dive computers and reverse profiles

[Steve_C]

When I took OW a dozen years ago my insturctor (SDI/PADI) said that the deep then shallow recommendation was not really there because it was not safe. He felt the value of it was if you did shallow first and then deep you went into the deepest part of your dive having already spent a chunk of NDL and it was easier for new divers to get into NDL trouble then.

Not saying it is a good reason but it was the only value of the recommendation he could think of.

 

[dmaziuk]

That's interesting! Where can we find these papers (or references to them)?

If you're serious, NEDU study is the one that proved their basic starting assumption wrong: that faster tissues need more protection -- by shifting decompression stops deeper. The other stuff around and to the side of it has come under question too, but for that, "proven wrong" would be an overstatement.

 

[wetb4igetinthewater]

That's interesting! Where can we find these papers (or references to them)?

This isn't the best answer, but a link somewhere in Rubicon Research Repository is generally where I wind up. I then ask people with more knowledge to translate to layman's terms.

 

[Subcooled]

Not bad - Is bad - Not bad

Rubicon research repository on reverse diving profiles:
(and as is typical for any research, one has to read it very carefully, as the devil is in the details)

2000: "We find no reason for the diving communities to prohibit reverse dive profiles for no-decompression dives less than 40 msw (130 fsw) and depth differentials less than 12 msw (40 fsw)." Proceedings of Reverse Dive Profiles Workshop.

2005: "There is now sufficient evidence to demonstrate that FDPs and RDPs with analogous exposures within the recommendation of the Workshop have different decompression obligations, with the RDPs being more hazardous, at least in some situations. We conclude that the current practice of advocating forward dive profiles should be retained at this time." Reverse dive profiles: the making of a myth.

2006: "Edmonds, McInnes, and Bennett fail to impose the desired level of uncertainty on the subject of RDPs, in the context of the Workshop's findings and conclusion, and have added little to the debate that took place at the Workshop. We find no reason for the diving communities to prohibit reverse dive profiles within the no-decompression limits for dives less than 40 msw (130 fsw) and depth differentials less than 12 msw (40 fsw)." Reverse dive profiles: the making of a myth. A response.

 

[tbone1004]

That's interesting! Where can we find these papers (or references to them)?

@dmaziuk I think that the bubble models as a whole have been disproven by the current research. They may not have been setting out specifically to disprove the bubble models, but the the general profiles created by the bubble models has definitely been disproven by the last couple of studies, especially the Spisni study. Subcooled, search for spisni on here and it will give a good rundown and link to that study. It compared a UTD ratio deco profile which is based on the same theory as the bubble models and exhibits similar profiles, and compares it against a Buhlmann algorithm and the results were pretty obvious...

 

[tursiops]

Not bad - Is bad - Not bad

Rubicon research repository on reverse diving profiles:
(and as is typical for any research, one has to read it very carefully, as the devil is in the details)

2000: "We find no reason for the diving communities to prohibit reverse dive profiles for no-decompression dives less than 40 msw (130 fsw) and depth differentials less than 12 msw (40 fsw)." Proceedings of Reverse Dive Profiles Workshop.

2005: "There is now sufficient evidence to demonstrate that FDPs and RDPs with analogous exposures within the recommendation of the Workshop have different decompression obligations, with the RDPs being more hazardous, at least in some situations. We conclude that the current practice of advocating forward dive profiles should be retained at this time." Reverse dive profiles: the making of a myth.

2006: "Edmonds, McInnes, and Bennett fail to impose the desired level of uncertainty on the subject of RDPs, in the context of the Workshop's findings and conclusion, and have added little to the debate that took place at the Workshop. We find no reason for the diving communities to prohibit reverse dive profiles within the no-decompression limits for dives less than 40 msw (130 fsw) and depth differentials less than 12 msw (40 fsw)." Reverse dive profiles: the making of a myth. A response.

The 2005 paper misread and misunderstood and misinterpreted the 2000 paper. The 2006 paper is right on the mark.
Not all publications are equal; this is a good example.

 

[dmaziuk]

@dmaziuk I think that the bubble models as a whole have been disproven by the current research. They may not have been setting out specifically to disprove the bubble models, but the the general profiles created by the bubble models has definitely been disproven by the last couple of studies, especially the Spisni study.

Spisni study is how you spin it: ratio deco people say their profiles generated on the fly without any computer are "no worse" (nobody got bent) than computer-generated ones, hoorray ratio deco. Some "inflammatory markers" nobody used before or since, are worse, as are "silent bubbles" that aren't hurting.

Dr. Wienke's argument against "reverse profiles" and "cave profiles" does not seem to bend the actual cave divers on the actual cave dives, but that's a far cry from "disproven by studies".

There was one study suggesting that perhaps we grow accustomed to "repeated decompression stress" and so RGBM's penalty for repeated dives is not necessary -- but again the best "disproof" is the statistics showing that most DCS incidents happen on the first day of a trip, and on the first dive of the day, and not on the last dive of the last day as you'd expect if DSC stress "accumulated" like Wienke says.

I think it's mostly growing amount of evidence that the practice doesn't support bubble theories.

 

[Subcooled]

ratio deco people say their profiles generated on the fly without any computer are "no worse" (nobody got bent) than computer-generated ones

What decompression algorithm does ratio deco use?

"Precomputed, simplified and memorized" does not equal "without any computer".
I thought that ratio deco is based on and roughly approximates an actual decompression algorithm (which again is based on statistics).

Some "inflammatory markers" nobody used before or since, are worse, as are "silent bubbles" that aren't hurting.

Not hurting. Just like smoking one cigarrette or drinking one glas of beer does not hurt.
My point: not all damage is obvious. Why should I take a hit from silent bubbles and stress my body if I can avoid that?
Lack of DCS does not mean no harm was done.
Prove me I am wrong.

the statistics showing that most DCS incidents happen on the first day of a trip, and on the first dive of the day, and not on the last dive of the last day as you'd expect if DSC stress "accumulated" like Wienke says.

You forget that lacking skill causes DCS. First dive in a year...
If one would only study divers who dive the year around, the study would probably show that they get DCS on the last dive, not on the first one.

 

[BlueTrin]

For info
https://www.scubaboard.com/communit...ssion-profile-study-results-published.542299/
UTD Decompression profile study results published

And

https://www.researchgate.net/public...ory_responses_compartmental_versus_ratio_deco

 

[dmaziuk]

Not hurting. Just like smoking one cigarrette or drinking one glas of beer does not hurt.
My point: not all damage is obvious. Why should I take a hit from silent bubbles and stress my body if I can avoid that?

Maybe you shouldn't be diving, then.