4E969D546867BD9842C4B1D764FB850

AutoignitionTemperature(AIT):Theautoignitiontemperatureofasubstance,

whethersolid,liquid,orgaseous,istheminimumtemperaturerequiredtoinitiateorcauseself-sustainedcombustion,inair,withnoothersourceofignition.

BasicProcessControlSystem(BPCS):Thecontrolequipmentthatisinstalledto

support normal production functions.

BoilingLiquidExpandingVaporExplosion(BLEVE):Theexplosivelyrapid

vaporization,andcorrespondingreleaseofenergyofaliquid,flammableorotherwise,uponitssuddenreleasefromcontainmentundergreater-than-atmosphericpressureatatemperatureaboveitsboilingpoint.ABLEVEisoftenaccompaniedbyafireballifthesuddenlydepressurizedliquidisflam-mableanditsreleaseresultsfromvesselfailurecausedbyexternalfire.Theenergyreleasedduringflashingandvaporizationmaycontributetoashockwave.

Bonding:Theprocessofconnectingtwoormoreconductiveobjectstogetherby

means of a conductor.

CarSeal:Ametalorplasticcableusedtofixavalveintheopenposition(carseal

open)orclosedposition(carsealclosed).Properauthorization,controlledviaadministrativeprocedures,mustbeobtainedbeforeoperatingthevalve.Thephysicalsealshouldhavesuitablemechanicalstrengthtopreventunau-thorized valve operation.

CatastrophicIncident:Anincidentinvolvingamajoruncontrolledemission,

fireorexplosionthatcausessignificantdamage,injuriesand/orfatalitiesonsiteandhaveanoutcomeeffectzonethatextendsintothesurroundingcommunity.

CombustibleLiquid:Atermusedtoclassifycertainliquidsthatwillburnonthe

basisofflashpoints.TheNationalFireProtectionAssociation(NFPA)definesa“combustibleliquid”ashavingaflashpointof100°F(37.8°C)orhigher.Seealso,“FlammableLiquid.”ClassIIliquidshaveflashpointsatorabove100°F,butbelow140°F.ClassIIIliquidsaresubdividedintotwosubclasses.

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GLOSSARY

•ClassIIIA:Thosehavingflashpointsatorabove140°Fbutbelow200°F.•Class IIIB:Those having flash points at or above 200°F.

CommonModeFailure:Aneventhavingasinglecausewithmultiplefailure

effects, which are not consequences of each other.

CovertFault:Faultsthatcanbeclassifiedashidden,concealed,unannounced,

undetected,unrevealed,latent,etc.Inthecaseofsafetyinstrumentedsys-temscovertfaultsimpairtheintendedsafeguardingfunctionwithoutbeingapparenttotheoperator.Covertfaultscanonlybedetectedbytestingorchallenging the system.

DamageLimitingConstruction:Constructionofequipment(building)with

weaksectionstolimitthedamagetotheequipment(building).Theweaksectionsfailearlyandpreventdamagetotherestoftheequipment(building).

Dead-heading:Ablockageonthedischargesideofanoperatingpumpwhich

resultsintheflowreducingtozeroandanincreaseinthedischargepres-sure.Theenergyinputfromthedeadheadedpumpincreasesthetempera-ture and pressure of the fluid in the pump.

Deflagration:Apropagatingchemicalreactionofasubstanceinwhichthereac-tionfrontadvancesintotheunreactedsubstanceatlessthanthesonicvelocityintheunreactedmaterial.Whereablastwaveisproducedthathasthepotentialtocausedamage,thetermexplosivedeflagrationmaybeused.DeflagrationtoDetonationTransition:Areactionfrontthatstartsoutwith

velocitiesbelowthespeedofsoundandsubsequentlyacceleratestoveloci-tieshigherthanthespeedofsoundintheunreactedmaterialissaidtohaveundergoneaDeflagrationtoDetonationTransition.Thepossibilityoftransitionisenhancedbyconfinement/turbulencegeneratorsinthepathofthe reaction front.

