociated sociatedwithchemica withchemical l processinggoaway.Forexample,inmanycasesitisnotpossibletoeliminateor reducethehazardbecausethecharacteristicofamaterialortechnologywhichmakesit hazardousisthesameasthecharacteristicwhichmakesituseful. Jetairlinerstypicallytravelatabout600milesperhour.Thisiswhatmakesthem useful–theycantransportyouhalfwayaroundtheworldinlessthanaday.But thatspeedalsomakesthemhazardous–anairplanetravelingat600milesper hourhasalargeamountofkineticenergywhichcancausemajordamageifithits something,aswellaslikelykillingallofthepassengers. Gasolineisflammable,andhasthepotentialforamajorfire.Buttheflammability ofgasolineisalsowhygasolineisuseful–itstoresalargeamountofenergyina smallmassofmaterialmakingitavaluabletransportationfuel. Chlorineistoxic.Thismakesithazardoustomostlife,includingpeopleand animals.Butthisisalsowhatmakesitusefulforkillingpathogenicorganismsin drinkingwatersothatpeoplecandrinkthewatersafely. •

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Fortheseandotherhazardousmaterialsortechnologies,theimportantfactorin attainingthebenefitsofthetechnologyandmanagingthehazardiscontrol.Insome casestheremaybealternativetechnologieswhicharelesshazardousorwhichare easiertocontrol.But,formanytechnologies,therearenoinherentlysafertechnologies, thosetechnologiesarenoteconomicallyfeasible,orotherrisks(environmental,chronic healthrisks)areimportantenoughthatsocietychoosestouseatechnologywhichis lessinherentlysafe.Inthesecases,wemustrelyonpassive,active,andprocedural safetystrategiestomanagetherisk.Thesestrategiescanbehighlyeffective–travelby airplaneisextremelysafedespitethesignificantinherentrisksofflying.Thisisbecause ofthehighlyeffectivesafetymanagementsystemsinplaceintheairtransportsystem. Everytechnologyhasmultiplehazards.Asaneverydayexample,considerautomobile travel.Hazardsincludethespeedofthecar(kineticenergy),flammablefuel,toxicityof exhaustgases,hotsurfacesintheengine,apressurizedcoolingsystemfortheengine, electricity,andothers.Forachemicalprocess,hazardsmightincludeacutetoxicity, flammability,corrosiveness,chronictoxicity,reactivity,adverseenvironmentalimpacts, andothers.Thestatementthataprocessisinherentlysafercanonlybeinthecontextof onehazard,orperhapsseveralspecific,butnotall,hazards.Itishighlyunlikelythatany


