The WP page for the ISS says that it has a fairly earth-like, sea-level atmosphere: 21% oxygen, balance nitrogen at 101.3 kPa. Supposedly it's because a pure-oxygen environment is dangerous as in the Apollo 1 disaster, but in that case "pure-oxygen" meant 1.15 atm of O₂. It seems like a pure, 0.21 atm O₂ atmosphere (or even lower) with no inert balance gas should be fine for people and would be ~80% less structurally demanding.

One strange aspect might be an effective drop in boiling point to ~60 °C, but I'm not sure if anyone'd be boiling water for tea up there. My presumption is that it's not for any safety or human reason but solely for the sake of making ISS experiments more similar (and directly comparable, save for the microgravity environment) to those on earth. Am I not considering something?

The Wikipedia page for the International Space Station says that it has a fairly Earth-like, sea-level atmosphere: 21% oxygen, balance nitrogen at 101.3 kPa. Supposedly it's because a pure-oxygen environment is dangerous as in the Apollo 1 disaster, but in that case "pure-oxygen" meant 1.15 atm of O₂. It seems like a pure, 0.21 atm O₂ atmosphere (or even lower) with no inert balance gas should be fine for people and would be ~ 80% less structurally demanding.

One strange aspect might be an effective drop in boiling point to ~ 60 °C, but I'm not sure if anyone would be boiling water for a tea up there. My presumption is that it's not for any safety or human reason but solely for the sake of making ISS experiments more similar (and directly comparable, save for the microgravity environment) to those on Earth. Am I not considering something?