Detonation:Apropagatingchemicalreactionofasubstanceinwhichthereac-tionfrontadvancesintotheunreactedsubstanceatequaltoorgreaterthanthe sonic velocity in the unreacted material.

DesignInstituteforEmergencyReliefSystems(DIERS):Instituteundertheaus-picesoftheAmericanInstituteofChemicalEngineersfoundedtostudyreliefrequirementsforreactivechemicalsystemsandtwo-phaseflowsystems.

DistributedControlSystem(DCS):Asystemthatdividesprocesscontrolfunc-tionsintospecificareasinterconnectedbycommunications(normallydatahighways)toformasingleentity.Itischaracterizedbydigitalcontrollers,typicallyadministeredbycentraloperationinterfacesandintermittentscanning of the data highway.

DowFireandExplosionIndex(F&EI):Amethod(developedbyDowChemical

Company)forrankingtherelativefireandexplosionriskassociatedwitha

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process.Analystscalculatevarioushazardandexplosionfactorsusingmaterial characteristics and process data.

EmergencyReliefDevice:Adevicethatisdesignedtoopenduringemergencyor

abnormalconditionstopreventriseofinternalfluidpressureinexcessofaspecifiedvalue.Thedevicealsomaybedesignedtopreventexcessiveinter-nalvacuum.Thedevicemaybeapressurereliefvalve,anonreclosingpres-sure relief device, or a vacuum relief valve.

EmergencyShutdownDevice:Adevicethatisdesignedtoshutdownthesystem

to a safe condition on command from the emergency shutdown system.EmergencyShutdownSystem:Thesafetycontrolsystemthatoverridesthe

actionofthebasiccontrolsystemandshutsdowntheprocesswhenprede-termined conditions are violated.

EquipmentReliability:Theprobabilitythat,whenoperatingunderstatedenvi-ronmentconditions,processequipmentwillperformitsintendedfunctionadequately for a specified exposure period.

Explosion:Arapidorsuddenreleaseofenergythatcausesapressuredisconti-nuity or blast wave.

Fail-Safe:Designfeatureswhichprovideforthemaintenanceofsafeoperating

conditionsintheeventofamalfunctionofcontroldevicesoraninterrup-tionofanenergysource(e.g.,directionoffailureofacontrolvalveonlossofsignal).Asystemisfail-safeiffailureofacomponent,signal,orutilitythatwouldcreateahazardinitiatesanactionthatmaintainsthesysteminasafe condition.

Failure:Anunacceptabledifferencebetweenexpectedandobservedperformance.FailureModeandEffectsAnalysis(FMEA):Afailureidentificationmethodol-ogywherethefailuremodesofacomponentsub-systemareidentified.Ananalysisofthesefailuremodesonthesafetyoftheentiresystemisperformed.

FirePoint:Thetemperatureatwhichaliquidcontinuestoburnwhentheigni-tion source is removed.

FlameArrester:Aflamearresterisadevicepermeabletogasflowbutimperme-abletoanyflame.Itquenchestheflameandcoolstheproductssufficientlytopreventreignitionatarresteroutlet.Arrestersareusedtopreventaflamepropagatingintothesystemfromoutside(suchasviaatankvent)oronepart of the system to another (such as through connected piping).

FlammabilityLimits:Theminimumandmaximumconcentrationsofcombusti-blematerialinahomogeneousmixturewithgaseousoxidizerthatwillpropagate a flame.

FlammableLiquid:A“FlammableLiquid”isdefinedbyNFPAasaliquidwitha

flashpointbelow100°F(37.8°C).Flammableliquidsprovideignitablevaporatroomtemperaturesandmustbehandledwithcaution.Precautions

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GLOSSARY

suchasbondingandgroundingmustbetaken.FlammableliquidsareClassI liquids and may be subdivided as follows:

•Class1A:Thosehavingflashpointsbelow73°Fandhavingaboilingpoint below 100°F

•Class1B:Thosehavingflashpointsbelow73°Fandhavingaboilingpoint at or above 100°F

•Class 1C: Those having flash points at or above 73°F and below 100°FFlashFire:Thecombustionofaflammablegasorvaporandairmixturein

whichtheflamepropagatesthroughthemixtureinamannersuchthatneg-ligible or no damaging overpressure is generated.

