Electric vehicles (EVs) have drastically changed the global car industry over the last decade thanks to the rapid development of high-energy Li-ion battery technology. However, it is these same batteries that have created a safety concern for EVs. With several fire incidents hitting the headlines over the past years, we look at the risks and hazards associated with battery-powered EVs and how they are impacting the adoption of EVs.
A Recent History of EV Fires
It wasn’t long ago that people doubted whether EVs could become mainstream. Fast forward to 2021: the Biden administration is pushing for half of all car sales to be EVs by 2030. However, public opinion remains divided. While the cars have obvious environmental benefits, they don’t have the same long-term safety data as internal combustion engine (ICE) vehicles.
Several major fires have shaped public opinion so far.
November 2011: Chevrolet Volt
After safety testing by the National Highway and Traffic Safety Administration (NHTSA) three weeks prior, the car suddenly started to smolder and burn. Investigators determined the battery as the source of the fire.
May 2012: BYD e6
Following a crash in Shenzhen, China, an EV hit a tree and caught fire, killing all three of its occupants. The fire was caused by short-circuiting of high-voltage lines, which ignited combustible material in the vehicle.
October 2012: Fisker Karma
A fleet of 16 Fisker Karma EVs were covered by over five feet of seawater by Superstorm Sandy for several hours. The saltwater left corrosive residue on the control unit, causing a short circuit.
October 2013: Tesla Model S
A car caught fire in Seattle when it was accidentally driven over some metal that punctured the undercarriage and penetrated the battery pack. Within 30 minutes, the car was in flames.
October 2017: Tesla Model S
A fire initiated in the battery at the front of a vehicle in Arlberg, Austria, after a collision with a concrete wall. The severe fire produced toxic gases and required large amounts of water to cool down the battery.
August 2018: LiIfan 650
A car in Guangzhou, China, spontaneously combusted after a heavy rainstorm. Water leaking into the battery pack, creating a short circuit and leading to thermal runaway.
July 2021: Chevrolet Bolt
An EV parked in a private driveway in Thetford, Vermont, burst into flames while being charged. The fire within the passenger compartment was reportedly caused by an undetermined electrical system failure.
EV Fires vs. ICE Vehicle Fires
There have been many EV incidents in the past few years. However, while receiving less attention, there have also been many ICE vehicle fires. One study by the London Fire Brigade found that in 2019, there was an incident rate of 0.04% for petrol and diesel car fires compared to 0.1% for EV fires. Meanwhile, reports from Tesla, incorporating data from the National Fire Protection Association and US Department of Transportation, suggest that ICEs catch fire at a vastly higher rate than EVs: one fire for every 205 million miles traveled compared with one for every 19 million miles traveled in a Tesla.
Regardless of the frequency, a major concern is the cause of these fires. Many EV fires occur as the battery slowly degrades over time after an incident. It’s not a problem confined to cars; when chemical energy build in a small space, fire or explosions are a risk. But it’s worth noting that the best Li-ion batteries only hold two percent of the energy compared to gasoline. However, once a battery fire gets started, it can be harder to put out than a gasoline fire, taking up to 24 hours to fully extinguish.
Under the hood of the Chevrolet Bolt. Image used courtesy of Inside EVs
Opinions have been skewed significantly by General Motors’ recent recall of its Chevrolet Bolt EV, covering all 2019–2022 models. The recall is due to rare instances of manufacturing defects in the batteries, which have caused recent EV fires. In a prior investigation of Chevy Volt fires, the NHTSA reported that it did not believe that Chevrolet Volts or other EVs pose a greater risk of fire than ICE vehicles. The administration hopes this assurance will build customer confidence, but this recall could well be a step back for overall EV adoption.
What Systems Are in Place to Prevent Fires?
EV fires are caused in three main ways:
- Overcharging faults or insecure charging stations
- Traffic accidents
- Reignition after the initial damage
However, there are systems in place to prevent these fires from happening. Internal firewalls built into the battery pack structure aim to stop the fire from entering the passenger compartment and prevent mishaps in one module from spreading to another. The battery packs are also cooled with a glycol-based chemical cocktail to remove excess heat. One of the biggest safety measures is the battery management system (BMS).
Infineon says their product offerings satisfy the many functions of a BMS. Image used courtesy of Infineon
The BMS within EVs offer a level of safety not found in ICE vehicles. They control and optimize the performance of multiple battery modules. This gives the car the power to disconnect systems, improve performance, and identify faults.
The battery system is kept within operational limits via bus communication, ensuring the voltage, current, and temperature profiles comply with safety procedure requirements. This should stop over- and under-charging issues and can alert the navigation systems, as seen in the Tesla 2013 fire. While these systems clearly make a difference, some studies suggest that there are gaps within the current standards for BMS safety and that a technical review is required.
Safety Remains a Pressing Concern
Some fire risk relating to EVs is inevitable due to high demands in driving performance and charging speeds. As the market share increases, reports of these novel fires are going to become more common. However, studies show that EV fires are comparable to fossil-fueled fires, and the combustion potential is, in fact, lower.
Still, safety protocols for electric vehicles are clearly an industry concern. EV engineering will be pivotal as collaborations and future research drive the market forward.
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