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I've been reading on safety protocols on Li batteries and I seem to remember that Lithium itself is extremely reactive to water.

However, FAA regulations recommend using water to douse the device to keep it cool.

Is the FAA's recommendation incorrect or is there a particular threshold where water causes more problems?

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  • \$\begingroup\$ Hmm. That doesn't sound quite right to me but I've never needed to put out a lithium battery fire. \$\endgroup\$ – DKNguyen Jul 18 at 3:47
  • \$\begingroup\$ I'm pretty sure this has been asked before, this isn't really an electronics question \$\endgroup\$ – Voltage Spike Jul 18 at 3:52
  • \$\begingroup\$ From what I understand, the recommended approach WHEN POSSIBLE is to douse the fire with a truly copious amount of water. If that is not available, you may be best off letting the batteries burn and just using your limited extinguishing media to prevent secondary fires (keep the fire from spreading beyond the battery pack). Avoid breathing the smoke and warn others who may be in danger, etc. \$\endgroup\$ – mkeith Jul 18 at 7:31
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There is actually very little lithium in a Li-ion battery, typically only about 1% by weight (source). What makes Li-ion battery fires hard to put out are the other materials such as the plastic separator, organic chemicals, carbon anode coating and aluminium plates. Lipo cells are particularly nasty because they are contained in a soft polymer pouch which ruptures and allows bits of flaming battery to 'explode' all over the surrounding area.

Throwing a burning li-ion battery in water does two things: firstly it cools the battery down which reduces the formation of combustible gasses and removes heat which prevents them from burning. Secondly it deprives the fire of oxygen which most gasses need to burn (though not Lithium).

If the battery has not yet 'exploded' then the Lithium is contained in the cells where water can't easily get to it, so the explosion which occurs when exposed Lithium metal is thrown into water is unlikely to occur. If the battery has already exploded then the small amount of Lithium in it has probably already burned, and the water is just putting out whatever is left.

I have decommissioned a lot of damaged Lipo batteries. I do this by first discharging each cell with a resistor until the open-circuit voltage is less than 1V. Then I hammer a nail through the battery to short out all the plates. Sometime the battery gets a little warm and may even emit a bit of smoke, so I keep a bucket of water nearby. One time I put a nail through a large fully charged battery that I had forgotten to discharge. Flames shot out of it and a huge amount of smoke quickly developed, but the fire went out and smoke subsided as soon as I threw it into the water.

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  • \$\begingroup\$ After piercing the battery with a nail, does liquid electrolyte leak out? \$\endgroup\$ – mkeith Jul 18 at 21:11
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    \$\begingroup\$ No. there is very little liquid in a Lipo battery, and what there is tends to stick to the separator and plates. diydrones.com/profiles/blogs/lipo-teardown \$\endgroup\$ – Bruce Abbott Jul 18 at 22:53
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Case: The Lithium battery is super hot, to hot to touch but the case isn't broken. Throwing this in water will help cool the cell down, nothing will happen.

Case: The Lithium battery case is broken and super hot/on fire, the lithium will react quiet violently with water the lithium will become Lithium hydroxide (LiOH) which i 10/10 wouldn't recommend getting in the eyes. This process will generate hydrogen gas, which i 10/10 wouldn't recommend getting near open fire.

there seems to be a trade off between cooling the cell down / risking your eyesight / burning down the building.

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  • \$\begingroup\$ A plane full of passengers v your eyesight .... decision time.. hero or ... \$\endgroup\$ – Solar Mike Jul 18 at 6:19
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    \$\begingroup\$ There is no elemental lithium in the battery, there is more cobalt. The oxidation reaction of the electrodes produces more oxygen for, especially the electrolyte, and surroundings to burn. That is why it's so difficult to extinguish. \$\endgroup\$ – Jeroen3 Jul 18 at 6:36
  • \$\begingroup\$ I see, thank you for the clarification @Jeroen3 \$\endgroup\$ – Sorenp Jul 18 at 7:00

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