Slow tissue on gas from stops

[dmaziuk]

The new argument is "deep stops are not unsafe." Of course the double negative implies you're trying to support, with all the research out there, that "deep stops are safe."

I'll see that double negative a raise it a double positive: yeah right.

(sorry, couldn't resist)

 

[Dan_P]

So, first you say that your use of deep stops is for logistical convenience. I ask what you mean by logistics. You provide four examples, none of which require deep stops, but rather argue for RD. You are being inconsistent, and arguing for the sake of arguing. That is tiresome to the point of being irritating. I can only assume you are a sock puppet for Ross, except more articulate.

Hardly - sure, you can reinvent the wheel for every dive to maybe accomodate some of the things I mentioned, if you can get exactly the right gases, but that's not the same as saying that the same things RD does, is thus achieved.
In all respect, I find the notion ridiculous, to be quite honest.

The new argument is "deep stops are not unsafe." Of course the double negative implies you're trying to support, with all the research out there, that "deep stops are safe."

Clearly that is not what the research is showing us. The clear message of the research out there is that the bubble-model-style, RD-style, deep stops reduce safety in a profile.

You're seeing something that I'd like you to reference. Where in the NEDU report does it state that deep stops are unsafe?
To "deep stops are safe.", you say "Clearly that is not what the research is showing us".
I think the extent of added stress expectedly required to show any significant difference, and thus applied, in the NEDU study, speaks volumes to the contrary of your statement, sir.
I have read the NEDU report and Doolette's explanation of the motivation to add stress, and I get it. It made sense to frame the trials as they did. But I really think you're overextrapolating on that here. Which is a big part of my point about the discussion. So is this;

And now we have (from a dive instructor) an admission that deep stops are less safe, but "not unsafe". I doubt many tech divers will be planning dives thinking, "I could have a safer profile, but I'd rather have one that's not unsafe." Doublespeak at best.

Gibberish, sir. I think the added stress imposed in NEDU is wildly disproportionate to that of a normal technical dive, as addressed. That made sense, but that's not to say that the difference is even significant under "normal" conditions. The trial framing of NEDU actually indicates that it may well not be.

If the factors applied to add stress in the NEDU study truly had zero impact on the outcome, bene - but at this point in time, I still do have reservations about that notion, but that's another matter.
What's on the table here and now is, you're effectively saying (sorry for the use of analogy) that a Ford Mondeo with a 100,1m breaking distance is unsafe when there is a Formula-1 racer that can do it in 100,0m. Obviously, if you zoom in on the last metre, that's a whopping 10% difference! Groundbreaking!

 

[Storker]

Where in the NEDU report does it state that deep stops are unsafe?

AFAICU, it "only" states that distributing the stops deeper is less safe than distributing them shallower. With all the caveats required in a scientific publication. But the message is quite a bit stronger than most scientific publications give.

I think [...]

I like to believe that I do so, too. I "think" a lot. However, when world-leading scientists in a field I'm not an expert in give a message as powerful as the one given by the NEDU study, I prefer to shut up and listen. YMMV.

 

[Dan_P]

@Storker it's not about "caveats".

What we know is that NEDU needed a tangible difference and therefore, pushed the envelope leaps and bounds beyond ordinary bounds on two approaches.

You may deduct that the difference found has the same scale of application in the diving you or I do, and label that deduction "science", but we shouldn't need an expert telling us that this would be skewing perception of the magnitude in play.

I prefer to shut up and listen

This is about unsupported ultimative statements by non-experts e.g. to the effect of 'deep stops are unsafe'. Specifically.

 

[Storker]

You may deduct that the difference found has the same scale of application in the diving you or I do, and label that deduction "science", but we shouldn't need an expert telling us that this would be skewing perception of the magnitude in play.

Um, care to translate that to English? The style used in most peer-review journals is good enough for me.

 

[leadduck]

Even for ratio deco rule of thumb type ascents, it’s super easy to modify the plan to eliminate time spent before the gas switch. Maybe on a 240’ Dive for 25mins, instead of 30fpm to 75% avg depth, then 10fpm from there till 50% avg depth, then 5fpm from 50% to the 1st switch, change it to 30fpm to 50% and then 10fpm to the 1st switch. Whatever mirrors non deep stop gradient factors. I’m not even looking at deco software but it’s clear the approach #2 skips time spent dilly dallying before you get on a deco gas and is still easy to remember.
It’s not even difficult.

