NEDU Study

[rossh]

For the benefit of all readers, let us remind ourselves what the nedu really tested:

No deep stops in any nedu profile. The real difference is the exaggerated time in the 60 to 20 ft area. nedu divers were made cold though no wet suits.

i.e. a test of two shallow profiles against thermal stress. Not connected to tech practices or profiles.

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[PfcAJ]

For the benefit of all readers, let us remind ourselves what the nedu really tested:

View attachment 398558

No deep stops in any nedu profile. The real difference is the exaggerated time in the 60 to 20 ft area. nedu divers were made cold though no wet suits.

i.e. a test of two shallow profiles against thermal stress. Not connected to tech practices or profiles.

.

Thermal stress wasn't tested. Thermal was a controlled variable.

The manipulated variable was stop distribution with the deeper one producing more DCS.

 

[rossh]

Thermal stress wasn't tested. Thermal was a controlled variable.

The manipulated variable was stop distribution with the <invalid text removed> (exaggerated shallow stop) one producing more DCS.

The most significant stress on the test was thermal stress - deliberately elevated to be much higher than normal levels (to compensate for the 2x normal shallow stop time), and far beyond typical tech profiles.

The nedu test profiles are both considerably different in gas loading, supersaturation patterns, off gas patterns, compared to normal tech profiles, or any other profile for the schedule. i.e. the test profiles are not normal.

The bridge or connection from the nedu test profiles, over to tech profiles, is one of an opinion based position only. No existing conventional science measure has been shown to connect the nedu test profiles to tech profiles or practices.

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[Beau640]

Here we go again...didn't we just have a thread about needing to fully disclose private interests that could be influencing what you are recommending to people.

Not to insult Ross but on the original thread there was a lot of concern for an ulterior motive.

 

[PfcAJ]

The most significant stress on the test was thermal stress - deliberately elevated to be much higher than normal levels (to compensate for the 2x normal shallow stop time), and far beyond typical tech profiles.

The nedu test profiles are both considerably different in gas loading, supersaturation patterns, off gas patterns, compared to normal tech profiles, or any other profile for the schedule. i.e. the test profiles are not normal.

The bridge or connection from the nedu test profiles, over to tech profiles, is one of an opinion based position only. No existing conventional science measure has been shown to connect the nedu test profiles to tech profiles or practices.

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Dude, third grader science students can figure out that thermal stress was controlled for.

 

[Kevrumbo]

Hi Kevin,

No, I was not there. But you and Simon have been touting this story as a deep stop failure, and an extension of the nedu test, when in fact its something very, very different.

Despite popular myth, there is not some hidden accumulation of slow tissue gas that creates this multi-day condition. If you are in the water 4 times a day doing 2 hour dives, its still only 6 or 8 hours in 24 hours, (20 min total deep time and 4+ hours shallow time). Its not enough to carry over any significant gas volume. Yes, the computed deco time goes up a little bit, but not by much. This notion that a few minutes of deep stops was the problem all on its own, is pure baloney and nonsense. Your suggestion that some Slow Tissue Supersaturation is the cause is just plain silly in this situation.

Your full description here is one of accumulated multi-day fatigue, where you "reached your bodies limit", and exceeded it. It is not a model failure. Its a failure of the person to follow the experience and wisdom that predicted the very occurrence.

The wisdom that you have come to realize here - is to take it easy on multi-day dives. This multi-day issue and wisdom, existed long before DIR, RD, VPM and any other deeper stop approach existed. The multi-day problem is one that affects us all, and occurs regardless of the model used.

In my opinion, The conditions here is that your body gets fatigued and exhausted over many days of big diving, and it does not perform the on/off gassing as expected, compared to when you started out on day one. If you choose to deco close to the edge, day after day, then any minor variation in your bodies response, puts you over the edge. And the result is usually a big hit, because your body is in a fatigued or weakened state when it occurs.

