E-mobility Facts and myths about e-car fires

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FAULHABER Drive Systems

Reports of burning e-cars regularly appear in social and traditional media. However, this happens quite rarely. A clarification.

One of the more common reservations against e-cars is their alleged fire hazard. Compared to combustion engines, however, they tend to fare rather well. These are the most frequent questions and the corresponding answers regarding the fire hazard of e-vehicles.

Do e-cars catch fire more often than combustion engines?

Currently, all indications suggest that battery electric vehicles (BEVs) are less likely to catch fire than vehicles with internal combustion engines. Data from Norway shows that between 2016 and March 2022, BEVs accounted for only 2.3 percent of car fires, while their share of the total vehicle population was 8.9 percent. Other statistics point in a similar direction, such as data from the German Insurance Association (GDV), the Swedish government, and the Australian Department of Defence. However, e-cars are on average significantly younger than the combustion engine stock, which could slightly skew the data.

How are electric vehicles protected against fires?

Electric cars are equipped with several safety systems. The minimum required provisions are outlined in the ECE Regulation R 100, which details specific requirements for the battery and the entire electric drive system. Mandated are various vibration, shock, and thermal tests. Protection against short circuits, overcharging or discharging, and overheating is also specified. To fulfill all these requirements, numerous technical measures are implemented. For example, a Battery Management System (BMS) continuously 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 responds with automatic shutdown in case of over or under voltage, overcurrent, excessive temperature, or vehicle rollover. Additional protective measures include heat shields, ventilation openings, and mechanical impact protection for the battery.

What are the most common causes of fires in electric vehicles?

With combustion engines, there are a multitude of fire causes: ranging from leaks in the fuel system and electrical faults to parking with a hot catalytic converter on a dry summer meadow. In electric cars, almost exclusively battery issues are the cause. These arise from excessive thermal, electrical, or mechanical stress on the battery cells. Possible causes include mechanical damage from traffic accidents or errors in the battery management system. An external fire can also trigger the so-called thermal runaway of the energy storage system.

What does thermal runaway mean?

Whether due to an external or internal fault, if a cell in the battery becomes too hot, the so-called thermal runaway threatens. The cell ignites, the fire spreads to neighboring cells, and quickly the entire battery pack burns, sometimes even exploding under pressure. Another problem is that all the elements necessary for a fire are present in the casing: the electrolyte chemically related to gasoline, the graphite similar to charcoal at the anode, and the separator often made of organic material. In addition, oxygen-containing compounds come from the electrodes. The fire feeds itself and is difficult to reach from outside due to the comprehensive battery casing, which makes extinguishing it difficult. This "runaway" likely contributed significantly to the fear myths about e-car fires.

Do e-cars burn hotter or longer than combustion engines?

The majority of the thermal energy released during a car fire does not come from the energy storage system. Instead, tires, plastic cladding, and fabrics make up the bulk of the fire load. In this regard, e-cars and combustion vehicles of comparable size differ little. In terms of the total amount of heat released and the peak temperature, fires in battery electric vehicles and combustion vehicles are also similar, as indicated by documents from the state National Hydrogen and Fuel Cell Technology Organization (NOW).

Do more pollutants arise from an e-car fire than from a combustion engine fire?

The environmental impact differs at least in terms of the substances released. According to NOW, when extinguishing a burning battery, concentrations of nickel, cobalt, lithium, manganese, and hydrogen fluoride can be higher in the wastewater compared to 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 engine vehicles. The concentration of per- and polyfluoroalkyl substances (PFAS)—non-biodegradable "forever chemicals"—in the wastewater is also four times higher.

Are there differences between cell types in terms of fire safety?

Fundamentally, all cell types used in cars are safe. Lithium iron phosphate (LFP) cells are considered particularly safe, as their cathode material has higher thermal stability than nickel-based cells (NMC, NCA). LFP cells are cheaper and less powerful than nickel cells, and are therefore increasingly used, especially in smaller passenger cars or commercial vehicles. Sodium-ion batteries could be even safer, although they are not currently used in Europe. Truly inflammable might be real solid-state batteries—the mere absence of the flammable liquid electrolyte could increase the safety level again. For all current cell types, the risk of thermal runaway is highest when fully charged and significantly lower at lower charges. For this reason, batteries are only charged to about a quarter of their capacity during sea transport.

How are burning electric cars extinguished?

As with combustion engine vehicles, the fire department uses water for extinguishing and cooling. Because it can burn inside the battery casing, the fire department needs to adjust its strategy for e-car fires. To deliver the extinguishing agent into the battery pack, special extinguishing lances or access points are used. After extinguishing, continuous temperature monitoring is necessary since the battery could reignite. Handover to towing companies only takes place after at least 30 minutes of observation. Subsequently, the electric cars must be placed in quarantine for safety reasons, in case the fire should flare up again.