Crazy question from the family table
- Thread starter krulle
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There will be a lot of variation in the answers you may receive, since decompression is an individual science based on a lot of choices regarding conservative vs efficient vs quick, etc.
Personally, with the deco algorithm I am comfortable with (Buhlmann ZH-16 with GF 50/80), with an oxygen set point of 1.2 (again a personal, though common, choice) and no additional spiking of extra oxygen for decompression purposes, a descent rate of 30m/min (arguably a bit quick for a CCR dive) and an ascent rate of 10m/min, a dive to 60m with a BT (bottom time) of 3 hours would look like this:
Runtime Depth Stop time Comments
2 60m
180 60m Start ascent
186 39m 3
194 36m 8
204 33m 10 This is where you exceed 100% of the allowed oxygen exposure
219 30m 14
235 27m 16
255 24m 20
282 21m 26
315 18m 33
356 15m 41
411 12m 54
485 9m 74
746 6m 261 total of 356% of Oxygen exposure
So, for 180 min at the bottom you would spend 567 min ascending, for a total of 747 min or 12 1/2 hours.
That dive would utilise around 350L of oxygen so that's not an issue, its where the rebreather fails that you have a serious issue.
If you bailed onto open circuit gas at the end of the bottom portion, you would need around 17000 L of assorted gases to get to the surface safely, that's around 8 AL 80 tanks.
Aside from all of that, the scrubber of the rebreather would be hard pressed to deal with that on nearly very unit out there. In theory, it could be done by taking 2 or 3 rebreathers down with you, but the short answer is that a 3 hour dive to 60m would only be done by saturation divers in a commercial environment or by VERY serious explorers in a cave environment where there would be a LOT of prior preparation (pre-positioning tanks etc etc etc).
Of course there are ways to shave time off but this should hopefully suffice to demonstrate how serious dives to these depths can get.
This schedule is NOT a good idea in any form shape or size, it is purely for comparative purposes. Anyone diving a deco schedule they got off the Net is REALLY going to have a bad day!
Personally, with the deco algorithm I am comfortable with (Buhlmann ZH-16 with GF 50/80), with an oxygen set point of 1.2 (again a personal, though common, choice) and no additional spiking of extra oxygen for decompression purposes, a descent rate of 30m/min (arguably a bit quick for a CCR dive) and an ascent rate of 10m/min, a dive to 60m with a BT (bottom time) of 3 hours would look like this:
Runtime Depth Stop time Comments
2 60m
180 60m Start ascent
186 39m 3
194 36m 8
204 33m 10 This is where you exceed 100% of the allowed oxygen exposure
219 30m 14
235 27m 16
255 24m 20
282 21m 26
315 18m 33
356 15m 41
411 12m 54
485 9m 74
746 6m 261 total of 356% of Oxygen exposure
So, for 180 min at the bottom you would spend 567 min ascending, for a total of 747 min or 12 1/2 hours.
That dive would utilise around 350L of oxygen so that's not an issue, its where the rebreather fails that you have a serious issue.
If you bailed onto open circuit gas at the end of the bottom portion, you would need around 17000 L of assorted gases to get to the surface safely, that's around 8 AL 80 tanks.
Aside from all of that, the scrubber of the rebreather would be hard pressed to deal with that on nearly very unit out there. In theory, it could be done by taking 2 or 3 rebreathers down with you, but the short answer is that a 3 hour dive to 60m would only be done by saturation divers in a commercial environment or by VERY serious explorers in a cave environment where there would be a LOT of prior preparation (pre-positioning tanks etc etc etc).
Of course there are ways to shave time off but this should hopefully suffice to demonstrate how serious dives to these depths can get.
SAFETY WARNING
broncobowsher
Contributor
Half a day. Give or take a few hours.
That's all that needs to be said.
That's all that needs to be said.
The crazy thing is how much shorter your deco time becomes if you do it on open circuit. Still a long day and I don't know anyone doing OC deco from a CCR dive like this.
For a 3 hr dive at 200ft (or deeper) OC deco is shorter. Unless you subscribe to the dil switch concept.
3hrs at 200ft, 10/50 dil with a setpoint of 1.0 and 50/70 gfs = 894min dive
vs
3hrs at 200ft, 10/50 dil, setpoint of 1.0 on the bottom, 10/70 gf with 25/25, EAN50 and 100% OC deco gases = 701 min runtime.
Nobody would do that do that dive that way.
There's a few things you'd have to assume. First, it depends on where you stand on helium penalty. Second, you'd have to stay on your Dil, which no one that I know does. We are plugging in air as soon as we're 150'ish feet. And last, remember that a perfect PPO2 for the entire dive is better than a perfect PPO2 just for the max depth of the dive, at least for the purposes of deco.
I have 100's of dives at 300+ on CCR with buddy on OC, my deco is significantly less than theirs.
There's a few things you'd have to assume. First, it depends on where you stand on helium penalty. Second, you'd have to stay on your Dil, which no one that I know does. We are plugging in air as soon as we're 150'ish feet. And last, remember that a perfect PPO2 for the entire dive is better than a perfect PPO2 just for the max depth of the dive, at least for the purposes of deco.
I have 100's of dives at 300+ on CCR with buddy on OC, my deco is significantly less than theirs.
The big difference seems to be the 6m stop. In theory I can see how doing a 5 hour stop at 1.2 would be shortened by doing it on OC 100% but the gas amounts get pretty big pretty fast. Using an O2 breather for that deco stop would probably be the optimal ito deco duration.
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