HAZOP STUDY
INTRODUCTION:
Thetechniqueofhazardandoperatibilitystudies,orinmore
commontermsHAZOP,hasbeenusedanddevelopapproximatelydecadesforidentifyingpotentialhazardandoperatibilityproblems
causedbydeviationfromthedesignintentofbothandnewandexistingprocessplants.Beforeprocessingfurther,itmightbeaswellto
clarifysomeaspectsofthesestatements.
POTENTIALHAZARDSANDOPERATIBILITYPROBLEMS
YouwillnotetheboldANDintheabovehanding,itsbecausehighprofileofproductionplantaccident,emphasisistoooften
placedupontheidentificationofhazardstotheneglectofpotentialproblems.YetitisthelatterareathatbenefitsofHAZOPstudyare
usuallythegreatest.
INDUSTRIESINWHICHTHETECHNIQUEISAPPLIED
HAZOPwereinitiallyinventedbyICIintheunitedkingdombutthetechniqueonlystartedtobemorewidelyusedwithinthe
chemicalindustriesaftertheFixboroughdisasterinwhichachemicalplantexplosionkill28people,manyifwhichwereordinaryhouse
holderslivingnearby.Throughthegeneralexchangeofideasandpersonnel,thesystemwasadoptedbythepetroleumindustries,which
hasasimilarpotentialformajordisasters.Thiswasthenfollowedbythefoodandwaterindustry,wherethehazardpotentialisasgreat,
butofadifferentnature,theconcernbeingmoretodowithcontaminationratherthanexplosionsorchemicalrelease.
BASICCONCEPT:
EssentiallytheHAZOPprocedureinvolvetakingafulldescriptionofprocessandsystematicallyquestioningeverypartofit
toestablishhowdeviationfromthedesignintentcanarise.Onceidentified,anassessmentismadeastowhethersuchdeviationsand
theirconsequencescanhaveanegativeeffectuponthesafeendandefficientoperationofplant.Ifconsidernecessaryactionisthen
takentoremedythesituation.
ThecriticalanalysisisappliedinastructuredwaybyaHAZOPteamanditreliesuponthemreleasingtheirimaginationinaneffortto
discovercrediblecausesofdeviations.
Inpractice,manycauseswillbefairly,obvioussuchaspumpfailurecausinglossofcirculationinacoolingwaterfacilitymentioned
above.However,unlikelytheymayseematfirstconsideration.Inthiswayhestudymuchmorethanamechanisticchecklisttypeof
review.Theresultisthattheregoodchancethatpotentialfailuresandproblemswillbeidentified,whichhadnotpreviouslybeen
experiencedinthetypeofplantbeingstudied.
KEYWORDS:
AnessentialfeatureinthisquestioningandsystematicanalysisintheuseofKeywordstofocustheattentionofthe
teamupondeviationsandtheirpossiblecauses.Thekeywordsaredividedintotwosubsets.
Primarykeywords:whichfocusuponaparticularaspectofthedesignintentoranassociatedprocessconditionorparameter.
Secondarykeywords:whichwhencombinedwithaprimarykeyword,suggestpossibledeviations.
PRIMARYKEYWORDS:
Thesereflectboththeprocessdesignintentandoperationalaspectsoftheplantbeingstudied.Typicalprocessorientedwords
mightbeasfollows.Thelistbelowispurelyillustrative,asthewordsemployedinareviewwilldependupontheplantbeingstudied.
Flow
Temperature
Separate(settle,filter,centrifuge)
React
Pressure
Level
Composition
Corrode
RememberingthatthetechniqueiscalledHazardandoperatibilitystudies,addedtotheabovemightberelevantoperationalwordssuch
as:
Isolate
Vent
Inspect
Startup
Drain
Purge
Maintain
Shutdown
SECONDARYKEYWORDS:
Asmentionedabove,whenappliedinaconjunctionwithaprimarykeyword,thesesuggestthepotentialdeviationsorproblems.They
tendtobeastandardsetaslistedbelow.
Word
No
Less
More
Reverse
Other
Meaning
Thedesignintentdoesnotoccur(e.g.flow),ortheoperationalaspectisnotachieved(isolate/No)
Aquantitativedecreaseinthedesignintentoccur(e.g.Pressure/Less)
Aquantitativeincreaseinthedesignintentoccur(e.g.Temperature/More)
Theoppositeofthedesignintentoccurs(e.g.Flow/Reverse)
Theactivityoccurs,butnotinthewayintended(e.g.Flow/other)couldindicatealeakorproduct
flowing where it should not, or composition/other might suggest unexpected proportions in a
Aswellas
Partof
feedstock
Aquantitativeincrease
Aquantitativedecrease
HAZOPSTUDYMETHODOLOGY:
InsimpletermstheHAZOPstudyprocessinvolvesapplyinginasystematicwayallrelevantkeywordscombinationtothe
plantinquestioninanefforttouncoverpotentialproblems.Theresultsarerecordedinacolumnarformatundertheheadings,
Deviation
Cause
Consequences
Safeguard
Action
Inconsideringtheinformationtoberecordedineachofthesecolumnsisgivenbelow.