FlashPoint:Thelowesttemperatureatwhichvaporsabovealiquidwilligniteat

apressureof760mmHgabsolute.Thetemperatureatwhichvaporwillburnwhileincontactwithanignitionsource,butwhichwillnotcontinuetoburnaftertheignitionsourceisremoved.Thereareseveralflashpointtestmethods,andflashpointsmayvaryforthesamematerialdependingonthemethodused.Consequently,thetestmethodisindicatedwhentheflashpointisgiven.Aclosedcuptypetestisusedmostfrequentlyforregulatorypurposes.Thelowertheflashpointtemperatureofaliquid,thegreaterthefire hazard following a release.

Froth-over:Whenwaterispresentorentersatankcontaininghotviscousoil,

thesuddenconversionofwatertosteamcausesaportionofthetankcon-tents to overflow.

FugitiveEmissions:Emissionsofmaterialfromprocessequipmentdueto

leakage.

Grounding:Groundingisaconductingconnectionbetweenapieceofequip-ment or electrical circuit and the earth.

Hazard:Aninherentchemicalorphysicalcharacteristicthathasthepotential

for causing harm to people, property, or the environment.

HazardAnalysis:Theidentificationofundesiredeventsthatleadtothemateri-alizationofahazard,theanalysisofthemechanismsbywhichtheseunde-sired events could occur and usually the estimation of the consequences.HazardandOperabilityStudy(HAZOP):Asystematicqualitativetechniqueto

identifyprocesshazardsandpotentialoperatingproblemsusingaseriesofguide words to study process deviations.

AHAZOPisusedtoquestioneverypartofaprocesstodiscoverwhatdeviationsfromtheintentionofthedesigncanoccurandwhattheircausesandconsequencesmaybe.Thisisdonesystematicallybyapplyingsuitableguidewords.Thisisasystematicdetailedreviewtechnique,forbothbatchandcontinuousplants,whichcanbeappliedtoneworexistingprocessestoidentify hazards.

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163

HazardousMaterial:Inabroadsense,anysubstanceormixtureofsubstances

havingpropertiescapableofproducingadverseeffectsonhealth,safetyortheenvironment.Thesedangersmayarisefrombutarenotlimitedtotox-icity, reactivity, instability, or corrosivity.

HumanFactors:Adisciplineconcernedwithdesigningmachines,operations,

andworkenvironmentssothattheymatchhumancapabilities,limitations,andneeds.Includesanytechnicalwork(engineering,procedurewriting,workertraining,workerselection,etc.)relatedtothehumanfactorinoper-ator–machine systems.

InertGas:Anoncombustible,nonreactivegasthatatsufficientconcentrations

rendersthecombustiblematerialinasystemincapableofsupportingcombustion.

InherentlySafer:Asystemisinherentlysaferifitreliesonthechemistryand

physics(thequantity,propertiesandconditionsofuseoftheprocessmate-rials)ratherthanoncontrolsystems,interlocks,alarmsandprocedurestoprevent incidents.

InterlockSystem:Asystemthatdetectsout-of-limitsorabnormalconditionsor

impropersequencesandeitherhaltsfurtheractionorstartscorrectiveaction.

IntrinsicallySafe:Equipmentandwiringwhichisincapableofreleasingsuffi-cientelectricalorthermalenergyundernormalorabnormalconditionstocauseignitionofaspecifichazardousatmosphericmixtureorhazardouslayer.

Likelihood:Ameasureoftheexpectedfrequencywithwhichaneventoccurs.

Thismaybeexpressedasafrequency(e.g.,eventsperyear),aprobabilityofoccurrenceduringatimeinterval(e.g.,annualprobability),oracondi-tionalprobability(e.g.,probabilityofoccurrence,giventhataprecursorevent has occurred).

