The Elusive Definition of "Deep Stops"

[Kevrumbo]

Quick review:

Ratio Deco Deep Stop Strategy is referenced on the fastest of the Fast Tissue Comparments, Buhlmann's 5min Half-Life Tissue Compartment which initially controls the ascent from operational depth. Also remember in Ratio Deco that the NDL's at significant depths beyond recreational limits starting at 39m (130'), and deeper to 42m (140'), 45m (150'), 48m (160'), 51m (170') . . .etc are the same: 5 minutes.

The first deep stop at 75% of maximum depth is a rule of thumb based on this leading 5min TC: that is by 10 minutes at a particular maximum depth listed above, the 5min TC will have undergone two half-lives and will be 75% saturated. By ascending to 75% of maximum depth, and holding a deep stop, the theory is that this Fast Neuro TC will just begin to desaturate and keep inert gas in solution for venous blood transport to the lungs -and not supersaturate or worse bubble out of solution if we were to decrease ambient pressure by ascending shallower to the actual limiting M-value equivalent depth, or critical tension of Buhlmann's Model. (There are five Fast Tissue/Tissue Half-Life Compartments at play: 5min, 10min, 15min, 20 min and 30min. To understand how they all dynamically figure in to generate a Ratio Deco Deep Stop Profile see here )

The implications of the NEDU Deep Stops Study shows that the above strategy now may in fact supersaturate the Slow Tissues later in the deco profile with an increase risk of DCS. The practical application from all this is using a Dual Phase/Bubble Model Deco Program with DeepStops may result in having to extend the shallower stop times on Oxygen to compensate for this Slow Tissue supersaturation. Alternatively, using a Buhlmann GF 40/70 Deco profile for example reduces the emphasis on the "deeper" DeepStop, while still maintaining some margin from Buhlmann's M-value critical tissue tension limits via the Gradient Factors (GF's). . .

 

[Jack Hammer]

Similar to Boulderjohn, I first learned to do my 1st stop ("deep stop") at half my max depth. Then later I was taught to do my first stop ("deep stop") at 3/4 my max depth, then go to half max depth and make stops every 10' to the surface. More recently it's changed to average bottom depth, vs max depth and stops begin shallower in general. I go with where the science leads us and with what my body tells me.

I truly feel that until folks get into the 200'+ range that most algorithms are relatively well tested for 'shorter' dives. The deeper one goes beyond that and/or the longer one stays the more important subtle differences in planning and execution will make.

 

[Doppler]

John: why did you open this can of worms up again! LOL!!

My definition of Deep Stops has changed a little over the last several years, but my practice has changed a whole lot.

When I started teaching, PDCs were ****. That's changed. So much so that when using something like a shearwater, the diver has exquisite control over his/her ascent profile... we can even adjust things in situ! No real need to **** with anything.

However, from what I'm reading, people are regularly second-guessing what their 4th Gen PDCs are suggesting and throwing in arbitrary stops deeper than the algorithm is calling for.

That's fine...

But please be aware by so doing you are working outside the parameters of the algorithm... you are making **** up... take notes, because like it or not, you are conducting decompression stress research.

 

[lv2dive]

this is tangentially related to deep stops but specifically related to points made by BoulderJohn and JackHammer. I learned different things about deep stops as I progressed through different training, but where I got the most learning about decompression stress was outside of training. And decompression stress is why we care about deep stops, right?

So a few points which I believe that cannot be emphasized enough include relatively slow progression and listening.

Regarding the first, I may have progressed in tech diving relatively quickly in terms of time, but that is a whole lot easier to do when one is diving one- three times a week for months at at a time.

Regarding the second, the largest benefit afforded me, as I progressively dove longer and deeper, was to learn to listen. Listen to people I truly respected, including:
1) people who were doing the dives I wanted to be doing
2) people who have been around for decades, diving the love of the sport but who have no internet following
3) people who have made mistakes and are not so concerned with their rep that they will share, so it others will learn and hopefully not make the same bone-headed moves
4) experts in the field such as David D and Simon M. who are constantly doing research, and following the science, even if takes them in a different direction than their original hypotheses.

And finally, and perhaps most importantly, listen to my own body. I say most importantly bc people I've respected have told me some of my observations about my body's reactions to decompression stress are wrong - even though I've experienced the same reaction multiple times. I've experimented with different approaches and have (knock wood) so far been very successful in taking other people's thoughts into consideration with what I know to be true from close observation of my body's reactions.

