Which ascent profile to use when?

[BigTuna]

I've been studying the PDF file included in the 5thD-X DVD production titled "Essentials of Recreational Diving." I'd like to ask some questions about how to connect its suggested ascent profile with two recreational ascent profiles--PADI's and my own.

I apologize if my questions show ignorance of details of technical diving and medicine that need to be filled in. I'm just an AOW recreational wreck and resort diver. I just want to be as safe as reasonably possible in the face of possibly conflicting recommendations. I dive dry on nitrox, and I'm looking forward to rescue, continual skills and knowledge improvement, and possibly a DM or MD cert.

For discussion purposes, let's consider an air dive with 15 minutes at 100 feet. [If it matters, assume everything is optimal: open water, perfect visibility, a buddy close by, a vertical up-line, a dive boat at the top of it, and perfect weather.]

PROFILE ONE
As a baseline, we have the PADI teaching of a maximum ascent rate of 60 fpm to the surface, plus an optional 3 min safety stop at 15 feet.

PROFILE TWO
For my own profile, I've modified the PADI ascent rate to 30 fpm max, per recommendation of my dive computer manufacurer, and I ALWAYS include a safety stop of at least 3 min at 15 feet (sometimes 5 min). I try to ascend from the safety at 10 fpm max, because I've read on this board that a super-slow final ascent is good (I managed 5 fpm once).

I've read that a deep stop at 1/2 max depth is good, too. For the reference dive, that would add 1 min at 50 feet to the ascent I just described. I've tried that, and after the dive I compared the resulting nitrogen compartment loading bar graphs with graphs for a similar dive without the deep stop. If anything, it looked like the deep stop ADDED nitrogen to the slow tissues, so I discontinued the deep stop.

PROFILE THREE
Now on to the "Essentials" profile. View graph 62 in the PDF file depicts an assent from 100 feet. If I understand the guidelines in VG 65 correctly, the ascent is 30 fpm to 1/2 max depth (i.e., 50 feet), followed by additional deep stops every 10 feet from then on, with 1 minute per deep stop (including ascent time between stops).

Now for my questions:

1- The shapes of the PADI profile, my modified PADI profile, and the Essientials profile are different. Yet all would claim to be based on years of experiments and countless numbers of dives by countless divers. Can they all be right? Are they all right, but at in different situations, such as air vs. nitrox? Is one ALWAYS best?

2- WHICH PROFILE SHOULD I (or anybody else) BE USING TO MINIMIZE THE CHANCE OF GETTING BENT? Does it matter which one I use? If it matters, how do I figure out which one is best for me?

3- To what extent is it useful to add a deep stop at 1/2 max depth to Profile 2? Is my conclusion correct that it might have a negative benefit in that profile?

4- This is a niggling question about the Essentials profile (Profile 3): Can one just ascend at continuous rate of 10 fpm from the 1/2 max depth deep stop, without pausing every 10 feet?

I hope this isn't too hard to discuss in a forum and without a lecture hall and chalk board. But if somebody can boil it down for me, I'd be grateful!

 

[Doc Intrepid]

For discussion purposes, let's consider an air dive with 15 minutes at 100 feet. [If it matters, assume everything is optimal: open water, perfect visibility, a buddy close by, a vertical up-line, a dive boat at the top of it, and perfect weather.]

I hope this isn't too hard to discuss in a forum and without a lecture hall and chalk board. But if somebody can boil it down for me, I'd be grateful!

I am sure that other deco experts on the board may be able to speak with greater authority. I am not an expert. But I can offer an informed opinion that may at least refine your questions a bit...

First, here is your profile as my V-Planner (e.g. my default values) renders the output:
V-Planner 3.71 by R. Hemingway, VPM code by Erik C. Baker.

Decompression model: VPM - B

DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 0ft
Conservatism = + 1

Dec to 30ft (1) Air 30ft/min descent.
Dec to 100ft (2) Air 60ft/min descent.
Level 100ft 12:50 (15) Air 0.85 ppO2, 100ft ead
Asc to 70ft (16) Air -20ft/min ascent.
Asc to 20ft (21) Air -10ft/min ascent.
Stop at 10ft 1:30 (23) Air 0.27 ppO2, 10ft ead
Surface (24) Air -10ft/min ascent.

