More technical notes… (a) Pure oxygen is toxic at pressures of 1.6 bar or higher. 1.6 bar is the equivalent to about 6 m underwater. 10 minutes to a depth of 200 m would be fatal. (b) If it isn’t fatal in your world, then there would likely be no need to decompress on the ascent since the bends is an effect of high partial pressures of inert gases (like nitrogen or helium) which they’re not breathing.

Sweet! Ya, I did some research into “longest dives” and “shortest times” and atmospheric pressure stuff. I tried to pick ranges that made (fantastical) sense to me and the rebreather/symbiotic unit they use. I wanted to get somewhere in between real and fantasy.

I read about divers reaching phenomenal depths in minutes, to then take many hours to ascend. I took that as a guideline for the enhanced elemental-rebreather while still keeping ascent dangerous (maybe so that the elemental symbiote itself had to accomodate the pressure changes?!)… frig does that still make sense?

Your knowledge in the real world counterpart stuff is so appreciated as I’m reluctant to go all-out fantasy with this.