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technologywilleverbeinherentlysaferwithrespecttoallpossiblehazards.Anychange toatechnologydesignedtoreduceoneormorehazardswillalsoimpactotherhazards, perhapssuchthatthesehazardswillbeincreasedornewhazardswillbeintroduced. Chlorofluorocarbon(CFC)refrigerantsprovideanexampleofISDconflicts.Whenfirst developedinthe1930s,CFCswereconsideredtobesaferalternativestoexisting refrigerantssuchasammoniaandlighthydrocarbons(theterm“inherentlysafer”was notinuseatthattime).CFCshavelowacutetoxicityandarenotflammable.Towardthe endofthe20 thcentury,theadverseenvironmentalimpactsofCFCswererecognized, andmanyofthemhavebeenphasedout.But,CFCsarestillinherentlysaferthanmany alternativeswithrespecttoflammabilityandacutetoxicityhazards.Societyhasdecided thatthepreviouslyunknownhazardofadverseenvironmentalimpactisunacceptable, andiswillingtoapplypassive,active,andproceduralriskmanagementstrategiesto managethehazardsassociatedwithCFCreplacementsforrefrigerationsystems. Differentpopulationsofpotentiallyimpactedpeoplemayperceivetheinherentsafetyof technologyoptionsdifferently.Forexample,foraprocesswhichrequiresrelativelysmall quantitiesofchlorinegas,aplantmayhaveachoicebetweensupplyin1toncylinders or90tonrailroadtankcars.Aneighborlocatedseveralmilesawayfromtheplantwould considerthe1toncylindersupplytobeinherentlysaferbecauseitisunlikelythataleak wouldimpacthimatthatdistance.Ontheotherhand,theplantoperatorswouldhaveto connectanddisconnectcylinders90timesforeveryonetimetheywouldhavehadto connectanddisconnectarailroadcar.Theywouldconsidertherailroadcartobe inherentlysaferbecausetheywouldbeimpactedbyanyrelease,evenasmallone.The operatorswouldhaveamuchhigherfrequencyofrelativelyhighriskoperations– connectinganddisconnectinghoseswhichcouldpotentiallycontainchlorine.Ofcourse, thesehazardscanbemanagedwithprocedures,personalprotectiveequipment,and othersafetymanagementsystems,butthesearenotinherent.Boththeneighborand theoperatorarecorrectintheirperceptionoftheISDcharacteristicsofthechlorine supplyoptions,buttheyareconcernedaboutdifferentkindsofincidents.Thechallenge forthedesignerofthesystemistounderstandtheseconflictingrequirementsandmake anintelligentchoice,includingconsiderationoftheentireriskmanagementsystem (inherent,passive,active,andprocedural). ItisalsoimportanttoconsiderwhetheranISDoptionactuallyreducesriskortransfersit somewhereelse,perhapsincreasingoverallrisk.Aplantmightreducethesizeofa hazardousmaterialstoragetankatthesite,reducinginventoryandsiterisk.Butuseof thesmallertankmayrequireachangefromshipmentofthematerialtotheplantfrom railroadtankcars(typicallyabout300,000poundshipmentsformanymaterials)to trucks(typicallyabout30,000poundshipments)becausethesmallertankcannot containmorethanatruckloadofmaterial.Nowtherewillbe10timesasmany shipments,andtheywillgobyroadratherthanbyrail.Dependingonthespecific characteristicsofaparticularplantlocation,roadshipmentmaybemorehazardous. Whilethesiteriskisreduced,theoverallrisktosocietymayactuallybeincreased.


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Howdoweincorporateinherentlysaferdesignphilosophiesintothedesignand operationofchemicalprocessingplants?Thebestansweristostartearlyinthelife cycle,andneverstop(Figure4).Thegreatestopportunitiesforfundamentalchangesto processesoccurearlyintheprocesslifecycle,duringinitialprocessconceptionand earlydevelopment.Atthisstage,theresearchermayhaveopportunitiestoselectless hazardousrawmaterialsandintermediatesorlesshazardouschemicalsynthesispaths fromamongthemanyoptionswhichmightbeavailable.However,itisnevertoolateto considerinherentsafety.Therearemanypublishedreportsofsignificantinherentsafety improvementsinplantswhichhavebeenoperatingformanyyears.

Thebestopportunitytoconsiderinherentlysaferdesignatallstagesintheprocesslife cycleistoincorporateinherentsafetyconsiderationsintotheprocesssafetyreviews thatarenormallydoneatthesestagesinthelifecycle.CCPSandothershave publishedchecklistswhichareusefulindoingthis.Inthenew2 ndeditionoftheCCPS bookoninherentlysaferdesign,thesechecklistsaresignificantlyimproved.And, inherentlysaferdesignphilosophycanbeconsideredinthecourseofaprocesshazard analysis,indetermininghowtorespondtoanidentifiedhazard.ThePHAteamis challengedtothinkaboutwaystoeliminateorminimizehazards,ratherthanaccepting thatthehazardexistsandfocusingitseffortsoncontrollingthathazard.Theteam shouldaskthefollowingquestions,inthisorder,onceithasidentifiedahazard: 1. Canthehazardbeeliminated? 2. Ifnot,canthemagnitudeofthehazardbesignificantlyreduced? 3. Dothealternativesidentifiedinquestions1and2increasethemagnitudeofany otherexistinghazards,orcreatenewhazards?Ifso,considerallhazardsin selectingthebestalternative.


12

4. Whattechnicalandmanagementsystemsarerequiredtomanagethehazards whichinevitablywillremain? DesignersandPHAteamsoftenskipdirectlytothe4 thquestion,identifyingsystemsto managehazardswhoseexistenceisacceptedandbelievedtobeunavoidable.This maybetrueinmanycases,butnoPHAteamwillevereliminateorreduceahazardifit doesnotaskifthisispossible.PHAteamsshouldchallengethemselvestoeliminateor reducehazards,andthen,onlyifthisisnotpossible,shifttodesigningsystemsto manageriskfromhazardswhichcannotbeeliminated.

