Safety of an electric car in practice

Sep 05, 2023

With the increasing number of electric cars on the road, some concerns have arisen regarding their safety. Are electric cars crashworthy? And what about the risk of battery fires? Numerous independent tests indicate that electric cars are at least as collision resistant as combustion engine cars. Moreover, in terms of fire safety, electric cars perform better than gasoline and diesel cars.

Vehicle safety fundamentally revolves around the vehicle itself, the road, and the driver. All three factors need to interact to ensure safety on the road. The past decade has seen tremendous advancements in the technological development of passenger vehicles. Crash safety, or passive safety, has improved significantly through the implementation of deformation zones that effectively absorb forces during a collision, while minimizing damage to the car's cabin space.
Active safety has also seen remarkable enhancements, focusing on preventing accidents from occurring. Safety systems like ESC (Electronic Stability Control) or ESP (Electronic Stability Program), along with anti-lock braking systems (ABS), are virtually standard in all new cars sold in Sweden today. Combined with technological solutions such as airbags, the risk of fatality in a modern car collision has decreased by up to 90 percent compared to a car from the early 80s. The risk of sustaining disabling injuries has also decreased by 25 percent, according to statistics from Swedish insurance companies.
Crash safety equivalent to conventional cars
Collision tests conducted by DEKRA and Euro NCAP demonstrate that electric cars maintain a crash safety standard equivalent to conventional combustion engine cars. In 2019, DEKRA carried out a series of crash tests on two different electric car models, the Renault Zoe and Nissan Leaf, revealing that these cars sustained similar damages to combustion engine cars in the same type of tests. Although the electric cars' batteries deformed during the crash tests, they did not catch fire, primarily due to the automatic disconnection of the high-voltage systems.
Another crucial aspect regarding road safety is a car's susceptibility to tipping over during maneuvers, such as sudden swerves. The distribution of weight in an electric car significantly differs from that in a combustion engine car, as the battery packs are positioned at the bottom and centered on the car's chassis. This design, combined with the additional weight contributed by the batteries, results in electric cars being generally more stable if the driver needs to make a sudden turn or brake abruptly.
Advanced battery protection boosts fire safety
A modern electric car is never charged to 100 percent, and it charges at a reduced rate as the battery approaches full capacity. The built-in systems of electric cars are inherently very safe, and most significant risks are often linked to external factors. To minimize the risk of fires, the single most important measure for an electric car owner is to have a charging station installed.
In many new electric cars, the battery is protected within a shock-resistant enclosure or frame, designed to prevent damage or combustion in the event of an accident. Since lithium-ion batteries are sensitive to significant temperature variations, especially during charging, many modern electric cars are equipped with built-in temperature control systems, often with liquid-cooled channels. This allows the battery to maintain an optimal temperature during use, charging, and storage.
In an electric car, the battery is connected to the electric motor via a secure contact that is switched on and off by a fuse attached to the battery box. This fuse, often referred to as a "pyrofuse," helps isolate the battery box from the rest of the car in case of a disturbance. For instance, in the event of a vehicle collision, the fuse disconnects the cable connection to the high-voltage battery using a mini-explosion, immediately cutting off the power circulation in the car. This also eliminates the risk of electric shocks or fires during potential rescue operations.
Battery fires during "thermal runaway"
When it comes to fire incidents in combustion engine cars, especially gasoline cars, they ignite almost immediately and spread rapidly. In the case of fires in electric cars, it typically takes some time to reach the required temperature for a lithium-ion battery to catch fire.
If the battery in an electric car is heated by an external fire, there is a risk of "thermal runaway," where the temperature inside the battery cells increases uncontrollably. This triggers a chain reaction between the battery cells, releasing a large amount of energy that can lead to the battery catching fire. However, it is rare for thermal runaway to occur in an electric car battery because it requires mechanical impact or prolonged external flames.
The gases produced during a fire in a lithium-ion battery are primarily carbon monoxide and carbon dioxide, the same types of gases found in the exhaust emissions of conventional combustion engine cars. There is also a formation of toxic hydrogen fluoride, but at a limited level. However, for emergency responders, it is an important occupational safety issue because their methods and firefighting approaches differ depending on whether it's a fossil-fueled car or an electric car that needs to be managed in the event of an accident.
How common are fires in electric cars?
In 2022, a total of just over 3,400 passenger cars caught fire in Sweden, according to MSB, “Myndigheten för samhällsskydd och beredskap”. Out of these vehicles, only 23 were electric cars or plug-in hybrids.
Among all EVs registered in Sweden last year, approximately 0.04 percent experienced fires, compared to about 0.08 percent of all cars with internal combustion engines. Statistically speaking, this means there's roughly half the risk of a fire occurring in a rechargeable car compared to a car with an internal combustion engine.