Recreational Ascent Rate in the last 15 feet
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Models derived from empirical data basically say if you stay within these parameters, you'll have an x in y chance of developing clinical DCS on any given dive. They don't say if you scale these parameters down 50% you'll be safe-er, for whatever value of "safer" you chose to employ. They have no data to support that.
It's one of those black and white binary things: yes data - no data. The scary change in surfer girlfriend falls squarely into "no data" bucket, the way I see it.
OP
You know, you're right.
But the theory is attractive. And on the 25th dive of my week-long vacation, I think I'll still slow down my last 15 feet of ascent, even without data.
After all, it can't be worse than all the diving that followed that similarly data-less bubble model.
I liked that one too, even though I now don't believe in deep stops. It made a lot of sense, even though the data isn't bearing it out.
A far as this theory goes, I'll take my chances. If I've got the gas, I'll watch fishies.
OP
Actually, @dmaziuk 's persistence on this issue has me thinking...
I'm concluding, at a theoretical level, that the Bubble Model has it right. But it's maybe just wrong on a matter of degree.
We're protecting the fast tissues, but they don't need it until right at the end.
If we accept that at least on early Rec dives in a series, the slow tissues are all ongassing, then the only compartments that we're dealing with are the fastest, since they were saturated during your hour's dive to three ATA. The slower compartments don't (yet) have enough saturation to have a worrisome gradient upon surfacing. So "slower is better" only applies shallow, in order to protect the slower compartments from unnecessary ongassing in preparation for dive #25 during your vacation, when they may be fuller, yet less able to offgas. Since faster compartments have been stated to have more resistance to bubbling at higher gradients, "slower is better" only applies shallow, where the gradient is higher. That is why I'm supposing that the NEDU and Spisni studies turned out the way they did.
If the above is true (and the deep stop guys may disagree), then the "bloom" in GF99 in the last 15 feet may bear addressing, and the final supersaturation (SurGF) is, as always, important as your measure of how much excess saturation you choose to accept.
As a separate issue for a separate thread, this may support even reverse GF's, at least for the early dives in a series, to protect the slower tissues in anticipation of dive #25 on your trip.
But to answer @dmaziuk , yes! I guess I am just protecting the fast tissues with this deceleration in the last 15'. Whether or not they need it. Because the lack of data leaves me in the dark as to just how much protection they really need. I think I've fixed my level of risk by choosing my GFHi. But I still can't ignore the visual of that Coke can. Hence the attention to the rate at which I reach that SurGF.
Now we have to consider where the deceleration needs to start once your slower compartments are filling up by dive #5 in a day, on day #6 of your vacation. Maybe we'll need to add a "deeper pause", by which I really only mean 30 feet (just so the deep stops guys are clear).
Bubble theory is still attractive. Maybe we just took it too far.
But @dmaziuk had it right. No data is no data. I'm on a blind date with my Surfer Girlfriend!
I'm concluding, at a theoretical level, that the Bubble Model has it right. But it's maybe just wrong on a matter of degree.
We're protecting the fast tissues, but they don't need it until right at the end.
If we accept that at least on early Rec dives in a series, the slow tissues are all ongassing, then the only compartments that we're dealing with are the fastest, since they were saturated during your hour's dive to three ATA. The slower compartments don't (yet) have enough saturation to have a worrisome gradient upon surfacing. So "slower is better" only applies shallow, in order to protect the slower compartments from unnecessary ongassing in preparation for dive #25 during your vacation, when they may be fuller, yet less able to offgas. Since faster compartments have been stated to have more resistance to bubbling at higher gradients, "slower is better" only applies shallow, where the gradient is higher. That is why I'm supposing that the NEDU and Spisni studies turned out the way they did.
If the above is true (and the deep stop guys may disagree), then the "bloom" in GF99 in the last 15 feet may bear addressing, and the final supersaturation (SurGF) is, as always, important as your measure of how much excess saturation you choose to accept.