******

This was not a deep stop problem, This is not a VPM-B problem. This is not a bubble model theory problem. The nedu test is not relevant to any of this. This is a multi-day dive fatigue issue.

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Ross, these were symptoms of a developing acute inflammatory response (DCS) to surfacing tissue inert supersaturation over a duration of days of loading/unloading deco dive cycles. I think that's a more definitive etiology than your nebulous explanation above.

The short simple practical lesson learned is not to handicap yourself in multi-day deco diving from Day One "getting behind the eight ball", by using inefficient strategies like deep stops to further compound the problem. Compensate by extending out the shallow O2 stop profile after each consecutive day and take a day off after three or four days in a row.

 

[UWSojourner]

The chart Ross posted here (and shown above) makes the claim that the NEDU profiles were "exagerated" with twice the needed decompression time (i.e. an extra 90 minutes). Of course, it's hard to support the idea that 90 minutes of the deco was unneeded when the divers experienced about 5% DCS in the deep stop profile and about 1.6% in the shallow stop profile???

So why would the NEDU divers have needed that decompression time? The NEDU test profiles were WORKING DIVES.

The rule-of-thumb I've heard for working dives is that the decompression needed is roughly equivalent to that required for 2x the bottom time. If you use VPM-B+1 with 57 minutes bottom time (3 min descent + 27x2 bottom time), then you get a runtime within a few minutes of the NEDU runtimes. In other words, the time is not "wasted", it's expected. The time is needed to account for the fact that the divers were working. And the VPM-B+1 "Working Dive" profile compares very closely to the Navy's A2 profile that demonstrated the inefficiency of deep stops.

Every way these dives are compared -- either using a higher conservatism (i.e. VPM-B+7) or adjusting the bottom time to account for working divers -- you still get the same results. VPM-B compares very closely to the Navy's A2-deep-stop profile.

 

[leadduck]

View attachment 398625
The rule-of-thumb I've heard for working dives is that the decompression needed is roughly equivalent to that required for 2x the bottom time.

I think you refer to Gerth WA, Ruterbusch VL, Long ET: The Influence of Thermal Exposure on Diver Susceptibility to Decompression Sickness. NEDU Technical Report 06-07, November 2007. Summary: https://www.tdisdi.com/dont-dive-cold where it says "The effects of a 9 °C increase in water temperature during decompression was comparable to the effects of halving bottom time."

I like that as an idea for setting conservatism: using a factor on bottom time instead of tweaking rather abstract model-internal parameters such as gradient factors or critical radius.

 

[UWSojourner]

I think you refer to Gerth WA, Ruterbusch VL, Long ET: The Influence of Thermal Exposure on Diver Susceptibility to Decompression Sickness. NEDU Technical Report 06-07, November 2007. Summary: https://www.tdisdi.com/dont-dive-cold where it says "The effects of a 9 °C increase in water temperature during decompression was comparable to the effects of halving bottom time."

I like that as an idea for setting conservatism: using a factor on bottom time instead of tweaking rather abstract model-internal parameters such as gradient factors or critical radius.

Hey leadduck,

Interesting to see that associated with temperature, but I did hear that rule-of-thumb stated with regard to working at depth.

 

[leadduck]

I don't know a paper comparing the influence of warm water and work-at-depth, is there any? Both should increase perfusion in limbs, work-at-depth should also increase heart rate and perfusion in general. Better perfusion should reduce half-times, mathematically equal to extending bottom time.

I wonder about the impact of work on the assumptions of a bubble model. An analogue to a bubble model -style ascent could be opening a bottle of soda so carefully that bubbles remain small and supersaturation high, leading to fast off-gassing. Nice idea. How well does that work if someone shakes the bottle while I try to open it slowly? Muscle fiber produces a force of about 30 N/cm2, that's 3 bar of pressure or tension for example in a leg while finning, or in a shoulder while switching gases. How well can we control bubbling in presence of a random +-3bar variation on top of ambient pressure?