The true concern with these vehicles is not extrication but fire. We already have vehicles with a significant fire load without adding in a drivetrain that adds hundreds of power cells of either NiCad, NMHiD or Li-ion, pounds of combustible alloy and the ability to burn for days!
This is correct Rescuers. I did a presentation ten years ago on Fires involved with these vehicles. There was not a lot of information out there on the subject but a lot on conventional drivetrain vehicles, which was scary enough.
But one area pointed me in the direction I needed to go and that was the gallons estimated needed to extinguish one vehicle fully involved with nothing around it. Now this was in the US and up to 1980 it’s estimated that 250 gallons was needed to extinguish the fire. During 1980 to 1990 it went up to 500 gallons; 1990 to 1995 it went to 750 gallons and by 2000 it bounced to 1250 gallons. But by 2007 it’s over 2,000 gallons.
Why the changes? Plastics, fire load and finally hybrids. New vehicle technology in construction and hybrids bring about the use of large amounts of combustible alloys usually mag aluminium but magnesium is in higher quantities as well. Why combustible alloy for hybrids? A number of reasons and this applies to EVs as well. Strength, lightweight and non-conductor of electricity. But bad in a fire and highly reactive with water as you all know. Every vehicle today has a piece of combustible alloy in the steering column, that’s the crash box that absorbs kinetic energy in a crash. How many times have you seen the fireworks show in a vehicle fire when you put water onto the steering column?
So let’s look at specific topics in vehicle fires involved with electric and hybrid vehicles. The key factor first off is whether the vehicle was damaged or not, i.e. involved in a collision.
We need to really know quickly if the HV battery pack is damaged and its contents of power cells are on the road. Or is the vehicle intact? To note quickly there is one vehicle manufacturer, Renault, that makes a firefighter access into its HV battery packs. It has a melt away access port for a hose nozzle to be placed into to flood the HV battery.
Well thought of! So what is really burning on this vehicle? Sometimes we might have a fire that does not involve the HV system. Sometimes we might have a fire involved with the vehicle charging system and the fire might be with the charger unit itself. However, we need to do an accurate and rapid size up, due to the simple fact if this is an EV or a hybrid, you will need resources for assistance. This is not a single engine response nor your everyday car fire. You will need water and a lot of it. Tesla’s recommendation is access to 5,000 gallons of water and I believe their recommendation is on target.
Now some of you are thinking about foam and yeah, foam works great for car fires. Well yes and no, not for EVs. More due to the power cells in the HV battery pack. Foam actually enhances thermal runaway by helping conductivity in the HV battery pack if it uses lithium-ion power cells. We’re still unsure how wetting agents work on those HV battery packs. Hybrids tend not to use lithium power cells so foams or wetting agents are OK, although I would say to stick with wetting agents more so. So why so much water? Well it’s really simple. First off, the vehicle has a huge fire load rolling around on four wheels.
Plastics, combustible alloys and that HV battery. But if the fire is a thermal runaway you need to cool the battery (really the power cells inside). The cooling system of the HV battery pack is completely done if there’s a thermal runaway so you are facilitating an ‘external’ cooling system on that HV battery pack. How do you physically do this? Lift the vehicle 6 to 8 inches on one side, crib it and chock it. Also useful are gojacks, wheel dollys and Rapid Stairs as we tried these recently in training just for this type of event. Use your TIC (thermal imaging camera) and view the bottom of the vehicle and look for the hottest location. Direct the hose stream to the hot spot and keep it there till it cools down. Then keep scanning the floor/battery pack for heat and keep cooling it. It might take hours to bring the temperature down! Now many of the European fire services have invested in vehicles that take this ‘external’ cooling system replacement concept and put it on steroids. Basically it’s a roll on/roll off container truck, some with a 10-ton knuckle boom crane to facilitate sling lift vehicles or PTO winch inside the container to pull the vehicle in. The container is plumed with jets to fill the container with water once the vehicle is inside the container and has connection to standard fire service hoses. North American fire services have yet to adopt this concept. And I believe I know why but we will come back to this.
So I’ve alluded to what happens if the vehicle is damaged as in the fire is a result of a motor vehicle crash. This will depend upon what exactly is damaged and what is burning in the vehicle. If we are speaking of vehicle interior contents, treat it like today’s vehicle fire. But if you have a fully involved vehicle with the high voltage battery pack actually opened and what appears to be hundreds of D battery cells on the road, this is a problem. It will take time, like mentioned above, to get the fire under control. But once you start to move the vehicle debris around and get ready to be loaded to move to a salvage yard, these loose power cells and the damaged HV battery pack with whatever power cells are still inside can and probably will go back into thermal runaway. It’s not unheard of for fire departments to respond to salvage yards 48, 72 hours or even longer after the fact to extinguish fire and re-cool a thermal runaway. Now if you attempted to ‘dunk’ an EV with a damaged HV battery pack into a container of water and the power cells were in thermal runaway the sudden temperature change would create an explosive reaction. Not a good thing! This is why I believe that this tactic has spread so widely in Europe due to the fact that there have been no EV fires thus far involved with a motor vehicle crash and the HV battery pack has been damaged.
On the opposite side of the Atlantic, here in North America most EV fires have been secondary from motor vehicle crashes, many of those involving Teslas. And with the floor being the HV battery pack many times there has been power cells released onto the roadway as the pack is breached. I’m painting with a wide brush, but I believe you can understand the direction that I have laid out for you. One last item, making entry into the hood of the vehicle. With EV and hybrid vehicles remember there will be high voltage components and the motor in the engine bay. Normally a fire situation should depower the HV system by the time you arrive on scene. But if your favorite tactic is to use a rotary saw to plunge cut the hood remember that you might not want to make a deep plunge cut. You don’t know what you are cutting into. I tell my students to never blind cut into a vehicle today. You never know what is behind what you are cutting into or through.
Trauma is the disease of Time Rescuers.We need to always move with a purpose. We have tools today that ten years ago would have amazed. But we have vehicles with technology which is leaping over us constantly. We need better and more comprehensive information about what we are dealing with everyday.
As part of my involvement with the SAE task force with First Responders, I would ask you to take a few minutes to complete our survey on education dealing with EVs and hybrids during emergency response. The survey can be completed at: https://forms.gle/HRr2vecfptHPxPAi9
Because every day people get injured and die in motor vehicle crashes we must read, train and constantly improve our skills. Honing our craft is essential. If you have any questions, please feel free to contact me. Reach out. Listen to my Xtrication Radio podcast on iTunes.
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