Comment by waste_monk

>Can halon systems not put out lithium fires?

As the other commenter said, Halon hasn't been a thing for a fair while, but inert gas fire suppression systems in general are still popular.

I would expect it wouldn't be sufficient for a lithium ion battery fire - you'd temporarily displace the oxygen, sure, but the conditions for fire would still exist - as soon as enough nitrogen (or whatever suppressant gas is in use) dissipates, it'd start back up again.

Also as I understand thermal runaway is self-sustaining, since the lithium ion batteries have a limited capacity to provide their own oxygen (something to do with the cathode breaking down?), so it might continue burning even while the area is mostly flooded with inert gas.

I believe it would be similar to an EV car fire, that is, you'd have to flood the area with water and wait for it to cool down enough that thermal runaway stops. Maybe they can do better these days with encapsulating agents but I'd still expect the rack housing the UPS to be a write-off.