LimitingOxidantConcentration(LOC):Thelimitingoxidantconcentration

(LOC)isthatconcentrationofoxidant,belowwhichadeflagration(flamepropagationinthegas,mist,suspendeddust,orhybridmixture)cannotoccur.FormosthydrocarbonswhereoxygenistheoxidantandnitrogenisthediluenttheLOCisapproximately9to11vol%oxygen.TheLOCfordustsisdependentonthecompositionandparticlesizedistributionofthesolid.ValuesofLOCformostorganicchemicaldustslieintherangeof10to 16 vol% oxygen, again where nitrogen is the diluent

MinimumExplosibleConcentration(MEC):Thelowestconcentrationofcom-bustible dust necessary to produce an explosion.

MinimumIgnitionEnergy(MIE):Initiationofflamepropagationinacombusti-blemixturerequiresanignitionsourceofadequateenergyanddurationtoovercomeheatlossestothecoolersurroundingmaterial.Dustandvapor

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GLOSSARY

cloudsmaybereadilyignitedifexposedtoelectricdischargesthatexceedthe minimum ignition energy (MIE) for the combustible mixture.

Mitigation:Reducingtheriskofanaccidenteventsequencebytakingprotective

measurestoreducethelikelihoodofoccurrenceoftheevent,and/orreducethemagnitudeoftheeventand/orminimizetheexposureofpeopleorproperty to the event.

NetPositiveSuctionHead(NPSH):Thenetstaticliquidheadthatmustbepro-vided on the suction side of the pump to prevent cavitation.

Overt Fault:Fault that can be classified as announced, detected, revealed, etc.Oxidant:Anymaterialthatcanreactwithafuel(gas,dustormist)toproduce

combustion. Oxygen in air is the most common oxidant.

PlausibilityAnalysis:Acomparisonofvaluesforprocessvariablesthatallows

faultsinthemeasurementchannelsofthesafetysystemtoberecognizedwhile the process is still in its normal operating range.

PoolFire:Thecombustionofmaterialevaporatingfromalayerofliquidatthe

base of the fire.

ProcessSafety:Adisciplinethatfocusesonthepreventionandmitigationof

fires,explosions,andaccidentalchemicalreleasesatprocessfacilities.Excludesclassicworkerhealthandsafetyissuesinvolvingworkingsurfaces,ladders, protective equipment, etc.

PipingandInstrumentDiagram(P&ID):Adiagramthatshowsthedetailsabout

the piping, vessels, and instrumentation.

ProcessFlowDiagram(PFD):Adiagramthatshowsthematerialflowfromone

pieceofequipmenttotheotherinaprocess.Itusuallyprovidesinforma-tionaboutthepressure,temperature,composition,andflowrateofthevariousstreams,heatdutiesofexchangers,andothersuchinformationper-taining to understanding and conceptualizing the process.

ProcessHazardAnalysis(PHA):Astructuredprocedurewherebyhazardsasso-ciated with a process are identified and evaluated.

PressureReliefValve(PRV):Areliefvalveisaspring-loadedvalveactuatedby

staticpressureupstreamofthevalve.Thevalveopensnormallyinpropor-tiontothepressureincreaseoveropeningpressure.Areliefvalveisnor-mally used with incompressible fluids.

PressureSafetyValve(PSV):Asafetyvalveisaspringloadedvalveactuatedby

staticpressureupstreamofthevalveandcharacterizedbyrapidopeningorpop action. A safety valve is normally used with compressible fluids.

ProcessSafetySystem(PSS):Aprocesssafetysystemcomprisesthedesign,pro-cedures,andhardwareintendedtooperateandmaintaintheprocesssafely.ProgrammableElectronicSystem(PES):Asystembasedonacomputercon-nectedtosensorsand/oractuatorsinaplantforthepurposeofcontrol,

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165

protectionormonitoring(includesvarioustypesofcomputers,program-mablelogiccontrollers,peripherals,interconnectsystems,instrumentdis-tributed control system controllers, and other associated equipment).

ProgrammableLogicController(PLC):Amicrocomputer-basedsolid-state

controlsystemwhichreceivesinputsfromuser-suppliedcontroldevicessuchasswitchesandsensors,implementstheminaprecisepatterndeter-minedbyinstructionsstoredinthePLCmemory,andprovidesoutputsforcontrol or user-supplied devices such as relays and motor starters.