ThedesignerandoperatorofachemicalmanufacturingprocessshouldconsiderISD optionsthroughouttheprocesslifecycle,frominitialconceptionthroughresearchand development,plantdesign,construction,operation,modification,andeventual shutdown.UsuallythebestopportunityforimplementingISDisearlyinresearchand developmentbeforesignificantresourceshavebeenexpendedinprocessorproduct development,andbeforeaplanthasbeenbuilt.Thecompleteprocessandproductlife cyclealsoneedstobeconsideredtoavoidlocaloptimizationandtransferofriskfrom onesectoroftheoveralleconomytoanother.Thismeansconsiderationofraw materials,themanufacturingprocess,transportation,storageatallstagesinthesupply chain,enduse,andthesafetyconsequencesofchangingtechnology–demolitionofold facilitiesandconstructionofnewones. Allhazardsmustbe Allhazardsmustbeconsider consideredsotha edsothatinformed tinformeddecisions decisionscanbema canbemadeabout deabout conflictinggoalsandimpacts.Otherfactorsmustalsobeconsidered–economics, resourceallocation(includingcapital,researchanddevelopmentresources,operating costs),thefeasibility,reliability,andeffectivenessofotherprocessriskmanagement features(passive,active,procedural).Thismayresultindifferentchoicesfordifferent situations,evenforthesametechnology.Inadifferentenvironment,therelative importanceofdifferenthazardsorotherfactorsmaybedifferent,leadingtoadifferent choiceabouttheoptimaltechnology.


13

JustaftermidnightonDecember3,1984,watercontaminationofatankofmethylisocyanate inBhopal,Indiainitiatedaseriesofeventsthatledtoacatastrophictoxicrelease,killingmore than3000residentsandinjuringover100,000. InFebruaryof1985,leadersfrom17oftheleadingchemicalandpetroleumcompaniesasked theAmericanInstituteofChemicalEngineers(AIChE)toleadacollaborativeglobaleffortto eliminatecatastrophicprocess incidentsby: •ADVANCINGstate-of-the-artprocesssafetytechnologyandmanagementpractices •SERVINGasapremierresourceforinformationonprocesssafety •FOSTERINGprocesssafetyinengineeringandscienceeducation •PROMOTINGprocesssafetyasakeyindustryvalue OnMarch25,1985,AIChEformedtheCenterforChemicalProcessSafety(CCPS)with chartermembercompanies.Intheyearsthatfollowed,CCPShasbeentheworldleaderin everyareaofprocesssafetyinformation,withover60guidelineandresourcebooksinprint, andanever-growingwebknowledgebase.CCPSmembershipnowexceeds100companies, headquarteredinmorethan15companiesinfourcontinentsandoperatingineverypartof theworld. ViewtheCCPSbookcatalog www.wiley.com/go/ccps www.wiley.com/go/ccps  LearnaboutCCPSmembership www.aiche.org/CCPS/Corporate/index.aspx  BrowsetheCCPSWebKnowledgeBase www.aiche.org/CCPS/Resources/KnowledgeBase/overview.aspx  AttendCCPSeven AttendCCPSevents tswww.aiche.org/CCPS/Conferences/index.aspx www.aiche.org/CCPS/Conferences/index.aspx  ContactCCPS[email protected] ContactCCPS [email protected]or+1.646.495.1372 or+1.646.495.1372 1

Center for Chemical Process Safety. Inherently Safer Chemical Processes: Hoboken, NJ, John Wiley & Sons, 2009.

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Center for Chemical Process Safety. Guidelines for Hazard Evaluation Procedures . 3rd Edition. Hoboken, NJ, John Wiley & Sons, 2008.


A Life Cycle Approach. 2nd Edtiion.

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CCPS members share a vision of a safer process industry Working together, The Center for Chemical Process Safety (CCPS) and its member companies pool the resources, expertise, and knowledge needed to develop superior process safety management and technology. Members guide research research initiatives and enjoy access to the latest research findings by participating in the development of CCPS guideline, concept, and safety alert publications. Members also contribute to and benefit from CCPS’ extensive and coded databases of safety information. Representatives may serve on over 15 subcommittees and attend four Technical Steering Committees each year, as well as world-class conferences. They join a community of peers with whom they can confidentially discuss safety concerns and benchmark programs.

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CCPS MEMBERS: A POWERFUL ALLIANCE

Introduction to Inherently Safer Design

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