Board Thread:Off Topic/@comment-25396609-20190908002326/@comment-25396609-20191028035529

EmBELLEm wrote: not just underwater. i was also thinking of poisoned areas, smoke, thin air without oxygen The rebreather/self-contained oxygen mask option is still effective for those; and more dependable too.

That said, I see no reason you can't have a Semblance that simply filters the contents of your lungs (or straight up converts whatever they're filled with into breathable air). One of my characters can convert the air in his lungs into super dense smoke; which comes with a passive immunity to airborne poisons and pathogens.