Off gassing starts at 62.6ft

Notice that V-planner calls for a 1.5 minute stop at 10' (assuming a square profile - that is, you descended to 100' on a wreck or something and remained there until your bottom time = 15 minutes). The slower initial descent is due to checking cameras, powering up lights, and any drills etc. done after entering the water but before dropping like rocks down the line.

Now for your questions. Please note that everything below is in my humble opinion:

1- The shapes of the PADI profile, my modified PADI profile, and the Essientials profile are different. Yet all would claim to be based on years of experiments and countless numbers of dives by countless divers. Can they all be right? Are they all right, but at in different situations, such as air vs. nitrox? Is one ALWAYS best?

Yes, they all can be right. Yes, they can all be right but in different situations depending on which gas mixes are being breathed. Yes, generally speaking one is broadly preferable in most situations.

[PONTIFICATION]Divers have been doing decompression dives since before the 1970s. A 1970's vintage NOAA manual discussed the use of nitrox. Throughout the 1980s most divers decompressed on air (other gasses not being widely used then). PADI's 60 fpm ascent rate was standard in 1982-1984 when I was becoming a divemaster and instructor. Like most things, standards and criteria evolve over time. Currently "how to deco correctly" continues to be a hotly debated topic. In reality, many divers perform their decompression differently and yet 99% of them manage to be successful. Some spend less time in the water than others, some spend more, some breath trimix, nitrox, heliox, etc.; and some breath air. In a manner of speaking, so long as the diver emerges unbent "they are all right/correct". That said, for longer, deeper exposures, clearly doppler research (which moved the field forward significantly - and which was sponsored by PADI in the 1980s) indicates that the use of gases other than air can provide a "cleaner" decompression. Finally, there is a saying that "all dives are deco dives", meaning that on-gassing occurs to some extent whenever gas is breathed under pressure, ...but for recreational diving commensurate off-gassing generally occurs without the need for stops. Nevertheless, in nearly all cases, (particularly when divers are pushing the NDL limits) a slower 30 fpm ascent rate is safer than a faster 60 fpm ascent rate. It allows a greater chance for dissolved gasses to come out of solution and be removed before bubbles form. (The choices a diver makes may also be informed by each individual diver's specific characteristics and/or environmental parameters. DCI has been indicated to be influenced, for example, by variables as diverse as "diver's physical condition", "diver's weight and body fat index", water temperature (colder water = greater stress), degree of exertion while submerged (currents = greater physiological stress), ambient light (very dark, very cold, low vis water = more stressful than warm, clear, 100'+ vis water), hydration, alcohol consumption, psychological anxiety, and many, many other factors. If a dive is anticipated to be more stressful, a prudent diver may select a more conservative dive deco profile.) [Decompression is an unbelievably complex phenomenon that even now is incompletely understood. We're reducing broad systemic physiological processes to very simple levels in this discussion.][/PONTIFICATION]

2- WHICH PROFILE SHOULD I (or anybody else) BE USING TO MINIMIZE THE CHANCE OF GETTING BENT? Does it matter which one I use? If it matters, how do I figure out which one is best for me?

For recreational profiles, (and your hypothetical dive profile is - generally speaking - a recreational profile,) consider using your Profile #2. For longer, deeper exposures of the type you'd expect to find doing planned decompression dives deeper than your hypothetical example you might consider Profile #3. (For example, you gain very little benefit by inserting a "deep stop" on a 100' dive. You gain significantly greater benefit from inserting a "deep stop" on a 200' or 300' dive.) In nearly all recreational cases you should be safer using a 30 fpm ascent rate until you hit 10', and then a much slower 10 fpm ascent rate from 10' to the surface.

3- To what extent is it useful to add a deep stop at 1/2 max depth to Profile 1? Is my conclusion correct that it might have a negative benefit in that profile?

