Originally Posted by
SFflyer123
Imagine you're on the UA DEN-NRT 12 hour flight on a 787 and it decides that a battery starts to ignite. You can't put it out. The oxygen is consumed. The toxic fumes are filling the cabin.
Putting aside the dramatics:
1) The 787 is certified to fully vent smoke in the lower bays to the outside, preventing smoke from filling the cabin.
2) When they close the doors and seal the plane up, that isn't all of the air you're going to have for the full journey. In very simple terms, the air conditioning packs bring fresh air into the cabin.