[Mr. K]

I can’t believe someone thought it was a good idea to use pure oxygen...

[JRandomFreeper]

At 15 PSI.

/johnny

[RayChuang88]

The biggest problem was all the exposed combustible materials inside the Apollo capsule, which really worried the astronauts even well before the Apollo 1 fire. North American Aviation should have flown an unmanned mission with the then-production capsule in early 1967 to check out systems in space before Apollo 1 flew—and it’s likely they would have identified the combustible material problem early on.

[Da Coyote]

“I can’t believe someone thought it was a good idea to use pure oxygen...”

Agree. I would not have guessed that early Microsoft engineers were on the program. /s

It did result in a complete redesign of the capsule air system, however.

[chimera]

I think the idea was to purge nitrogen from the bloodstream so there would not be adverse effects from unplanned pressure changes. Cabin pressure is lowered to 5 psi during ascent which causes nitrogen to come out of solution. In hindsight it would have been better to use an air-like mixture during launch and ascent with gradual replacement with pure oxygen as the mission progressed.

[Hegewisch Dupa]

The thinking was that if you are going to make the capsule atmosphere 80% nitrogen like Earth's, then you are adding a lot of weight for something that is completely unnecessary. Except that yeah, it was only a good idea on paper, and nitrogen's inherent ability to prevent fires starting was a pretty damn useful thing.

Another problem with the Apollo 1 fire is that when on Earth, the capsule pressure has to be much, much higher to prevent the capsule from collapsing under the pressure of Earth's atmosphere. So the oxygen concentration was far higher than it would have been in space.