Electric cars on fire have made headlines all over the world as the new technology reaches its way to mainstream consumers. But how often does this really happen compared to gasoline or diesel vehicles? And what causes it?
Today we'll explain the numbers and science behind these electric vehicle fires, to give you a clear picture beyond the headlines and Twitter arguments.
What causes an EV to catch fire
Electric vehicles (EV's), generally use lithium-ion batteries. These are the same type of batteries found in your phone, camera, or laptop - just much larger.
Batteries can catch fire because of production issues and external damage. As battery manufacturers aim to develop ever lighter, cheaper and more powerful batteries, safety can sometimes suffer. The global battery industry is highly competitive, and in an effort to balance improvements with safety, mistakes can be made in the design or production of the batteries to make them more likely to catch fire.
External factors like high heat, pressure, and punctures from damage, can cause or help cause fires.
One of the three largest battery producers, LG Chem, recently had a manufacturing issue that resulted in 82,000 Hyundai vehicles being recalled. GM reported that another 140,000 Chevrolet Bolt's were recalled, which used the same batteries. The manufacturing defect was a folded anode and folded separator, that could result in a short circuit and fire.
A short circuit is one the main causes of battery fires. In a nutshell, it's when two parts of an electrical circuit touch by accident. The electrical current chooses the path of least resistance, the short cut, and so a very high amount of current gets concentrated in a short amount of time - which can cause a fire.
A short circuit can cause a fire by itself, but more often can set in motion a process called 'thermal runaway', a domino effect of sorts.
Thermal runaway is a negative chain reaction of overheating, with three different phases in terms of scale.
In phase 1 a single battery cell fails or short circuits, and heats up more than it can cool off. This can spread to other cells, causing it to happen to a battery-pack, in phase two. In the last phase, the entire battery made up of many battery-packs can be affected, potentially causing large damage to the vehicle.
There are many safety mechanisms and standards for all three phases to make sure thermal runaway doesn't spread. From insulation, to smart-controls, to safety release valves. But in a perfect storm, it can still happen.
Now you're up to speed on the summarized version of 'why'. Next we'll talk numbers, and put them into perspective.
What causes an ICE to catch fire
Just like EV's, ICE vehicles (internal combustion engines) can have design flaws that cause a production to have to be recalled. Last year, Nissan recalled almost 700,000 gasoline vehicles for an issue that could cause power-controls to misfunction, and potentially cause a fire.
ICE vehicles generally catch fire because of a combination of two factors: damaged electrical wiring, and leaking fluids.
Cars are full of electrical wiring, necessary for starting the car, climate control, or power steering. Damaged or faulty electrical wiring can cause sparks that can ignite a fire. But sparks aren't enough, you also need something to catch fire.
ICE cars are also full of flammable liquids. The most obvious, and most flammable, is the gasoline itself.
But there is also engine oil, which can catch fire - or overheating of the engine can cause hot oil to spill out of its container, potentially damaging or setting on fire other pieces of the car.
Lastly, all of the above can be caused by a crash damaging the vehicle, and/or adding sparks to the mix.
How many EV's catch fire / How many ICE's catch fire
Understanding the causes of fire in the different types of cars, what's important now is a comparative statistical study into the prevalence of fires among electric, and traditional ICE cars.
Because of the media attention around electric vehicles catching fire, Tesla has start publishing their own data compared to the US average, in their annual impact report.
"When the media reports a story about a vehicle fire, it is usually reporting on an EV fire. This is likely a result of the novelty of EV technology, rather than the prevalence of EV-related fires compared to ICE vehicle-related fires. The reality is, when compared to Tesla vehicles, ICE vehicles catch fire at a vastly higher rate.
From 2012 to 2020, there has been approximately one Tesla vehicle fire for every 205 million miles traveled. By comparison, data from the National Fire Protection Association (NFPA) and U.S. Department of Transportation show that in the U.S. there is one vehicle fire for every 19 million miles traveled."
