Let’s talk EV fires

We’ve already covered several reasons why consumers put off the conversion to electric vehicles. Major factors include dreaded range anxiety or the misinformed belief that electric vehicles are always more expensive than internal combustion engines. These concerns are alleviated easily enough when the available data is examined, often reorienting EVs as a viable— or even preferable— choice. There is, however, another shadowy figure causing some reserve for auto aficionados looking to purchase the machine of their dreams: a looming threat of battery fires.

Several recent, high-profile EV fires have found quick purchase in auto-industry headlines, scaring some consumers into reconsidering their decision to convert to an EV at the time of their next purchase. A Tesla that ignited last month in a wreckage yard in Sacramento required firefighters to entirely submerge the car in water after earlier extinguishment efforts failed and the fire kept reigniting. Last year, GM issued a stop-sale recall on Chevrolet Bolt EVs (2022) and Bolt EUVs (2022) due to manufacturing defects that posed fire risks in some of the lithium-ion battery cells. While a largely overblown problem, there remains a lot of education and myth-busting needed to alleviate consumer worries and reassure potential buyers.

While these fires can certainly seem like a good enough reason to forgo the cost-saving shift to electric, data compiled by various sources over the last several years reveals the issue of EV battery fires to be more of a non-issue than anything else. A study released earlier this year analyzed vehicle fires by their fuel sources, separating internal combustion engine vehicles, hybrids and EVs. Hybrids were found to be the most frequent auto type for vehicle fires, followed by gasoline engines and then EVs. There were 3,474.5 fires per 100,000 hybrid vehicle sales, 1,529.9 fires per 100,000 ICEV sales, and a measly 25.1 fires per 100,000 EV sales. EVs made up just 52 of the vehicle fires in 2021 while ICEVs comprised a whopping 199, 533 fires by comparison. While the total number of vehicle fires is obviously impacted by the substantially larger fleet of ICEVs, the overall fire rate per vehicles sold illustrates just how large the fire risk discrepancy is between fuel types.

Even though hard to put-out fires remain the main safety issue most people associate with EVs, there are additional safety elements at play that impact statistics favoring EVs. The Insurance Institute for Highway Safety (IIHS), in a partnership with The Highway Loss Data Institute (HLDI), conducted a study finding that “the frequency of injury claims by drivers and passengers of EVs was more than 40% lower than for identical conventional models during the eight years between 2011-2019.” While this statistic doesn’t address fire claims specifically, it does highlight an important facet of any EV: they aren’t just safer due to decreased fire risk, they’re also safer more generally. Likewise, the IIHS found several EV models to be top-performers in crash-testing and crash prevention features, attributing part of the safety findings to the fact that “…the large batteries used in both types of vehicles [hybrids and EVs] make[s] them substantially heavier than their conventional counterparts.” The Alternative Fuels Data Center, run by the Department of Energy, addresses this heavier weight as a possible explanation for the reduction in injuries and fires in EV-involved crashes: “All-electric vehicles tend to have a lower center of gravity than conventional vehicles, making them more stable and less likely to roll over.”

Let’s get back to the fire issue: The National Fire Protection Association, which conducts analysis on all recorded fires in the United States every year, also offers compelling evidence in their 2020 vehicle fire report. When comparing vehicle fire statistics for the year, the report found that “roughly two-thirds of the car fire deaths specifically and highway vehicle deaths overall in the US during 2013-2017 resulted from fires that began with a flammable or combustible liquid or gas. Gasoline was first ignited in more than half of all highway vehicle fire deaths.” Considering this study’s findings, the threat of battery fires seems less heinous: without the presence of gasoline, fire risk actually goes down overall, even if lithium-ion battery fires do burn hotter and are more difficult to extinguish. Unless you often find yourself in the presence of a burning car, your risk of vehicle fire actually goes down when you choose to drive an EV.

Unfortunately, EV battery fires have a unique characteristic that causes the infernos to be particularly devastating when they do occur: thermal runaway. This volatile phenomenon occurs “when a cell, or area within the cell, achieves elevated temperatures due to thermal failure, mechanical failure, internal/external short circuiting, and electrochemical abuse… [until] Eventually, the self-heating rate of the cell is greater than the rate at which heat can be dissipated to the surroundings…and stability is ultimately lost,” according to Cambridge EnerTech. This “loss in stability” ultimately “results in all remaining thermal and electrochemical energy being released to its surroundings.” The translated version for the non-materials scientists among us: When lithium-ion battery cells are damaged in certain ways they generate heat that, after a certain point, results in an explosive fire that often re-ignites after extinction due to self-heating properties of the materials.

