Studies on outcomes of omitted decompression - how badly do you get bent for x minutes of skipped deco, aka how risky is a dive?

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DiveLikeAMuppet

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Are there any good studies that would classify a statistical link between skipped deco and medical outcomes, outside of anecdotes and freak incidents? I'm trying to a get a feeling for how risky some of the diving might be.

Let's ignore rapid ascents and gas embolism. I'm assuming that skipping deco, with appropriate medical treatment if required such as reaching a staffed chamber within 3-4 hours, could result in an outcome roughly on this spectrum:
  1. No long term impact: can return to diving, possibly after a chamber treatment
  2. Life-changing injuries: wheelchair or too "broken" to ever dive again
  3. Death, despite treatment, within hours or days
Decompression theory is obviously a very blurry line, different algorithms and settings, gas mixes, depths and profiles will make any estimates quite unreliable.

A lot of the DCS incidents that happen every single day fall into category 1 - it's the standard newbie who skips few minutes of stops because who needs to read a computer manual or the tech diver who had had a drysuit flood, surfaced at GF99 and now self-medicates with O2 because their shoulder was a bit niggly, most likely from carrying too much gear rather than bubbles.

I can also place the other extreme with no chance of survival - think U-869/The last dive or a diver skipping 2 hours of deco after a 100 meter dive.

What is difficult to place are some of the in-between scenarios. Think:
  • 10 minutes of back gas air deco at 6 meters - most likely 1?
  • 20 minutes of back gas 32% deco at 6 meters - most likely 1?
  • 20 minutes of deco on 50% at 6 meters - somewhere between 1 and 2?
  • 30 minutes of deco on oxygen at 6 meters - somewhere between 2 and 3?
I'm not even sure what would be a good way to model the risk - SurfGF?
 
  • 10 minutes of back gas air deco at 6 meters - most likely 1?
  • 20 minutes of back gas 32% deco at 6 meters - most likely 1?
  • 20 minutes of deco on 50% at 6 meters - somewhere between 1 and 2?
Unless on pure O2 you are dropping offgas efficiency by sticking to 6 meters. Why?
 
Unless on pure O2 you are dropping offgas efficiency by sticking to 6 meters. Why?
Those were examples - I just needed something comparable to explain the types of dives and magnitude of deco. I'm not looking for the most efficient decompression plan here.

Obviously some of those dives might have deeper stops and if the conditions are right, you might run some of the deco at 3 meters etc. but that's not the point here.
 
The first question is: what is for example 10 minutes of omitted deco? it is a very big difference if you dive 100/100 buhlmann or 50/70 for example.

If you just look to NDL tables, the DCIEM gives you only 15 minutes on air at 30m. But naui or padi tables for example give you 20 minutes of NDL time. So does this mean that if you stay 20 minutes and you go up without a safetystop you already have omitted deco? Of is this only the truth if you have a cmas cert?
Here already small differences are starting, but on a nice wreck, 5 minutes difference is a lot.

On a 100m dive, there are for sure more risks, but for example, if you put in Multideco a bottomtime of 15 minutes, oc-dive, 12/65 bottomgas, 21/35 travelgas, ean50 and 100%. GF40/70. This gives you a total divetime of 96 minutes if the last stop is at 6m for 36 minutes with the last 6m to surface with 1m/minute.

If you use the same gases, same other parameters, but GF100/100, it gives a total divetime of only 67 minutes. With GF35/85, the ones which the shearwaters came as standard with gives you 87 minutes.

My first 100m dive was done with the 'standard' GF of 35/85. Now I dive most times 40/75 and sometimes 40/70. So does this mean I skipped 10 minutes deco on my first 100 dive? I did not get bent happely. But as you can see, all these factors can give you a 'safe' divetime.
More or less you can say that if you go to 100m with a 15 minute bottomtime that all dives around 95 minutes (a little bit more, or a little bit less) are all fine.
You also can use pragmatic deco to make the stops smoother to remember, easier to remember, because deco is not absolute science. So if you forget the 15m stop, do it at 12m and you will be fine.
If you stay 1 minute longer at 100m, you will get 8 minutes deco more. Just make it easy, 4 minutes of that 8 on 6m, the other 4 between 21m and 9m 1 minute on each depth, so at 9, 12,15,18 1 minute extra.
If you need to do 22 minutes extra deco, do again around the half at 6m, the rest between 21 and 9m.

So you cannot say you forgot to do 10 minutes of deco. What 10 minutes from what? Of the planned schema? Yes, then it is possible. But if you dove on a 40/70, you are probably safe. If it was a 100/100, the risks are higher that you get bent.

But there is no straight boundery between 'not bent' and 'bent'.

