OP
PSAI Narcosis Management course - 73m on air
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LiteHedded
Contributor
I just like to do a slow ascent on o2. the last twenty feet are a critical part of deco. offgassing becomes much less efficient when you switch to backgas.
to say that the deco is 'complete' after ur 20' stop is a little misleading
Just put the reg in your mouth and descend. Its got more oxygen than skydivers get to breath (or many mountain climbers). After 5+ mins of breathing it at the surface you'll be a bit winded but it would take a LONG time to pass out from 15% O2 (if ever). I can tell you 1st hand its fine.
OP
Fair enough. We plan to complete deco at 4.5m and then take 3 minutes to get to the surface on backgas (in this case air) before handing the stage bottles up to the boat while still keeping our regs in due to the swell
Not really, let me explain.
Your DECO SCHEDULE may give you the OK to surface, but your body is STILL DECOMPRESSING, even on the surface. Your DECO is not done. If it was, why would you need a surface interval to offgas residual Nitrogen?
Your body will keep decompressing until the gases are in equilibrium with atmospheric pressure. Depending on the various tissue compartments, this can take a long time. Your decompression schedule has accomplished its task. It has allowed you to get to the surface without exciting the bubble micronuclei enough into forming bubble seeds.
This is the basis for decompression theory. You can look up "Gradient Factors" if you wish to further understand the dynamics.
It is generally accepted that going from a low N2 gas to a higher N2 gas is counterintuative to proper accelerated decompression.
In other words, once you are on o2, you stay on o2 until you surface (and even breathe it for a bit while on the surface). I can think of NO AGENCY that advocates switching to air after o2. (other than Air Breaks)
Yes, you will be breathing air once you are on the surface, the difference is that you are no longer under pressure from the water column.
Hope that clears it up a bit.
Safe Diving,
Blackwood
Contributor
Depends on how long your oxygen segment lasts.
OP
Blackwood
Contributor
Looks like if you both followed the vpm schedules to a T, he'd actually be below you for part of the deco. He'd still be at 6m as you are moving up to 3m, and still be at 3m as you are surfacing.
But really, it's not a big deal. You could easily extend your 6m and 3m stops by one minute each and hold to the same schedule (which would be my own preference).
For the sake of making a point, I was not considering total Oxygen exposure for his bounce dive. Yes of course it becomes part of the plan, but at which time do you think his OTU numbers were tracked during the deep air course?
He would have to dive quite a bit to get to the point of Air Breaks. And if you look at the profile, he was never on o2 for over 15 minutes.
As for his air bounce dive my point still stands. Stay on o2 until you take your gear off.
PS: After re-reading my original post, I included the "air breaks" reference so as not to confuse anyone. Thanks for bringing it up Blackwood.
Safe Diving
Blackwood
Contributor
^^ I know, it's a non-issue for this dive.
I was just pointing that out because yours seemed like a blanket statement.
I was just pointing that out because yours seemed like a blanket statement.
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