Hope this wasn't too off topic.

 

[stuartv]

For most dives, your avg depth (avg pressure) is a perfectly reasonable way to figure out your gas absorption for deco.

That is just ridiculous.

Here are two dive profiles. They have the same average depth. Tell me how the gas absorption is anything alike between the 2:

Dive A: 30 min at 95', then 30 min at 5'. Run time: 1 hr. Avg depth: 50'

Dive B: 30 min at 5', then 30 min at 95'. Run time 1 hr. Avg depth: 50'

Totally different inert gas tissue loading after 1 hour.

Is this a ridiculously extreme example? Yes. It still illustrates the point. Very different profiles yield the same average depth.

You did say "for most dives". So, here is a more realistic example of the same concept:

Dive A: you dive to 90' and hang out on the main deck area of a wreck for 15 minutes, then go over the side and drop to the sand at 130' for 15 minutes

Dive B: you drop to the sand at 130' fro 15 minutes, then ascend to the main deck and hang out at 90' for 15 minutes.

Your tissue loading will be VERY different at the end of those two dives. But you'll have the same average depth after 30 minutes, either way.

Model that in Multi-Deco and you'll get very different ascent plans. If you use the more conservative plan for both dives, then you are just wasting time and gas on the dive that started deep. If you use the quicker plan for both dives, then you are cuckoo for doing so on the dive that started shallower.

If your protocol includes the proviso "always start with the deepest part of the dive and only move shallower", then it could be both workable and reasonable. But, that's pretty limiting if you're on a wreck with a lot of relief and you're going up and down a lot as you swim around. Or if you are swimming up and over reefs and down the other side as you go.

Average depth for deco calculations is ridiculous. It's either ridiculously conservative and wasteful, or it's ridiculously complicated or restrictive, and limiting to your dive profile, or, of course, it could be ridiculously dangerous. From the few actual examples I've seen, it looks to me like a lot of dives with RD would have you doing one or more deco stops where, if you were following most any recreational NDL table (and definitely most any Rec dive computer), you'd have no stops at all. So, I'm inclined to think it's too conservative and wasteful AND too complicated. I'll just dive with 2 computers, thank you.

 

[tursiops]

That is just ridiculous.

Here are two dive profiles. They have the same average depth. Tell me how the gas absorption is anything alike between the 2:

Dive A: 30 min at 95', then 30 min at 5'. Run time: 1 hr. Avg depth: 50'

Dive B: 30 min at 5', then 30 min at 95'. Run time 1 hr. Avg depth: 50'

Totally different inert gas tissue loading after 1 hour.

Is this a ridiculously extreme example? Yes. It still illustrates the point. Very different profiles yield the same average depth.

You did say "for most dives". So, here is a more realistic example of the same concept:

Dive A: you dive to 90' and hang out on the main deck area of a wreck for 15 minutes, then go over the side and drop to the sand at 130' for 15 minutes

Dive B: you drop to the sand at 130' fro 15 minutes, then ascend to the main deck and hang out at 90' for 15 minutes.

Your tissue loading will be VERY different at the end of those two dives. But you'll have the same average depth after 30 minutes, either way.

Model that in Multi-Deco and you'll get very different ascent plans. If you use the more conservative plan for both dives, then you are just wasting time and gas on the dive that started deep. If you use the quicker plan for both dives, then you are cuckoo for doing so on the dive that started shallower.

If your protocol includes the proviso "always start with the deepest part of the dive and only move shallower", then it could be both workable and reasonable. But, that's pretty limiting if you're on a wreck with a lot of relief and you're going up and down a lot as you swim around. Or if you are swimming up and over reefs and down the other side as you go.

Average depth for deco calculations is ridiculous. It's either ridiculously conservative and wasteful, or it's ridiculously complicated or restrictive, and limiting to your dive profile, or, of course, it could be ridiculously dangerous. From the few actual examples I've seen, it looks to me like a lot of dives with RD would have you doing one or more deco stops where, if you were following most any recreational NDL table (and definitely most any Rec dive computer), you'd have no stops at all. So, I'm inclined to think it's too conservative and wasteful AND too complicated. I'll just dive with 2 computers, thank you.

Stuart, forget it. You are arguing religion and faith. Facts are irrelevant.

