Halon - oxygen depletion
Having once been involved in a very large fire whereby halon
was released, I can say that halon reduces fire by interfering
with the combustion process. In my case it was safe for humans
to be exposed to the halon atmosphere for in the order of hours.
That said surely halon might be useful in the boeing battery box.
If it is certain that there is no way for the contents of the box to
generate oxygen, then an inert atmosphere of any kind should
also work. If the batteries have a major short there still remains
the problem of the heat generated.
By the way, I looked up the battery rating of my ancient diesel's
12v lead acid battery and it is 920 amps for 30 seconds,
with a final voltage of at least 6 volts, and chemical recovery thereafter.
Still I suppose Boeing chose their particular li-ion
technology for some good reason. I see that many electric cars
use li-ion manganese. For the 'ZOE' the makers state that all
cells are monitored for condition, and charging is possible from any state of charge.