In the case of Apollo 1, when they had the capsule pressurised to 16.7 PSI at 100% O2, how did they avoid having the crew exposed to high levels of O2 for too long? 14.7 PSI = 1 Atmosphere = 760 mmHg. oxygen toxicity starts at about 425 mmHg, so the crew should only be exposed to O2 levels above that for short periods.
So in the Apollo 1 case, they should have been exposed at a reduced pressure or at least at a reduced partial pressure of O2. I can't see how the regulator / ECS did it.
The way to do it would be to seal the suit, and run at a lower internal (suit) pressure and thus a lower O2pp... but would the higher external (cabin) pressure cause the suit to "cling"? Strapped in for a CDDT, etc, I wouldn't see a big problem... but I'd like to deal in facts, not guesses, and I don't understand.
Help!