this post was submitted on 30 Aug 2024
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I mean, it's funny and ironic in that Alanis Morrisette kind of way. But it actually makes sense.
Fire hydrants are heavily engineered hunks of metal. Metal getting rammed into at speed is a great way to generate sparks. And lithium fires are scary as hell. There is areason ANYONE futzing around with lipos should have a bucket of sand handy and why, as the article states, first responders need to handle these specially.
It is a similar principle as to how you don't pour water on a grease fire.
Ok a few things:
Batteries don’t need “a few sparks” to catch fire. They will generate plenty of heat if punctured and self-ignite.
You don’t pour water on a grease fire because grease floats and it will spill out of your pot and catch the rest of your kitchen on fire. Also the water will boil and splatter oil everywhere.
Also pouring water on a battery fire is the preferred way to put it out. Many of the chemicals in the battery will release oxygen when heated, so the best way to put it out is to cool it down as much as possible by dousing it with a shitload of water. It isn’t always possible to apply enough water to the core of the fire which is why they are hard to put out. Sand won’t do anything because the fire is self-oxidizing.
Yes lithium metal reacts with water, but that’s not what makes batteries hard to put out.
Upvote me then!
An aqua teen hunger force reference in thos day and age? Amazing.
That's the second one this decade. We are truly blessed
From my understanding the recommendation to have a bucket of sand around when handling lithium batteries is not to put the fire out with it, but to have something to throw the battery into that's not gonna catch fire as well, and then to carry the whole bucket somewhere where the battery can just burn out on its own. Is that wrong?
Yes and no. I think.
What I was taught was to dump the battery in the sand and cover it in sand. Then drench with water if possible. This also keeps the now toxic water from reaching a drain.
I expect you know as you were mainly talking about batteries (on this post about batteries) - but grease fires are not quite dangerous just because grease floats and adding water causes it to spill fire - when you introduce the water it does sink, but then it superheats to vapour, rapidly expanding and almost erupts the oil, chucking a poor man's napalm round everything in the vicinity
It doesn't have to even be on fire, if the oil is >100 degrees and there's enough of it to superheat adding water will do the same thing (minus the flames) - a melted face is better than a melted face and a house fire, but neither are recommended
Water turning into steam soaks up an enormous amount of heat. I assume that thermal runaway happens somewhere above 100C, right?
CO2 extinguishers work by displacing oxygen, not by cooling.
The rapidly expanding co2 does get very cold though. It’s not any different from freezing things with compressed air cans.
I don’t hover, know which would absorb more heat per pound though. Someone who knows more math than I can do it though.
If I’m reading Wikipedia correctly, it takes 348 Joules of heat to boil a gram of CO2.
Water is 2257 Joules per gram. As long as you don’t need anything cooled under 100C, water is the way to go for cooling. It’s also a hell of a lot cheaper and easier to deal with than liquid CO2.
I've heard plenty of times to never use water on a grease fire, but never learned why or what happens if you do. Thanks for that!
It's a lot more aggressive than what comes through in their description. It can create a giant fireball since the water boils instantly on contact and causes the burning oil to fling up into the air almost like a flame thrower.
17 second demonstration: https://www.youtube.com/watch?v=NgO_uZA5vXg
I once set oil on fire while making stovetop popcorn while drunk. This knowledge likely saved my house.
Here's another good one with some slo-mo action. You can see it's just a normal pot and what looks to be a single coffee mug full of water. The resulting fireball is massive.
https://youtu.be/3LWYXJvU7yM?si=h0Uz41HQS9-gJyLT
Yeah, this one is even scarier.
I'm wondering if EVs shouldn't have mechanism where if fire is detected the bottom part (which holds the batteries) would simply separate and fall to the ground exposing the batteries to firemen and making it easier to stop the fire.
Sounds like it could also work as a hot-swap battery pack, where you could drive up to a carwash style apparatus which takes your low charge battery and puts in a fully charged one.
In the majority of cases, its still going to be stuck under a mangled car that you cant move because it is on fire. A better solution might be to route multiple 'flood tubes' to the battery compartment and place them in easy accessible places. That way you would just need to pop pff an access panel and hook up a hose.
Could help, but could also add a lot of weight and complexity to handle an issue that is exceedingly rare.
Do ICE vehicles ever eject their gas tanks?
Yes. Apologies. I did not do a proper deep dive as a "Well ackshually" response to a joke post. I will endeavor to do better in the future.
out of curiosity, what do you pour on a water fire? I sure as hell know it's not grease.