According to these numbers, the average car in the US is 10 times as likely to catch fire as a Tesla, though Tesla does have the advantage of having newer vehicles compared to the US national average.
Other research by AutoinsuranceEZ, using data from the National Transportation Safety Board and the Bureau of Transportation, points to an even greater divergence. In their data, per 100,000 vehicles sold, 25 electric vehicles caught fire compared to 1529 gasoline vehicles. Thus the same trend is observed of EV's being a lot less prone to fires, but a more interesting part of their data is the number of hybrid (electric + ICE engine) vehicles; of which 3500 go up in flames per 100,000 sold - making the combination of a traditional combustion engine plus heavy lithium battery packs the most vulnerable combination.
In Europe, electric vehicles are less likely to catch fire too.
Norway has the highest percentage of passenger electric vehicles of any country, and is thus a good sample to draw from. In this country, research from 2014-2016 points to electric vehicles making up roughly 3% of vehicle fires, against a total penetration of the market of over 10%. These numbers include hybrid vehicles, it's thus likely that the fire risk would be significantly worse if measuring only pure battery EV's.
In The Netherlands, where electric cars + hybrids make up 4,3%, 1,25% of car fires involved an electric car - of which around half was due to the battery pack, and the other half due to charging infrastructure or the internal combustion engine in hybrids.
Why EV fires are difficult to put out
While the data supports the case that battery electric vehicles are less of a fire risk than internal combustion engines, there is one important negative factor for batteries; once they do set fire, they are incredibly hard to extinguish.
For gasoline vehicles, a fire ignites fast but is over relatively quickly once the main propellant (gasoline) is burned up. For EV's it is a different story however. Their battery packs can get ignited only partly, with other parts of the battery still retaining 'stranded energy' that can reignite hours later - and even multiple times. Similar to the causes explained earlier, this reignition can happen either through thermal runaway, or mechanical reignition in the form of a short circuit. In one example in Fort Lauderdale, an EV fire that was put out reignited twice when it was being loaded into a truck, and once more when chains to keep the vehicle in place touched the battery.
Electric vehicles can burn hotter, longer, and can reignite. They certainly require fire departments around the world to adapt to new approaches and tools. Many of these issues can be reduced by improved battery design and safety measures, preventive heat detection, and better equipped emergency services.
Do electric cars catch fire?
Yes, but so does every vehicle storing large amounts of energy. Electric vehicles though, are less likely to catch fire than their ICE counterparts.
The reality is that electric vehicles are the car of the future - the EU now proposing to ban all fossil-fuel car sales by 2035 - and the more intense fires that batteries are at risk of need to be prepared for and handled well.
This might take some getting used to, but will ultimately lead to broad social gains in the form of reduced pollution, higher energy efficiency, and safer cars.
The total cost of ownership for most EV's in Europe is already lower than their fossil fuel counterparts, the only thing holding back uptake is the higher initial investment, lacking infrastructure, and general knowledge about these numbers.
The EU is currently debating a proposal that would ban the purchase of new gasoline and diesel cars by 2035. Other European countries are pushing an even earlier deadline of 2030.
According to the National Transportation Safety board, in 2020 50% of US fire brigades said they had no specific strategy for EV fires. As EV uptake increases year on year, this is an important bottleneck to address - an emergency service unequipped to handle electric vehicles will harm the public's perception and adoption of EV's.
It's of high importance that fire fighters and first responders know how to handle this new threat - and are able to identify vehicles as being EV's. Which isn't always easy now that electric vehicles increasingly look identical to ICE vehicles.
"There is no denying that EVs are accompanied by new risks, but there is no evidence that points at EVs being less safe than conventional vehicles. Automotive LIBs are also inherently safer than those used for small consumer applications. This is achieved through chemistry, design and high-quality Battery Management System (BMS). However, failures will happen and will become more common with increased number of EVs."