Keeping up with Changing Thinking in Scuba

[Lorenzoid]

The trimix diving course I teach has a section imploring students to keep up with the changing research in the world of scuba. You don't want to base critical diving decisions on ideas that have been repudiated and are no longer believed to be true. The course itself is in example for that. It has extensive information on putting deep stops into a dive profile, and the standards require students to plan and execute a dive using deep stops. That standard, however, was dropped from the course last year, because recent research does not support the use of deep stops. The course, then, set a good example for its students when it changed the standards in light of recent research.

So how does a scuba diver keep up with changes in scuba knowledge?

That's encouraging to hear your trimix course includes a section on keeping up with the changing research. I know not all do, and that's a shame. I would think that the skill of keeping up with developments--knowing how to do the "research" or "continuing education" or whatever one wishes to call it--is an advanced diving skill like any other and should be actively taught in advanced courses. From my perspective, a trimix diver's understanding ought to be analogous to a graduate student's. Sure, when a student finishes the course, they can do things exactly as the instructor taught them, but as they do increasingly challenging dives over a number of years, they themselves are now at the vanguard, like a Ph.D.-level diver, and had better be keeping up with what's going on in their "field." Those kinds of divers ought to be actively searching for secondary sources that summarize primary research, and giving back to their community by helping others find and read them.

Fortunately for the average OW diver, the thinking on the kinds of issues being discussed in this thread evolves slowly, and the change in impact on OW dives is minimal, so keeping up with the changing research, while certainly to be encouraged, is not a necessary skill for the average OW diver.

 

[Blasto]

We're saying the same thing: there's no reason not to dive reverse profiles, as long as you understand that you're either going to have to do longer surface intervals or shorter NDLs on the second dive.

This is not quite universal. Everything else equal, it's better to do short deep dives before long shallow dives.

Everything else is rarely equal - scheduling, weather, convenience all play a role.

Some proponents of the "no reverse profiling" thing will even deliberately go deeper than they otherwise would on their first dive. No need to explain how ridiculous it is, you're always better off shallower than deeper. 25m, 35m, 16m, 22m dives of 30 min each are safer than 35m, 33m, 25m, 22m dives of 30 min each.

Where reverse profiling comes into play is if you're scheduling a 60 min 12m dive and a 20 min 30m dive. It also matters if you're pushing the limits, as you'll be simultaneously stressing more tissue compartments after a day of reverse profiling. When diving well within the limits, with single tank air and boat schedules rather than NDL or deco governing your dive times, reverse profiling is not a serious concern.

 

[Cowfish Aesthetic]

This is not quite universal. Everything else equal, it's better to do short deep dives before long shallow dives.

Everything else is rarely equal - scheduling, weather, convenience all play a role.

Some proponents of the "no reverse profiling" thing will even deliberately go deeper than they otherwise would on their first dive. No need to explain how ridiculous it is, you're always better off shallower than deeper. 25m, 35m, 16m, 22m dives of 30 min each are safer than 35m, 33m, 25m, 22m dives of 30 min each.

Where reverse profiling comes into play is if you're scheduling a 60 min 12m dive and a 20 min 30m dive. It also matters if you're pushing the limits, as you'll be simultaneously stressing more tissue compartments after a day of reverse profiling. When diving well within the limits, with single tank air and boat schedules rather than NDL or deco governing your dive times, reverse profiling is not a serious concern.

Again, I'm not suggesting that reverse profiling is a serious concern, or even a minor concern. I'm not suggesting that you (or anyone) not dive reverse profiles. I'm not saying that I wouldn't dive a reverse profile if I had a reason to do so.

I was simply was taking issue with the implication that a computer-shortened NDL for a reverse profile is an unjustified "penalty," when it is actually in line with the tables and current decompression theory as I understand it (and as everyone else apparently understands it because no one has argued that point).

 

[sea_ledford]

If memory serves, Dr. Mitchell can be quoted for more public statements of similar nature.
My understanding of it is, any risk difference may very well be neglible, and in either case, not presently quantifiable.

That is, we can't quantify the risk delta - but it's been attempted in this string and others (in my opinion, crudely and oversimplifyingly so) with basis in the Spisni-trial[1]. Interestingly, this month, the Spisni-trial has become publicly available in Diving and Hyperbaric Medicine as one year has lapsed since it's publishing. Link posted in reference below.
Rather than carry on the discussion on that particular perspective, I would invite anyone curious about the study and it's findings, to read the report which is now publicly available.

[1] A comparative evaluation of two decompression procedures for technical diving using inflammatory responses: compartmental versus ratio deco. Spisni et al. Diving and Hyperbaric Medicine, 47(1), March 2017
[2] Redistribution of decompression stop time from shallow to deep stops increases incidence of decompression sickness in air decompression dives. Doolette et al. US Navy Experimental Diving Unit Technical Report 2011-06

I just read the Spisni paper, and given the limitations of the small sample size and limited ability for extrapolation, the author says "Overall, our findings contradict the idea that adding longer and/or deeper stops is useful to achieve a more effective decompression." And that is despite the fact that the ratio deco profile was 12 minutes (17%) longer than the 30/85 GF profile.

I am failing to see why people keep defending deep stops or ratio deco. Are there any articles that point to deep stops being better? Or is it all "but Rich Pyle... and but AG!"

I really don't understand how one would think that having to do arithmetic underwater to determine your profile is superior to looking at a computer that will certainly do the work in higher resolution and with fewer errors.

