Are Battery Electric Trucks A Greater Fire Risk than Internal Combustion Engines?
This edition explores the fire risk profile of electric trucks and electric vehicles
The first (as far as I’m aware) fire on a Tesla Semi happened on the Californian I-80 after the truck hit a roadside post and subsequently a tree as it veered off road. The vehicle caught fire following the crash, required 190,000 litres of water and 10 hours to extinguish and closed both travelling directions of the I-80 for approximately 15 hours. This event brought back questions on the risk profile of electric trucks and electric vehicles as a whole, questions that haven’t really been answered well so far.
The Tesla Semi fire is one of few relatively high profile incidents involving battery electric trucks. Another one involved a converted battery electric truck from the Australian company Janus that caught fire on the West Gate Highway in Melbourne in November 2023. According to EV FireSafe, as of March 2024, there were 10 “documented fires” in electric trucks.
This safety record looks decent, however two questions that remain and are persistently unanswered:
Are electric trucks (and vehicles for that matter) are more likely to spontaneously combust while in operation or stationary (including while charging) than internal combustion counterparts and
Is the vehicle damage greater, similar or smaller in case of incidents for electric trucks as opposed to traditional vehicles;
Ultimately these two questions are about risk and risk management. Would a truck operator be introducing additional risk into its business by transitioning to electric trucks due to spontaneous combustion and would incidents take electric trucks out of service for longer than in the case of traditional vehicles.
What Do the Data on EV Fire Risk Say?
It’s impossible to do statistical analysis on 10 truck incidents. However, there is significantly more data available on electric passenger vehicles and their fire risk. In fact, the data there is rather clear. EVs are 29 times less likely to catch fire than internal combustion engine vehicles according to a 2022 Swedish MSB study (a study cited by many, however, the link provided by publications citing it was broken). Salary sacrifice company Tusker also corroborated the Swedish study findings and stated that not one of the 30,000 EVs in their fleet had caught fire as of February 2024. A 2024 AutoinsuranceEZ study in the US also found that EVs were far less likely to catch fire, with only 25 fires every 100,000 vehicles sold for EVs compared to 1529 fires per 100,000 vehicles for internal combustion vehicles. The statistics are therefore quite clear, that EVs are significantly less fire-prone than internal combustion vehicles.
However, something did catch my eye. Hybrids are more than twice as likely to catch fire than internal combustion engine vehicles and 140 times more likely to catch fire than electric vehicles! So I dug a bit deeper.
This finding was quite surprising and apparently it surprised others as well. In response to this, Professor Paul Christensen from the School of Engineering at Newcastle University in England said for Popular science that he was surprised to hear that hybrids topped the charts in that study when it comes to fires, but not surprised to see EVs at the bottom. AutoinsuranceEZ attributed the high fire rate of hybrid vehicles to the “combination of technologies under the hood”.
As for the report from AutoinsuranceEZ, Christensen says he was surprised to hear that hybrids topped the charts in that study when it comes to fires, but not surprised to see EVs at the bottom [emphasis added]. Laura Adams, a senior analyst with AutoinsuranceEZ, attributes the relatively high rate of fires they saw in hybrid vehicles to the “combination of technologies under the hood” that those types of cars have [emphasis added]. As with all studies, this represents just one set of findings at one point in time—expect more research on the topic to surface in the future, especially as EVs continue to penetrate the market.
The combination of technologies under the hood! So, take one ultra-safe technology (EVs) and combine it with a not-so-safe technology (ICE) and the result is a much more unsafe technology?! What surpised me most was how little time was spent on such an important finding. Hybrids are more dangerous than ICEs? Since when? Why isn’t this making the news? And more importantly, why is the only explanation available the “combination of technologies under the hood”?
The AutoinsuranceEZ report did investigate fire-related recalls for various types of vehicles. The interesting finding is that the fire-risk for both hybrid and electric vehicles was the battery. This is again somewhat surprising. EVs have 60-120 kWh batteries while most hybrids have significantly smaller batteries. The best selling Toyota Prius is equipped with a 13.6 kWh Li-Ion battery on the third generation model. Batteries are a (main?) reason for fire-related recalls in both hybrids and EVs and hybrids fire have a 140-times higher fire risk despite operating similar battery chemistries?
What Do the Data on EV Fire Risk FAIL to say?
Aggregate data such as the one in the Swedish study, Tusker or AutoinsuranceEZ present a coherent story. However, data aggregation fails to answer more specific, yet extremely relevant questions, mainly:
What is the impact of vehicle age?
What is the key reason the fire started?
What are the differences in fire management requirements?
Partial answers to these questions can be found dispersed across the three reports.
Vehicle Age
For instance, the MotorTrend, while discussing the Swedish report, mentions that 77% of ICE vehicle fires occurred in vehicles 10 years or older. However, their sample included extremely few EVs that were 10 years or older (of the 3,384 fires in Swedish ICE vehicles, 2,605 occurred in vehicles older than 10 years). A reasonable conclusion would be that newer vehicles are less likely to catch fire than older ones.
