Possibly amateurish take: dumping water on an alkali metal seems like not a great idea (unless you want _more_ fire, in which case by all means go for it)
So spraying water, while it can make it spicier for a bit, allows you to suck away enough heat fast enough that it works okayish. It's the scalable, but not ideal, solution generally.
Current guidance is don't bother with anything else, just spray it until the flames stop.
I've also wondered if maybe EV's should be designed with an easy-to-access coolant loop. For instance, maybe you have a fixture you can connect a garden hose to in order to pump cold water through channels in the battery modules for emergency cooling. (Most EVs have liquid cooling already, so this could be in addition to that, or maybe you hook into the existing system and the already-present coolant gets flushed out.)
just add something gel-forming into the water or some fiber/dust (even just gluten flour) that absorbs a lot of water and turns into kind of watery dough.
The problem it turns out is making large quantities of water based foam (without making it flammable somehow) is easiest when using perflourinated compounds.
Oops.
Let's say you have a battery immersed in a tank of water (aside from the contacts), and you wanted to match the amount of water to the stored energy of the cell, such that, in the event that the stored energy is accidentally released, the last of the water boils away when the battery is empty.
Apparently it takes about 2.37 kwh to boil a gallon of water. That's a lot of energy, but if you have a car with an 80kwh battery pack, you'd need about 33 gallons of water, which is probably too heavy to be a realistic option.
(Granted this is oversimplistic because the energy that comes from a burning battery might be more than the electrical energy you could get out of it just by discharging it the normal way.)
I found a wikipedia article that lists joules per gram required to vaporize various substances:
https://en.wikipedia.org/wiki/Enthalpy_of_vaporization
Water is way up there. Iron and aluminum are even higher, but it's hard to imagine even an EV fire being enough to vaporize large amounts of those. I don't think I'd want to be breathing that either, though given the "battery fire" scenario I guess that's already a given.
That length of time may be zero if the reason it is on fire is due to traumatic damage to the battery pack from a crash or similar.
It’s easier and less error prone to spray it from a distance. If it isn’t on fire yet, maybe it keeps it cool enough it never starts. If it is on fire, just keep spraying until the bad flames stop.
if you don’t have enough water, it will just spread the fire
It’s also relatively simple training and equipment wise (‘spray it with water until the bad flames stop’), and most locations have teams of people on call and ready to do it.
Not perfect, but it’s the best we’ve been able to come up with outside of specialized industrial environments. shrug