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Electric Vehicles


Fires in electric vehicles may undermine the widespread adoption of these vehicles and

the transition to renewable fuels. A strong concern related to burning electric vehicles is

the release of toxic gas. This threatens the health of first responders and may even

contribute to greater hesitation in their firefighting and response strategy. Hydrogen

fluoride (HF) is of certain interest due to that it can be absorbed through the skin, but

results from this project show that the total quantities might be lower than potentially

expected from electric vehicles and the simulations of a potentially worst case scenario

in a parking garage also show relatively low maximum concentrations.

The general aim of the project was to provide a basis for relevant risk assessment in

case of fires in electric vehicles. This was done through literature search, full-scale

vehicle fire tests, battery fire tests and simulations. The gained information will

contribute to more effective firefighting and strengthen the public’s confidence in

electric vehicles. The knowledge is also expected to be relevant for other battery

applications such as stationary energy storage.

Three full-scale vehicle fire tests have been performed. The vehicles comprised of two

battery electric vehicles (BEVs) and one conventional internal combustion engine

vehicle (ICEV). The ICEV and one of the BEVs were of the same vehicle model from the

same manufacturer which enable a good comparison between the powertrains. In

addition, some standalone battery tests have been performed with the purpose to

compare heat release and gas emissions from small-, medium- and large-scale tests

with the same type of battery to analyse the scalability of the measured quantities.

The test results obtained, both from vehicle tests and battery tests, are consistent with

previous data compiled in the literature study, both with regard to heat release and gas

production. Peak heat release rate and total heat release are affected by the fire

scenario and vehicle model, but not significantly by the powertrain. However, HF

together with some specific metals, e.g. Ni, Co, Li and Mn (depending on the battery

cell chemistry), in the smoke exhaust constitute a large difference between electrical

and conventional vehicles. When smoke from a vehicle fire is inhaled however there are

several acute toxic gases present regardless of the type of vehicle burning, e.g. CO, HF,

HCl and SO2. This is based on a comparison between listed health exposure limits and

total quantities measured in vehicle and battery fire tests both in this project and in

previous studies.

The objective with the simulation and modelling efforts in this project was to assess

risks attributed to spreading of toxic gases in confined spaces with limited natural or

mechanical ventilation such as garages. A model including different fire locations and

ventilation scenarios was developed which can be considered a reasonable “worst case”

parking garage. Results and information from the project will be a good basis for risk

assessment and have already increased confidence among rescue services regarding

electrical vehicles. An important condition for society’s shift towards electromobility.

Sammanfattning Uppmärksammade bränder i elfordon riskerar att undergräva implementeringen av dessa fordon och fördröja övergången till förnyelsebara bränslen. Toxiska gaser vid brand i elfordon är oroande för personsäkerheten, och att räddningstjänsten idag tvekar att göra insats och rökdykning då elfordon brinner kan bero på rädsla för exponering av rökgaserna. Vätefluorid är särskilt uppmärksammat bland räddningstjänst på grund av att den kan absorberas genom huden, men resultat från detta projekt visar att de totala mängderna från elfordon troligtvis är lägre än befarat och simuleringarna av brand i ett parkeringsgarage visar också relativt låga maximala koncentrationer. Syftet med projektet var att ge en grund för relevant riskbedömning vid brand i elfordon. Detta har gjorts genom litteraturstudie, brandtest med kompletta fordon, brandtest på batterier och simuleringar. Den höjda kunskapsnivån kommer förhoppningsvis att bidra till effektivare räddningsinsats och stärka allmänhetens tilltro till elfordon. Information från projektet är också relevant för andra batteritillämpningar såsom stationär energilagring. Tre brandprov i full skala har utförts i projektet med två batterielfordon (fullelektriska) och ett konventionellt fordon med förbränningsmotor. Ett av elfordonen var av samma modell och från samma tillverkare som fordonet med förbränningsmotor vilket möjliggör en bra jämförelse mellan drivlinorna. Utöver fordonstesterna har brandprov på fristående batterier utförts i syfte att jämföra värmeproduktion och gasutsläpp från cell, modul och batteripack för att analysera skalbarheten för dessa data. De erhållna resultaten från fordonstester och batteritester överensstämmer med tidigare data som sammanställts i litteraturstudien, både vad gäller värme- och gasproduktion. Maximal värmeeffekt och total värmeproduktion påverkas av brandscenariot och av fordonsmodellen, medan typ av drivlina inte har någon signifikant påverkan. Däremot utgör vätefluorid samt vissa specifika metaller, t.ex. Ni, Co, Li och Mn (beroende på battericellkemi) i rökgaserna en stor skillnad mellan elfordon och konventionella fordon. Vid inandning av rökgaser finns det dock flera akuttoxiska gaser oavsett vilken typ av fordon som brinner, t.ex. CO, HF, HCl och SO2. Detta baseras på jämförelse mellan publicerade hälsogränsvärden och de totala mängder som uppmätts i antingen fordonstester eller batteritester inom projektet eller från de andra tester som sammanställts i litteraturstudien. Målet med simuleringarna i projektet var att bedöma risker som relaterar till spridning av toxiska gaser i trånga utrymmen med begränsad naturlig eller mekanisk ventilation såsom parkeringsgarage. En modell med olika brand- och ventilationsscenarier valdes som kan betraktas som ett rimligt ”värsta fall”. Resultat och information från projektet kommer att ge en bra grund för riskbedömning och har redan lett till ökad trygghet bland räddningspersonal angående elfordon. En viktig förutsättning för samhällets övergång till elfordon.