DEVIATION
Thekeywordscombinationbeingapplied(e.g.Flow/No)
CAUSE
Potentialcausewhichwouldresultinthedeviationoccurring(e.g.strainerblockageduetoimpuritiesinDosingtankmightbeacause
ofFlow/No).
CONSEQUENCES
Theconsequenceswhichwouldarise,bothfromtheeffectofthedeviation(e.g.Lossofdosingresultsincompleteseparation)and,if
appropriatefromthecauseitself(e.g.cavitationsinpumps,withpossibledamageifprolonged).
SAFEGUARDS
Anyexistingprotectivedevices,whicheitherpreventthecauseorsafeguardsagainsttheadverseconsequences,wouldberecordedin
thiscolumn.ForexampleyoumayconsiderrecordingLocalpressuregaugeindischargefrompumpmightindicateproblemwas
arising.Notethatsafeguardneednotberestrictedtohardwarewhereappropriate;creditcanbetakenforproceduralaspectssuchas
regularplantsinspections(ifyouaresurethattheywillactuallybecarriedout!).
ACTION
Whereacrediblecauseresultsinanegativeconsequence,itmustbedecidedwhethersomeactionshouldbetaken.Itisatthisstagethat
consequencesandassociatedsafeguardsareconsidered.Ifitisdeemedthattheprotectivemeasuresareadequate,thennoactionneedto
taken,andwordstothateffectsarerecordedintheactioncolumn.
Actionsfallintotwogroups:
Actionthatremovethecause
Actionsthatmitigateoreliminatetheconsequences
Whereasformeristobepreferred,itisnotalwayspossibleespeciallywhendealingwithequipmentsmalfunction.However,always
investigateremovingthecausefirstandonlywherenecessarymitigatetheconsequences.
Finallyalwaystakeintoaccountthelabeloftrainingandexperienceespeciallyofpersonnelwhowilloperatetheplant.Actions,which
callforelaborateandsophisticatedprotectivesystems,arewasted,aswellasbeinginherentlydangerous,ifoperatorsdonotandnever
will,understandhowtheyfunction.Itisnotunknownforsuchdevicestobedisabled,eitherdeliberatelyorinerror,becausenoone
knowshowtomaintainandcalibratethem.
Havinggonethroughtheoperationsinvolveinrecordingasingledeviation,thesecannowbeputintothecontextoftheactualstudy
meetingprocedure.Fromtheflowdiagrambelowitcanbeseenthatitisverymuchaniterativeprocess,applyinginastructuredand
systematicwaytherelevantkeywordcombinationsinordertoidentifypotentialproblems.
HAZOPSTUDYOFASHELLANDTUBEEXCHANGER
Inthisstudy,pressure,temperatureandlevelwillbeusedasvariables(secondarywords)differentguidewords(primarywords)willbe
appliedtothesewords.
Pressure
Deviation1:
Shellsideveryhighpressure
Cause:
ExchangeroutletdischargeSDVcloses.
Consequence:
Exchangershellsidewillbeoverpressurized.
ActionRecommended:
HighpressuresecuritymustbeinstalledonshelloutletwhichifactuatedwillcloseallSDVs.
Deviation2
Lowpressureonshellside.
Cause:
Feedpumptrips
Consequence:
Nosignificanceeffectassystemremainswithinthedesignlimits
ActionRecommended:
Notavailable
Deviation3
Tubesidehighpressure.
Cause:
Tuberuptures.
Consequences:
Tubemayoverpressurize,butsinceshellandtubesidearedesignedatsamepressurehencenosignificanteffectisthere.
ActionRecommended:
HighpressuresecuritymustbeinstalledontubeoutletwhichifactuatedwillcloseallSDVs.
Temperature
Deviation4
Tubesidehightemperature.
Cause:
SDVontubesideoutletissuddenlyclosed
Actionrecommended:
HightemperaturesecuritymustbetherethatwillclosetubesideSDVs
Flow
Deviation5
Noflowonshellside
Cause:
ShellsideoutletSDVclosessuddenly
Consequences:
Flowthroughcompressorwillreduceandtubesidetemperaturewillshootup.
ActionRecommended:
Lowflowsecuritytobeinstalledonpumpdischargewhichifactuatedwilltripfeedpumpandcantripthewholeplant.
