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DNV

WHENTRUSTMATTERS

RISKASSESSMENTOFBATTERYENERGY

STORAGEFACILITYSITES

Mainauthors:

MarisaPierce

VijayRaghunathan

Editors:

StephenJonesCarolLiffman

CarrieKaplan

MichaelKleinberg

WHITEPAPER

Riskassessmentofbatteryenergystoragefacilitysites

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CONTENTS

Executivesummary03

1.Definingriskintheenergystorageindustry10

1.1Currentenergystorageindustrypositioning11

1.1.1Industrialsectorcomparison12

1.1.2Vehiclecomparison13

1.2Theconceptof'risk'13

1.3Identifyingandmanagingrisk14

1.3.1Step1:Hazardidentification14

1.3.2Step2:Consequenceanalysis14

1.3.3Step3:Frequencyanalysis14

1.3.4Riskassessmentandmitigation15

2.Li-ionbatteryfailureriskandmitigation17

2.1Commonfailurescenariosofli-ionbatteries18

2.2Consequenceanalysis19

2.2.1Toxicimpacts19

2.2.2Fireradiation20

2.2.3Flammability20

2.2.4Overpressureimpacts20

2.3Frequencyanalysis21

2.4Riskassessment22

2.5Safeguardsandbestpractices24

2.6Layersofprotection27

3.Conclusions30

4.References32

Riskassessmentofbatteryenergystoragefacilitysites

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LISTOFFIGURES

Figure1-1Deathsperunitofelectricityproductionbyenergysource[4]12

Figure1-2Genericriskmatrix13

Figure1-3Riskassessmentprogression14

Figure1-4Sampleriskmatrixexercise15

Figure2-1Comparisonofcommonriskscenarios27

Figure2-2Bowtieoverview28

Figure2-3Simplifiedthreadpathwayportionofthebowtie(leftsideofFigure2-2)28

Figure2-4Simplifiedconsequencepathwayportionofbowtie(rightsideofFigure2-2)29

Figure3-1ComparisonofriskofBESSwithoutsafeguardsinplace(A)andwithsafeguardsinplace(B)31

LISTOFTABLES

Table2-1CommonLi-ionbatteryfailuresandsafeguards18

Table2-2MaximumdownwinddistanceofCOat8.5feetheightreleasepoint(feetfromsource)19

Table2-3Firehazards-radiationlevelsat3.3feetheightabovegroundlevel(feetfromsource)20

Table2-4LFLat8.5feetheightabovegroundlevel(feetfromsource)20

Table2-5Commonfailurecausesandfrequencyoffailure(CCPS,Ref.[22])21

Table2-6ComparisonofexamplescenariolikelihoodoffatalitywithUKHSEriskcriteria

(withoutsafeguards)24

Table2-7Commonsafeguardsandprobabilityoffailureondemand24

Table2-8ComparisonofexamplescenariolikelihoodoffatalitywithUKHSEriskcriteria

(withsafeguards)26

Table2-9Safeguardorbarriereffectivenesscategories27

EXECUTIVESUMMARY

3

Riskassessmentofbatteryenergystoragefacilitysites

EXECUTIVESUMMARY

Assessingriskforbatteryenergystoragesystems

Interestinenergystoragehassurgedinrecentyears.

AstheworldimplementstheParisAgreement(fromthe

UnitedNationsClimateChangeConference(COP21)heldinParis,Francein2015),utilitiesandenergyprovidersmustcontinuetoreduceemissionssafelyandequitably.BatteryEnergyStorageSystems1(BESS)havegrowninpopularitybecauseoftheirnumerousbenefitstoelectricutilitiesandtheircustomers.

BESSstorelargeamountsofenergygeneratedby

renewable(typicallysolarandwind)andotherpower

generationtechnologies,allowingincreasingrenewable

energygenerationandcostsavingsovertime.Lithium-ion(Li-ion)batteriesrevolutionizedhowwepowerconsumer

productssuchasportableelectronicsandelectricvehicles.BESShelpmanageinstantaneoussupplyanddemandon

thepowersystem,replacefossil-fuel-poweredpeakerplants(whichoperateinfrequently,onlyduringpeaksystem

demand),andserveasbackuppowersourcesintheeventofequipmentfailures.

