Electric Vehicle Fires: How Often Do They Really Occur?
Author: Markus Strehlitz
"Electric cars catch fire faster than conventional vehicles." This is a common misconception with little to no evidence to support it. In fact, very much the opposite is true: Electric vehicles are less prone to fires compared to combustion and hybrid vehicles.
When discussing electric vehicles (EVs) in social circles, the issue of fire hazards inevitably arises – and the belief that a car with electric drive is more fire-prone is widespread. However, the basis for this conception is unclear as there is little reliable data available. "In Germany, there is not even a statistic on how often vehicles actually catch fire," Markus Egelhaaf from DEKRA Accident Research states.
Instead of electric vehicles being fire-prone, the few figures available suggest a different situation entirely. Referring to a recent study conducted by a US insurance company, Markus Egelhaaf reports that, relative to registration numbers, most fires occur with hybrid vehicles, followed by petrol cars. Battery electric vehicles are least likely to catch fire.
According to Egelhaaf, it is no surprise that hybrid vehicles rank first in the statistics. The causes of vehicle fires can generally be divided into three categories: Causes that are unrelated to the propulsion system include the standard 12-volt on-board electronics, where shorts circuits or defective equipment can cause a fire. In a second scenario, the entire scope of the battery, including battery management and electric drive, can cause a fire. Lastly, we have specific causes related to petrol engines, such as defective fuel lines or hot surfaces. Hybrid cars combine all three risk factors, hence the higher number of fire incidents compared to other types of vehicles.
Electric vehicles do not pose an increased fire risk
Overall, the conclusion is that the risk of fire is no greater with battery-electric vehicles than with other cars. This is not only supported by the study cited by Egelhaaf and findings from accident research, but also by the German Fire Brigades Association (DFV). "Neither the likelihood of a fire nor the extent of damage is increased with electric vehicles," the DFV states in a press release on the matter.
Nonetheless, there remain some differences between the vehicle types. “A traditional petrol-powered car is more likely to catch fire during or immediately after use," says Egelhaaf. This is due to the fact that certain surfaces heat up during use and fuel only circulates through the pipes while driving, which can escape in case of defects. The 12-volt system is mostly deactivated when the car is parked and therefore poses only a minor residual risk of electrical ignition.
Should an electric vehicle catch fire, it is more likely to happen while being parked or during charging. And where there is electricity, there are potential ignition sources," says Egelhaaf. However, the electric vehicle itself is rarely the cause." The cause can be an improper charger or that the building's electrical installation is not designed for charging electric cars," explains Egelhaaf.
This has also sparked debates on whether electric cars should be allowed to park in underground car parks. According to Egelhaaf, there's no reason why they should not as the fire hazard with EVs is low. The DFV agrees: "Parking and charging electric vehicles at a certified charging station within a code-compliant car park does not go against current building regulations," it says in a press release. "From a fire protection point of view, banning alternative engines from car parks is not a necessary measure.”
Thermal Runaway – Shorts within the battery cell
When batteries catch fire, it's either due to prior mechanical damage, e.g. following an accident, or the result of damage within a cell. Both can lead to a phenomenon called Thermal Runaway, where a short within the battery cell triggers a chemical reaction and extreme rise in temperature. This causes the cell to eventually rupture, releasing flammable gas that can ignite due to high temperatures. Additionally, the temperature increase can also damage adjoining cells in the battery pack, potentially triggering another Thermal Runaway.
Despite this particularity, batteries are not necessarily affected in every electric or hybrid vehicle fire. "Fire tests indicate that lithium-ion batteries have to be exposed to heat or significant mechanical damage over a long period of time to cause said internal reaction," the German Social Accident Insurance (DGUV) informs on a fact sheet specifically addressing the most common battery type, lithium-ion batteries.
Fire extinguishing process for electric vehicles
The fire department can extinguish electric vehicles on fire. However, this may pose a somewhat bigger challenge than fighting fires when conventionally powered cars burn: High-voltage batteries are typically fitted into a waterproof case. "In case of an intact or only slightly damaged lithium-ion battery, the extinguishing water cannot reach the seat of fire," says the DGUV. "External cooling is also hardly effective as the cells are thermally insulated from the outer casing."
However, solutions are at hand. With specialized equipment such as extinguishing lances for batteries, the extinguisher can be inserted into the battery. Therefore, fire department units need appropriate training, according to Egelhaaf.
He further reports that DEKRA is currently working on a study to improve the evidence base surrounding the fire risk of electric vehicles. This study will compare petrol, diesel, hybrid, and electric vehicles regarding their fire risk and henceforth provide reliable data on the matter.