The discussion about the hazards and risks arising from fires involving lithium-ion batteries and electric vehicles continues to hit the global headlines with much debate on the topic. You only need to look at the media reports and stories about serious fires, injuries and deaths to see that the risks are very real, regardless of the frequency of such fires. In May of last year, the International Association of Fire and Rescue Services reported that ‘the frequency of fires had increased over the past six years’.
As the popularity of lithium-ion-powered devices increases, it is also likely that the potential for fire (thermal events) will also increase. The consumer is generally not aware of the actual hazards associated with a thermal event involving e-mobility or other devices. When such an event does happen, the situation is difficult to bring under control and make safe. Larger batteries mean greater challenges for the fire and rescue service.
What are the Hazards?
It may be worth looking at this problem as two events. The first is thermal runaway where a lithium-ion battery enters an uncontrollable self-heating state. During this phase, high temperatures are produced, toxic and corrosive gases can vent from the cell(s), shrapnel or glowing particulates can be ejected, and gases can ignite, sometimes with flaming jets extending from the cell.
The gases released are both heavier and lighter than air, forming two separate layers. Many describe it as smoke, but that is not the case. The heavier gasses will seek out the lowest areas, flowing some distance from the source. If either layer comes into contact with an ignition source, it is likely that an unconfined vapour cloud explosion (UVCE) will occur.
The second part of the equation is when the surrounding (normal) combustibles become involved and a fire occurs. This can be related to a family home, a business or an electric vehicle when the plastics/fabrics used in construction ignite.
Whilst I have described this as two events (for the sake of discussion), the development of thermal runaway to a fully involved fire can be both rapid and devastating. Emergency responders, fire engineers and researchers around the world are trying to keep pace with the issue of fires involving battery powered devices, energy storage systems and vehicles. Currently there is no silver bullet.
Whilst the fires associated with or resulting from these thermal events can be extinguished, thermal runaway is harder to resolve. In the case of vehicles, many thousands of liters of water are required in an attempt to cool the cell(s) involved. Even if the flames are extinguished, thermal runaway continues and so too will the production of flammable gases, thus increasing the risk of a UVCE occurring.
Maritime Sector
Now transfer this risk to the marine environment, specifically an electric vehicle on a car deck. The battery pack is larger and the volume of any gas produced is greater. It is around this time that the alarm may be raised and crew respond. At this point, thermal runaway is progressing through the cells. The gases may have ignited, and the normal combustibles used in construction may be alight.
By this time the drenchers should be in operation, reducing the fire and heat being released. Whilst the spread of the fire may be reduced, the construction of the vehicle will have shielded the battery pack from the cooling effects of any water, leaving a question mark over the control of the thermal runaway. If flames are absent and flammable gasses are still venting near hot surfaces – or come into contact with other ignition sources – the consequences could be fatal.
Much research is being undertaken to ascertain how lithium-ion batteries and electric vehicles can be safely transported, and should the need arise, how to manage a thermal or fire event. There are different views about the complexities and dangers associated with transporting this type of cargo. On one end of the scale, there is little difference between a fire involving electric vehicles compared to a fire in a vehicle with an internal combustion engine. On the other end, some might say from ‘real world experience’ that the hazards are significant and vessels and crew are ill-equipped to deal with the event.
Looking at this from the perspective of a former firefighter and current marine casualty investigator, it appears to me that there is a gap in knowledge between the research field and the experiences of emergency responders. If we are to improve not only consumer safety but also the safety of those seafarers who transport goods around the globe, there needs to be much closer alignment between the two worlds.