: The Pfhor (at least, some of them) breathe Oxygen/Nitrogen mix (?).
: I presume the Fighters with their Breath Masks only have them because they
: like their air more humid (or arid, as the case my be) than normal ship
: environments permit.
The fighters always wear masks because Bungie didn't want to make separate sprites for different environments ;^)
Actually, the more plausable explanation is protection against alien microbes. Perhhaps the Enforcers have a genetically enhanced immune system that protects them, whereas the fighters do not. In any case, that still doesn't explain why they wear masks on board their own ships. Now as to breathing different types of atmosphere, this is a much more complex situation and in reality, we would all wear environmental suits, even in oxygen-rich atmospheres as even moderate deviations from the mix of O2, CO2 and other gasses would significantly alter the pH of our blood, not to mention the possibility of causing other gasses to come out of solution, as does nitrogen when divers get the bends. BTW, extracting energy from CO2 would require a metabolism based on something even more reactive with O2 than carbon - elemental sodium, perhaps. In that case, oxygen would be so toxic to the Nebulons that they would spontaneously combust in an oxygen-rich environment. In fact, water would be like napalm to them. That provides some interesting possibilities in terms of story, doesn't it?
