Facts and myths
Fire safety of electric cars – what is it really like?
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Burning electric cars are regularly reported on social and traditional media. This happens quite rarely. A clarification.
One of the more common reservations about electric cars is their alleged fire hazard. However, compared to combustion engines, they tend to perform rather well. These are the most frequently asked questions and the corresponding answers about the risk of fire in electric vehicles.
Do electric cars burn more often than combustion engines?
Currently, everything indicates that battery-electric cars (BEVs) catch fire less often than vehicles with combustion engines. Data from Norway shows that between 2016 and March 2022, the share of BEVs in car fires was only 2.3 percent, while their share of the total vehicle population was 8.9 percent.
Other statistics also point in a similar direction, such as data from the German Insurance Association (GDV), the Swedish government and the Australian Ministry of Defense. However, on average, electric cars are significantly younger than the combustion engine population, which could lead to a slight distortion of the data.
How are electric vehicles protected against fires?
Electric cars have several safety systems. The minimum number that must be present is determined by the ECE regulation R 100. It lists specific requirements for the battery and the entire electric drive system. Various vibration, shock and heat tests are required. Protection against short circuits, overcharging or discharging and overheating are also specified.
There are numerous technical measures to achieve all of this. A battery management system (BMS) constantly monitors the current, voltage and temperature of the battery cells. In collaboration with the thermal management system, it regulates the battery temperature using air or liquid cooling. If problems still arise, the BMS reacts by automatically switching off, for example in the event of over- or under-voltage, over-current, excessive temperature or a vehicle rollover. There are also structural protective devices, such as heat shields, ventilation openings and mechanical impact protection for the battery.
What are the most common causes of fires in electric vehicles?
There are a whole range of causes of fires in combustion engines: from leaks in the fuel system to electrical faults to parking with a hot catalytic converter on a dry summer meadow. In electric cars, problems with the battery are almost exclusively the cause. They arise from excessive thermal, electrical or mechanical stress on the battery cells. Possible causes include mechanical damage caused by traffic accidents or errors in the battery management system. An external fire can also cause the so-called thermal runaway of the energy storage device.
What does thermal runaway mean?
Whether due to an external or internal fault: If a cell in the battery gets too hot, there is a risk of so-called thermal runaway. The cell ignites, the fire spreads to neighboring cells, the entire battery pack quickly burns, sometimes even exploding under the pressure.
Another problem: All the elements necessary for a fire are present in the housing; the electrolyte, which is chemically related to gasoline, which removes charcoal-like graphite at the anode and the separator, which is often made of organic material. In addition, oxygen-containing compounds come from the electrodes. The fire feeds itself and is difficult to reach from the outside due to the extensive battery housing, which makes it difficult to extinguish. This “runaway” may have contributed significantly to the fear myths about electric car fires.
Do electric cars burn hotter or longer than combustion engines?
Most of the thermal energy released in a car fire does not come from the energy storage system. Instead, tires, plastic cladding and fabrics make up the majority of the fire load. E-cars and combustion engines of comparable size hardly differ in this respect. Fires in battery-electric cars and combustion engines are also similar in terms of the total amount of heat released and the maximum temperature, according to documents from the state-run National Organization for Hydrogen and Fuel Cell Technology (NOW).
Does an electric car fire produce more pollutants than a combustion engine fire?
The environmental impact differs at least in terms of the substances released. According to NOW, when extinguishing a burning battery, nickel, cobalt, lithium, manganese and hydrogen fluoride can occur in higher concentrations in the wastewater than in vehicles with internal combustion engines.
However, higher concentrations of lead, polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs) can be detected in the extinguishing water of combustion cars. The concentration of per- and polyfluorinated alkyl substances (PFAS) – non-degradable “forever chemicals” – in wastewater is four times higher.
Are there differences between cell types in terms of fire safety?
Basically, all cell types used in cars are safe. Lithium iron phosphate cells (LFP) are considered particularly safe, as the cathode material has a higher thermal stability than nickel-based cells (NMC, NCA). LFP cells are cheaper and less powerful than nickel cells and are therefore increasingly being used, especially in smaller cars or commercial vehicles. Sodium-ion batteries, which are currently not used in Europe, are likely to be even safer. Real solid-state batteries are likely to be extremely difficult to ignite – the lack of the flammable liquid electrolyte alone should raise the safety level even further. The following applies to all current cell types: The risk of thermal runaway is highest when fully charged and significantly lower when charged less. For this reason, the batteries are only about a quarter charged during ship transport.
How are burning electric cars extinguished?
As with combustion cars, the fire department uses water to extinguish and cool. Because there can be fires inside the battery housing, the fire department has to adapt its strategy when it comes to electric car fires. In order to get the extinguishing agent into the battery pack, special extinguishing lances or extinguishing accesses are used. After extinguishing, continuous temperature monitoring is necessary as the battery could re-ignite. The handover to towing companies therefore only takes place after at least 30 minutes of observation. The electric cars then have to be quarantined for safety reasons in case the fire flares up again.
