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The lesser known risks of electric and hybrid electric vehicles

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James Mountain, director at Fire Shield Systems, explores the lesser known risks associated with electric and hybrid electric vehicles.

As the global transition towards sustainable solutions and renewable energy carriers continues at pace, vehicle propulsion is experiencing its greatest challenge to date – electrification. 

This shift in attitude is driving increased demand for electric and hybrid electric vehicles (EVs and HEVs). With significant rises in UK fuel levies on the horizon, proposed in the government’s 2020 budget, this demand is only set to continue rising over the coming years. 

As we undertake this cultural shift towards a more environmentally-friendly world, with transport operations primarily powered by lithium-ion (Li-ion) batteries, new safety risks need to be both considered and accounted for. 

User knowledge of the new risks associated with Li-ion batteries is currently very limited, but the consequences of malfunction can be severe – potentially causing large explosions or toxic gas emissions. 

Fire protection for combustion engines vs Li-ion powered vehicles

Fire prevention and suppression systems for vehicles have been available for decades, and, as a result, are used and regulated across a wide variety of industries. 

However, existing systems are designed and manufactured to be most effective when used on vehicles with combustion engines, and are tested to standards and regulations with this in mind. Currently, testing methods, regulations and standards to support the fire prevention and safety of EVs and HEVs are limited. 

The sustained growth of the EV and HEV market has accelerated the need for new fire suppression technologies. 

“With the rapid introduction of electric and hybrid electric vehicles in public transport, there are new challenges, because they present totally different risk scenarios,” says Anders Gulliksson, senior quality executive at Dafo Vehicle Fire Protection. 

So, how are the risks different for EVs and HEVs?

Multiple fire hazards

There are a range of fire hazards associated with EVs and HEVs, including: power electronics, drive systems, battery packs, and heaters. For HEVs, the risks associated with combustion engines are still pertinent. In order to power the vehicles, EVs and HEVs also carry a large battery – which in itself poses a significant safety risk. 

Each of these risks needs to be controlled in a vehicle’s fire suppression solution. In addition to the above risks, many EVs and HEVs are used in warehouse environments, under harsh conditions, which can add to the risks. 

Risk of thermal runaway

One of the major differences between EVs and HEVs, and vehicles with combustion engines, is the risk of a state termed ‘thermal runaway’. Thermal runaway is the result of a chemical reaction caused by a failure within the engine’s Li-ion battery cells, resulting in a rapid increase in temperature. Once a battery enters thermal runaway, the propagation process is more or less self-sustained, as it will begin to produce its own oxygen, propelling the fire. 

“When the commonly used Li-ion batteries fail through short circuiting, overcharging, high temperatures, mechanical damage and overheating, this might cause thermal runaway and the release of a flammable electrolyte, which makes fire extinguishing very difficult,” says Gulliksson. 

Potential for toxic emissions

The risk of thermal runaway brings about the risk of toxic gas emissions. As a battery enters thermal runaway, a range of gases will be emitted – carbon monoxide (CO) being a particularly commonly emitted gas. 

How do you control EV and HEV fires?

The primary aim of any fire suppression system for EVs and HEVs should be to avert thermal runaway from occurring.

A failing or malfunctioning battery will vent its over-pressure, prior to entering thermal runaway. At this point, the fire suppression system should act to prompt battery cooling, preventing acceleration to thermal runaway. With efficient detection and activation, the risk can be quickly reversed, and possibly even eliminated entirely. 

However, preventing thermal runaway is not always possible. In these situations, the system should work to delay propagation, allowing the safe evacuation of the vehicle before the battery enters thermal runaway. This is particularly important for vehicles carrying a number of passengers, such as buses.

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