Introduction While the risks associated with conventional vehicles are well-defined and generally accepted by society; time and education are needed to achieve this comfort level for electric vehicles. Toxic gases, especially from lithium-ion batteries experiencing thermal runaway, have received attention and is cause of great concern. This report addresses that concern through a review of available literature, through fire tests and through simulations. Results are presented and discussed, providing a scientific basis for relevant risk assessment in case of fires in electric vehicles. The report is divided into three major parts: • PART 1 – Literature Review • PART 2 – Fire Tests • PART 3 – Simulations Part 1 presents some statistics on electrical vehicles and fire incidents and an extensive compilation of previous fire tests on electrical vehicles and Li-ion batteries. Both gas and heat release are presented where available and toxic gases are further investigated with regard to health effects. A simple analysis was performed where maximum measured or estimated amounts of gases or compounds from any of the compiled studies were compared with listed health exposure limits, to give an idea of substances that might be worth focusing on. In addition, one section is provided where current rescue tactics and methodology in Sweden are presented together with tests on turnout gear materials and their protection capacity against toxic gases. Presented in part 2 are actual fire tests performed in the project. These include three full-scale vehicle fire tests as well as battery tests from cell to pack level with the purpose to analyse the scalability of the measured quantities. Test results are presented and discussed and put into the context of the findings from the literature study. In the third part, background and definition of the simulation model is described in detail, including model philosophy, geometry, fire definition and ventilation scenarios. The simulations cover an underground parking garage that can be considered a reasonable “worst case” scenario. Results are presented and discussed including a sensitivity analysis.

Arson fires are likely to affect EVs in the same extent as other vehicles. In Sweden there is an increasing trend of arson fires. In ten years, between 2007 and 2017, the number of emergency calls to passenger car fires due to arson increased by over 70 % [13]. Referring to the statistics provided by Tesla, about 15 % of their vehicle fire incidents are caused by arson, structure fires and other things unrelated to the vehicle [8]. 1.2 Fire Tests Fire testing is a critical part in the process of designing for a fire safe environment and will provide useful data. Benchmark tests can provide data for particular structures or materials such as heat release as well as smoke generation and species composition [14, 15], or they may be purpose made to gather information on specific hazards [16, 6, 17, 18]. Information that can be obtained, for example, are the heat and gas release. Both play an important role in estimating tenability as well as the engineering design of structures and their ventilation and evacuation systems. This chapter will review this information in the context of EVs, and their energy storage system. 1.2.1 Full-Scale Electric Vehicle Tests Few full-scale fire test results on electric vehicles are available in literature to date. A total of 4 studies [19, 20, 21, 22] were performed in recent years where modern ICEVs and EVs were considered. A large amount of data can be collected from full-scale fire tests however, ranging from visual burning behaviour to heat release and combustion gas analysis. They are normally easier to understand than small-scale tests. Visual observations can also make the performed measurement results more meaningful and easier to understand. However, these studies may be very expensive. The studies including full-scale fire tests with electric vehicles are listed in Table 1. The ignition source and position are two of the things that vary between the considered studies as it depends on the fire scenarios one is interested in. For the purpose of comparing the fire behaviour and toxic gas emissions between conventional and electric vehicles, a fire scenario that applies to both of them is beneficial, for example an arsonist attempt. Scenarios unique to the vehicle type, such as a localised thermal runaway in the battery pack of an EV, will be interesting in their own, but could complicate direct comparisons to other vehicle types such as ICEVs. For example, the local failure may not propagate from the battery pack and thus not yield a complete loss of the vehicle. This is affected by variables related to the construction, design, failure initiation method, battery cell type etc. These could be better evaluated at the cell, module, or pack level rather than that of the entire vehicle. An external fire, such as that considered by Lam et al. [20], represents a scenario in which a fuel spill spreads underneath the car and ignites. In this case, this fuel spill was modelled by exposing the undercarriage of the vehicle to a 2 MW fire for 30 minutes. Tests performed by the French National Institute for Industrial Environment and Risks (INERIS) [19, 23] considered a lacerated front seat ignited by a propane burner and with windows to the passenger cabin left open. That scenario is more representative of a fire caused by car arsonists. Once this fire was established, it was left to develop freely. Watanabe et al. considered an ignition source placed close to the rear bumper of the vehicle.

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