FailuresofbatterieswithinBESSarerare.

FailurecausesforLi-ionbatteriesincludeelectricalfailures,mechanicalfailure,extremeenvironment,thermalfailure,andhumanerror.

Aswithothertechnologies,BESSincludeapplicationsandrisksthatmeritthoughtfulconsideration.Li-ionbatteries

commonlydeployedinBESScontainmaterialsthatcanburnorexplodewhenoverheatedorotherwiseabused,anda

seriesoffires(particularlyfromconsumerproducts)haveincreasedconcernsoverthesafetyandefficacyofthesesystems.

Untilrecently,publiclyavailabledataonbatteryincidents

waslimited.DNV,however,conductednumerousstudiestounderstandbetterhowLi-ionbatteriesfailandwhich

safeguardsandbestpracticesreducethelikelihoodofincidentsandtheseverityofconsequences.

1Batteryenergystoragesystemsaresometimesconfusedwith,forexample,awarehouseinwhichbatterieswouldbestored.Thispaperdiscussessystemsthatstoreelectricity,oftenusingbatteries.

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Riskassessmentofbatteryenergystoragefacilitysites

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DNVconducteddestructivetestingonhundredsofbatterycellswithcapacitiesrangingfrom2Amp-hours(Ah)to

300Ahfrom20differentmanufacturers,aswellasdozensofmedium-andlarge-scaletestsandnumerousfireandfailureinvestigations.Destructivetestingisatypeoftesting

methodologywheretheprimarygoalistointentionallydamageordestroyacomponent,material,orproductto

evaluateitsperformance,durability,andfailurecharacteristicsunderextremeconditions.InLi-ionbatterytesting,

destructivetestinginvolvessubjectingthecellstoconditions

suchasovercharging,over-discharging,short-circuiting,

mechanicalabuse,andextremetemperatures.Thesetestshelpusunderstandbatterybehaviorduringfiresandotherfailureconditions.Thedataderivedismeanttoguide

manufacturers,systemdesigners,safetyexperts,and

permittingauthoritiesindeterminingthenecessaryfireandexplosionprotectionforaBESSfacility.

Further,weevaluateddatafromtheoilandgas,utility,and

petrochemicalindustrieswhenassessingscenarioswhen

BESSandotherfacilitiesoperateoutsideintendedconditions(potentiallyleadingtofires).DNVusesthesesourcesand

statisticalanalysisandriskassessmenttoolstoestimatetheriskofcatastrophicbatteryfailures,includingtoxicgas

releases,fires,andexplosions.However,wedidnotanalyzefailuresordeterminefailureratesbasedonknownbattery

failureincidents.Instead,weofferaquantitativeassessmentofthelikelihoodofBESSfailureandtheimpactonworkersandthegeneralpublicwithandwithoutsafeguards.WealsocomparedtheBESSsectorwithotherindustriesand

applicationsfamiliartothepublictodeepentheconversationofbatteryBESSsafetyacrossindustries.

ThefollowingareDNV’sfindingsinresponsetocommonlyaskedquestions.

?WhyareLi-ionbatteriesbecomingsopopular?

Amongvariousenergystorageoptions,Li-ionbatteriesstandoutbecauseoftheirhighenergydensityanddecreasingcosts.

Despiteincidentsleadingtoscrutiny,Li-ionbatteriescontinuetobefavoredfortheirversatilityinapplicationsrangingfrompersonalelectronicstoelectricvehiclestostationaryBESS,whichservetobalancesupplyanddemandontheelectricpowersystem.

Variouscountries,especiallytheUnitedStates,activelypursuestrategiestoenhanceenergystoragedeployment.Theseincludeaddressingcostcompetitiveness,regulatoryframeworks,andindustryacceptance,withstateslikeCalifornia,Texas,andNewYorkleadinginBESSdeployment.

?WhyandhowoftendoLi-ionbatteriesinBESSfail?

