Fires involving cars, trucks, and other highway vehicles are a common concern for emergency responders. Between 2009 and 2011, there was an average of 187,500 highway vehicle fires per year.1,2 Fire service personnel are accustomed to responding to conventional vehicle (i.e., internal combustion engine [ICE]) fires, and generally receive training on the hazards associated with those vehicles and their subsystems. However, in light of the recent proliferation of electric-drive vehicles (EDVs), a key question for emergency responders is, "What is different with EDVs and what tactical adjustments are required when responding to EDV fires?”

A research program was conducted to develop the technical basis for best practices for emergency response procedures for EDV battery incidents, with consideration for suppression methods and agents, personal protective equipment (PPE), and clean-up/overhaul operations. A key component of this project goal was to conduct full-scale fire testing of large format Lithium-ion (Li-ion) batteries as used in EDVs.

This article summarizes the full scale fire tests performed, reviews the current emergency response tactics, and discusses what, if any, tactical changes relating to emergency response procedures for EDV battery incidents are required.

Project History

In 2009, the National Fire Protection Association (NFPA) began a partnership with the U.S. Department of Energy (DOE) and the automotive industry to develop and implement a comprehensive training program to provide safety training to emergency responders to prepare them for their role in safely handling incidents involving electric drive vehicles (EDVs). This program had a lack of data to draw on to address the potential hazards associated with damaged EDV batteries.

Full-scale fire suppression tests were conducted to collect data and evaluate differences in EDV fires as compared to traditional internal combustion engine (ICE) vehicle fires. In particular, members of the emergency response community had questions regarding: (1) personal protective equipment (PPE); (2) firefighting suppression tactics; and (3) best practices for overhaul and post-fire clean-up.

To answer these questions, the research program they developed included six primary tasks:

  1. A review of industry best practices for ICE and EDV firefighting tactics;
  2. Identification of additional EDV PPE required for emergency responders;
  3. Identification of battery technologies and representative battery types for full-scale fire testing
  4. Development of a full-scale EDV fire testing program;
  5. Full-scale EDV battery fire tests;
  6. A report on final results and summary of best practices for emergency response to incidents involving EDV battery hazards.

For the full text describing each of these tasks and the fire test results, see the NFPA Fire Protection Research Foundation (FPRF) report titled, "Emergency response to incidents involving electric vehicle battery hazards.”3

Industry Best Practices for Firefighting Tactics for Ices and EDVS

Existing guidance4,5,6 describes the potential consequences associated with hazards posed by EDVs and suggests common procedures to protect emergency responders, tow and/or recovery, storage, repair, and salvage personnel after an incident has occurred involving an EDV. Nickel metal hydride (NiMH) and Lithium-ion (Li-ion) batteries used for vehicle propulsion power are the assumed battery systems addressed in these recommended practices and guides.

The recommended practices and guides4,5,6 outline the same basic steps for fire service personnel responding to an EDV fire: identify the vehicle; immobilize the vehicle; disable the vehicle; extrication; extinguishment; and overhaul operations. EDV tactics are generally consistent with current recommendations for ICE tactics; however, first responders must now identify the vehicle prior to immobilizing the vehicle. Other key differences between the two include: the need for copious amounts of water to extinguish an EDV battery fire, the high voltage electrical hazards associated with EDVs, and the recommendation to store all damaged EDVs at least 50 ft (15 m) from other structures or vehicles post-fire.

Identify Battery Types for Full-Scale Testing

Li-ion battery cells arranged in large format Li-ion battery packs are being used to power many EDVs currently in the marketplace. This chemistry is different from previously popular rechargeable battery chemistries (e.g., NiMH,7 nickel cadmium, and lead acid).8 Most notably, Li-ion batteries contain a high energy density coupled with a flammable organic electrolyte rather than an aqueous solution typically employed in previous battery chemistries. This has created a number of new challenges with regard to fire suppression for first responders.

