First of all, there are actually parts of the car that are on fire (plastics, fabrics, etc.) and may spread fire to the surrounding environment. You need to extinguish those.
Secondly, the battery system is not "on fire" in the classical sense. It's undergoing a self-sustaining thermal runaway. You pour as much water as you can on it to remove heat and break the chain reaction.
...For long enough to remove the immediate danger of the fire to the surrounding people. Such a damaged fully charged battery will probably undergo thermal runaway and reignite repeatedly as soon as it stops being cooled. The best bet is to just keep the fire under control and not let it expand while it burns itself out.
We're talking about $50 worth of water. Negligible compared to the overall costs.
That assumes household consumption. It could be as high $420 if the highest marginal rate applies.
Still fairly inconsequential overall.
eta: Even hot water still has a high latent heat of vaporization.
> USE WATER TO FIGHT A HIGH VOLTAGE BATTERY FIRE. If the battery catches fire, is exposed to high heat, or is generating heat or gases, use large amounts of water to cool the battery. It can take approximately 3,000 gallons (11,356 liters) of water, applied directly to the battery, to fully extinguish and cool down a battery fire; always establish or request an additional water supply. If water is not immediately available, use dry chemicals, CO2, foam, or another typical fire-extinguishing agent to fight the fire until water is available.
> Battery fires can take up to 24 hours to extinguish. Consider allowing the battery to burn while protecting exposures.
In March: https://efahrer.chip.de/news/warum-die-feuerwehr-diesen-bmw-...
Recommendation to firefighters (in German): https://publikationen.dguv.de/widgets/pdf/download/article/3...
According to Tesla's information, battery fires can be extinguished by using a lot of water. So, it is possible to do with an ordinary fire truck (and self-contained breathing apparatuses so firefighters can get near a burning car without breathing the fumes), but it might actually be a rare case where putting the fire out is consequential to the outcome for the occupants: I'd imagine in most cases they either got out in time or it was already too late by the time putting the fire out is a plausible option. Maybe I'm wrong about that, though.
My comment is more addressed to people such as myself whose natural inclination is to regard a burning car as a bad situation that the fire department aught to be able to quickly remedy, and to suggest that most of the time putting out the fire may be a low priority.
I could imagine the fire department dousing a car if it was already too hot to get people out of safely, but I'm not a fire fighter and I don't know what they'd normally do in that situation.
The people will pay for it because it's necessary and times have changed.
[1]https://www.npr.org/2018/10/05/654670146/its-been-25-years-s...
I understand why they're not raising it, though.
Water 1c change is 4184 J/kg (1 kcal)
Water to steam 2260 kJ/kg.
So 25c cooler is 25 * 4.184 kJ extra, which is:
25 * 4184 / (2260k + 75 * 4184) = 104600 / 2573800 => 4% more energy than 25c to steam.
And then you need a refrigerator to cool tons of water, instead of just carrying more water.
This whole "we couldn't put out the fire" nonsense is click bait. Battery fires burn longer, and that's important to know and requires different techniques to manage. But objectively they are safer than gas fires. Period. There is no serious debate on that point.
Going full-on didactic on you: Vehicles have huge energy requirements to move them around. To meet those requirement they need to store energy on-board in some manner. This creates known failure modes where damage to the vehicle releases that energy in an uncontrolled way. That's bad. But it's completely unavoidable given the constraints of the system.
You seem to want Tesla to do the impossible and invent batteries that don't burn. Which seems ridiculous, given e.g. Ford's nearly-century-long failure to invent gasoline that doesn't burn.
The question you should be asking is "Are battery fires safer than gasoline fires?". And... duh. Yes, they are. And it's not even close.
Just as the environmental externalities of fossil fuels need to be internalized, so do the public safety externalities of the kinds of batteries in use, here. If its going to be a “price of doing business”, the right parties ought to pay the price.
Then, whether or not it is sensible to mitigate in manufacturing will be handled by the properly-aligned incentives.
How is that a bad thing? What are you asking for battery or car manufacturers to do that they aren't already doing simply by replacing existing more-dangerous technology?
I'm simply arguing from first principles: car batteries store less energy than fuel tanks and release that energy slower and over a longer period of time in a fire. Ergo, they are safer for pretty obvious reasons.
If gasoline is spilled, foam works well to extinguish it and keep it from igniting.
Once a gasoline fire is out and cool, it is going to stay that way,
Lithium-ion battery fires are self-sustaining thermal runaways. You cannot put out such a battery fire by smothering it; it does not need oxygen from the air. All you can do is try to keep it cool by running water on it.
Even after such a fire seems cool, it can reignite unexpectedly.
The actual gross volume of energy is not necessarily what makes fighting a fire dangerous or not; it's the unpredictability. Firefighters may be more worried about compressed gas-strut explosions (from hatches, hoods etc) than they are about the gas tank exploding.
I don't know if they could have done more with their batteries to prevent damage from causing thermal runaway. Maybe they could isolate modules from each other better, or use the built-in liquid cooling system in clever ways. (Maybe use the coolant to boil a reservoir of water, so all the excess heat gets used to make steam?) Maybe add heat shielding between the battery and the rest of the car. Maybe design the battery to detach from the car if it gets too hot.
At any rate, I don't think cars can be made to be perfectly safe, and a modern Tesla is reasonable, especially compared to a gas-powered car. However, the possibility always remains of improving upon Tesla's current design along every desirable vehicle attribute, including safety.