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Thermal risk assessment and rankings for reaction hazardsThermalriskassessmentandrankingsforreactionhazardsinprocesssafetyQingshengWangÆWilliamJ.RogersÆM.SamMannanReceived:10October2008/Accepted:10March2009/Publishedonline:15July2009�Akade´miaiKiado´,Budapest,Hungary2009AbstractReactionhazard...

Thermal risk assessment and rankings for reaction hazards
ThermalriskassessmentandrankingsforreactionhazardsinprocesssafetyQingshengWangÆWilliamJ.RogersÆM.SamMannanReceived:10October2008/Accepted:10March2009/Publishedonline:15July2009�Akade´miaiKiado´,Budapest,Hungary2009AbstractReactionhazardsremainthemostseriousconcerninthechemicalindustryinspiteofcontinualresearchandattentiondevotedtothem.Manycommercialcalorimeters,suchastheDifferentialScanningCalorimetry(DSC),areusefulscreeningtoolsforthermalriskassess-mentofreactionhazards.Someimportantthermodynamicandkineticparameters,includingonsettemperature,adia-batictimetomaximumrate,andmaximumadiabatictemperature,wereanalyzedinthispaper.Akinetic-basedmodelunderadiabaticconditionswasdeveloped,andtheadiabatictimetomaximumratewasestimated.Correla-tionsbetweenonsettemperature(To)andactivationenergy(Ea),andbetweenonsettemperature(To)andadiabatictimetomaximumrate(TMRad)werefound,andwereillustratedbysomeexamplesfromthepreviousliterature.Basedontheheatofreactionandtheadiabatictimetomaximumrate,athermalriskindex(TRI)wasdefinedtorepresentthethermalriskofaspecificreactionhazardrelativetodi-tert-butylperoxide(DTBP),andtheresultsofthisindexwereconsistentwiththoseofthereactionhazardindex(RHI).Thecorrelationsandthethermalriskindexmethodcouldbeusedasapreliminarythermalriskassessmentforreactionhazards.KeywordsThermalrisk�Differentialscanningcalorimetry�Onsettemperature�Adiabatictimetomaximumrate�ReactionhazardindexListofsymbolsA0Pre-exponentialfactorBDEBonddissociationenergyCAConcentration(mol/m3)CpSpecificheatcapacity(J/kg�K)CpcSpecificheatcapacityofcontainer(J/kg�K)C0pSpecificheatcapacity(J/mol�K)DSCDifferentialScanningCalorimetryDTBPDi-tert-butylperoxideEaActivationenergy(kJ/molorkcal/mol)hPlanck’sconstant(J�s)-DHrHeatofreaction(kJ/molorcal/g)kRateconstant(1/s)kBBoltzmann’sconstant(J/K)mMassofchemicalsample(kg)mcMassofcontainer(kg)_qHeatreleaserateatanytemperature(W/kg)_qoHeatreleaserateatTo(W/kg)RGasconstant(J/mol�K)rAReactionrate(mol/m3�s)RHIReactionhazardindextTime(sormin)TAbsolutetemperature(K)TBPAt-ButylperoxyacetateTmMaximumadiabaticdecompositiontemperature(K)TMRadTimetomaximumrateatadiabaticconditions(sormin)ToOnsettemperaturewheretheheatreleaserateis0.1�C/min(K)TRIThermalriskindexVReactionvolume(m3)GreeksymbolsbRatioofconsequencecpTransfercoefficientQ.Wang�W.J.Rogers�M.S.Mannan(&)MaryKayO’ConnorProcessSafetyCenter,ArtieMcFerrinDepartmentofChemicalEngineering,TexasA&MUniversity,CollegeStation,TX77843-3122,USAe-mail:mannan@tamu.edu123JThermAnalCalorim(2009)98:225–233DOI10.1007/s10973-009-0135-zeRatioofprobabilityUThermalinertiacoefficientIntroductionThermalriskevaluationofreactionhazardsisofgreatimportancetothesaferoperationofchemicalprocesses[1,2].Thethermalreactivityorthermalinstability[3,4]ofacompoundisaninherentpropertyofthecompoundandthecharacterizationofthethermalreactivityisconsideredasadynamicproblem.Boththermodynamicandkineticstudiesarenecessarytoevaluatethethermalrisk.Inpre-viousresearchbyAndoetal.