Given the current direction of the automotive industry, Li-ion batteries were chosen for full-scale testing. Batteries were procured from two automobile manufacturers, designated Battery A and Battery B. Both batteries procured were based on a Li-ion technology currently being used in production vehicles. Battery A is a 4.4 kWh battery utilized in a plug-in hybrid electric vehicle (PHEV) that is installed under the rear cargo compartment of the vehicle. The 4.4 kWh battery pack is enclosed in a metal case and is rigidly mounted in the lower portion of the rear cargo area behind the rear seat.

Battery B is a 16 kWh battery that is utilized in an extended range electric vehicle (EREV). The T-shaped battery spans nearly the length of the vehicle from the rear axle to the front axle and is rigidly mounted underneath the vehicle floor pan. A vehicle passenger compartment floor pan separates the battery assembly from the passenger compartment.

Development of a Full-Scale Testing Program For EDV Batteries

The testing program developed included one full-scale heat release rate (HRR) test of a EDV battery (HRR test) and six tests involving suppression of EDV batteries installed within a generic vehicle fire trainer (VFT) prop (fire suppression tests). The fire suppression tests were conducted with and without vehicle interior finishes to demonstrate the impact of the burning battery on the overall vehicle fire, if any.

All tests subjected the batteries to simulated exposure fires originating underneath the battery/ vehicle chassis, and all fire suppression activities were conducted by qualified, active duty firefighters. The simulated exposure fires were produced using an external propane gas burner system that provided a steady and repeatable exposure of approximately 400 kW to the batteries, which is equivalent to a moderate-size gasoline pool fire.

Figure 1: Battery B configuration and burner locations for HRR testing

Gas samples and fire suppression water samples were collected for analysis of potential contaminants (chemical hazards). Voltage and current measurements were recorded at the battery, VFT chassis, and suppression nozzle for analysis of electrical hazards. Instrumentation also monitored fire growth and development, including, but not limited to, HRR, temperature, and heat flux (thermal hazards).

Full-Scale Fire Tests

Full-scale HRR testing was performed at Southwest Research Institute (SwRI) in San Antonio, Texas. The primary objective of the HRR testing was to determine the amount of energy released from the battery alone when ignited by an external ignition source. The full-scale suppression testing was performed at Maryland Fire Research Institute (MFRI) in College Park, Md. The primary objectives of the suppression testing were to evaluate tactics and procedures for first responders, PPE of first responders, adequacy and amount of water as a sole suppression agent, and procedures for overhaul and post-fire clean-up.

HRR Testing

Due to the limited number of EDV batteries provided, only one battery was subjected to HRR testing. Battery B was centered under a 20 ft by 20 ft (6 m by 6 m) hood supported by five stainless steel legs. The leg supports held the battery in place 20 in (500 mm) above the ground to provide a viewing angle to the bottom of the battery during testing. Four propane-fueled burners were placed six inches (150 mm) underneath the battery to provide a steady and repeatable approximate exposure fire to the battery that could be easily controlled (Figure 1).

Temperature and heat flux measurements were recorded on the exterior battery casing, interior battery, and at standoff distances of 5 ft and 10 ft (1.5 m and 3 m) from the battery. Gas samples were collected for analysis for toxic or corrosive compounds. The battery was allowed to burn until completion (i.e., no suppression).

The maximum HRR measured during testing was approximately 700 kW at 17 minutes and 30 seconds into the test. Removing the 400 kW propane burners, the peak heat release the battery attributed to the fire was approximately 300 kW. Once the burners were turned off, around the 20-minute mark, the HRR plateaued as the battery underwent self-sustaining combustion and then slowly decayed (Figure 2).

A total of 14 air samples were collected and analyzed after the test. The results showed only carbon monoxide (CO) and carbon dioxide (CO2) present in significant quantities.

After approximately one hour and 34 minutes of elapsed time, all visible flaming ceased. Thermal images were recorded as the battery cooled and were captured for an additional three hours and 15 minutes. When visible flaming ceased, the observed exterior maximum temperatures were approximately 400 °C. Three hours after all visible flaming ceased, maximum observed temperatures were approximately 150 °C.