TTBOMK, a deep stop on a 100' 15 min dive accomplishes nothing measurable. The only benefit it might offer is slowing your total ascent. OTOH, it offers no negative consequences either. (This is not universally true. Depending on the depth/time maximums of a dive, and the gas mix a diver is breathing, a "stop" where no stop is necessary can add to the partial pressure exposure of the diver to a gas in their breathing mix. Notice in the V-planner output above the sentence "offgassing starts at 62.6'". Obviously, stops deeper than 62.6' will not allow nitrogen to be off-gassed...)

4- This is a niggling question about the Essentials profile (Profile 3): Can one just ascend at continuous rate of 10 fpm from the 1/2 max depth deep stop, without pausing every 10 feet?

You essentially do. The idea is to pause for approximately 30 seconds at any given "stop", then spend the remaining 30 seconds drifting upward to the next 10' stop. Doing so results in a smooth 10 fpm ascent which resembles a nearly continuous upward movement punctuated by 30 second pauses every 10'. It is a demonstration of control and precision.

There are other threads that discuss decompression in the archives, and I commend them to your attention. In particular there are true experts on this board in the fields of medical physiology, physics, hyperbaric medicine and related matters, to include Dr. Michael Powell, Doc Vikingo, I.G. Saturation, Ross Hemingway, Dr. Bruce Weinke, and Cameron Martz, and doing searches in the archives using their names as key words might produce additional resources.

Hope this helps,

Doc

 

[Charlie99]

https://www.daneurope.org/eng/whatascent2.pdf is a report on actual studies, including doppler measurements, done by Dan Europe.

It shows the test results of ascent from 25m/82.5' 25 minute dives using 3/10/18 meter per minute (10/33/60 foot-per-minute) ascent rates, both with and without a deep stop and 6m/20'/safety stop.

They also did some repetitive dive tests where the initial dive was followed up with 25m/82.5' 20 minute dive after a rather lengthy 3 hour 30 min SI.

Other articles on this subject can be found at https://www.daneurope.org/eng/lettmed1.htm

 

[Uncle Pug]

I don't know if this will help since it is not an answer to your question but rather a different way of looking at the dive and might not be meaningful at all for the kind of diving you do:

For most diving I don't do an *ascent*... the dive just gets shallower with time and more time as it gets shallower. I enjoy the whole dive from max depth to surface... in fact each level holds special interest for me.

But like I said, this may not be meaningful at all for you.

 

[Charlie99]

1- The shapes of the PADI profile, my modified PADI profile, and the Essientials profile are different. Yet all would claim to be based on years of experiments and countless numbers of dives by countless divers. Can they all be right? Are they all right, but at in different situations, such as air vs. nitrox? Is one ALWAYS best?

Best, right, safe, efficient are all ways to describe ascent profiles. All of the ones you described have been proven by experience to be safe. In a perverse sense, the problem is that recreational diving is "too safe". By that I mean that since the incidence rate of DCS is very low, it is difficult to tell which one of several reasonably safe profiles is the safest. Only by artificially forcing it to be relatively unsafe in some manner (such as by testing 100' 25' minute profiles) will one generate enough dcs to discriminate between the tested profiles. Alternatively, one has to extrapolate --- through the use of venous doppler measurement as done by DAN Europe; by calculating the theoretical compartment loadings or theoretical bubble size/total freephase volume of a particular theoretical model; by adding in artificially high level of conservatism in a decompression program to generate multiple required deco stops for a dive that in reality doesn't need them; or look at the depth-time shape of required decompression stops for much more agressive decompression dives and somehow try to extrapolate that to an ascent from a much shorter and/or shallower dive.

2- WHICH PROFILE SHOULD I (or anybody else) BE USING TO MINIMIZE THE CHANCE OF GETTING BENT? Does it matter which one I use? If it matters, how do I figure out which one is best for me?

