FEATURE | Efficacy of vessel drencher systems in relation to battery electric vehicle fires
Concerns have been raised over ferries carrying battery electric vehicles (BEVs) as there have been instances of catastrophic failure in the vehicle’s battery pack, resulting in fires that cannot be extinguished. The efficacy of conventional seawater drencher systems in relation to BEV fires has been evaluated under the auspices of LASH FIRE, an EU research project aimed to significantly reduce the risk of fires on board Ro-Ro ships by developing and validating effective operative and design solutions. Interferry is a member of the LASH FIRE project, which runs from September 2019 to August 2023.
LASH FIRE tested a fixed water-based extinguishing or drencher system on a simulated Ro-Ro deck in relation to thermal runaway fire in a BEV. The drencher system was capable of containing the fire and the overall risk of carrying BEVs should be considered equivalent or lower than that of internal combustion engine vehicles (ICEVs), providing the drencher system is correctly operated and designed in accordance with SOLAS.
Addressing the challenge of BEV fires on vehicle decks
Relative to the total number of vehicles, the number of BEV fires is lower than that of ICEV fires. Even so, stringent measures related to the carriage of BEVs have been discussed, all the way from the installation of additional firefighting capabilities, to segregating BEVs on board or an outright prohibition of carrying BEVs on Ro-Ro decks. This stance is partially due to the fact that it is very difficult to extinguish a fire within a battery pack as:
- The plastic housing of the battery pack itself acts as a shield for the extinguishing agent (e.g. water).
- The battery pack will also be shielded by the vehicle’s body.
- The chemical components within the battery cells provide a very high density energy source to sustain the fire locally.
This shielding effect is mostly relevant if the fire starts in the BEV’s battery, typically caused by a short-circuit, leading to a so-called thermal runaway. When the fire does not originate in the battery, the suppression activities will hinder fire spread and significantly reduce the risk of a thermal runaway. When stowed adjacent to a vehicle that catches on fire, a BEV may also catch on fire, but in this scenario, the consequences are not worse than if it were a petrol or diesel car by virtue of the unlikeliness of the BEV’s battery experiencing a thermal runaway. In fact, a non-battery-related fire in a BEV will likely release less heat than one involving liquid fuel in a tank as a plastic fuel tank will catch fire much faster than a Li-ion battery.
What follows are some key findings of LASH FIRE’s test series, comparing the fire suppression performance of a drencher system for fires involving ICEVs and BEVs, respectively. The tests simulated a Ro-Ro space with a five-metre ceiling height with a fire suppression system design in line with IMO’s revised guidelines for the design and approval of fixed water-based firefighting systems for Ro-Ro spaces and special category spaces.
Representative of today’s modern vehicles, two pairs of geometrically similar SUV-type ICEVs and BEVs were used in the tests. The tests illustrated that while the BEV fires presented a different fire scenario to those of an ICEV fire, the performance requirements of existing fixed water-based extinguishing systems on both closed and open Ro-Ro decks were sufficient to contain a BEV fire, at least to a level equivalent of an ICEV fire. A fuel spill fire associated with an ICEV develops very rapidly, peaks high but burns out fast, whilst a fire starting in the battery pack of a BEV develops slower, is not as large – resulting in a lower heat release – but burns longer. The scenario of the fire in other combustibles such as tires, exterior and undercarriage plastic parts and inside the car is similar.
Similar risks as with internal combustion-powered vehicles
As the drencher system was capable of containing the fire, the tests clearly illustrated that the overall risk of carrying BEVs should be considered equivalent or lower than carrying ICEVs. As for the latter vehicle type, there is the additional risk of the fire spreading horizontally, i.e. when a fuel tank ruptures, burning fuel on the deck risks to spread under the adjacent cars.
As drencher systems are able to contain a BEV fire and prevent spread to other vehicles, we recommend our members to not make any special provisions for carrying BEVs, and even charge them if that’s an option, provided that equipment and training are compliant the requirements in SOLAS and ISM – which they of course always have to be!
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Johan Roos is Director of Regulatory Affairs for worldwide ferry industry association Interferry.