I think yes you could come up with a variant of RD that approximates a GF50/80 ascent and avoids deeps stops with bottom gas, and it's not difficult.
I saw one version of RD (GUE's?) where they say deco time equals bottom time for a 40msw dive, and then spend half of the deco time between 21m-9m , and the other half at 6m and 3m. This 1:1 distribution is very much on the deep stop side with very short shallow stops. If you simply change that to 1:2, i.e. spend 33% between 21m-9m and 66% at 6m and 3m, then the ascent approximates a GF50/80 much better.

 

[PfcAJ]

I think yes you could come up with a variant of RD that approximates a GF50/80 ascent and avoids deeps stops with bottom gas, and it's not difficult.
I saw one version of RD (GUE's?) where they say deco time equals bottom time for a 40msw dive, and then spend half of the deco time between 21m-9m , and the other half at 6m and 3m. This 1:1 distribution is very much on the deep stop side with very short shallow stops. If you simply change that to 1:2, i.e. spend 33% between 21m-9m and 66% at 6m and 3m, then the ascent approximates a GF50/80 much better.

Yeah. It’s easy to come up with a ratio that approximates the ascent plan you want.

 

[Patoux01]

Yeah. It’s easy to come up with a ratio that approximates the ascent plan you want.

Finally, someone said it.

 

[admikar]

It's been previously mentioned that there would be less DCS risk to do the same deco time without the deep stops. This begs the question: why not eliminate the deep stop altogether and run flat GF's. An 80/80 profile will give less deco time than a 50/80. You'll probably say, "Well, a not-so-deep stop will protect the faster tissues. But, fast tissues can be protected by slowing down the ascents. Now, what say you?

Point is to not have less deco time, but to redistribute your time on deep vs. shallow. Flat GF might be great is you consider only fast vs. slow tissues, but what about medium ones? It's not only protecting fast or slow tissues, it's about protecting ALL of your tissues.

And I think it seems that you're not open to the possibility that when or if you call something "unsafe" some might think that implies "some degree of certainty of harm" (or, the actual meaning of the word).

Everything we do in our everyday lives implies "some degree of certainty of harm". Quoted part does not mean,to me, that I will get harmed, but that there is some possibility that I might get harmed.

Edited:not the best analogy.

 

[UWSojourner]

I think the added stress imposed in NEDU is wildly disproportionate to that of a normal technical dive, as addressed ... you're effectively saying that a Ford Mondeo with a 100,1m breaking distance is unsafe when there is a Formula-1 racer that can do it in 100,0m. Obviously, if you zoom in on the last metre, that's a whopping 10% difference!

Your posts seem to have conceded that the research shows that bubble-model-style deep stops increase the risk of DCS. But evidently you've concluded that the risks are only increased by 1 in 1000, and thus irrelevant. Given the wide range of diving that occurs that estimate seems simplistic in the extreme.

Substantial dives are occurring where stop distribution will matter as demonstrated by the research (not just the NEDU's). It seems irresponsible, given the available data, that an instructor of any agency would attempt to discount available information in such a cavalier manner. Perhaps it points to a larger problem within the agency itself. In any case, in my opinion the chances that the increased risk of the deeper stops imposed by RD and bubble models is limited to 1 in 1000 are remote indeed.

There is NO advantage to deep stops per se. They increase gas requirements, keep divers deeper than needed, and, even as conceded by you, increase the risk of DCS. I think most divers are going to side with the research and not the hand-waving.


"The impact of deep stops is not that they target some different physical reality. It is actually quite simple; the extra time spent deep allows more inert gas uptake in the relatively undersaturated intermediate and slow tissues. This is simply a loading problem that subsequently produces a higher degree of decompression stress. If there is less uptake at depth, ascent to a relatively shallow stop has much less risk. The idea that deep stops controlled bubble growth is one of the armchair arguments that has not lived up to human testing ... As with all the protocols we developed and subsequently saw fail, it is time to respect the data over the hand-waving." Dr. Pollock