Don't firefighters carry some kind of foam by default? After all there's a lot of grease fires(cars, kitchens) out there.
> Use copious amounts of water to cool the battery to extinguish the fire
https://www.nfpa.org/-/media/Files/Training/AFV/Emergency-Re...
The advice is to use copious amounts of water to cool the batteries, removing the "heat" leg of the triangle. This works but requires extended periods of cooling support due to the possibility of internal shorts re-supplying the heat, and starting the process again.
I think the general practice for EVs around here (in larger cities at least) is to extinguish it with water, then put them in a container full of water for 24 hours.