In e most likely to catch fire and the risk of fire increases the older a car gets. A total of 77 percent of all car fires that occurred in 2017 involved vehicles made in 2007 or earlier, so those at least 10 years old or older [emphasis added]. The original Tesla Roadster didn't come out until 2008, and only 2,500 of those were built. The first mass-market EV, the Nissan Leaf, wasn't released until 2010. Only the earliest modern EVs, of which very few were sold, are 10 years old today. The NFPA report cites worn-out parts and deferred maintenance as the likely cause of increased fire danger for older cars.
(Source: https://www.motortrend.com/features/you-are-wrong-about-ev-fires/)
Vehicle age may matter as it is often correlated with battery age. Hybrids have been on the market for longer than EVs (hence some are older than 10 years) and have seen a far more widespread adoption. The expectation being that as vehicles and batteries age, their fire risk may also increase. In my view, this is perhaps one of the few explanations as to why hybrids have higher fire risks than ICE vehicles. It may also be one of the reasons why EVs have such a favorable fire-safety profile - they’re not that old, not that worn, have not been exposed to the elements as much.
Fire Cause
The reason for the fire also matters. Tusker mentioned that none of the 30,000 EVs in their fleet had caught fire. However, 65% of the fires (presumably in the remainder of their fleet, i.e., ICE vehicles) had been caused by arson. Others by smoking and others as collateral damage. The only reasonable conclusion we can draw from this statement is that owning an EV is correlated with a smaller probability of arson! This says very little about the fire-safety profile of EVs.
Acknowledging that some fires are inevitable – not least due to arson, which is the cause of around 65% of car fires each year – Tusker’s managing director Kit Wisdom told Fleet News: “We had two or three fires because somebody was smoking carelessly in a vehicle. Another one resulted out of the Luton Airport Blaze, one of our vehicles was parked there and that was destroyed as a result of that.
(Source: https://www.fleetnews.co.uk/news/tusker-fleet-data-reveals-the-truth-about-ev-fires)
Vehicle Fire Management
At least with regards to vehicle fire management there is some level of agreement that EV fires are harder to put out, typically require more water (~14,000 litres of water) and risk reignition. The guidance some fire departments have issued is to let EV fires burn if there’s no risk of the fire spreading. Based on this guidance, once an EV is on fire, the chance that there is anything recoverable drops to zero.
In the meantime, many fire departments are issuing much simpler guidance: If an EV battery is on fire and there's minimal risk of the fire spreading to other vehicles, structures, or the environment, just let it burn itself out. The International Association of Fire Chiefs recommends "consideration and tactics [that] may be categorized in offensive or defensive mode. This may be based on exposures and the extent of fire which may include actions to let the vehicle burn." The city of Phoenix, Arizona, suggests in its official handbook "once life safety has been addressed, fire companies should determine if they should suppress the fire or simply allow the vehicle to burn … once the batteries have gone into thermal runaway, we understand that the vehicle is most likely a total loss. Control efforts must consider life safety, property conservation, exposure protection, environmental protection, and firefighter safety."
(Source: https://www.motortrend.com/features/you-are-wrong-about-ev-fires/)
So What Is the Fire Risk Profile of Electric Trucks and Electric Vehicles?
The key questions I sought to find answers to were:
Are electric trucks (and vehicles for that matter) are more likely to spontaneously combust while in operation or stationary (including while charging) than internal combustion counterparts and
Is the vehicle damage greater, similar or smaller in case of incidents for electric trucks as opposed to traditional vehicles;
There’s little evidence that electric trucks are more fire-prone than internal combustion peers. That being said, there’s little evidence that electric trucks are less fire-prone than internal combustion engines as well. Absence of evidence isn’t evidence of absence. This inconclusiveness may well be an artifact of amount of trucks on the road (spoiler alert, there’s not that many). What is becoming increasingly clear is that should a fire start, for almost any reason, there’s a high likelihood that the vehicle will be written off. That may be an issue considering the lead time for manufacturing and acquiring these trucks.
There are significantly more electric vehicles on the roads that provide a bigger dataset (not necessarily a richer one). The three studies I’ve looked at (if there are others please let me know) support the thesis that the fire risk profile of electric vehicles is substantially lower than that of internal combustion engines. The data aggregates however a heterogeneous internal combustion engine fleet (of various ages, maintenance conditions) and a diversity of fire triggers (including a substantial proportion of arson) with a relatively homogeneous electric vehicle fleet that is relatively newer and perhaps, attracts a different type of clientele (i.e., fewer people owning electric vehicles that live in areas where arson may be considered an enjoyable Friday night activity).
Perhaps the finding that hybrid vehicles are twice more prone to fires than internal combustion engine vehicles, finding that is as baffling as unexplained is the most surprising as much as it is unexpected. This is extremely interesting and at the same time may be worrying news for some countries where hybrids sales have gone through the roof, but more on that in the next post.