[5],theonsettemperature(To)andtheheatofreaction(–DHr)areconsideredastwosignificantparameterstoassessreactionhazards.Itwassuggestedthatthermalriskofchemicalreactionscouldbecharacterizedbothbytheirseverityandbytheirprobability[6].First,theseverityofachemicalreactionhastobedetermined.Usuallyseveritycanbedescribedbytheheatofreactionortheadiabatictemperaturerise[7].Iftheprocesstemperatureisabovetheonsettemperature,thetimetomaximumrateunderadiabaticcondition(TMRad)couldbeusedtodescribetheprobabilityofthermalrisk[7,8].Itiswellknownthattoevaluatethethermalreactivityandtodesignasafechemicalprocess,allthethermody-namicandkineticparameters,includingonsettemperature,adiabatictimetomaximumrateandmaximumadiabatictemperaturemustbedetermined.Butacorrectdetermina-tionofthethermo-chemicalkineticsforareactionistimeconsumingandtherefore,preliminaryscreeningmethods,suchastheDifferentialScanningCalorimetry(DSC),areusuallyappliedinthechemicalindustry.DSCisregardedasausefulscreeningtoolforthermalriskassessmentandfortheinvestigationofdecompositionmechanismsofexothermicreactions[9,10].Thepurposeofthisworkistodemonstratethatarea-sonablerankingofthermalriskispossible.Thedemon-strationisbasedonakineticmodelandcorrelationsbetweenToandEa,andbetweenToandTMRad,whicharederivedfromalimitednumber,37sets,ofDSCdata[5].Anewapproachforassessingreactionhazardswasalsoproposedandcomparedwithapreviousevaluationmethodofreactionhazards.Webelievethattheproposedrankingmethodofreactionhazardscanbeusedtoscreenreactionhazardsduringchemicalprocessdesigns.DatacollectionExothermiconsettemperatures(To)andheatsofreaction(-DHr)werecollectedfromapreviouslypublishedmeasurementsinapressureDSC(DUPont910pressure-type)[5].Theseexperimentswereperformedwithabout1–2mgsamplesinanaluminumcellandascanningrateof10�C/minfor820reactivehazardsofwhich37reactivehazardswerechoseninthiswork.Thedatasetswereselectedonthebasisofdifferentfunctionalgroupsforcompoundsundergodecompositionwithabondscissionasthefirstreactionstep.Thedecompositionofthesetypesofcompoundsmaybefirstorder,whichwillhelptoobtainareasonablemodellater.Theconcernedphysicalproperties,suchasmolecularweight(MW)andspecificheatcapacity(Cp),areavailablefromtheNationalInstituteofStandardsandTechnology[11].Forthoseexperimentalvaluesthatareunavailableintheliteratureorhandbooks,Gaussian03programswereusedtoestimatethemwithgoodaccuracy.Specificheatcapacityvalues(J/mol�K)werecalculatedusingthequickerandlessexpensivesemi-empiricalAM1method[12].BothexperimentalandcalculateddataaredisplayedinTable1.ModeldevelopmentInordertorelatecalorimetricdata(To,-DHr)toactivationenergyandtimetomaximumrate,anunsteadystatemodelinanadiabaticbatchreactorwasemployed[13].Ithasbeenshownthatsuchamodelcanfairlywellrelatecalo-rimetricdatawithactivationenergyandisbasedonthefollowingassumptions[14]:•Thereactionsystemisassumedtobeadiabatic,andthereforeheatlossesarenegligible.•Themassandvolumeoftheliquidphaseremainconstant(i.e.evaporationlossesareneglected).Thespecificheatoftheliquidisconsideredtobeconstantduringthereaction.•Auniformtemperatureexiststhroughouttheliquidphase.