Why S-Curve
I have being getting this question a little since some people don't quite understand. So I wanted to explain it a little and open the floor for questions....
We use a deco bottle to both reduce the requirements of rock bottom and to accelerate the decompression by 50%. The way we do this is by elevating the FO2 in the bottle, so that when we first switch to the deco bottle we have the highest tolerable PPO2 of 1.6, and then slowly reduce it over the 5 stops until it reaches a PPO2 of 0.8, and then we can switch again or do a dissolved profile. This will give us an average PPO2 of 1.2 over the 5 stops. In order to take advantage of the oxygen window, we will need to do an S-Curve shape for the 5 stops, so we will emphasize the time at the higher PPO2 of 1.6 and 1.4 and then reduce the time to ascend to the lower PPO2 while still allowing the top of the curve for dissolved gas profile. The advantages we get from an elevated oxygen include off-setting the inert gasses and lessoning the on-gas in the slower tissues of the inert gases during the deco ascent as well as the bubble mechanics of keeping the bubble smaller. These include the Surface Tension plus the ambient partial pressure keeping the internal pressure when relating to the ongas from tissue to the bubble and the O2 gradient between bubble and blood. We are also taking advantage of what is known as the Oxygen Window – when we use oxygen in the shallowest part of the deco we are treating the slow tissues with the best gradient between ambient and dissolved gas.
Questions?
We use a deco bottle to both reduce the requirements of rock bottom and to accelerate the decompression by 50%. The way we do this is by elevating the FO2 in the bottle, so that when we first switch to the deco bottle we have the highest tolerable PPO2 of 1.6, and then slowly reduce it over the 5 stops until it reaches a PPO2 of 0.8, and then we can switch again or do a dissolved profile. This will give us an average PPO2 of 1.2 over the 5 stops. In order to take advantage of the oxygen window, we will need to do an S-Curve shape for the 5 stops, so we will emphasize the time at the higher PPO2 of 1.6 and 1.4 and then reduce the time to ascend to the lower PPO2 while still allowing the top of the curve for dissolved gas profile. The advantages we get from an elevated oxygen include off-setting the inert gasses and lessoning the on-gas in the slower tissues of the inert gases during the deco ascent as well as the bubble mechanics of keeping the bubble smaller. These include the Surface Tension plus the ambient partial pressure keeping the internal pressure when relating to the ongas from tissue to the bubble and the O2 gradient between bubble and blood. We are also taking advantage of what is known as the Oxygen Window – when we use oxygen in the shallowest part of the deco we are treating the slow tissues with the best gradient between ambient and dissolved gas.
Questions?
Replies to This Discussion
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Permalink Reply by Lynne Flaherty on -
I can understand the potential utility of the S-curve for very deep dives, where the decompression times are long. But is it likely that it really makes much difference for deco in the T1 range, where your stops at the point of your gas switch are fairly short, anyway? In other words, how likely is it that moving two or three total minutes around changes anything significantly?
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Permalink Reply by Andrew Georgitsis on -
Keep in mind there is an Oxygen Window at the gas switch and although the times maybe small there is still benefit from the window and other bubble mechanics at work.
Where I do agreed is that 1 or 2 min may be no big deal overall. BUT :) there is always a but.. Keep in mind that we are consistent and unified. Meaning, we try our hardest to keep a consistent approach throughout all our training, diving and experience. So our goal and build block approach is to build good habits and skills from Day 1 or the ground up. I certainly don't want to keep changing my approach every time I move up a level or dive deeper or longer or change environment.
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Permalink Reply by kevrumbo on -
Well . . .It's tough to insist on using S-curves with teams trained by other agencies, especially when you're traveling by yourself. For example, instead of a 6, 6, 2, 2, 4 progression by S-curve, they would be resolute in using a 5, 4, 4, 4, 5 linear/symmetric profile for the eanx50 deco.
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Permalink Reply by Andrew Georgitsis on
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Team :)
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Permalink Reply by Marc Blackwood on -
The shallow portion isn't S-Curved. Rather, the 20' stop is emphasized.
In the example you presented (150 for 30), a common ratio schedule would be deep stops on 21/35 + 50% for 4, 4, 2, 2, 3, 10, 5.
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Permalink Reply by Jeanna Edgerton on -
I'm not sure if this is what you are asking, but remember, when using both 50% and O2 the 30 foot stop requires a gas switch (return to back gas) and also the time to "reset the O2 window", so you won't be breathing the marginal 50% gas.
At 30 feet, the time is not extended - it is left the same, in this example at 3 minutes. The 40 and 50 foot times are reduced and those reductions added to the 60 and 70 foot times.
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Permalink Reply by Marc Blackwood on
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My understanding:
In addition to what Jeanna mentioned about facilitating two-bottle dives, I think an important thing to note is that after the switch, you are in the O2 window portion of the deco, after which you transition over to dissolved gas methodology (i.e. gradient).
The O2 window is only open for so long after you switch to a higher FO2 gas, and is most effective at a high PO2. So we extend the time at the deeper (bottle) stops and take it away from the intermediate depths where you don't have an appreciable window OR gradient (the 50 and 40) working for you.
We aren't emphasizing the 30. Rather we are leaving it alone.
It's been a while since I went through AG's seminar, though. Maybe he'll chime in.
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Permalink Reply by Jeanna Edgerton on
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That's my understanding also.
In addition, with 2 bottle dives - the time at 30 feet acts as a bit of an O2 break as you have elevated your PPO2 with the 50% bottle and now plan to go onto pure O2 for another 15 minutes.
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Permalink Reply by Brian Wiederspan on -
It comes back to the building block approach, Rainer. If you moved that time somewhere else now, and eventually went on to Trimix, where you'll need that extra time at 30', you'd have to change your procedures. This approach keeps it consistent, regardless of the dive you're doing (1 or 2 deco bottles).
Plus, the 30' stop is a nice transition in to the dissolved gas phase.
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Permalink Reply by Brian Wiederspan on
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Primarily consistency, an extra minute at 30 instead of 40 probably isn't going to make much difference, though, as you know, it's all theory.
However, at 50fsw and 40fsw, you're really not getting much of an O2 advantage, nor are you creating much of a gradient. They're more transitional depths between the two. At 30fsw you're at least beginning to get a bit of a gradient as well as time to start preparing for the next phase of deco.
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Permalink Reply by Brian Wiederspan on
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Rainer, I can't reply directly to your last post, so I'll reply here....
Your concern for having the team on the same page is exactly what this addresses. If one of my teammates signals (let's make this easy) avg depth 150 for :20, everyone on the team can do a very quick calculation, knowing that we've got 3, 3, 1, 1, 2, 6, 4 ( or 7, 3, etc. Numbers edited...stupid trying to post while you're busy at work). Everyone knows to leave 30 as is, and work the remaining depths. If we change the 30' stop according to # of deco bottles, etc, you lose that consistency.
I think this is what you were saying anyway, but I wanted to clarify.
As far as inflection point....I'm not sure exactly what you're asking for, but you want to stay within the ratio for each stop. Does that answer your question?
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Permalink Reply by Douglas Steding on -
I dunno, I find that when I'm doing squarish profile dives (140-150 range) doing 3,3,1,1,2 feels better than straight 2's.
I also like to do most of my 20 foot and up time at 20 feet, and then pad things with a nice, slow, ascent to the surface (the old 6 minute ascent drill, with a couple minutes at 10).
I do that, I get out of the water feeling better than when I got in it, the deco just feels super duper clean.
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