As a separate issue for a separate thread, this may support even reverse GF's, at least for the early dives in a series, to protect the slower tissues in anticipation of dive #25 on your trip.
But to answer @dmaziuk , yes! I guess I am just protecting the fast tissues with this deceleration in the last 15'. Whether or not they need it. Because the lack of data leaves me in the dark as to just how much protection they really need. I think I've fixed my level of risk by choosing my GFHi. But I still can't ignore the visual of that Coke can. Hence the attention to the rate at which I reach that SurGF.
Now we have to consider where the deceleration needs to start once your slower compartments are filling up by dive #5 in a day, on day #6 of your vacation. Maybe we'll need to add a "deeper pause", by which I really only mean 30 feet (just so the deep stops guys are clear).
Bubble theory is still attractive. Maybe we just took it too far.
But @dmaziuk had it right. No data is no data. I'm on a blind date with my Surfer Girlfriend!
But you're not: fast tissues are the ones that are first to react to pressure change, therefore they're leading at the start of the ascent. By the time you get to safety stop depth, they're no longer leading; it's some "intermediate" one(s) that are.
FWIW I'm happily diving an RGBM computer myself, deep stops or not (and it seems to favour longer safety stops and slower ascents in the top 10 metres). On actual dives I keep it simple stupid: I have a computer and I follow it. To me these threads are just an amusing exercise in counting angels on the pin during slow spells at work.
OP
Lol! You always keep me on my toes. I am guilty of sloppy writing.
By fast tissues, I didn't just mean the 5 minute compartment. For the average Rec dive to 60-100 feet, let me be more specific and suggest that this approach might have some benefit for any compartment under three half lives of your dive duration. So for the "typical" hour's dive that hits 70 ft and averages 45 feet, that would be any compartment with a 20-min half life or less. What's that? Maybe Buhlman's first four compartments? I'm suggesting extending your safety stop and slowing down to 1m/min from SS up is a good thing.
Running out of gas aside, what could be wrong with it? If irrelevance is its worst sin, I'll accept that.
It does not vary the length, nor ascent rate. The way RGBM works, you get "reduced gradient" on subsequent dives, which really translates to shorter NDL.
What I meant was on shore dives we'd typically follow the sand all the way to waist-deep. Which effectively means having an extended safety stop with very slow ascent rate in the last 25-30 feet. On those profiles, w/ 60-ish minutes runtimes and max depths up to 30 metres, I never see single-digit NDLs after a week of 2-3-4 dives/day. We do 60 minutes SIs as well.
On squarish profiles with straight 3 minutes SS on the line and 40-45 minutes SI -- boat rules -- I had single-digit NDLs after a few days of only 2 tanks/day.
So from my very representative sample of 2 it looks like Cressi Leo likes slow ascent rates and longer stays in the top 15-20 feet and dislikes short surface intervals and "bare minimum" safety stops.
OP
Here are some numbers. Using @EFX wonderful spreadsheet at GF 50/75, I dived three profiles down to an NDL of 1 minute. The variables are only Safety Stop duration and ascent rate from 15' to the surface. Ascent rate from depth to SS was 30 fpm for all dives.
The results below are leading compartment (LC) number and compartment half-time, and Surfacing GF (SurGF) [IF %AoM is @EFX equivalent in his spreadsheet]
Here's 48 ft x 57 min:
3min SS; 30 fpm ascent from SS to surface:
LC #6 (38 min); GF 86
5min SS; 30 fpm ascent from SS to surface:
LC #6 (38 min); GF 85
3min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 82
5min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 81
10min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 80
Here's 60 ft x 24 min:
3min SS; 30 fpm ascent from SS to surface:
LC #4 (18.5min); GF 77
5min SS; 30 fpm ascent from SS to surface:
LC #5 (27 min); GF 76
3min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 73
5min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 73
10min SS; 3 fpm ascent from SS to surface:
LC #5 (27 min); GF 73
Here's 100 ft x 9 min:
3min SS; 30 fpm ascent from SS to surface:
LC #4 (18.5min); GF 66
5min SS; 30 fpm ascent from SS to surface:
LC #6 (38 min); GF 65
3min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 64
5min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 64
10min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 64
Where going from a 3' to 5' safety stop drops 1% off your SurGF,
doing 5' and slowing your descent drops an additional 1-4% off that.
