While the global transition towards a more sustainable environment, with increased use of renewable energy carriers, continues at pace, vehicle propulsion is experiencing its greatest challenge to date – electrification.
This shift to a more eco-conscious society is causing rapidly increasing demand for electric vehicles and hybrid electric vehicles (EVs and HEVs). The growth in demand is only set to continue over the coming years, as the UK government introduced its plans for high rises for fuel levies in the near future in its 2020 budget statement.
However, as we undergo this cultural change towards a more sustainable planet, with an increased reliance on lithium-ion (Li-ion) batteries to power our transport operations, there are new safety risks that need to be both considered and controlled. Existing user knowledge surrounding these new risks is currently very limited, but the consequences of malfunction in Li-ion battery cells can be severe – having the potential to cause large explosions or toxic gas emissions.
Fire protection in Li-ion-powered vehicles vs vehicles with combustion engines
Fire prevention and suppression systems for vehicles have been on the market for decades, and, as such, are widely used and regulated across a range of sectors and businesses. However, existing solutions have been specifically developed to prevent and suppress fire for vehicles with combustion engines, and they are tested to regulatory standards that are built with this in mind. There are currently very limited testing methods, regulations and standards designed to support fire prevention and safety for EVs and HEVs.
The sustained growth in demand for EVs and HEVs has rapidly accelerated the need for new fire-suppression technologies to be developed.
‘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, Dafo Vehicle Fire Protection.
So, how are the risks different for EVs and HEVs, in comparison to those associated with traditional combustion engine vehicles?
1. Multiple fire hazards
There are a vast range of fire risks associated with EVs and HEVs, including: battery packs, power electronics, heaters and drive systems. An effective fire-suppression solution should address and mitigate each of these risks. For HEVs, the fire risks associated with combustion engines also remain pertinent and therefore should still be considered and controlled. In order to power the vehicle, EVs and HEVs carry a large battery pack, which in itself can pose a substantial safety risk.
2. Risk of thermal runaway
The fundamental difference between fire prevention and suppression in EVs and HEVs and combustion engine vehicles is the risk of ‘thermal runaway’. Thermal runaway is a state that occurs when an EV or HEV engine’s Li-ion battery cells malfunction, causing a chemical reaction and rapid temperature increase. Should a battery enter thermal runaway, the propagation process will quickly become self-sustained, as it produces its own oxygen to propel the flames.
‘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 Anders.
3. Potential for toxic emissions
With the risk of thermal runaway, comes the risk of potentially toxic gas emissions. As a battery enters thermal runaway, it will begin to emit a number of gases, one particularly common and harmful gas being carbon monoxide (CO).
How can the risks be mitigated?
When designing a solution to ensure safety in EVs and HEVs, the predominant aim of the system should be to prevent thermal runaway from occurring within the battery cells.
As a battery is about to enter thermal runaway, it will signal this by beginning to vent its over-pressure. At this stage, the suppression system should commence measures to trigger battery cooling, preventing its acceleration to thermal runaway. If your suppression system quickly detects the fault, and activates the deterrent, it can begin to quickly reverse the process, and potentially even eliminate the risk entirely. However, in some situations, preventing thermal runaway in this way may not be possible. In which case, the system should initiate measures to delay propagation, allowing enough time for the vehicle to be safely evacuated before the battery enters thermal runaway. This stage is particularly important for vehicles carrying a large number of passengers, such as coaches or buses.
Due to the potential for toxic emissions from a failing Li-ion battery, it is also essential that all EVs and HEVs have a heavy-vehicle specialist sensor installed. This will act to alert the operator to the presence of any toxic emissions, enabling safe evacuation and mitigating the safety risk.
A new fire-suppression solution – Li-IonFireTM
In collaboration with Dafo Vehicle Fire Protection, a recent EU initiative has built a fire-protection system that addresses and mitigates the risks associated with EVs and HEVs, safely and effectively.
In developing the new solution, Dafo Vehicle and the RISE Research Institute of Sweden, amongst other project partners, explored the different techniques to detect potential battery failure, as early as possible, and take immediate action to stop, or delay, a potentially hazardous situation.
The various risks related to battery spaces, including specific risks when charging, and the procedures for handling electric vehicles and batteries were all studied. The extent to which fixed and integrated fire-suppression systems, which are widely used to protect engine compartments on heavy vehicles, can be applied to vehicles powered by Li-ion batteries, and how they should be designed, was also explored in depth.
Through extensive testing, it was understood how a breakdown occurs within the battery cells, and how it can be detected.
‘If a system is activated at this early stage, the battery can be “brought back” to a safe state, without the fire developing further,’ explains Anders.
‘The tests have also shown that even with a late deployment of the fire suppression system, there’s a possibility of delaying the battery reaching a critical state, meaning that the chance of safe evacuation is very high.’
The project team successfully validated and demonstrated a highly innovative fire-protection system for electric and hybrid electric vehicles. The new system provides an early fire-warning system, and spot cooling to prevent thermal runaway while localising and suppressing fire.
The system was officially unveiled at in 2019, and has generated tremendous interest from both end users and vehicle manufacturers.
‘Li-IonFire delivers to the market a product that didn’t exist until now: a system that can offer real protection against battery fires, using a new suppression agent, Forrex EV™, which is specifically developed for these applications,’ concludes Anders.
‘Li-IonFire will significantly boost the safety of operators and the protection of valuable assets.’
Li-IonFire is available now.
Safeguarding EVs and HEVs
Existing fire prevention and suppression solutions for vehicles are designed to be most effective for use in combustion engine vehicles, and, as such, they will only go so far in protecting EVs and HEVs.
For more information, go to www.fireshieldsystemsltd.co.uk