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Ever wonder what thermal runaway looks like?

wk057

Vendor & Senior Tinkerer
Feb 23, 2014
6,069
14,207
Hickory, NC, USA
I posted this in my battery tear down thread, but I figure it could use its own.

so yeah... about that damaged module I was liberating cells from... done with that.

Somehow one shorted out while I was removing glue/plastic. Immediately went red hot, popped, flew off like a firework and of course, directly up into an open door to my basement ~15' away. (I was working on this outside by the pool, which is 3 steps down from the basement door and ~15' away.) Slid across the tile floor and landed in front of my fiance's PC another 25' away. Sat there for several seconds while I was chasing after it with a fire extinguisher in hand. Hit it a few times with the ABC chemical, and the chemical boiled on the shell. Seemed to cool is a bit, though, so hit it a few more times, grabbed it with a pair of pliers and leather gloves and threw it back outside in the dirt..... along with the entire rest of the module and the rest of the cells I removed previously.

So, think I'm done with that project.

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David99

Well-Known Member
Supporting Member
Jan 31, 2014
5,002
7,808
Nomad (mostly US)
From what I have heard, water is the best for a Lithium cell that is burning. The key thing is to reduce the temperature because the heat continues the chemical process in which it creates it's own oxygen. That's why the typical fire extinguishers don't work well. They are trying to prevent a fire to get oxygen. That doesn't help with burning Lithium cells that produce their own.
 
From what I have heard, water is the best for a Lithium cell that is burning. The key thing is to reduce the temperature because the heat continues the chemical process in which it creates it's own oxygen. That's why the typical fire extinguishers don't work well. They are trying to prevent a fire to get oxygen. That doesn't help with burning Lithium cells that produce their own.

Liquid nitrogen would probably cool an 18650 cell off in a hurry. :wink:
 

stopcrazypp

Well-Known Member
Dec 8, 2007
12,426
8,298
From what I have heard, water is the best for a Lithium cell that is burning. The key thing is to reduce the temperature because the heat continues the chemical process in which it creates it's own oxygen. That's why the typical fire extinguishers don't work well. They are trying to prevent a fire to get oxygen. That doesn't help with burning Lithium cells that produce their own.
That's what the first responder guides recommend too. Even though it may seem counter-intuitive to use water (because most places teach to never use water on electrical fires because of the conductive properties), the core thing is to control the temperature. However, the caveat is that it must be large amounts of water (a typical handheld class A water-based fire extinguisher probably isn't going to do much for a car battery pack or even a whole module).
 

stopcrazypp

Well-Known Member
Dec 8, 2007
12,426
8,298
The ABC extinguisher did it's job. It cooled the cell from red hot pretty quickly, although it took quite a bit for just one cell.
From what I read, dry chemical ABC extinguishers have very little cooling effect. However, part of its function is interfering with chemical reactions that allow fires to occur, so I guess that is the mechanism that is working in this case.
 

wk057

Vendor & Senior Tinkerer
Feb 23, 2014
6,069
14,207
Hickory, NC, USA
From what I read, dry chemical ABC extinguishers have very little cooling effect. However, part of its function is interfering with chemical reactions that allow fires to occur, so I guess that is the mechanism that is working in this case.

Most likely. Whatever it was, it was pretty effective overall.

In any case, I've decided I may invest in some high temp aerogel fire insulation for between the modules in my storage setup to go along with the other fire protection items on my list, based on today's event.
 

wk057

Vendor & Senior Tinkerer
Feb 23, 2014
6,069
14,207
Hickory, NC, USA
Do any of you carry a fire extinguisher in your tesla even though fires compared to ICE are a lot less likely to happen?

Or do you carry one anyway in case you come across another car on fire?

I don't really see the need. While a fire is uncommon, a portable extinguisher is going to do little to prevent or control thermal runaway of a Model S pack. The protective measures in place already should do as good of a job as any.
 
I bet you did not experience thermal run-away. Probably an internal short from physical damage.
The temperature you show is nowhere near thermal run-away temp, but perhaps you took that picture after cooling it.
If you hit thermal run-away... the cell should have vented, but perhaps the plastic and glue restricted the burst disc... :-/
 

wk057

Vendor & Senior Tinkerer
Feb 23, 2014
6,069
14,207
Hickory, NC, USA
I bet you did not experience thermal run-away. Probably an internal short from physical damage.
The temperature you show is nowhere near thermal run-away temp, but perhaps you took that picture after cooling it.
If you hit thermal run-away... the cell should have vented, but perhaps the plastic and glue restricted the burst disc... :-/

Yeah, the FLIR pic was at least 5 minutes after the incident. When it launched off it did so with enough force to extract itself from the remaining glue on that part (one side removed, probably half removed on the other so far). It went off like a rocket, had to grab the fire extinguisher I had on hand, run and chase it into the house, spray it down for a bit (took a lot of the extinguisher's charge), grab some pliers from my tool room, spray it again, pick it up with the pliers and throw it outside, go back in and check for anything that may have ignited (lots of papers and boxes near the path)........ relaxed for a moment with a sigh of relief...... grabbed all of the remaining loose cells I had indoors and threw them outside.... went back in, sat for a few minutes, then thought to grab the FLIR. After all that it was still showing 172F. It didn't drop to outside ambient until well over an hour later.
 

stopcrazypp

Well-Known Member
Dec 8, 2007
12,426
8,298
After all that it was still showing 172F. It didn't drop to outside ambient until well over an hour later.
The melting point of the ABC extinguisher mono-ammonium phosphate dry chemical is 190C (374F) at which point it appears to "boil" as you saw (the peak heat absorption is at this point; when it cools down it becomes white). So the cell must have reached at least that temperature.
 

tga

Active Member
Supporting Member
Apr 8, 2014
4,199
3,394
New Hampshire
I'm surprised no one has mentioned a CO2 fire extinguisher yet. Yes, water will cool them, but spraying them with dry ice "snow" will really cool them!

I have three fire extinguishers in my garage: a big ABC dry chemical as the panic catch-all, a rechargable Class A 2.5 gallon water extinguisher (fill with water and pressurize with the air compressor), and a 10 lb Class BC CO2 extinguisher.

Amerex #240 2.5 Gallons Water Fire Extinguisher: Amazon.com: Industrial Scientific
Kidde 466181 Pro 10 CD Fire Extinguisher, UL Rated 10-B:C, Carbon Dioxide, Red - - Amazon.com

The water extinguisher stays near the wood stove in the winter, and is handy for the occasional minor "oops" when welding. I'm sort of embarrassed to admit that I had to learn the hard way that wooden sawhorses aren't really the best welding support:
IMG_1514 (Custom).jpg


I keep the CO2 extinguisher handy if I'm working with the torch on a project car. One thing I like about both (vs ABC dry chemical) is since cleanup is completely trivial, so when in doubt, spray away.
 

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