Continuous Decompression AND Staged Decompression

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Kevin A.

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*Edit* - Stressing out that this query is not in relation to formal continuous decompression methods employed in some saturation or chamber operations. I meant 'continuous' also in the context of a staged decompression, but where the ascents are calculated micro-stops themselves. Thus curving the gap between stages, a following the curve profile.


Hi all,

Any recent research/analysis/reasoning in favor or against continuous decompression?

If you recount the old 'diver on the line' thing on the VR3.. I used to like it. The aim was to keep your off-gassing tension relatively constant, well it still involved stops but with a gradual ascent to the following shallower stop rather than the traditional 'hold the stop and move to the next when prompted'. Then with the @Shearwater I had abandoned this (not following their CEIL option) as you'l be getting a Missed Deco warning should you ascend past your fixed ceiling to your shallower variable ceiling.

I'd be interested to learn of anything new on this or if it's just discouraged because there's no basis to support it?

Thanks
 
This reflects my imperfect understanding of early decompression history.

In the earliest days of decompression theory, there were two approaches: the slow, linear ascent preferred by Leonard Hill and the multiple stop approach favored by John Haldane. During their first decades of diving, the US Navy favored the slow ascent method, but eventually changed to the multiple stop approach. It is my understanding that research supported the multiple stop approach, but I cannot find specific references to such research at this time.

The more recent Maronni study definitely favored a stop approach, referencing the earlier Hill approach. That study compared ascent rates in recreational dives and determined that the slowest rate (10 FPM) produced the worst results, with an ascent featuring stops being superior to one without stops regardless of the ascent rates. That study suggests a benefit to deep stops in recreational diving; however, subsequent studies have not confirmed that benefit, and the DAN website that originally posted the study now has attached a warning that the study does not reflect current thinking. That warning is almost certainly about the fact that deep stops for recreational diving do not appear to be beneficial and not to the overall concept of stops v. slow continual ascents. Using stops rather than a continuous slow ascent is certainly current thinking.

I believe (not sure) that GUE now uses a slow and continuous ascent for the deepest portion of the ascent, but I don't know of anyone else doing that.
 
To clarify.. asking if it's more or less acceptable to still follow a staged decompression, but ascending according to a variable ceiling from a deeper stop to the shallower stop.

e.g. a 20min@40ft followed by 30min@30ft would resolve; hold 40ft for 17min, ascend to 37ft on the 18th minute, ascend to 34ft on the 19th, arrive 30ft at 20th minute etc..
 
@Kevin A. I think the main issue is the ability for divers to control ascent rates for long decompression and where you may or may not be able to hold your stop. Probably worth looking into how chambers are operated since they would have accurate control of their ascent rates.

@Duke Dive Medicine may be able to weigh in
 
I think the issue with a variable ceiling is that it involves a potentially large number of points on a curve which mean continually altering buoyancy and ascent rates. Having that level of control takes a lot of skill and would potentially require a fair amount of task loading. Add in potentially performing gas switches while on this curve and I think a lot of people would become overloaded.

Easier to split that curve into a smaller number of manageable sections where the diver can get their buoyancy sorted before moving to the next one. That allows switching at specific stops where buoyancy is already sorted.
 
To clarify.. asking if it's more or less acceptable to still follow a staged decompression, but ascending according to a variable ceiling from a deeper stop to the shallower stop.

e.g. a 20min@40ft followed by 30min@30ft would resolve; hold 40ft for 17min, ascend to 37ft on the 18th minute, ascend to 34ft on the 19th, arrive 30ft at 20th minute etc..

I would say not if the decompression algorithm you're using tells you to spend the time at 40 fsw. Even the best decompression algorithm is imperfect and is something of a blunt instrument. If you start playing with it and operating outside the algorithm's recommendations you go from that blunt instrument to an even blunter one, so to speak. Not that your individual physiology couldn't handle it, but what's the motivation to do this aside from curiosity? I'm not aware of any current research on this but I'll tag @Dr Simon Mitchell because he's closer to it than I am.

<edit> What @Neilwood said, too. Was trying to think of how to formulate that. Elegantly put.

Best regards,
DDM
 
My mistake, title is somewhat misleading making reference to continuous decompression. What I am really referring to is not strictly THE continuous decompression in terms of no stop ascents worked in various rates of ft/min.

Perhaps it's easier to explain; I bet most will be familiar with the old VR3 'diver on the line' option. You had your stop depth and at approaching your next leg at the next shallower depth, the ceiling would start go shallower so as to meet the next stop depth. It was still a stop, but the transition was curved rather that say from 40ft to 30ft @ normal ascent rate. A following-the-curve approach.

I used to employ this when practicable back in the days of the VR3. So my question; what's the reasoning in view of this in 2019.

Shearwater have this data available to the diver as the CEIL (ceiling) display option, but you still have to stick to your stop ceiling unless you don't want a missed deco warning.
 
I suspect as @Duke Dive Medicine and @Neilwood both said. Its not practical to ascend in 1ft increments. Keeping you at the lower 10ft increment is not that more "inefficient" (and in the case of using 100% depth doesn't matter for offgassing efficiency) so moving in 10ft steps ends up being a practical implementation. If there is little or nothing in terms of measurable offgassing efficiency to be achieved by moving up 1ft (which really means slight ups and downs in a ~2-3ft window) then why do it when you have a wing, drysuit, and/or gas switches/loop volume/ppO2 to manage throughout these microsteps.

In a chamber there are dedicated operators and slow acting valves and adiabatic cooling going on so those staff can manage all of the knobs and buttons to ascend 1ft/min while the patient just relaxes.
 
Not referring to the formal continuous decompression methods as employed in some sat or chamber operations here.. my bad referring to it as continuous deco, my query is more about.. micro-stops. Did some editing to clear it up
 

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