 

[Kevrumbo]

That is just ridiculous.

Here are two dive profiles. They have the same average depth. Tell me how the gas absorption is anything alike between the 2:

Dive A: 30 min at 95', then 30 min at 5'. Run time: 1 hr. Avg depth: 50'

Dive B: 30 min at 5', then 30 min at 95'. Run time 1 hr. Avg depth: 50'

Totally different inert gas tissue loading after 1 hour.

Is this a ridiculously extreme example? Yes. It still illustrates the point. Very different profiles yield the same average depth.

You did say "for most dives". So, here is a more realistic example of the same concept:

Dive A: you dive to 90' and hang out on the main deck area of a wreck for 15 minutes, then go over the side and drop to the sand at 130' for 15 minutes

Dive B: you drop to the sand at 130' fro 15 minutes, then ascend to the main deck and hang out at 90' for 15 minutes.

Your tissue loading will be VERY different at the end of those two dives. But you'll have the same average depth after 30 minutes, either way.

Model that in Multi-Deco and you'll get very different ascent plans. If you use the more conservative plan for both dives, then you are just wasting time and gas on the dive that started deep. If you use the quicker plan for both dives, then you are cuckoo for doing so on the dive that started shallower.

If your protocol includes the proviso "always start with the deepest part of the dive and only move shallower", then it could be both workable and reasonable. But, that's pretty limiting if you're on a wreck with a lot of relief and you're going up and down a lot as you swim around. Or if you are swimming up and over reefs and down the other side as you go.

Average depth for deco calculations is ridiculous. It's either ridiculously conservative and wasteful, or it's ridiculously complicated or restrictive, and limiting to your dive profile, or, of course, it could be ridiculously dangerous. From the few actual examples I've seen, it looks to me like a lot of dives with RD would have you doing one or more deco stops where, if you were following most any recreational NDL table (and definitely most any Rec dive computer), you'd have no stops at all. So, I'm inclined to think it's too conservative and wasteful AND too complicated. I'll just dive with 2 computers, thank you.

For manual Ratio Deco on-the-fly calculations, you simply "weight" the average deeper for a profile like 15min at 90' then going to 15min at 130' -->so this figures out as a bottom time of 30min at 120'. Or to be even more conservative and if you have plenty of O2 & time for deco, treat it as 30min at 130'. . .

 

[PfcAJ]

That is just ridiculous.

Here are two dive profiles. They have the same average depth. Tell me how the gas absorption is anything alike between the 2:

Dive A: 30 min at 95', then 30 min at 5'. Run time: 1 hr. Avg depth: 50'

Dive B: 30 min at 5', then 30 min at 95'. Run time 1 hr. Avg depth: 50'

Totally different inert gas tissue loading after 1 hour.

Is this a ridiculously extreme example? Yes. It still illustrates the point. Very different profiles yield the same average depth.

You did say "for most dives". So, here is a more realistic example of the same concept:

Dive A: you dive to 90' and hang out on the main deck area of a wreck for 15 minutes, then go over the side and drop to the sand at 130' for 15 minutes

Dive B: you drop to the sand at 130' fro 15 minutes, then ascend to the main deck and hang out at 90' for 15 minutes.

Your tissue loading will be VERY different at the end of those two dives. But you'll have the same average depth after 30 minutes, either way.

Model that in Multi-Deco and you'll get very different ascent plans. If you use the more conservative plan for both dives, then you are just wasting time and gas on the dive that started deep. If you use the quicker plan for both dives, then you are cuckoo for doing so on the dive that started shallower.

If your protocol includes the proviso "always start with the deepest part of the dive and only move shallower", then it could be both workable and reasonable. But, that's pretty limiting if you're on a wreck with a lot of relief and you're going up and down a lot as you swim around. Or if you are swimming up and over reefs and down the other side as you go.

Average depth for deco calculations is ridiculous. It's either ridiculously conservative and wasteful, or it's ridiculously complicated or restrictive, and limiting to your dive profile, or, of course, it could be ridiculously dangerous. From the few actual examples I've seen, it looks to me like a lot of dives with RD would have you doing one or more deco stops where, if you were following most any recreational NDL table (and definitely most any Rec dive computer), you'd have no stops at all. So, I'm inclined to think it's too conservative and wasteful AND too complicated. I'll just dive with 2 computers, thank you.

