What? Sand weighs in at about 13 pounds/gallon. Water is under 9.

While storage may be easier in some ways (you can just have a giant pile), you’d have to add storage spaces for it compared to the already ubiquitous water supplies like reservoirs, lakes, ponds, rivers, etc that a pump can fill up a fire tanker/tender with.

Then you run into how the hell the sand gets ON the fire. You can’t just pump sand on through existing equipment, that’s for sure. And, pumping sand is brutal on the equipment that’s designed for it. So you’d have to not only buy new trucks just for sand, but the upkeep is going to skyrocket.

As far as highways go, there are some places where hydrants are available along the route because highways are usually planned. And, again, that’s why they have tanker/tender trucks to bring in water in the thousands of gallons instead of the hundreds a regular fire truck carries. It isn’t any more cumbersome than handling a fire way out in the country with no hydrants.

Sand, there’s no such thing as hydrants at all. You CAN’T have them. You don’t have the flexibility of infrastructure to set up sand depots either, not reliably.

As far as freezing, that would be a good thing. The entire point is to bring down the temperature of the battery below the point where it is self sustaining. Which sand can’t do by itself in the first place. But, even if you did end up with a frozen block of ice (and you won’t because you don’t freeze a thousand gallons of water in a few hours, though you might get a small amount on top), that’s just a matter of patience.

Not that a shit ton of water that’s specifically there to suck up the heat is going to freeze faster than the battery reaction can heat it. You pump the water, you let it work, you let the water drain out. Boom. Minimum cleanup because you either pump the water back into a tank and transport out, or (where safe and realistic) just let it run off by itself.

You get a tank full of sand, you have to move that sand. It won’t flow away by itself. You can’t pump it back into a tank the same way you can water (it is possible, but it’s a damn sight more complicated and expensive).

I know not all of this is intuitive, but do you not know any firefighters? They have a lot of options for fires of various types. This includes sand, but sand just isn’t practical or useful for the vast majority of fires where smothering is going to work right. It’s just not efficient enough to be a primary, or even secondary secondary tool.

And that’s the other big issue. Sand isn’t a fast cooling thing. It isn’t going to work right for a battery fire. Again, you can’t smother them, they’re self oxidizing. That’s the entire reason for the extra efforts. Most car fires, they’re out in minutes (less if they’re small). Battery fires are so bad because you can’t extinguish them like you can with most fuels like gasoline. Sand just doesn’t pull the heat away fast at all. It even holds the heat as it pulls it from the source because the molecules involved are not able to move enough to do it. Water being a liquid is more efficient at that.