•Thedecompositionreactionisfirstorderwithconcen-tration,thereforerA¼kCAð1ÞWiththeseassumptions,thefollowingheatbalancecanbewrittenð�DHrÞð�rAÞVþUmCpdTdt¼0ð2ÞwhereDHristheheatofreaction(kJ/mol),rAisthereactionrate(mol/m3�s),Visthereactionvolume(m3),mandCparethemass(kg)andspecificheatcapacity(J/kg�K)ofthechemicalcompound,respectively.UisthethermalinertiacoefficientwhichisdefinedasU¼mCpþmcCpcmCpð3Þ226Q.Wangetal.123Table1DSCdataandphysicalpropertyvaluesforvariouscompoundsCompoundnameMolecularformulaMolecularweight(g/mol)Heatcapacity(J/mol�K)Heatofreaction(cal/g)Onsettemperature(�C)OrganicperoxidesBenzoylperoxideC14H10O4242243438108t-butylhydroperoxideC4H10O29012325298CumenehydroperoxideC9H12O2152169448187DilauroylperoxideC24H46O439938723286Di-tert-butylperoxide(DTBP)C8H18O2146219133162MethylethylketoneperoxideC8H18O621022034599NitrocompoundsNitrobenzeneC6H5NO2123186a3124002,4,6-TrinitrotolueneC7H5N3O6227243a12873142-NitroanilineC6H6N2O2138166a4853413-NitroanilineC6H6N2O2138159a6053454-NitroanilineC6H6N2O2138167a6013472-NitrotolueneC7H7NO2137172a3173383-NitrotolueneC7H7NO2137172a2603614-NitrotolueneC7H7NO2137172a372366OximesBenzaldoximeC7H7NO121126410236BiacetylmonoximeC4H7NO2101122220159CyclohexanoneoximeC6H11NO113199a527207DimethylglyoximeC4H8N2O2116142455254AzocompoundsAzobenzeneC12H10N2182229a191321AzoxybenzeneC12H10N2O198185405307Epoxycompounds2,3-Epoxy-1-propanolC3H6O274832411971,2-EpoxypropaneC3H6O58125a67160ChloridesBenzoylchlorideC7H5ClO141187a481190BenzylchlorideC7H7Cl127182269172o-ChlorobenzoylchlorideC7H4Cl2O1751258651642-Amino-4-chlorophenolC6H6NClO144134481642,6-DichlorobenzoylchlorideC7H3Cl3O2091406942292,4,5-TrichlorophenolC6H3Cl3O1971416992681,3-DichloropropaneC3H6Cl2113125a81243N-oxidesPyridine-N-oxideC5H5NO9588380288c-picoline-N-oxideC6H7NO109113368285PicolinicacidN-oxideC6H5NO3139130307224TrimethylamineN-oxideC3H12NO7598213202HydrazineBenzoylhydrazineC7H8N2O1361442592601,2-DiformylhydrazineC2H4N2O28899a3042342-HydroxyethylhydrazineC2H8N2O76952512404-NitrophenylhydrazineC6H7N3O2153151432178aHeatcapacitydataarefromtheopenliterature,otherheatcapacitydataarecalculatedbyGaussian03programsThermalriskassessmentandrankingsforreactionhazards227123wheremcandCpccorrespondtothemass(kg)andspecificheatofthecontainer(J/kg�K).Thethermalinertiacoef-ficientisoneofthemostimportantparameterstoinsurethatthecalorimetermatchesascloseaspossibletothechemicalprocess.Fortypicalindustrialreactors,Uislargerthanbutcloseto1.However,tosimplifythekineticmodel,U=1willbechoseninthiswork,whichistheworsecaseforathermalrunawayreaction.InthiscaseofU=1,allofthethermalenergyreleasedbythedecompositionreactionwillincreasethetemperatureofthereactingsystemandacceleratethereaction.CombiningEqs.1and2dTdt¼�DHrkCAVUmCpð4ÞwithC0p=(m/CAV)Cp(C0pisspecificheatofthesampleinJ/mol�K)andU=1,Eq.4canbesimplifiedasdTdt¼�DHrkC0pð5ÞAccordingtoTransitionStateTheory(TST),therateconstantkcanberepresentedbyk¼kBThexp�EaRT��ð6ÞwherekBistheBoltzmann’sfactor(J/K),hisPlanck’sconstant(J�s),Eaistheactivationenergy(kJ/mol),Tistheabsolutetemperature(K)andRisthegasconstant(J/mol�K).SubstitutingEq.6into5dTdt¼�DHrkBTC0phexp�EaRT��ð7ÞIfthetemperatureatwhichthegradientoftemperaturewithtime(dT/dt)increasesatthespecifiedrateof0.1�C/ministakenastheonsettemperature,activationenergycanbecalculatedfromEq.7.Foradecompositionreactionwithrelativehighactiva-tionenergy,ithasbeenshownthattheadiabatictimetomaximumrate(TMRad)canbeapproximated[15].TMRad¼CpRT2_qEað8Þwhere_qisthecorrespondingheatreleaserate(W/