Bang for the buck appears to be in the final ascent rate more than the length of the SS.
Just for grins, I then did a max multilevel dive taking each level to an NDL of 1 min -
100 ft x 9 min; ascend to 60 ft x 10 min; ascend to 40 ft x 40 min. Here are the SurGF numbers:
3min SS; 30 fpm ascent from SS to surface:
LC #6 (38 min); GF 88
5min SS; 30 fpm ascent from SS to surface:
LC #6 (38 min); GF 88
3min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 85
5min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 85
10min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 85
Again, bang for the buck appears to be in the slow final ascent.
On the other hand, the results of slowing the final ascent were disappointing in the small magnitude of improved SurGF. @dmaziuk may be right.
It may just be pissing into the wind...
The results below are leading compartment (LC) number and compartment half-time, and Surfacing GF (SurGF) [IF %AoM is @EFX equivalent in his spreadsheet]
Here's 48 ft x 57 min:
3min SS; 30 fpm ascent from SS to surface:
LC #6 (38 min); GF 86
5min SS; 30 fpm ascent from SS to surface:
LC #6 (38 min); GF 85
3min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 82
5min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 81
10min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 80
Here's 60 ft x 24 min:
3min SS; 30 fpm ascent from SS to surface:
LC #4 (18.5min); GF 77
5min SS; 30 fpm ascent from SS to surface:
LC #5 (27 min); GF 76
3min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 73
5min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 73
10min SS; 3 fpm ascent from SS to surface:
LC #5 (27 min); GF 73
Here's 100 ft x 9 min:
3min SS; 30 fpm ascent from SS to surface:
LC #4 (18.5min); GF 66
5min SS; 30 fpm ascent from SS to surface:
LC #6 (38 min); GF 65
3min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 64
5min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 64
10min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 64
Where going from a 3' to 5' safety stop drops 1% off your SurGF,
doing 5' and slowing your descent drops an additional 1-4% off that.
Bang for the buck appears to be in the final ascent rate more than the length of the SS.
Just for grins, I then did a max multilevel dive taking each level to an NDL of 1 min -
100 ft x 9 min; ascend to 60 ft x 10 min; ascend to 40 ft x 40 min. Here are the SurGF numbers:
3min SS; 30 fpm ascent from SS to surface:
LC #6 (38 min); GF 88
5min SS; 30 fpm ascent from SS to surface:
LC #6 (38 min); GF 88
3min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 85
5min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 85
10min SS; 3 fpm ascent from SS to surface:
LC #6 (38 min); GF 85
Again, bang for the buck appears to be in the slow final ascent.
On the other hand, the results of slowing the final ascent were disappointing in the small magnitude of improved SurGF. @dmaziuk may be right.
It may just be pissing into the wind...
FreeFlyFreak
Contributor
Maybe.
But.
The bang for the buck may not be, solely, in the final GF, but in how you get to it. The slow release of pressure on the body when the leading compartments are highly loaded with gas.
Or if you prefer, slowly increasing the tissue over pressures during the last part of the ascent.
Like the soda bottle.
If you release the pressure above the dissolved highly loaded soda very slowly. Very little bubbling.
If you release the pressure, that is keeping that gas in solution quickly, the soda bubbles over.
The amount of gas in solution in the soda didn't change between bottles, only how quickly you changed the external pressure keeping it there.
Of course that is only one "compartment" and an extremely quick one at that i would imagine.
Just playing devils advocate.
Very similar to how exercise after diving is thought to trigger DCS if highly loaded.
You released the pressure slowly but then go back an hour later and shake up the container.
Or take a hot shower (heating up the soda so the fluid has less ability to hold gas in solution)
More devils advocate.
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