Suppression Testing

In lieu of procuring fully intact production vehicles for the full-scale suppression tests, a VFT prop was outfitted with the two different battery assemblies. This allowed for multiple tests of different batteries and battery sizes, dimensions, and installation locations, all while using the same VFT prop. The VFT prop was constructed to resemble a modern EDV both in size and design and opened in the back, similar to a hatchback, to allow for the installation of the batteries (Figure 3).

The batteries were placed on top of a ¼-in (6 mm) steel plate simulating the floor pan of the vehicle. The plate had two portals to allow the burners, positioned six inches (150 mm) below the batteries in the VFT prop, direct access to the bottom of the battery assemblies in their respective locations.

Figure 2: HRR test results with image of fully involved battery at peak HRR

The VFT prop was placed on a concrete burn pad at MFRI in the open air, as would be expected during a normal vehicle fire.

Electrical measurements were recorded to investigate the possibility of electric shock by a firefighter while suppressing an EDV fire, either through direct contact with the VFT prop or by applying a steady water stream to a high-voltage battery. Following a methodology similar to previous studies, the electrical measurements were conducted by measuring both the voltage and current at the fire suppression nozzle and at the body of the chassis in which the battery sat while inside the VFT prop.

Water samples were collected after each test to analyze any potentially harmful byproducts present in the water after being used to suppress an EDV battery fire. In addition, temperature and heat flux measurements were collected during testing until external battery temperatures dropped to near ambient levels. These measurements were collected at similar locations as the previous HRR testing: temperatures were recorded on the external battery casing and at internal battery locations, and heat fluxes were recorded at standoff distances of 5, 15, 20, and 25 ft (1.5, 4.6, 6, and 7.6 m) distances.

Figure 3: VFT: Side profile (top); rear profile with hatchback open (bottom left); and front profile with hood open (bottom right)

Suppression activities were handled by MFRI. No guidance was given to the firefighters regarding what they could and could not do tactically to suppress the fires. They were instructed to fight the fire as they would normally approach a vehicle fire with an offensive attack. Any tactics or modifications to those tactics during the fire tests were at the sole discretion of the MFRI staff and based on their many years of firefighting and training experience. The suppression teams were, however, restricted from using forcible tools to access the VFT prop and the battery for safety reasons and were restricted from fighting the fire from underneath the VFT prop (i.e., shooting water up to the undercarriage of the batteries) due to the presence of the four propane burners.

Water without additives was chosen as the suppression agent for all tests conducted. Water was supplied from a nearby hydrant connected to a municipal water system. A 1.75-in (44.5 mm) diameter hose line fed the nozzle, which discharged approximately 125 gallons of water per minute (7.9 lps) at 75 psi (520 kPa). The water usage was tracked during the tests so that an estimate of the total water used for suppression could be determined. In addition, interviews with firefighters after the tests were conducted to record firsthand observations.

In total, six tests were conducted – three using Battery A (designated A1, A2, and A3) and three using Battery B (designated B1, B2, and B3). For each battery type, two of the tests were performed with the battery pack alone positioned inside the VFT and one test was performed with typical interior finishes/upholstery installed within the VFT in addition to the battery pack.

The following is a summary of test observations/results, firefighter feedback regarding firefighting tactics, the adequacy of water as the lone suppression agent, and observations regarding overhaul and cleanup. Images from Test A3 are provided in Figure 4.


