Bubble model vs. Gradient Factors redux

[HKGuns]

Who is Ross?

 

[scubadada]

Who is Ross?

 

[StefinSB]

Who is Ross?

A software salesman.

 

[scubadada]

A software salesman.

Actually sells pretty good software, MultiDeco. It's his role as a decompression expert that gets him in trouble

 

[DavidFL]

Who is Ross?

A comprehensive answer to that question could be useful in taking up hours/days/weeks of fascinating reading of 'threads' on SB, and various cave, rebreather, and other forums.

The short, woefully oversimplified answer is there is a years (now decades?) long social media debate between advocates of 'deep stops' and those who support what might be called the long-standing, more shallow, distribution of decompression stops. Ross is a very persistent and prolific supporter of the deep stop view. Many well-known, well-regarded professionals from various appropriate disciplines with appropriate post-graduate educations and experience have posted about relevant research that they contend shows that deep stops may not be well advised unless additional shallow stops are taken, which generates profiles that take longer.

If you choose to take up the quest to try to understand the controversy and the protagonists and form your own view you will gain along the way exposure to a lot of useful information buried in bazillions of words and charts.

 

[cathal]

It's his role as a decompression expert that gets him in trouble

Spot on, the "self appointed decompression expert" bit is where the controversy begins, from having read his contributions to date on the subject.

 

[HKGuns]

A comprehensive answer to that question could be useful in taking up hours/days/weeks of fascinating reading of 'threads' on SB, and various cave, rebreather, and other forums.

The short, woefully oversimplified answer is there is a years (now decades?) long social media debate between advocates of 'deep stops' and those who support what might be called the long-standing, more shallow, distribution of decompression stops. Ross is a very persistent and prolific supporter of the deep stop view. Many well-known, well-regarded professionals from various appropriate disciplines with appropriate post-graduate educations and experience have posted about relevant research that they contend shows that deep stops may not be well advised unless additional shallow stops are taken, which generates profiles that take longer.

If you choose to take up the quest to try to understand the controversy and the protagonists and form your own view you will gain along the way exposure to a lot of useful information buried in bazillions of words and charts.

Thanks, I know very little on this subject as a new recreational diver only.

From the reading I have done (SImon MItchell) it seems the Bubble Model with deep stops were an ill advised course that should be abandoned. Dr. Mitchell has some very compelling talks on the subject that I find fascinating. (Plus he's a Navy guy, so he's got to be good!)

 

[scubadada]

I would also love to know what the dive profile was for these dives.

It's tough being constrained by having the comparisons having the same run time. the 50/75 profile has not only shallower initial stops, but it also has more shallow time and surfaces with a lower GF. Makes it hard to tease out the relative importance of the deep stops and the SurfGF. On this topic, I find myself siding with @ChuckP

 

[rsingler]

I would also love to know what the dive profile was for these dives.

It's tough being constrained by having the comparisons having the same run time. the 50/75 profile has not only shallower initial stops, but it also has more shallow time and surfaces with a lower GF. Makes it hard to tease out the relative importance of the deep stops and the SurfGF. On this topic, I find myself siding with @ChuckP

Without reopening old, old discussions before the data arrives, isn't the same run time the point? There have been too many arguments about the most "efficient" or the most "conservative" profile. But with two dives of the same run time, "Which one is at greater risk?" is a fair question.

And your comment about surfacing with a lower GF reveals your (and my own) prejudices about Gradient Factors. Many deep stop guys would say (or at least would have said) surfacing with a GFHi of 90 is no big deal; it's the deep stops that are important. Apparently you and I both believe that surfacing with a lower GF played a role in the outcome.

I understand a desire to compare GF 20/85 with GF 50/85 to tease out that component of deep stops. But my own (and I suspect your) prejudice would be that if GF20/85 had some better performance metric, you (and I) would attribute it to the longer hang time that GF20 imposes. Me, I suspect that 20/85 would still come out the worse, but that's a subject for yet another study.
I agree, it would have been nice to do that comparison, too.

It's a conundrum. Wouldn't it be nice...

But kudos to DAN for getting the volunteers (many of whom supplied and paid for their own gas) to take the risk to get us at least this much data.

 

[Umuntu]

This is a great overview presentation of the debate by Dr Simon Mitchell at a DAN Conference