Unlike ICE fires, lithium-ion battery fires are much harder to render inert. This self-heating exothermic reaction (heat releasing) and any resulting exothermic fire or explosion feed off of one another, causing an exponential rise in temperature― and there you have thermal runaway off to the races. Thermal runaway in one cell, however, is particularly dangerous because of the cell’s proximity to other, similarly potentially volatile cells. An electric vehicle’s battery is really just an Energy Storage System (ESS), where hundreds to thousands of cells (about 7-8,000 in Tesla models) are grouped closely together. The interior of each small, several inch-long cell is where chemical potential energy can be stored, similar to gasoline being the liquid form of chemical potential energy that your car converts whenever it runs. When an EV is plugged into a charging station, electricity is stored as energy in every cell in the ESS, which is then converted back to electricity when the EV is running.

The energy stored in the batteries can also be thought of as potential heat, which is where the difference between the two vehicle systems becomes more apparent: gasoline doesn’t have the same self-heating properties at high temperatures that lithium-ion batteries demonstrate, which means that once an ICE fire is adequately extinguished and cooled there isn’t enough energy to initiate another fire― unlike lithium-ion cells under certain circumstances. When a cell has a defect that causes thermal runaway to occur, the explosion in one cell could trigger a thermal runaway event in an adjacent cell, and propagation occurs. Propagation induces the type of fire that makes headlines: long-lasting, extremely hot, and nearly impossible to do anything with except wait for total burn-out. As of now, there’s a limited number of ways to adequately cool a highly-compromised pack undergoing a thermal runaway event enough so that auto-ignition doesn’t reoccur after extinguishment, sometimes even up to 24 hours later. However, these suppression processes are being improved as we speak and firefighters across the U.S. are being trained on battery-fire extinguishing techniques every day. Software used in EVs’ battery management systems (BMS) is similarly being developed and improved in order to implement safety features that detect and prevent this process from occurring.

That’s the science behind EV battery fires; now it’s time to dispel the unfounded fear. While these fires can certainly seem like a good enough reason to forgo the cost-saving shift to electric, data compiled by various sources over the last several years reveals the issue of EV battery fires to be more of a non-issue than anything else. When comparing ICE vehicle fires to EV fires, The National Fire Protection Association’s report addressed the issue of thermal runaway by stating that “it takes some time for enough energy to accumulate to trigger thermal runaway in a battery…this makes them different from ICEVs, which can be quickly ignited by a spark or flame.” This is a pragmatic view to the issue of battery fires: yes, when they do happen, they can be pretty bad. Fortunately, a lot of things need to happen in a specific order for the entirety of the ESS to ignite and cause a thermal runaway issue that results in a large fire. When we take a holistic view of the ongoing research, there’s an argument that EVs are actually safer to drive than an internal combustion engine vehicle: with a lower center of gravity, roll-over is less of a threat, which also means less of a threat of compromised batteries in the case of a crash. A heavier weight means collisions are less worrisome, and provides a similar protection to the integrity of the ESS as a lower center of gravity. Lack of combustible gasoline substantially reduces the risk of fire overall, especially in the case of structural damage sustained during a collision. Soft and hardware safety technologies are only going to improve as the industry grows, which offers a possible reduction in the already low fire and accident rates of electric vehicles. Despite the sensationalized headlines, it seems that EVs are a sensible, safe choice for the average consumer.

There’s still a lot of data to be gathered and analyzed as EVs become an increasingly larger part of the light-duty fleet, but early analysis as shown above reveals the headline-grabbing issue of fire to be overblown and misinformative. As the electric vehicle industry continues to grow, it’s important that consumers stay informed about the actual— and not just perceived— safety of the vehicles they choose for their daily lives. Electric vehicles and their associated infrastructure are disruptive to long-dominant industry players, and reporting about emerging EV issues often takes the form of fear and exaggeration.