Can you do too much deco?

[PfcAJ]

20 years working deep on air.

So anecdote at best. Got it.

 

[Celt]

So anecdote at best. Got it.

There's nothing anecdotal about it. To ignore a person physical ability to do a job when calculating decompression is begging for trouble.

 

[grantctobin]

There's nothing anecdotal about it. To ignore a person physical ability to do a job when calculating decompression is begging for trouble.

Workload has no bearing on an individual divers decompression obligation once that person is physically fit enough to do the work. If you're out of shape and puffing and blowing on the bottom that's another story altogether and you're on the wrong job. Your going to get bent.

Definition of ANECDOTAL EVIDENCE

evidence in the form of stories that people tell about what has happened to them… See the full definition

www.merriam-webster.com

So it’s very relevant, until it’s not relevant? Hit this (arbitrary and highly variable) fitness threshold then nothing else matters?

 

[Trace Malinowski]

There is no question that exercise during the deepest portion of the dive increases perfusion and on-gassing. If you go with Michael Powell's (unproven) thinking on the bubbling they found when researching the PADI RDP, that exercise may even stimulate bubble formation. It would indeed be wise to compensate for that during decompression, but there is no reason to do it while very deep and still on-gassing. Pyle's team does it during final stops.

One caution we've been given by researchers are things like a forceful Valsalva or climbing a ladder might create a shunt in the presence of a PFO. If a diver with a PFO was to exert and create a shunt underwater, could time at a deep stop allow potentially problematic bubbles to be eliminated before they grew into a bigger problem as pressure is further reduced? I'm wondering if deep stops might be more beneficial in the presence of an unknown or known PFO vs. a diver without the condition.

 

[boulderjohn]

One caution we've been given by researchers are things like a forceful Valsalva or climbing a ladder might create a shunt in the presence of a PFO. If a diver with a PFO was to exert and create a shunt underwater, could time at a deep stop allow potentially problematic bubbles to be eliminated before they grew into a bigger problem as pressure is further reduced? I'm wondering if deep stops might be more beneficial in the presence of an unknown or known PFO vs. a diver without the condition.

As we go farther and down the rabbit hole of "what ifs," it might be good to remember that the idea that deep stops control bubbles in some way is a theory, but there is no evidence of it, and there likely will be no evidence because of the obvious problem of testing it. The only studies done so far testing divers for bubbles after their ascents finds no difference between divers who did deeper stops and those who did shallower stops.

The one exception to that is a recent study led by Mark Powell that did not have numbers or protocols worthy of scientific publication but which showed intriguing results nonetheless. Powell did something that I thought was brilliant and which I am surprised had never been done before. Yes, he tested both deeper stop divers and shallower stop divers for bubbles and initially found their scores to be similar immediately upon ascent. He then tested them again at intervals after the dive, and that is where it got interesting.

He found that with the shallower stop divers, the bubble scores decreased over time precisely as expected, but with the deeper stop divers, the bubble scores remained high or even increased (I am doing this from memory) for a surprisingly long time.

 

[L13]

While that's likely true, the NEDU research used pretty strenuous activity at depth and seems applicable to the OP's scenario without ad-hoc "compensation" for workload.

The NEDU research told us a lot and is, as you say, based on strenuous activity at depth. After reviewing most if not all of the modern research (the NEDU data dominates), as well as the writings of @Dr Simon Mitchell, Doolette, Buhlman, Haldane, and many others including much on SB, I think the following conclusions are fairly well supported by the data and science (and consistent with the design of the model):

GF-Low should be >= 50%
GF-High should be <= 85%
maybe GF-Low should be ~= .8 x GF-High (this seems much more tenuous)

So, for the proposed GF-High of 60% (which is not that unreasonable for a cautious response to the evidence) GF-Low should probably be at least 50%.

Regardless, a GF-Low of 30% is strongly contra-indicated by the research.

Of course, I am just a random voice on the internet, and may be wrong. But I strongly suggest the actual research be used by @RedSeaDiver2 for setting the GF's for this project and not prejudice like "bend and mend" which is definitely not consistent with the data/science which shows that 50/X is safer than 30/X.

 

[Celt]

Definition of ANECDOTAL EVIDENCE

evidence in the form of stories that people tell about what has happened to them… See the full definition

www.merriam-webster.com

So it’s very relevant, until it’s not relevant? Hit this (arbitrary and highly variable) fitness threshold then nothing else matters?

It's not that nothing else matters but heavy manual labour is normal for some and others would break into a sweat going upstairs.

 

[JonG1]

In Powells study deep stops produced less bubbles at surface but they declined slower, the shallow stops protocol produced slightly higher scores on surfacing but they declined quicker over time.

 

[Trace Malinowski]

 

[bubblemonkey2]

remember that MultiDeco is only giving us two deeper stops of 40 seconds at 39 metres and 2 minutes at 36 minutes when compared to a GF 50/80 plan
This obviously gives a longer dive profile than say a GF 50/80 plan (adds in 27 more minutes) the water is 21degC / 70degF

Lurker here among legends
While I too have keenly followed the 50/80 rationales, if you want a pee break at 39 metres and some more shallow hang time, then seems ok, no?

Will that extra 27 minutes mean the difference between a bend or not while climbing onto the boat before you sit down for another hour of relaxed surface deco? Idk. Probably depends a lot on the individual that day.

The END for 65% at 60m with 1.3 ppO2 (~18%) is like 5 metres? Nobody I know intentionally aims for a 5m END

Is there a conflict between:
a) trying to make the deco more conservative/safer, and
b) upping the fast-diffusing gas to levels higher than normal?