FailuresofbatterieswithinBESSarerare.FailurecausesforLi-ionbatteriesincludeelectricalfailures(e.g.,batterymanagementsystemfailurethatresultsinover-chargingorover-dischargingthebattery),mechanicalfailure(e.g.,defectivematerialsusedinmanufacturing),extremeenvironment(e.g.,batteryexposedtohighertemperaturesthanitisdesignedfor),thermalfailure

(e.g.,coolingsystemfailure),andhumanerror(e.g.,improperinstallation).Typesoffailuresalsovary–failurecouldmeanthebatterylosessomeofitsabilitytostoreenergy,couldmeanthebatterystopsworking,orcouldmeanthebatterycatchesfire.Thisreport

focusesonrisksrelatedtoLi-ionbatteryfires.

Estimatingthelikelihoodoffailurerequiresadualapproachusingqualitativeandquantitativemeans.Qualitativeanalysisrelieson

theexpertiseofsubjectmatterexperts.Incontrast,quantitativeanalysisutilizeshistoricalreliabilitydataorincidentdatabasesto

determineprecisefailurerates.DNVuseddatabasesfromvariousindustries,suchasnuclear,utility,oilandgas,andpetrochemical

sectors,andstatisticaltoolstoestimatefailurelikelihoodsquantitatively.TheresultingordersofmagnitudeoftheseBESScomponentfailureratesareoncein10yearstooncein100years.Itshouldbenotedthatthesearefailureratesoftheequipmentandnotinjuryorfatalityratesassociatedwiththefailures.

Riskassessmentofbatteryenergystoragefacilitysites

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?WhataretheconsequencesandseverityofLi-ionbatteryfailures?

Consequenceanalysisevaluatesfailurescenarios’severity,employingqualitativeexpertiseandquantitativemodelingtools.

Byusingdatafromourbatteryfiretestsanddatafrombatterycellmanufacturers,weassessedthetoxic,flammability,andthermal

impactsofLi-ionBESSfailuresonsurroundingcommunities.Ourmodellingincludedthefollowinggases:hydrogen(H2),carbon

monoxide(CO),carbondioxide(CO2),methane,andotherhydrocarbonsinlowerconcentrations(ethane,ethene,andpropane).

DNVmodeledanexampleBESSsitecontaining40cabinetsof2megawatt-hours(MWh)eachthatcanstore/discharge80MWhofelectricalenergy.Ourmodellingindicatedthatnoimpactcapableofcausingafatalityorseverepropertydamageoccurredmore

thanabout50feetfromthecenteroftheBESScabinets.Ouranalysisincludedrelevantatmosphericconditionsfortheexamplesite.

?Whataretherisks?

Riskisafunctionoftwocomponents:likelihood(alsoreferredtoasprobabilityorfrequency)oftheeventoccurringandseverity(alsoreferredtoasimpact).Asillustratedintheequationbelow:

Risk=LikelihoodxSeverity

AcommonmetricusedtoreportriskinthehydrocarbonindustryiscalledIndividualRisk,definedastherisktoapersoninthe

vicinityofahazardintermsofthenatureoftheinjury,thelikelihoodofinjury,andthetimeperiodoverwhichitoccurs.Anexampleofhowitiscommonlyreportedis“oneinjury/fatalityevery10,000years.”DNVmodeledtherisktobothworkersandthegeneral

public.BasedonourestimatesforthesampleBESSfacility,factoringinstandardsafetymeasures,thereisanestimatedriskofone

workerfatalityoccurringevery100,000years(equivalentto10-5fatalitiesperyear)andonefatalityinvolvingamemberofthepublicevery1,000,000years(equivalentto10-6fatalitiesperyear).TheUnitedKingdomHealthandSafetyExecutive(UKHSE)has

establishedcriteriafor“broadlyacceptablerisk”forbothworkersandmembersofthepublicforscenariosthatleadtoafatalitynomorethanonceinamillionyears.Scenarioswithfatalitiesareconsidered“tolerable”risksforworkersiftheyoccurnomorethan

oncein1,000yearsand“acceptable”forthepublicifthescenariosoccurnomorethanoncein10,000years.Perthesecriteria,theriskfromtheBESSexamplesitewemodelledisbroadlyacceptableforthepublicandtolerableforworkers.Also,whencomparingtheriskofBESSfailureswithinthecontextofeventsthatsocietyisalreadycomfortablewith,therisksarelow.

