The good news is, water is cold (generally), doesn't combust (generally), and there is a LOT of 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 wondered if maybe it's possible to pack batteries with a relatively harmless material that undergoes a very energy-intensive phase change. Water's the obvious choice, but it tends to drain away rather than stick around long enough to turn to steam. Maybe there's a better material, or ways to design battery cooling systems so that a burning battery turns into a very efficient steam generator, and thus can be cooled adequately with much less water.

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.)

>Water's the obvious choice, but it tends to drain away rather than stick around long enough to turn to steam.

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.

They do this at airports. The easy answer is foam.

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.

My Tesla caught fire but at least I now have a year's supply of sourdough bread

Problem with that is, it might block the addition of more water. If the 'way in' for the water gets blocked, but the battery continues to burn.

In buildings they call your hose idea a “standpipe”

The phase transition of water from liquid to gas requires an enormous amount of energy. It’s a very good substance for cooling very hot things.

It is, but I've wondered about whether there are even better materials?

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.

I wonder if they could add a "water flooding port" to the battery packs, to allow firefighters to hook up a water hose and flood that battery compartment directly. Seems like it'd be much more targeted/effective/efficient than trying to spray the exterior.

The challenge of course is that there is a very small window of time where you might suspect the pack will catch on fire and it’s feasible to be close enough to a battery pack to be able to plug something into it, without being horribly burned because it’s on fire.

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.

Teslas (and maybe others, I don't know) already have liquid cooling passages and piping leading to the batter pack. I do not know how feasible it would be to add a tap to that system.

only if you have enough water.

if you don’t have enough water, it will just spread the fire

Luckily, one of the first criteria for if a place is habitable or not is ‘easy access to large quantities of water’, and building code wise, access to large enough quantities to put out fully formed full structure fires is required too.

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

It's important to actually know the battery chemistry here. Lithium batteries contain metal lithium and as you say dumping water on them is not a good idea. Lithium-ion and lithium polymer on the other hand only contain lithium polymers that don't combust with water.

Lion (as me and others have come to call them, due to their "ferocious" nature) batteries contain no metallic lithium.