Understanding the risks of electric and hybrid buses

04 October 2023

The number of hybrid and electric vehicles on the road is increasing, and so are the fire risks. Due to a lack of public awareness of the risks and how these vehicles differ from those powered by conventional combustion engines, electric bus fires happen almost every day all over the world. Jonas Bergström, Business Manager for Dafo Vehicles bus and coach division, considers how the bus industry is evolving and how this is affecting the fire risks in the automotive industry: What steps can operators take to ensure driver and passenger safety.

All electric vehicles have the potential to cause a fire, therefore it's critical that drivers and those integrating greener cars into our transportation networks are aware of the risks and take action to reduce them whenever practical. Lithium-ion batteries can occasionally encounter a phenomenon known as 'thermal runaway'. This occurs when the battery's cells malfunction, which can be caused by physical damage, overheating, overvoltage or overcharging. When this arises, the temperature rises quickly, which,

if ignored, can lead to fire, the emission of poisonous gas, and even massive explosions. A battery is most dangerous during thermal runaway because, once it begins, it produces its own oxygen. This typically indicates that the bulk of traditional fire suppression techniques won't work and that a reignition is highly likely. Therefore, if a lithium-ion battery enters the stage of thermal runaway, it might take days or even weeks to completely extinguish a fire, which calls for a lot of water and extinguishing agent.

DAFO Jonas

Despite these new risks and the potential effects on people, fleets and revenues, legislation to protect electric vehicles from fire is lagging. By mandating that vehicles powered by combustion engines have onboard fire suppression equipment, the United Nations Economic Commission for Europe (UNECE) approved Regulation 107 in 2020 to increase the safety of traditional buses and coaches. However, there is now a legal loophole that exempts electric vehicles from the same standards, because the legislation only applies to vehicles with conventional combustion engines. To lead the fire safety movement, bus and coach makers must unite globally as technology advances and the push towards electrification grows.


An efficient fire suppression system is essential for preventing thermal runaway. Together, the Research Institutes of Sweden (RISE) and Dafo Vehicle Fire completed major research under an EU-funded programme that was aimed at understanding and addressing these new threats and using the findings to create a novel suppression solution. The research showed that the lithium-ion battery experiences a venting stage, where it releases gases, including carbon monoxide, in the early stages of thermal runaway before it fully takes control.

DAFO diagram

The study discovered that spot cooling can lower the temperature and prevent further heat buildup during this venting stage, which is impossible if thermal runaway totally seizes control. This means that if an early fire warning device is installed to detect carbon monoxide and begin spot cooling before it fully takes hold, thermal runaway can be halted from inflicting damage, protecting people, fleets, and businesses. For more information on how you can protect your bus and coach fleet as you move towards electrification, visit Dafo Vehicle in hall 9 at stand 934 at Bus World.