Trimix, o2 %

[omar]

......
generally speaking a .18 ATA is considered the lowest partial pressure needed to keep you conscious

Just to have a little fun here.... I spend a lot of time in the summer diving at high altitude lakes. The partial pressure of oxygen at the surface (campground) is significantly below 0.18 atm. For example a lake at 7010 above sea level (MSL) the surface ppO2 will be 0.16 atm. I have not passed out yet when camping at this and other spots up to 10,000+ MSL. I do make sure that when diving a hypoxic mix (one less than 21% O2) that I consider any possible surface swimming and plan accordingly.

omar

 

[H2Andy]

i wasn't even thinking of altitude diving

but i would imagine that if TDI requires a .18 ATA at the surface, they'd probably require the same at altitude.

you could probably do it lower (just like you could probably dive higher than 1.8) and get away with it ... but ...

not sure if it's the best practice

 

[dmdoss]

Thanks for the info, thats what i was looking for.