Hi Stuart,
You're correct, I said 'most' dives. You're absolutely able to come up with wacky scenarios where it won't fit. Its a tool, and like all tools, they don't work for literally every situation.

However, your 90'-130' example is actually pretty good for avg depth deco stuff.

For dive A on 30/30 with oxygen for deco (how I would approach that dive probably. Might consider 21/35 but 'meh'), you end up with 11mins of deco with 7 of those on Oxygen (buhlmann 40/85).

For dive B, same gases, you end up with 7mins of deco time and 5 of those are on oxygen. You've got less distance to travel (starting ascent from 90') and as such you don't get a stop at 40' on this plan.

For an average depth of 110' for 30mins, you end up with 9mins of deco, 6 of which are on oxygen. Right smack dab in the middle of dive A and B. Literally one minute of time on oxygen difference. One. Minute. That's pretty good, and I wouldn't say its "VERY" different at all.

 

[rjack321]

That is just ridiculous.

Here are two dive profiles. They have the same average depth. Tell me how the gas absorption is anything alike between the 2:

Dive A: 30 min at 95', then 30 min at 5'. Run time: 1 hr. Avg depth: 50'

Dive B: 30 min at 5', then 30 min at 95'. Run time 1 hr. Avg depth: 50'

Totally different inert gas tissue loading after 1 hour.

Is this a ridiculously extreme example? Yes. It still illustrates the point. Very different profiles yield the same average depth.

You did say "for most dives". So, here is a more realistic example of the same concept:

Dive A: you dive to 90' and hang out on the main deck area of a wreck for 15 minutes, then go over the side and drop to the sand at 130' for 15 minutes

Dive B: you drop to the sand at 130' fro 15 minutes, then ascend to the main deck and hang out at 90' for 15 minutes.

Your tissue loading will be VERY different at the end of those two dives. But you'll have the same average depth after 30 minutes, either way.

Model that in Multi-Deco and you'll get very different ascent plans. If you use the more conservative plan for both dives, then you are just wasting time and gas on the dive that started deep. If you use the quicker plan for both dives, then you are cuckoo for doing so on the dive that started shallower.

If your protocol includes the proviso "always start with the deepest part of the dive and only move shallower", then it could be both workable and reasonable. But, that's pretty limiting if you're on a wreck with a lot of relief and you're going up and down a lot as you swim around. Or if you are swimming up and over reefs and down the other side as you go.

Average depth for deco calculations is ridiculous. It's either ridiculously conservative and wasteful, or it's ridiculously complicated or restrictive, and limiting to your dive profile, or, of course, it could be ridiculously dangerous. From the few actual examples I've seen, it looks to me like a lot of dives with RD would have you doing one or more deco stops where, if you were following most any recreational NDL table (and definitely most any Rec dive computer), you'd have no stops at all. So, I'm inclined to think it's too conservative and wasteful AND too complicated. I'll just dive with 2 computers, thank you.

Using tables and depth averaging within reason has been going on for decades. At least as far back as 2006 when I started deco diving and it was well established at that time - although perhaps not well known. Is it "riskier"? Perhaps in some cases, in most cases the differences are such a trivial difference algorithms and settings within an alorithm will produce even more disparity. 110ft for 30mins is barely a deco dive, so as AJ points out the differences are slight. If you cave dove 10 or 15 yrs ago there were no decent computers, so you absolutely came up with an average from your sawtoothing profile and matched that up with your tables. Nobody would use max depth for that kind of profile, although if they were timid they probably weighted the average deeper than mathematical accuracy would suggest.

You could learn a lot by shouting less and listening to what experience has to say about this practice before calling it ridiculous.

 

[DevonDiver]

I consider 'Deep Stops' to be arbitrary stops that are manually diver-added to the pre-calculated profile and not considered/compensated for by the initial dive-planning algorithm.

In short... the 'Pyle Stops' that we used to use when running basic Bühlmann algorithms on old MS-DOS deco software...

I do not consider the deeper stops created by dual-phase (bubble) models as 'Deep Stops'.

In general day-to-day parlance, I use the term 'deep stops' to describe deco stops at 9m and below... and 'shallow stops' to describe the 6m and 3m (O2) stops.... I have pondered, on occasion, whether I could use 'deep stops' to describe any stops conducted before gas-switching.... above that 'stops are just stops'.... and then, as before, there are still 'shallow stops' in the 6-3m range.