5 ms·

The entire point is that you can't "deal" with it. Since car batteries contain the fuel and the oxidizer, there isn't a way to separate them short of blowing th

The entire point is that you can't "deal" with it. Since car batteries contain the fuel and the oxidizer, there isn't a way to separate them short of blowing the whole thing up. Fires can stop and start spontaneously, and often do (see pictures and videos of Teslas on fire in junkyards).

bragr 4y ago
This is not really true. There are tools and agents to address lithium fires, but you have to have them. If you just try to put them out with water, you're going to be there all night fighting reignition.
- DoneWithAllThat 4y ago
  Please don’t leave us in suspense: what are these tools and agents? Got a link?
  - marcosdumay 4y ago
    For lithium, sand is enough. If you have HF like a sibling said, sand won't do, but I can't imagine you would get enough of it to sustain a fire.
  - bragr 4y ago
    Lithium fires are considered class B so any chemical agent such as found in any standard ABC or dry chemical fire extinguisher would be sufficient. As for tools, there's stuff that can be used to pierce the battery case and inject water or agents directly into the battery. https://arstechnica.com/cars/2021/11/new-firefighting-tool-delivers-water-directly-to-blazing-ev-batteries/ https://arstechnica.com/cars/2021/11/new-firefighting-tool-d...
- KennyBlanken 4y ago
  Lithium ion battery fires are not lithium fires. Water is the recommended method because it is the most effective way to stop thermal runaway. If you don't believe me, google "lithium ion battery fires water"
- deleted 4y ago
  [deleted]
londons_explore 4y ago
Electric cars could totally be designed to be re-ignite-proof. For example, you'd have the battery pack detect a breach - for example through a lack of pressurised coolant. That would then trigger each battery cell to have a PTC resistor discharge it - that could be entirely mechanical. The PTC resistors would discharge the battery in a few hours, maintaining the battery temperature at say 120C. As water is doused onto the battery, it will boil off. As soon as the battery temperature cools below 120C, then every cell is guaranteed to be discharged.
- kayodelycaon 4y ago
  How well do these safety feature survive 2,000+ºF fire burning next to them?
  - dymk 4y ago
    there’s a period of time between normal operation and 2000 degree fire where this could be detected
  - DoingIsLearning 4y ago
    PCB solder will reflow at about 240°C or 470°F so provided you have a thermal resistant container around the pcb it will probably outlive the fire long enough to fail-safe, these kind of hardware mitigations will probably latch with a latency in the microseconds scale.
  - marcosdumay 4y ago
    Badly. How well does gasoline containers survive it? If you have a 2000°F fire, you probably have buildings collapsing and a lot of fire everywhere surrounding it. As long as things do not explode, you can't make it much worse by any action. And exploding is something the batteries don't do.
- KaiserPro 4y ago
  So in a thermal event, where integrity of the coolant is compromised, you want to dump more heat into the system? Its not just the electrical issues at play, its the fact that hot battery fluid burns spontaneously with exposure to air (I suspect also water, but I'm less sure about that)
quartesixte 4y ago
Add to the fact that the fuel is Lithium and you’re in for a badddddd time
- kwhitefoot 4y ago
  There really isn't as much lithium in a battery pack as people seem to think. The 450 kg pack in a Model S has about 60 kg of lithium. Dutch fire fighters dump the whole car in a skip full of water to cool it down once they have contained the fire so that it burns out but doesn't set light to anything else. 60 kg is roughly 9 kmol and 1 mol has a heat of combustion of 300 kJ/mol so if burnt in air it would release 3e5 * 9e3 = 27e8 J which is about 75 kWh (coincidentally about the same as the battery capacity). Enough energy to raise a ton of water by 67.5 K. So if you can submerge it in water it will pose no further risk. I presume that the lithium water reaction releases a similar amount of energy if the hydrogen burns, someone with a better knowledge of the chemistry could correct me.

bragr 4y ago

This is not really true. There are tools and agents to address lithium fires, but you have to have them. If you just try to put them out with water, you're going to be there all night fighting reignition.

DoneWithAllThat 4y ago
Please don’t leave us in suspense: what are these tools and agents? Got a link?
- marcosdumay 4y ago
  For lithium, sand is enough. If you have HF like a sibling said, sand won't do, but I can't imagine you would get enough of it to sustain a fire.
- bragr 4y ago
  Lithium fires are considered class B so any chemical agent such as found in any standard ABC or dry chemical fire extinguisher would be sufficient. As for tools, there's stuff that can be used to pierce the battery case and inject water or agents directly into the battery. https://arstechnica.com/cars/2021/11/new-firefighting-tool-delivers-water-directly-to-blazing-ev-batteries/ https://arstechnica.com/cars/2021/11/new-firefighting-tool-d...
KennyBlanken 4y ago
Lithium ion battery fires are not lithium fires. Water is the recommended method because it is the most effective way to stop thermal runaway. If you don't believe me, google "lithium ion battery fires water"
deleted 4y ago
[deleted]

londons_explore 4y ago

Electric cars could totally be designed to be re-ignite-proof. For example, you'd have the battery pack detect a breach - for example through a lack of pressurised coolant. That would then trigger each battery cell to have a PTC resistor discharge it - that could be entirely mechanical. The PTC resistors would discharge the battery in a few hours, maintaining the battery temperature at say 120C. As water is doused onto the battery, it will boil off. As soon as the battery temperature cools below 120C, then every cell is guaranteed to be discharged.

kayodelycaon 4y ago
How well do these safety feature survive 2,000+ºF fire burning next to them?
- dymk 4y ago
  there’s a period of time between normal operation and 2000 degree fire where this could be detected
- DoingIsLearning 4y ago
  PCB solder will reflow at about 240°C or 470°F so provided you have a thermal resistant container around the pcb it will probably outlive the fire long enough to fail-safe, these kind of hardware mitigations will probably latch with a latency in the microseconds scale.
- marcosdumay 4y ago
  Badly. How well does gasoline containers survive it? If you have a 2000°F fire, you probably have buildings collapsing and a lot of fire everywhere surrounding it. As long as things do not explode, you can't make it much worse by any action. And exploding is something the batteries don't do.
KaiserPro 4y ago
So in a thermal event, where integrity of the coolant is compromised, you want to dump more heat into the system? Its not just the electrical issues at play, its the fact that hot battery fluid burns spontaneously with exposure to air (I suspect also water, but I'm less sure about that)

quartesixte 4y ago

Add to the fact that the fuel is Lithium and you’re in for a badddddd time

kwhitefoot 4y ago
There really isn't as much lithium in a battery pack as people seem to think. The 450 kg pack in a Model S has about 60 kg of lithium. Dutch fire fighters dump the whole car in a skip full of water to cool it down once they have contained the fire so that it burns out but doesn't set light to anything else. 60 kg is roughly 9 kmol and 1 mol has a heat of combustion of 300 kJ/mol so if burnt in air it would release 3e5 * 9e3 = 27e8 J which is about 75 kWh (coincidentally about the same as the battery capacity). Enough energy to raise a ton of water by 67.5 K. So if you can submerge it in water it will pose no further risk. I presume that the lithium water reaction releases a similar amount of energy if the hydrogen burns, someone with a better knowledge of the chemistry could correct me.