Commonrisksinperspective

Riskiestindustry

(transportation&warehousing)

1in1,000

1in10,000

1in100,000

1in1,000,000

1in10,000,000

Solorockclimbing(5hrs.perweek)HeartdiseaseSmoking

Accidentathome

Trafficaccident(driving10hrs.perweek)

Li-ionBESSsite

Fatallightning

strike

Riskassessmentofbatteryenergystoragefacilitysites

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?HowcantherisksofLi-ionbatteriesbemitigated?

Whenrisksaretolerableorworse,itisbestpracticetoidentifyandinstalladditionalsafeguardstoreducetheriskfurther.

SafeguardsincorporatedintoBESSlessenthelikelihoodandseverityofbatteryfailureevents.Examplesofcommonindustry-

standardsafeguardsthatDNVconsideredinthisstudyincludeheatingventilationandairconditioningunits(HVAC)whichcontrolthetemperatureandhumidityinbatterycabinets,batterymanagementsystems(BMS),fusesandcircuitbreakers,andactivefire

suppression.TheNationalFireProtectionAssociation(NFPA)listsotherfireprotectionrequirementssuchasexplosioncontrolandseparationdistancesfromthepublic.Safeguardsthatbothpreventfailuresandmitigatetheseverityoffailurescanberepresentedinbowtievisualizations2,asimplifiedexampleofwhichisshownbelow.Inabowtievisualization,foranidentifiedhazardandevent(forexample“aBESSfacilitycatchesfire”),thevisualizationidentifiesthreatsontheleftandconsequencesontheright.

Barrierswhichpreventthreatsfromcausingtheeventareshownontheleft,andbarriersthatreducetheimpactoftheevent,ifitdoesoccurdespitethepreventivemeasures,areshowntotherightofthebowtie.Managingthehealthofbarriersiscriticalforensuringtheirperformanceintheeventofanemergency.

Bowtieoverview

Hazard

Lossof

containment

event

Mitigative

controlmeasures

orbarriers

Preventcontrol

measuresor

barriers

Consequence

Threat

?HowdoBESSfailureriskscomparetootherindustries?

TheriskofBESSfailureiscomparabletoorevenlowerthantherisksassociatedwitheverydayactivitiessuchasdrivingorbeing

apassengerinacar.Forexample,workingatorlivingnearaBESSislessriskythanbeinginacarorworkinginindustriessuchas

agriculture/forestry/fishing/huntingortransportation/warehousingwhenconsideringthefatalityrate(numberofannualfatalities

per100,000workers).In2023,therewereapproximately1,000fatalitiesrelatedtocarandlighttruckcrashesintheUnitedStates[1].

Withapproximately243milliondrivers[2],theratewas17fatalitiesper100,000driversperyear(thoughcrasheskilldrivers,

passengers,occupantsofothercars,andthoseoutsidecarssuchaspedestriansandbicyclists)or12fatalitiesper100,000

populationperyear.Forevery100,000workersintheUSin2022,therewere19fatalitiesintheagriculture/forestry/fishingandhuntingindustry(417totalfatalities)and14fatalitiesinthetransportationandwarehousingindustry(1,053totalfatalities)[3].

WhilethefatalityratepernumberofworkersisunknownforBESSsites,itispossibletoestimatethefatalityrateperyearandperunitofpowergenerationandcompareitwiththefatalityratesofotherindustries.Withinthepowergenerationsector,thefatalityrateperunitofenergy(orterawatthours)forBESSsitesisconsiderablylowerperunitofelectricityproductioncomparedtoothersources

suchascoal,oil,ornaturalgas(seefigureonpage9).ThefatalityrateperyearisdiscussedinmoredetailinSection1.1.

2Thename“bowtie”isusedbecauseacompletedvisualizationoftenlookslikeabowtie.

Riskassessmentofbatteryenergystoragefacilitysites

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Deathsperunityofelectricityproductionbyenergysource[4]

30

DeathsperTerawatthourelectricity

25

20

15

10

5

0

25

18

4.6

2.8

1.3

Coal

Oil

Biomass

Gas

0.07

HydropowerLi-ionbatteryenergystorage

0.04Wind

0.03

Nuclear

0.02Solar

Energysector

*ThefatalityratefordriversintheU.S.isbasedonthenumberoffatalitiesreportedbytheU.S.NationalHighwayandTrafficSafetyAdministrationfortheyear2023pernumberoflicenseddriversintheU.S.in2023whichwasestimatedtobe243.35milliondriverspertheConsumerAffairsJournalofPublicResearch[2].

