We need to know this because EVs trigger the rollout of Water Tankers from surrounding towns, as many as we can get. Usually a Water Shuttle has to be set up. Not many Fire Hydrants on Highways, and EV fires require A LOT of water, like several house fires worth... Here is some external detail on this - https://www.businessinsider.com/tesla-crash-fire-lithium-bat...
Also, we need to start calling more manpower. EV fires burn a very very long time while ICE fires are usually put out in the first few mins, and with 1 engine's 1000gal tank water.
Adding to this, the fire is usually under the car, and quite hard to get too. We are very good at opening locked car hoods and cutting metal to get at the fire, but when its deep in the guts of the thing, its impossible. At my department, we have started working on ways to jack the car up safely while its on fire so we can get water onto it. Trust me, its even harder than you would think...
The Standard Operating Procedure is to put water on the car and surrounding area so that nothing else catches on fire, but basically we have to let the thing burn out, and that can take hours and hours...
EV car batteries do not rely on the environment for their fires to burn. The fuel brings its own oxidizer, and it doesnt need anything else. We can put out Liquid Fuel fires by robbing the oxygen or removing the heat(thats what the water does), but once EV fire gets to a particular point of no return (which it arrives at very quickly) there is really nothing that can be done to stop it, just make sure it doesnt get any worse...
Here is the current thinking from the NFPA (firefighting safety and standards organization in the US), you'll see EV car fires are long on problems, but even the most focused minds in the US Fire Prevention industry are short on answers at this time. https://www.youtube.com/watch?v=Sp3WvKON_W4