I attended a seminar by Nuno Gomes who was telling us about his nearly 1000 ft cave dives. He was asked what algorithm he used at those depths and he said that all these algorithms are reliable down to 500 feet. After that, they become unreliable and you will be surfacing with symptoms no matter what algo you use. You have to note down your symptoms and then modify your next dive based on your symptoms from previous ones and have an understanding of decotime vs bottom time ahem... RATIOS.

As per my understanding the notion that RATIOS are more reliable than computers and established algorithms also comes from this context where the limits of all algorithms have already been exceeded. Agencies who propagated the idea of abandoning computers, monitoring symptoms and using ratios were doing extreme exposures where decompression algorithms have already collapsed.

On scubaboard folks seem to think that these agencies do not trust computers because electronics are not reliable! Some are saying that carrying a back up computer will eliminate the need for ratio deco and You can see pages after pages of debate about how a modern computer is actually more reliable that an SPG. No one looks at the extreme dives that Jarod Jablonski, Sheck Exley and Nuno Gomes were doing. No computer would get them out from the mess they were putting. It would be gauges, ratios and symptoms from previous dives that would guide the way.

You are talking about people that are doing dives WAY out of bounds for the algorithms (and one of them died doing it, so maybe not a great example to follow), of course they don't work very well. The use of ratio planning is used because it is a step up from guessing. If someone were to develop an algorithm that was effective in the 500-1200 foot range, they would probably be using that, not ratio deco. The commercial guys probably do have an algorithm for it, but they aren't going to give it away and it wouldn't be appropriate for scuba anyway, unless you are going to use K-bottles for deco tanks.

Trying to extrapolate what extreme exposure divers are doing to barely survive a dive, to what Bob and Mary do on a 110 no-stop reef bimble, or me doing a 150' deco lite dive makes as much sense as expecting people to put on nomex suits and full helmets to drive their car to work.

-Chris

 

[RyanT]

If someone were to develop an algorithm that was effective in the 500-1200 foot range, they would probably be using that, not ratio deco. The commercial guys probably do have an algorithm for it, but they aren't going to give it away and it wouldn't be appropriate for scuba anyway,

Exactly, it's called saturation diving with a habitat and surface support. 1 day of deco for every 100' + a day. I'm sure this procedures varies depending on the actual dive, but this what a commercial diver told me is typical for his 600' dives.

 

[boulderjohn]

I really don't understand how one would think that having to do arithmetic underwater to determine your profile is superior to looking at a computer that will certainly do the work in higher resolution and with fewer errors.

The belief is that once in a very great while, that computer might make an error, so it can never be trusted to be right an any specific occasion.

The unspoken corollary to that is the assumption that the human mind never mistakes mistakes and consequently can always be trusted to be right.

 

[Divin'Papaw]

Perhaps this has already been mentioned (I haven't read the whole thread thoroughly yet), but I try and continue to network with technical instructors and technical divers I know and trust. Past instructors, current and past buddies, "famous" technical divers I've grown to trust, etc. I do that via following them on Facebook, subscribing to blogs and email newsletters, and networking in person when I have the opportunity. I always try to be in data gathering/learning mode. All too often people are a bit too pumped up with their own knowledge and skill level that, when given the opportunity, they don't shut up and listen. I try very hard to listen more than I speak when talking diving with folks both more and less experienced than myself.

 

[Blasto]

I really don't understand how one would think that having to do arithmetic underwater to determine your profile is superior to looking at a computer that will certainly do the work in higher resolution and with fewer errors.

It's pretty easy. Since Ratio Deco isn't based in science - just think of alchemy such as splitting stops into two groups and applying a separate S-curve within each group - it takes a really massive mistake to fall outside its limits of what counts as an interpretation.

As for the algorithms, to the best of my knowledge (I'm not involved in that), the same deco algorithms still apply to extreme diving. The only game-changing difference is the logistical difficulties in following them, so shortcuts are often taken at significantly more risk.

 

[boulderjohn]

As for the algorithms, to the best of my knowledge (I'm not involved in that), the same deco algorithms still apply to extreme diving. The only game-changing difference is the logistical difficulties in following them, so shortcuts are often taken at significantly more risk.

I don't know diddly about extreme depths, but I do know that regular algorithms do not translate well to extreme altitudes.

When some divers got bent using Bühlmann at (not too) high altitude, Bühlmann tweaked it for altitude diving. The tweaked Bühlmann ZH-L 16 was used successfully at Lake Titicaca in 1987--about 12,000 feet. If you input pretty much any altitude into that algorithm in Multi-deco, you will get a profile that will be consistent with the lower altitudes. That does not make it right. After a pair of divers had a failed dive attempt at 16,000 feet, I conferred with a diver who does decompression consultation with NASA and the Pentagon (U2 flights), and he said that those kinds of altitudes bring complications that are not in play at lower altitudes. He said there are only 5-6 people in the world capable of planning such a dive--even though you could download a profile from Multi-deco.

I am going to hazard a guess that extreme depths will also bring factors into play that are not present at depths those normally reached by technical divers.

 

[CAPTAIN SINBAD]

I really don't understand how one would think that having to do arithmetic underwater to determine your profile is superior to looking at a computer that will certainly do the work in higher resolution and with fewer errors.

I don't understand why people do not use GPS to go their bathrooms when they wake up in the morning. A GPS designed for that purpose will guide you to the bathroom in higher resolution with fewer errors so that you do not bump into the china cabinet along the way.