Fine dry sand as a fail-safe smothering agent for battery fires

Elmo

Elmo

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I haven't really been considering stationary lithium batteries much until just lately but the idea came to me a few years ago when building ebike batteries to use fine dry sand held back by a plastic dam or dams arranged so that if the dam or dams melt the sand floods the battery space. I don't think I've seen the idea anywhere else and this seems like the ideal forum to share it on.

That's about it, choice of plastic, thickness and configuration of the dams, arrangement of the sand reservoir, the battery space and so on to be determined.

I've seen a small lithium battery fire, a big one could be catastrophic, I'm sure thinking about doing this with my upcoming setup.
 
That would be interesting. Not sure how practical it would be, but it could be a possibility. I haven't looked into how the batteries react with water, or other types of retardants. Something worth looking up, though.

Questions to think about would be:
1) How hot does the liion get when on fire?
2) How hot does sand get to melt?
3) Could sand that has reached the temperature of an inflamed liion possibly ignite others?
4) What type of sand would be best to use?
5) What other types of materials could be used that could be easily cleaned up?
6) Add future questions here..... :p

But I do like the idea of being able to snuff out any kind of fires that may start within the confines of flammable building.
 
Silica sand is quartz granules, quartz is very stable and has a melting point of 1670C. Silica sand can be purchased as blasting media in various grades down to near-talcum powder consistency.

I did come up with a potential dam material, nitrocellulose cloth. It's possible to treat ordinary cellulose cotton cloth such as a tee shirt in order to make it into extremely flammable nitrocellulose but still mechanically almost identical to regular cotton cloth. There wouldn't be any melting with that stuff, one touch of a spark and it's gone in a moment and in comes the sand.

I lived near the beach for a few years in the days of my youth, we used to build fires in the dunes at night and a sure way to smother even the hottest campfire was to shovel sugar sand on it. That's what got me thinking about using sand as smothering agent for battery fires.
 
I had the idea of putting a pane of toughened glass between the cell compartment and whatever fire suppression material chamber.
Didn't think of using sand, I was going to use water as last defence measure.

Toughened glass, is pretty likely to shatter into a thousand pieces when subjected to uneven heat, shock, physical impact. Thus dumping the entire load of sand in at once.
I'd probably chose a coarser sand, as it's less prone to being blown around by cells venting etc.
 
Dumping sand on my pack would create a work of art I think... Imagine an archaeologist in a million years that digs up 4000 18650 cells encased in glass.
 
I think I have come up with a truly shade tree way of doing this, plastic freezer bags full of sand on top of each bank of cells.

station240 said:
I'd probably chose a coarser sand, as it's less prone to being blown around by cells venting etc.
Click to expand...

I thought about the granularity of the sand as well, coarse enough to be a better insulator due to lack of contact between grains and air space but not so coarse to allow enough air to get to the cells to continue the reaction.
 
The air itself does not do much to the cells. Lithium can burn in water as well where there are no "free" O2 molecules... (I hope i remember my chemistry correct now)

The problem with Lithium is that it do have all stuff needed to actually burn. Or at least kind of. And that makes it very very hard to stop burning.
 
I've seen lipo burn underwater, I'm sure 18650 will do the same. As I recall lithium is so reactive and the flame so hot it strips the oxygen from the hydrogen atoms in water.

I looked around and found a box of culled cells that haven't gone back to the recycle, I'm going to try a zip lock bag of sand on top of a few after I ignite them with a torch and see what happens.

As someone I know is fond of saying "One test is worth a thousand opinions."
 
Same here :) I did some burn tests the other day and that video is coming up today.

I also have some 100 cells more that i could fire of if needed :)
 
Elmo: If you dont mind i have an idea to test as well if im allowed to put up a video of that? (I ask since you came with the idea first... )

Thats how I am :)
 
Daromer, I'd be thrilled to see a video of your test, please by all means be my guest. I don't watch many videos because of bandwidth limitations on my connection but I'll make it a point to watch that.

I'm a big fan of fail-safe, if it can be done for DIY Powerwall packs as cheaply and easily as I suspect it might then it would be immoral of me not to share a potentially life and property saving idea.

A bag or bags on top of the individual packs keeps potential cleanup to only the one pack with a little forethought in the design to isolate the packs. Orient the cells vertically and each one will be the same relatively short distance from the plastic and the sand.

Does a sand-quenched pack require fuses? I admit I built 12s12p ebike packs from harvested cells without fuses before I knew better but nothing ever happened to them in quite a few thousand road miles. I kind of shudder to think of the meltdown I could have had between my legs. Talk about a hot time in the old town tonight...
 
daromer said:
The air itself does not do much to the cells. Lithium can burn in water as well where there are no "free" O2 molecules... (I hope i remember my chemistry correct now)

The problem with Lithium is that it do have all stuff needed to actually burn. Or at least kind of. And that makes it very very hard to stop burning.
Click to expand...

Elmo said:
As I recall lithium is so reactive and the flame so hot it strips the oxygen from the hydrogen atoms in water.
Click to expand...

Sigh, I see I have to have this discussion here too.
The fire comes from the unstable electrolyte (Ethylene carbonate) reacting with the positive anode (Cobalt Oxide, CoO2).
So you have fuel and oxygen created, hence the mini rocket nozzle.
The lithium is in the form of a compound, and in small quantities, so has minimal involvement in the chaos above.

See this page for a detailed breakdown of the chemical reactions within a failing Lithium Cobalt cell.
http://www.mpoweruk.com/lithium_failures.htm
 
We all have our areas of expertise and interests, electronics more so than chemistry happens to be mine. Lithium metal will in fact burn underwater by the process I mentioned, that may not be what is happening in a burning 18650 cell but it can and does happen.

It's difficult to get all the caveats and details into a brief forum post, I do know that lithium cells contain sufficient products for combustion on their own, I assume that extra added oxygen will not help matters when trying to extinguish such a conflagration.
 
Station240 Thanks for correcting :)
Was unsure there what parts was involved. Only remembered that when they go they go.

Elmo i will do a test to see. I have an idea i want to test.
 
In the meantime, let us enjoy some slo mo explosions:

 
I wonder how much sand would be required to snuff a fire before it got out of control? Think house fireand tossing a kid's sippy cup worth of water on it. You'll get a bit of steam but won't do anything else. Dump a water bomber's worth of water, it might flatten your house but it would likely put the fire out right away. Challenge is finding the happy medium.

I know if you look up fire extinguishers for lithium fires they always talk about type D instead of the more common ABC type we should all keep around the house.
 
[img=500x281]https://snag.gy/kzxXt4.jpg[/img]
This is my idea.

You have 2 boxes on top of each other. The bottom one will be the one with batteries inside. The top one holds the sand. Only thing between them is chicken net and the plastic.
Chicken net is there to keep the plastic from fall down and keep the sand up. And the plastic holds the sand. As soon as any fire comes the plastic will melt and let the sand fall through down on top of the batteries....

Lets see if i get some hours free this weekend to test it. And if you got any sugestions let me know.
My plan is to heat the batteries with a heating element placed under the batteries.
 
Now, I'm assuming that the packs would 'have' to have the positive side up, correct? That's the end with the vent holes and the designed end to fail under super-violent discharge.

This idea wouldn't really work for a lot of us who plan on or have our packs hanging end-to-end, like Pete's. Wonder what other idea could be use for snuffing out hanging packs. *ponders*
 
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