kg)atthetemperatureT,Eaistheactivationenergy(kJ/mol),andCpisthespecificheatofthereactionmass(J/kg�K).Inthismodeltheconcentrationdecreaseisneglected,sothatthecalculatedTMRadisalwaysshorterthanthetrueadiabaticvalueand,thus,thedifferenceisontheconservativeside.Theheatreleaserateisdefinedas_q¼ð�DHrÞðrAVÞð9ÞItisalsopossibletoestimatetheheatreleaserateatanytemperatureT_q¼_qoexpEaR1To�1T����ð10Þwhere_qoistheheatreleaserate(W/kg)attheonsettemperatureTo.Therefore,theadiabatictimetomaximumratestartingfromtheonsettemperaturecanbeestimatedasTMRad¼CpRT2o_qoEað11ÞCombiningEqs.2,9and10,theheatreleaserateis_qo¼dTdtCpð12ÞSubstitutingEq.12into11TMRad¼RT2oðdT=dtÞEað13ÞForanonsettemperaturecorrespondingtodT/dt=0.1�C/min,theadiabatictimetomaximumratecanbeestimatedfromtheonsettemperatureandtheactivationenergyaccordingtoEq.13.Itshouldbenotedthatthethermo-kineticanalysismentionedaboveisatbestapproximate(especiallyforthecalculationofTMRad).Therefore,themodelsdonotapplyincasesofmultiplereactions(inacompetitiveconsecutivereactionnetwork)orcatalysisreactions.ResultsanddiscussionCorrelationsAspointedoutabove,ifthetemperatureatdT/dt=0.1�C/ministakenastheonsettemperature,boththeactivationenergyandtheadiabatictimetomaximumratecanbeestimatedusingEqs.7and13.Alldataofonsettempera-ture,activationenergy,andadiabatictimetomaximumratearesummarizedinTable2.TwocorrelationsinEqs.14and15weredevelopedbasedonthetrainingsetof37reactionhazards.Equa-tion14showsthecorrelationbetweentheonsettempera-tureandtheactivationenergywithanR2valueof0.99.Figure1displaystheonsettemperatureagainsttheacti-vationenergy.To¼2:4953Ea�247:7ð14ÞThesecondcorrelationwasbasedontheadiabatictimetomaximumrateandtheonsettemperature,asshownbelowasEq.15TMRad¼0:2088Toþ61:885ð15Þ228Q.Wangetal.123ThiscorrelationalsohasanR2valueof0.99.ThedetailedinformationofthetimetomaximumrateagainsttheonsettemperatureisdisplayedinFig.2.Theseequationsandfiguresindicatethatthreethermo-kineticparameters,To,Ea,andTMRad,arecloselyrelatedtoeachother.Theonsettemperaturecanbeapproximatelydescribedasproportionaltotheactivationenergy.Theadiabatictimetomaximumrateisalsoproportionaltotheonsettemperature.Therefore,aspecificreactionhazardwithhighactivationenergyinthedecompositionreactionwillhaverelativelyhighonsettemperatureandtheadiabatictimetomaximumratewillbelarge,whichmeansthatthethermalriskofthisreactionhazardisrelativelylower.AccordingtoEqs.14and15,iftheactivationenergyisknownorcanbeestimated,thentheonsettemperatureandtheadiabatictimetomaximumratecanbeestimated.Itispossiblethattheactivationenergybeestimatedbasedoncertainassumptions:Table2SummarydataofadiabatictimetomaximumrateandactivationenergyCompoundnameHeatofreaction(cal/g)Onsettemperature(�C)Adiabatictimetomaximumrate(min)Activationenergy(kJ/mol)Benzoylperoxide43810883145t-Butylhydroperoxide2529882139Cumenehydroperoxide448187100176Dilauroylperoxide2328679135Di-tert-butylperoxide13316298161Methylethylketoneperoxide3459982141Nitrobenzene3124001472562,4,6-Trinitrotoluene12873141242312-Nitroaniline4853411332363-Nitroaniline6053451332394-Nitroaniline6013471332402-Nitrotoluene3173381332333-Nitrotoluene2603611392414-Nitrotoluene372366139245Benzaldoxime410236110195Biacetylmonoxime22015996162Cyclohexanoneoxime527207105183Dimethylglyoxime455254114202Azobenzene191321131224Azoxybenzene4053071252232,3-Epoxy-1-propanol2411971031771,2-Epoxypropane67160100156Benzoylchloride481190101177Benzylchloride26917298167o-Chlorobenzoylchloride865164931712-Amino-4-chlorophenol481641001602,6-Dichlorobenzoylchloride6942291071962,4,5-Trichlorophenol6992681152121,3-Dichloropropane81243116191Pyridine-N-oxide380288121216c-picoline-N-oxide368285121214PicolinicacidN-oxide307224108190TrimethylamineN-oxide213202105178Benzoylhydrazine2592601172021,2-Diformylhydrazine3042341111932-Hydroxyethylhydrazine2512401131944-Nitrophenylhydrazine43217898173Thermalriskassessmentandrankingsforreactionhazards229123•Thereactionfollowsaradicalmechanism.•Thefirststepisthedissociationoftheweakestbond,andtheremainingstepsarerelativelyfast.Thermaldecompositionreactionsofthenitrocom-pounds[16,17]ororganicperoxides[18,19]canbedepictedasbondscissionreactions.R�NO2!R�þNO�2ð16ÞRO�OR0!RO�þR0O�ð17ÞTherefore,forthesetypesofdecompositionreactions(oranysimilardecompositionbehaviorsthathaveweakestbondbroken),thebondscissionreactioncanberegardedastherate-limitingstep,andhencetheactivationenergycanbeestimatedas[20]:Ea¼cpðBDEÞð18Þwherecpisthepositivetransfercoefficient,BDEisthebonddissociationenergy(kcal/mol)inthebondscissionreaction,whichcanbecalculatedbyGaussian03programs.TheBDEdataforsomenitrocompoundswerecollectedfromthepublishedarticlebySarafetal.[20],andshowninTable3.Theexperimentalactivationenergyofdicumylperoxide[21],hydroxylamine[22],andt-butylperoxyacetate(TBPA)[23]wereobtainedfromthepreviouslit-erature.TheonsettemperaturesarethenpredictedaccordingtoEq.14.AsseenfromTable3,theaverageerrorpercentagesareverysmall,andwecanconcludethatthepredictionsarereasonableandcanbeusedtoassessreactionhazards.Thenextsectionofthispaperwillshowthethermalriskassessmentofreactionhazardsindetail.ThermalriskevaluationAswementionedabove,thermalriskisbasedonseverityandprobability.Ifthesetwoparameterscanberepresentedforacertainreactionhazardofchemicalprocesses,thermalriskassessmentofthereactionhazardispossible.SeverityandprobabilityTheprimaryfactorsdeterminingseveritiesinchemicalreactionsaretheenergiesthatcanbereleasedinthereactionsbasedonquantitiesofchemicalsandtheadiabatictemperaturerisepotentials.TypicaldecompositionthermalTo=2.4953Ea-247.70100200300400500100150200250300Activationenergy(kJ/mol)Onsettemperature(oC)Fig.1AcorrelationbetweenonsettemperatureandactivationenergyTMRad=0.2088To+61.88560801001201401600100200300400500Onsettemperature(oC)Timetomaximumrate(min)Fig.2AcorrelationbetweenadiabatictimetomaximumrateandonsettemperatureTable3SummaryofexperimentalandpredictedvaluesofonsettemperatureCompoundBonddissociateenergy(kcal/mol)Predictedactivationenergy(kJ/mol)Onsettemperature(�C)Predictedonsettemperature(�C)Error(%)2-Nitrotoluene73.4215290289-0.43-Nitrotoluene75.9222310307-1.04-Nitrotoluene76.7225320313-2.22-Nitrobenzoicacid66.4194270238-12.03-Nitrobenzoicacid74.7219300298-0.64-Nitrobenzoicacid76.52243103110.42-Nitroaniline80.123528033820.63-Nitroaniline76.52243003113.84-Nitroaniline80.923731034410.8Dicumylperoxide–147a1091199.3Hydroxylamine–160a1391529.0TBPA–163a160159-0.6aExperimentalvaluesarefromthepreviousliterature230Q.Wangetal.123energiescanleadtomassivedestructioneveniftheyareonlypartiallytransformedintomechanicalformsinathermalrunawayincident.Secondaryeffects,suchasthereleaseoftoxiccompounds,cansignificantlycontributetotheoveralldegreeoftheseverity.However,inthisworkwewillnotfocusontoxiceffects.Therefore,theheatofreaction,whichisameasureoftheenergyreleasepotentialofacompound,willbeusedasameasureoftheseverityofthereaction[7].Probabilitiesofthermalrunawayreactionsaremoredifficulttoevaluate.However,itisreasonabletoconsidertheirimmediateconsequencesbyreferringtotimescalesofrunawayscenarios,ortheadiabatictimetomaximumratestartingfromtheonsettemperature.Itisobviouslythatafailuremodethattriggersasevererunawayreactionwithinafewminutesfollowingtheonsettemperatureisdanger-ous.Therefore,theadiabatictimetomaximumratewillbeusedtorepresenttheprobabilityofrunawayreactionoccurrence[8].Thermalriskindex(TRI)Inordertoassessquantitativelyaspecificreactivehazard,itisnecessarytodefinetwoparametersrelatedtoseverityandprobability.Di-tert-butylperoxide(DTBP)isanextensivelystudiedchemical[24]foritsthermallyunstableandsimpleunimolecularfirst-orderdecompositionreactioninthegasphase[25].Therefore,DTBPisselectedinthisworkasareferencecompoundtostandardizethethermalriskindex.Theheatofreaction,-DHr=133cal/g,andtheadiabatictimetomaximumrate,TMRad=98min,forDTBPisusedtodefinetwodimensionlessparametersandthenestimatethermalreactivityrisk.Aratio,b,astheamountofenergyreleasedbyaspecificsubstancetotheenergyreleasedbyDTBPisdefinedb¼�DHr133ð19Þbismeasurementoftheseverityofthereaction.Thehigherthevalueofb,moreseverethechemicalreactionisrelativetothedecompositionreactionofDTBP.Wecanalsodefineanotherratio,e,astheadiabatictimetomaximumrateofDTBPtothatofthesubstance.e¼98TMRadð20Þeismeasurementofprobabilityofreactionoccurrence.Thesmallerthevalueofe,thesafertheprocessis,becausethereismoretimetomakeadjustmentstoavertarunawayreactionortoreducetheconsequences.Becauseriskisthefunctionofseverityandprobability[26],itmaybeexpressedbythesetwoparameters(althoughtherearesomeotherfactorsthatmaycontributetotherisk):Risk¼Severity�Probabilityð21ÞCombiningdefinitions(19),(20),and(21),thethermalriskofaspecificsubstancerelativetoDTBPcanberepresentedquantitativelybydefiningathermalriskindex(TRI)asfollowsTRI¼b�e¼�DHr133���98TMRad��ð22ÞThelowerthevalueofTRI,thelowerthethermalriskisduetoalowerreactivity.Thethermalriskindexvaluesforall37compoundsarecalculatedaccordingtoEq.22andshowninTable4.Inthiswork,weassignthermalriskrankingvaluesaccordingtotherulesasfollows:1forTRI\1;2for1BTRI\2;3for2BTRI\3;4forTRIC3Therefore,thermalriskrankingsforall37reactionhazardsareassignedandsummarizedinTable4.Reactionhazardindex(RHI)D.R.Stullhasdevelopedarankingsystem,whichiscalledthereactionhazardindex(RHI),toestablishtherelativepotentialhazardsofspecificreactivechemicals[27].TheRHIrelatesthemaximumadiabatictemperature(Tm)totheactivationenergy(Ea)ofadecompositionreactionandisdefinedasRHI¼10TmTmþ30Eað23ÞwhereEaistheactivationenergy(kcal/mol),andTmisthemaximumadiabaticdecompositiontemperature(K),whichcanbeestimateasTm¼Toþ�DHrC0pð24ÞwhereToistheonsettemperature(K),C0pisthespecificheatofthesample(J/mol�K),andDHristheheatofreaction(kJ/mol).Thereactionhazardindexvaluesforall37reactionhazardsarecalculatedandincludedinTable4.Thereac-tionhazardindexrelationshiphasalowvalue(RHI\4)forrelativelowreactivityandhighvalue(RHI[6)forhighreactivity.Inthiswork,RHIrankingsareassignedaccordingtotherulesasfoll
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