If you pay close attention to how you feel, you may be able to detect the effect of different ascent profiles, as well as differences in other factors such as hydration. For example, I felt a noticeable improvement in how I felt once I added some deep stops to the classic 60fpm + 3 minutes at 15'. This was only noticeable on dives where I was pushing the limits. The effect was similar to that "less post dive fatigue on nitrox" claim that has neither been proved nor disproved. For what it's worth, the nitrox vs. air difference pretty much disappeared after I started adding deep stops.

My personal preference on ascent profile is most similar to your Profile 3 / "Essentials", but with the addition of a bit more time shallow. One way would be to simply add 1 minute at 15' in addition to the minute at 20' and 10'. The more heavily loaded you are, the more time you should add in the 30' to 10' range. (Still referring to recreational depth, NDL or minimum deco dives).

4- This is a niggling question about the Essentials profile (Profile 3): Can one just ascend at continuous rate of 10 fpm from the 1/2 max depth deep stop, without pausing every 10 feet?

After reading the DAN Europe article The Speed of Acent Dilemma: "Instant Speed of Acent" or "Time To Surface" - which one really matters you will probably conclude, as have I, that 10fpm constant ascent or a series of 30 second move and 30 stops are essentially equivalent. On a practical basis, the easiest way to dive an average of 10fpm ascent is to leave each 10' mark as the minute rolls over on your dive comuter or watch.

Indeed, my ascent methodology is based upon leaving certain depths at predetermined times.
1. Upon starting my final ascent, based upon how heavily loaded I am, I choose a runtime on my computer at which I will surface. This time is typically 6 to 12 minutes from the current runtime.
2. Based upon my current depth, and a 30fpm ascent rate to 1st stop (typically 40') and the length of 40' stop (typically 1 minute), pick the runtime at which I will leave 40'.
3. Ascent rate above 40' is never more than 10fpm. Time gets split between 30' range and 15' range so that more time is spent shallow.

Typical total time of ascent from reaching 40' to reaching the surface is 5 minutes to 10 minutes, usually 7.

In practice, my preferred ascent end up similar to yet another one you can review, the one at www.dir-diver.com ---- 1@40, 1@30, 3@20', 3@10'

Lack of hard evidence and real testing (other than DAN Europe tests) make this topic a somewhat subjective one. If one looks at the history, ascent profiles were intially as straight 60fpm pop to the surface. Then deep stops were added and ascents slowed. They are good things, but like all good things, they CAN be overdone. THe trick is to find the right combination of safety, time and gas spent doing ascent/deco, and simplicity/probability that the profile will be executed correctly.

Charlie Allen

p.s. Look for the SIMILARITIES between all of the various profiles rather than the differences. The reason all of the ascents are safe is because of the common elements they share.

For example, if my ascent starts from the deck of a wreck at 100', then instead of first stop at 40', I'd really do it more like 50' or 60', more like the Essential profile. OTOH, even after a dive with max depth of 130', if I then spent time looking at the reef at 80', then 60', then 40', then my final ascent from 40' (although never exceeding 10fpm) is very much like the current PADI 30fpm to 15' and do long hang at safety stop. .

 

[DivesWithTurtles]

Other articles on this subject can be found at https://www.daneurope.org/eng/lettmed1.htm

One those articles that Charlie points to, "A Deep stop during decompression from 82 fsw (25 m) significantly reduces bubbles and fast tissue gas tensions.", covers BigTuna's questions quite directly. Especially read the Discussion and Conclusions sections. Note that the 30 second 10 foot move, 30 second stop (essentially a linear 10 ft/min ascent) may be a worst case profile according to Marroni's studies.

(I can about hear Uncle Pug saying, "Aw, geez, here's Turtles pushing Marroni again.", and Charlie saying, "Still too linear, too linear!". I agree with both of them now.)

 

[Dr Deco]

Hello BigTuna:

Not being familiar with the “Essentials” DVD, I cannot comment directly.

There are many paths up a hill and many “deco paths” from depth to the surface. If you are using very low nitrogen gas loads, as all good decompression tables do, they will all produce good results even though the shape of the profile might appear different.