ProofTesting:Arunthroughtheprocesssubstitutingnonhazardousmaterials

(e.g.,water)tocheckfortheadequacyoftheequipmente.g.,heating/cool-ing load, and to verify procedural steps.

PurgeGas:Agasthatiscontinuouslyorintermittentlyaddedtoasystemto

render the atmosphere nonignitable.

Quenching:Rapidcoolingfromanelevatedtemperature,e.g.,severecoolingof

thereactionsysteminashorttime(almostinstantaneously),“freezes”thestatus of a reaction and prevents further decomposition or reaction.Reactors:

•Continuous-flowStirredTankReactor(CSTR):Areactionvesselinwhichthefeediscontinuouslyadded,andtheproductscontinuouslyremoved.Thevessel(tank)iscontinuouslystirredtomaintainauniformconcentration within the vessel.

•PlugFlowReactor(PFR):Aplugflowreactorisatubularreactorwherethefeediscontinuouslyintroducedatoneendandtheproductscontinu-ouslyremovedfromtheotherend.Theconcentration/temperaturepro-file in the reactor varies with position.

•BatchReactor:Inabatchreactor,thereactantsareaddedtothereactoratthestartofthereaction.Thereactantsareallowedtoreactinthereac-torforafixedtime.Nofeedisaddedorproductwithdrawnduringthistime. The reaction products are removed at the end of the batch.

•Semi-BatchReactor:Inasemi-batchreactor,somereactantsareaddedtothereactoratthestartofthebatch,whileothersarefedintermittentlyorcontinuously during the course of the reaction.

Runaway:Athermallyunstablereactionsystemwhichexhibitsanuncontrolled

acceleratingrateofreactionleadingtorapidincreasesintemperatureandpressure.

SafetyInstrumentedSystem(SIS):Theinstrumentation,controls,andinterlocks

provided for safe operation of the process.

SafetyLayer:Asystemorsubsystemthatisconsideredadequatetoprotect

against a specific hazard. The safety layer

•is totally independent of any other protective layers

•cannot be compromised by the failure of another safety layer

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GLOSSARY

•must have acceptable reliability

•must be approved according to company policy and procedures•must meet proper equipment classification

•may be a noncontrol alternative (i.e., chemical, mechanical)•may require diverse hardware and software packages•may be an administrative procedure

Short-StopAgent:Amaterialaddedtoareactionmixturetostoporgreatly

reducethereactionrate.Thisisusuallydonetopreventarunawayreaction.

UpperFlammableLimit(UFL):Thehighestconcentrationofavapororgas(the

highestpercentageofthesubstanceinair)thatwillproduceaflashoffirewhenanignitionsource(heat,arc,orflame)ispresent.SeealsoLowerFlammableLimit.AtconcentrationshigherthentheUFL,themixtureistoo “rich” to burn.

ValveFailurePositions:Intheeventofinstrumentairorelectricalpowerfail-ure,valveseitherFailClosed(FC),FailOpen(FO),orFailinthelastposi-tion(FL).Thepositionoffailuremustbecarefullyselectedsoastobringthe system to, or leave the system in a safe operating state.

VaporCloudExplosion(VCE):Explosiveoxidationofavaporcloudinanon-confinedspace(notinvessels,buildings,etc.).Theflamespeedmayaccel-eratetohighvelocitiesandproducesignificantblastoverpressure.Vaporcloudexplosionsinplantareaswithdenseequipmentlayoutsmayshowacceleration in flame speed and intensification of blast.

VaporPressure:Thepressureexertedbyavaporaboveitsownliquid.The

higherthevaporpressure,theeasieritisforaliquidtoevaporateandfillthe work area with vapors which can cause health or fire hazards.

Venting:Emergencyflowofvesselcontentsoutofavessel.Thepressureiscon-trolledorreducedbyventing,thusavoidingafailureofthevesselbyoverpressurization.Theemergencyflowcanbeone-phaseormulti-phase,each of which results in different flow characteristics.