?HowdoBESSfacilitiesremainsafe?

ToensureBESSremainsatanacceptablerisklevel,itsownersandoperatorsshouldfollowdesignstandardsandbestpractices,regularlymaintainthesystem’sequipment(aswellassafetysystemsandrelatedequipment),trainpersonnel,andcommunicatewithlocalemergencyrespondersonthestoragesystem’shazards.

1

DEFININGRISKINTHE

ENERGYSTORAGEINDUSTRY

11

12

13

13

14

14

14

14

15

1.1Currentenergystorageindustrypositioning

1.1.1Industrialsectorcomparison

1.1.2Vehiclecomparison

1.2Theconceptof'risk'

1.3Identifyingandmanagingrisk

1.3.1Step1:Hazardidentification

1.3.2Step2:Consequenceanalysis

1.3.3Step3:Frequencyanalysis

1.3.4Riskassessmentandmitigation

3

Riskassessmentofbatteryenergystoragefacilitysites

1.DEFININGRISKINTHEENERGYSTORAGEINDUSTRY

Thefollowingsectionsdescribetheenergystoragemarketandintroduceriskasacombinationofhowsevereanincidentisandhowlikelyitistooccur.

US.However,ofthosevalues,intheUSandabroad,

approximately96%ofthecapacityisrepresentedbylarge

pumpedhydrostorage.Whileelectrochemicalbatteries

representnearly57%oftheprojectsinstalled,theycontributejust1,800MWtoworldwidecapacityand787MWtoUS

capacity.Ofthissubsection,Li-ionchemistriesaccountfor77%(1,390MW)ofinstallationsworldwideandnearly85%(667MW)ofUSelectrochemicalinstallations[8].

Assuch,BESSusingLi-ionbatteriesisthefocusofthispaper.Li-ionbatteries’high-energydensityanddecreasingcosts

supporttheiruseinapplicationsrangingfromportable

personalelectronicstotransportationtoutility-scalecapacitysupportandbeyond.IncidentswithLi-ionbatteriesoverthelasttenyears,includingtheBoeing787Dreamlinerfiresin2013[9],theUnionPacifictraincarexplosionin2017[10]

and,morerecently,utility-scaleBESSfires[11],anddozensofe-bikefiresinNewYorkCity[12][13][14][15],haveled

toscrutinyofLi-ionbatteries.Itisclearthataquantitative

assessmentofrisk,bothforthelikelihoodandtheimpactoffailure,iscriticaltoprovidesufficientmitigationmeasures.

Whiletheseandsimilarhigh-profilefailureshavereceivedmediaattention,reputablemanufacturersclaimhundredsofthousandsandevenmillionsofhoursofoperationwithnosignificantfailures.

ThetotalnumberofdeployedBESSandtheirfailureratesarebeingtrackedinincidentdatabases.Thesedatabases,alongwiththeresultsofbatteryburntests,recordedreliabilitydataforanalogoussystems,consequencemodellingandsome

statisticalanalysis,makeitpossibletoestimatetherisksofBESS.

1.1Currentenergystorageindustrypositioning

Batteryenergystoragesystemsareanincreasinglyattractiveoptionforutilityoperatorsandenergyproviderstoimprovethereliabilityandefficiencyoftheelectricgridwhile

reducingemissions.Variouscountries,includingtheUnitedStates(US),haveestablishedstrategiestoincreasetheuseof

energystoragebyaddressingcostcompetitiveness,

performanceandsafety,marketandpricingregulations,andindustryacceptance[5].IndividualUSstateshaveadopted

renewableportfoliostandards(RPS)andzeronetemissions

standards.TheyalsohavedevelopedincentiveprogramsthatsupporttheincreasedBESSdeploymentsofenergystoragegoals.Thirty-ninestateshaveanRPSorvoluntaryclean

energygoals,and19statesandWashington,D.C.passed

legislationtogroworexpandtheirrenewableorcleanenergytargets.Californiaisaleaderinthisspacewithover6,600MWofinstalledBESSenergystoragecapacity[6].Manystates

areexpandingtheirgoals.Forexample,NewYorkaimsfor

atargetof1,500MWofstorageforthestateby2025and

3,000MWby2030,withinthecontextofanoverall6,000MWenergystorageroadmap[7].TexasisanotherleaderinBESSinstallations.

