I didn’t know that planes wouldn’t try to keep the ppo2 at 0.21.A human needs at least 0.16 ppO2.
And everybody who has been on a plane, has experienced breathing 0.16 ppO2!
This photo is from a SW at cabin pressure at high altitude:
View attachment 609840
So using TMX 4/85 at 90m (10bar) gives 0.40 ppO2. Still way more than 0.16.
Below 30m (4bar) that mix is life sustaining. (And an extremely bad idea to ascend to 30m with that mix)
Did you have a O2 sensor connected to your perdix or was it extrapolating from a normal air mix setting ?