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Vehicle carriers – Risk from Lithium Ion (Li-ion) battery electric vehicles (EVs)
News & Insights 10 December 2021
This article has been written by David Townsend, the Principal Fire and Explosion Investigator with Andrew Moore and Associates (AMA).
In the next few years most of us will follow trend, or other market forces, and shift from using petrol or diesel driven cars to ones with electric motors driven by batteries or fuel cells. Many of the electric vehicles (EVs) on the road today are powered by Lithium-Ion batteries (Li-ion), but this technology has brought with it new risk. In the marine transport industry, these types of vehicles are now regularly transported on vehicle carriers, Ro-Pax and pure car carriers (PCC).
All vehicles transported by PCC are regarded as a form of Dangerous Goods (DG). They are a mix of combustible materials (mostly plastic), with inherent ignition sources. However, we must now consider the further and very specific risk that Li-ion battery EVs pose when carried at sea in the same manner as all vehicles.
Transported vehicles are stowed in close proximity to others with no segregation guidelines other than by the lashing requirements. Second hand cars are often stowed in direct contact and new cars may be as little as 0.5m apart.
The 2016 publication 'Fires on Ro-Ro Decks' by DNV- GL, stated in its conclusion at section 6.2 (d) that:
'A policy on how to handle alternative-fuel vehicles should be developed, if applicable (know-how on correct firefighting strategy/challenges), although this is not identified as a major risk (it is an unknown risk).'
At that time, Li-ion battery EVs were not an unknown risk but the risk had not been fully and comprehensively realised in many quarters.
The National Safety Transportation Board (NTSB) published a detailed Safety Report in 2001 (NTSB/SR-20/01)). In that report it states:
'Fires in electric vehicles powered by high-voltage lithium-ion batteries pose the risk of electric shock to emergency responders from exposure to the high-voltage components of a damaged lithium-ion battery. A further risk is that damaged cells in the battery can experience thermal runaway – uncontrolled increases in temperature and pressure – which can lead to battery reignition. The risks of electric shock and battery reignition/fire arise from the “stranded” energy that remains in a damaged battery.'
This was not the first such report and the problem gradually became better known and reported. This included fires in garages and car parks. Some underground car parks have banned EVs. The risk on any PCC is far greater than that in any car park.
The critical component, the Li-ion battery, is a technology that will be surpassed by further technologies. However, the legacy of Li-ion will persist for a number of decades and the second-hand car market will carry a significant quantity of such vehicles on PCCs.
Flame from a Li-ion vehicle battery fire spreads low and outwards. Direct flame and heat will come to bear on the sides and undersides of the cars on one or more sides. It is often an intense, projected, blowtorch-like flame, sometimes there is explosion. This is not typical, non-EV, car fire behaviour.
In 2020, in China, a battery fire in a single EV at a charge station resulted in the full involvement of two vehicles to one side of it in less than three minutes. It is easy to visualise from this particular video the likely spread of fire on any vehicle carrier deck. Further research is not required.
The EV industry tends to dilute the issue by, for example, comparing to the frequency of fire in non-EV vehicles. The fact remains that the Li-ion battery can and does malfunction catastrophically for no apparent reason known at the time to the owner or user. Currently, the underlying cause is generally stated to include poor manufacturing, damage or sub-standard quality. Poor software can also be a factor.
Unfortunately, some of the basic and widely relied upon fire safety principles are not available for Li-ion battery EV fires: there is no effective or practicable potential for early detection, warning, or fire suppression. There are no effective portable fire fighting appliances. There is, currently, no effective and capable fixed fire fighting installation. Even a modern, full-time, public fire service is unable to control a Li-ion EV fire in any timely manner. In short, at present, no ship’s system or crew nor any port or public fire service is capable of dealing effectively with the risk aboard.
This is a major dilemma for PCCs in particular; The quantity of cars carried and the journey-time per vessel is far greater than other vehicle carriers. This raises the statistical likelihood of an event. It is not possible to reduce the risk because, if and when the event occurs, it will be rapidly catastrophic in the immediate area and there is no effective structural fire spread prevention within existing CO2/hi. ex. zones.
In my opinion, where carried on current fleets, the fire safety strategy for Li-ion battery EVs should be one of presumption of a large fire at the outset that will be beyond any manual first response. Therefore, on discovery, the available fixed installation should be discharged and the vessel should seek refuge or assistance.
There are times when there is simply no effective means to reduce a risk to any acceptable level and serious consideration must be given to exclusion. Current fleets are not suitably equipped and it seems there is no existing means by which they could be effectively and economically adapted.
It is clear that a Li-ion battery EV fire must be tackled quickly by a cooling and blanketing media over a wide area such that surrounding vehicles are also immediately deluged. The only practical such medium is water but that has obvious vessel stability issues where an application would need to be active for a considerable period. The Li-ion battery EV fire will often continue to burn under this deluge thus the system must remain operating until professional fire fighting teams are available.
I have only outlined the issue in respect of a single Li-ion battery EV fire. When a Li-ion battery is subjected to a fire from another source i.e., a non-EV car fire, it will go into thermal runaway. The subsequent exponential fire growth and heat flux will be greater as the density of Li-ion battery EVs carried increases.
On PCCs there are rules about the level of fuel carried in vehicle tanks. This is a means to reduce the total fuel loading aboard. There is no equivalent requirement of Li-ion battery EVs yet the contribution to fire output is probably greater because the energy release will be of a greater intensity and duration. The Li-ion EV battery is all of the risk, the ignition source and the fuel (energy) load. Battery disconnection (or isolation) or reduced charge will not remove the risk.
At port there will be other complications; many zone doors will be open and there will be more hands to be accounted for before operation of water mist/CO2/hi ex. foam etc., systems.
Earlier, I used the term, 'if and when the event occurs'. Some may choose to react to this issue on the basis of 'if'. Others may think of 'when'. The longer the delay in any action the greater will be the likelihood of 'when'.
About the author: David Townsend is the Principal Fire and Explosion Investigator with Andrew Moore and Associates (AMA). He has served the fire industry for 45 years the last 25 of which have been dedicated to fire investigation. David served a full 30-year career in the London Fire Brigade the last 11 of which were in fire investigation. As an investigator in the private sector since 2006, he soon became involved in substantial marine casework worldwide.
类别: Loss Prevention