Theenergystoragemarketoffersvariousoptions,including

pumpedhydro,compressed-airenergystorageflywheels,

basedontheUSDepartmentofEnergy(DOE)energystoragedatabase[8](whichisself-reportedandresearchedanddoesnotmaintainpacewithallnewinstallations),thereare

174,000MWofenergystoragesystemsofalltypesinstalledandoperationalworldwide,with24,500MWinstalledinthe

andelectrochemicalbatteriesdeployedinBESS.Currently,

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Riskassessmentofbatteryenergystoragefacilitysites

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1.1.1INDUSTRIALSECTORCOMPARISON

Figure1-1isbasedondatafromOurWorldData[4]forall

ofthesectorsshown,exceptfortheBESSsector,whichwasseparatelycalculatedandaddedalongsidetheothersectors’data.Thefigureshowsthemortalityratefromaccidentsandairpollutionperunitofelectricityworldwideindifferent

sectors.Thefigureshowsfatalitiesperterawatt-hour3of

electricityproducedin2022perindustrysector.ThemortalityrateintheBESSsectorisbasedon4totalfatalitiesattributedtoBESSworldwidetodate,accordingtoadatabaserunby

UnderwritersLaboratoriesSolutions[16].Asof2023,roughly97,000MWhofelectricitystoragecapacityisinstalled

globally[17][18].Basedonthosevalues,theBESSsector’s

mortalityrateisapproximately0.074fatalitiesperterawatt-hourforLi-ionbatteryBESSfacilities.Withinthepower

generationsector,thefatalityrateperunitofenergy

(orterawatthours)forBESSsitesisconsiderablylowerper

unitofelectricityproductioncomparedtoothersourcessuchascoal,oil,ornaturalgas.However,itisworthnotingthatthedeathratesincludedinthisgraphaccountforindirectdeathsfromairpollutionaswellaswork-relatedincidentsanddirectimpactonsociety.Thedatafromupstream-relatedactivitiessuchasmining,fabrication,anddeliveryofthelithium-ion

energystoragesystemisnotavailable.Therefore,indirectimpactsforLi-ionstoragewerenotincludedaspartofthiscomparison.

DeathsperTerawatthourelectricity

30

25

20

15

10

5

0

25

18

4.6

2.8

1.3

Coal

Oil

Biomass

Gas

0.07

HydropowerLi-ionbatteryenergystorage

0.04Wind

0.03

Nuclear

0.02Solar

Energysector

FIGURE1-1

Deathsperunitofelectricityproductionbyenergysource[4]

3Aterawatt-hour(TWh)isequaltoonetrillionwattsofpowerusedforonehour.

OneTWhisequaltoonemillionMWh,roughlytheelectricityusedby80,000averageUShouseholdseachyear.

4Inourcalculations,DNVassumedthatallinstalledBESSwereutilized70%ofthetimeperyearwhichroughlyequatesto60TWhofenergyproducedfromlithium-ionbasedBESSsince2008.ThedataforthetotalcapacityofBESSinstallationsfrom2008-2020isfromRef.[18];datafrom2021-2023isfromRef.[17];2024valueswereestimatedbasedon2023data.

Riskassessmentofbatteryenergystoragefacilitysites

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1.1.2VEHICLECOMPARISON

EVfiresreceivemuchpublicity,whetherthefiresresultfromcrashes,occurduringcharging,orhappenwhilethevehicleisparkedbutnotbeingcharged.AsdeploymentsofEVs

increaseexponentially,increasingfireincidentsmayerodeconfidenceinthetechnology.Ofcourse,conventional

gasolineordiesel-fueledvehiclesalsocatchfiredueto

crashes,duringrefueling,andwhileparked,butthat

technologyhasbeenaroundforwelloveracenturyandsohasbeennormalized.

DNVisnotawareofpeer-reviewedcomparisonsonrates

offireamongEVsandconventionallyfueledvehicles.One

widelyreferencedstudy[19]claimsEVshaveamuchlower

rateoffirethanconventionalvehicles,whichmaywellbetrue.

However,thestudyusesrecentsalesdatatoder