Figure 4: Test A3: Ignition of propane burners (top left); rear involved (top right); initial suppression activities (bottom left); suppression complete (bottom right)


Overall Test Observations and Results

  • At a standoff distance of 5 ft (1.5 m) from the VFT, maximum heat flux measurements for tests without interior finishes were between 2.1 and 3.7 kW/m2. In comparison, maximum heat flux measurements for tests with interior finishes were between 8.1 and 11.9 kW/m2.
  • No projectiles were observed from the battery pack in any of the tests. None of the batteries tested "burst” or "exploded” when ignited externally by an exposure fire.
  • In all tests, "popping” and "arcing” sounds and off-gassing of white smoke consistent with internal battery cells from the battery pack during thermal runaway were observed. In addition, significant plumes of smoke were generated during all tests.
  • Water was used to successfully extinguish all fires during the suppression tests; however, the amount of time required applying water and the total volume of water necessary for extinguishment was significantly larger than what is typically required for extinguishing a traditional ICE vehicle fire.
  • The water samples collected during testing indicated the presence of chloride and fluoride (likely in the form of HF and hydrogen chloride [HCl]). However, the concentration of chloride in the solution was only two to three times greater than normally detected levels, while the concentration of fluoride was more than 100 times greater than normally detected levels. No other corrosive or toxic compounds were identified in the water samples.
  • In all tests, the chassis current was negligible, and the voltage levels at the chassis made it up to the approximately 0.3 or 0.4 V range, which was consistent with pre- and post-measurement tests.
  • In addition, voltage and current levels at the nozzle were negligible while the firefighters applied water to the batteries.
  • Following extinguishment of the batteries, temperatures were monitored after the tests until they returned to near ambient conditions. In one test, the battery reignited 22 hours after the battery was extinguished (i.e., no signs of visible flaming, no signs of significant off-gassing or smoking, and surface temperature readings on the battery were approximately ambient) after it had been removed from the VFT and set aside for storage.

Firefighter Tactics

  • After initial size up and knock-down of the visible flames, suppression activities were halted. In all tests, re-ignition occurred after the initial size up and knock-down of the visible flames. These events likely coincided with thermal runaway at the individual cell level internal to the battery packs. While visible flames from the batteries were clearly extinguished, it was evident that temperatures within the batteries were still high enough that thermal runaway of internal cells was occurring. These re-ignitions repeated until enough water had flowed to sufficiently reduce internal battery temperatures to the point where thermal runaway did not proceed.
  • Once the main battery fire had been controlled, continuous application of water to the battery with the nozzle set on fog, as was performed during several of the tests, further cooled the exterior of the battery, thereby helping to reduce the temperatures of the internal cells. This reduced the likelihood of additional off-gassing of electrolyte and re-ignition of internal battery cells, reducing the overall water quantity needed for suppression.
  • In two tests, the total time for extinguishment exceeded the available air supply for one of the firefighters.
  • Firefighters unanimously reported that access to the "hot spots” or "heat” was a significant barrier to extinguishing efforts. Firefighters were unable to get water where the heat and flames were originating to quickly extinguish the fire. In these tests, access to the batteries was much easier than what firefighters experience in real world vehicle fire scenarios, as the batteries were placed inside a VFT prop and not installed within an actual vehicle. It can be assumed that access issues experienced by firefighters during this test program will be magnified during real-world vehicle fire scenarios.



Water as Extinguishing Agent

  • Water was used to successfully extinguish all fires during the suppression tests.
  • Overall, EDV battery fires require significantly longer active suppression operations (up to 50 minutes in this test program) o battle re-ignitions and significantly larger total volumes of water — up to 2,600 gallons (approximately 10,000 liters) of water — than traditional ICE vehicle fires. This increase is attributed to the need for water to not only extinguish the visible flames, but to cool the battery component to the point where thermal runaway will not continue.

The authors would like to thank the SwRI and MFRI crews for their efforts in setting up, instrumenting, and conducting the HRR and full-scale fire suppression tests and providing access to the data and analysis gathered during testing.

The authors further thank Casey Grant and Kathleen Almand of Fire Protection Research Foundation; DOE/INL; DOT/NHTSA; Alliance of Automobile Manufacturers; Battery Technology Advisory Panel; Emergency Responder Advisory Panel; Project Technical Panel for Project on EV Battery Hazards; and Keith Wilson of Society of Automotive Engineers.

R. Thomas Long, Jr., and Andrew F. Blum are with Exponent, Inc.


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