In general, a diver will not get DCS on any profile or table that they use. This is because, again, the nitrogen loads are very conservative. There are very large safety margins incorporated into all tables. In addition, there are not any “table limits” in a physiological sense. It is not a fixed quantity such as the “sound barrier.”

There certainly are individual divers who are more prone to bubble formation and these they form might persist for a longer time. These are the “DCS sensitive” individuals.

For any procedure, slow ascents, safety stops, and the avoidance of stressful physical activity are paramount.

Dr Deco :doctor:

 

[BigTuna]

Gentlemen,

Thank you for your insights, particularly for the reference to the Marroni paper. I'm reassured that you think Profile 2, which I use, is OK. But I think I'll begin including a 5 minute stop at 1/2 max depth. Do you see anything that "contraindicates" doing this?


Gabe and Charlie,

Thanks for referring me to the Marroni paper. It confirms what I observed with my one deep stop, actually, with the fast tissues off-gassing while the slow tissues continue to on-gas.

The paper tells me that (for recreational dives, at any rate) getting the nitrogen out of the fast spinal tissue with minimum cascading is important. I can read the main point of the paper as being that increasing the ascent time to something comparable to spinal tissue's half time of 12.5 minutes is very useful for this if it's added where neurological off-gassing is best managed.

Let's revisit Profile 2 (this is my own analysis--blame only me!). The profile's ascent from 100 feet would take 8 minutes, assuming I make a 5 minute safety stop. This is less than spinal tissue's half time. Adding a 5 minute deep stop for continued and controlled off-gassing of neurological tissue would increase the total ascent time to 13 minutes. With this kind of time, the spine is starting to smile!


Doc Interepid and Charlie,

Double-digit ascent times would seem to be desirable. Why wouldn't you guys apply the Marroni results and increase your ascent times to neurological tissue half times? What am I missing?


Charlie

All three profiles I presented might be "safe," but that's not reassuring to me. I think there are two reasons:

1- Think of the relationship between special relativity and Newton's law. The former is more general, but the latter is correct in an asymptotic sense, at low speeds. All three profiles I described are for an "asymptotic," i.e., recreational diving, sense. But they are basically different. So I have to infer they're based on different models.

2- Something I've picked up is that bubble theory requires controlling off-gassing rather deep, and that dissolved gas theory requires
controlling it shallow. I'm guessing that this is the theoretical difference between Profile 3 and the other two.

Combining point 2 with the lesson of the Marroni paper, if I add a deep stop to the other two profiles, I in effect introduce some bubble management into their models. It's not complete bubble management (that would require something like Profile 3) but it attacks what's thought to be a very dangerous realm of bubbles and off-gassing.


Dr. Deco,

You may be correct that I won't get bent with any of the 3 profiles, but the Marroni paper seems to be telling me that some "insurance" might be useful.

Marroni says that the incidence of decompression sickness in sport diving has changed very little over 40 years. He also says that the majority of DCS cases in sport diving are neurological in nature. He hypothesizes that current approaches to ascent—controlling ascent rate and using shallow stops—don't provide enough time for critical off-gassing, particularly in neurological tissues.

His paper concludes that adding a deep stop can help to fix that. That's insurance to me! I assume adding a deep stop can't hurt. Is that assumption correct?

It also supports the basic notion I've picked up that deep stops manage bubble formation and cascading in fast tissues, whereas a safety stop manages transpiration of dissolved nitrogen from slow tissues.


Doc Intrepid

Thanks for introducing me to V-Planner. I've bought myself a copy and have been playing with it. It's especially interesting to see the depth at which off-gassing starts. It seems consistent selecting 1/2 max depth for a stop. The Marroni paper makes me wonder if ascent rates you use are too slow....

 

[Dr Deco]

Hi BigTuna:

You are correct in observing that slow ascents and safety stops are good insurance.

 

[rjack321]

You are also correct that deep stops control bubble formation. Distributing some of your stop time deeper than 15' is a prudent way to control bubbles deeper in your profile.

The "essentials" profiles work well IMHO, despite their apparent contradiction with the Marroni paper.

Using how you feel post dive is a better measure of success than any theoretical "best way".