If you stay at 100m and you go up without any stops after a bottomtime of 15 minutes, there is a very high risk of serious problems or death.
And what if you got bent and you dove exactly according to a 40/70 plan? That is still possible.

So it is no absolute science.
 
The first question is: what is for example 10 minutes of omitted deco? it is a very big difference if you dive 100/100 buhlmann or 50/70 for example.

If you just look to NDL tables, the DCIEM gives you only 15 minutes on air at 30m. But naui or padi tables for example give you 20 minutes of NDL time. So does this mean that if you stay 20 minutes and you go up without a safetystop you already have omitted deco? Of is this only the truth if you have a cmas cert?
Here already small differences are starting, but on a nice wreck, 5 minutes difference is a lot.

On a 100m dive, there are for sure more risks, but for example, if you put in Multideco a bottomtime of 15 minutes, oc-dive, 12/65 bottomgas, 21/35 travelgas, ean50 and 100%. GF40/70. This gives you a total divetime of 96 minutes if the last stop is at 6m for 36 minutes with the last 6m to surface with 1m/minute.

If you use the same gases, same other parameters, but GF100/100, it gives a total divetime of only 67 minutes. With GF35/85, the ones which the shearwaters came as standard with gives you 87 minutes.

My first 100m dive was done with the 'standard' GF of 35/85. Now I dive most times 40/75 and sometimes 40/70. So does this mean I skipped 10 minutes deco on my first 100 dive? I did not get bent happely. But as you can see, all these factors can give you a 'safe' divetime.
More or less you can say that if you go to 100m with a 15 minute bottomtime that all dives around 95 minutes (a little bit more, or a little bit less) are all fine.
You also can use pragmatic deco to make the stops smoother to remember, easier to remember, because deco is not absolute science. So if you forget the 15m stop, do it at 12m and you will be fine.
If you stay 1 minute longer at 100m, you will get 8 minutes deco more. Just make it easy, 4 minutes of that 8 on 6m, the other 4 between 21m and 9m 1 minute on each depth, so at 9, 12,15,18 1 minute extra.
If you need to do 22 minutes extra deco, do again around the half at 6m, the rest between 21 and 9m.

So you cannot say you forgot to do 10 minutes of deco. What 10 minutes from what? Of the planned schema? Yes, then it is possible. But if you dove on a 40/70, you are probably safe. If it was a 100/100, the risks are higher that you get bent.

But there is no straight boundery between 'not bent' and 'bent'.

If you stay at 100m and you go up without any stops after a bottomtime of 15 minutes, there is a very high risk of serious problems or death.
And what if you got bent and you dove exactly according to a 40/70 plan? That is still possible.

So it is no absolute science.
You are completely on money here. It would be a lot easier to compare if OP use SurfGF as a metric.
 
That's why I'm looking for any interesting, most likely empirical, studies - at the level of Haldane bending goats, but with humans in mind :wink: . And obviously there might not be a study that would bend people as that has all kinds of ethical problems.

So for all the accurate people - here is the US Navy table for air deco dives to 120 feet.
1708954673576.png


(Columns are bottom time - ascent time to first stop - stops in feet - total deco)

Assume an ascent at 18 feet/6 meters a minute, so reasonably fast but not uncontrolled, up to the surface.
  • After 20 minutes at depth, if you skip the 4 minutes of deco - most likely a niggle?
  • After 60 minutes at depth, if you skip the 172 (!) minutes of deco - most likely won't surface conscious?
What I'm after is the grey zone between these two extremes - what's the likely outcome of skipping for example 9 minutes of deco from this table. It's obviously difficult to relate US Navy table to the actual diving most people do, that's why I used the examples.
 
Any empiric study of significant omitted decompression on humans would be unethical. There are animal models that purposely omit large amounts of decompression, but those studies are mostly to examine the pathophysiology of DCS. And, some of those animals don't get bent despite the researchers' best efforts. We also know by experience what happens when divers omit significant amounts of decompression. Your question of
I'm trying to a get a feeling for how risky some of the diving might be.
might be better directed toward an exploration of how technical divers mitigate the known risks of DCS and avoid omitting decompression altogether.

Best regards,
DDM
 
Hugely grey area here, and I do speak from experience, I got horrendously bent by doing a 40m ccr dive on a run time of only 75min, I’ve never truly been the same since and had tests for hole in the heart etc etc, I didn’t get anywhere near busting any stops and did my usual habit of 100% O2 at the surface, and on to the boat, the boat was in choppy sea so required effort to sit, wiggle out of gear and secure equipment, and then help others aboard, between my input and various diving medical staff the conclusion was dehydration, the only positive that came out of it (except I know I haven’t a PFO) is that I can sort of sense in my body if it feels fizzy / something feels not right on a dive and I just pad stops a while and move on,,(I know others that also feel they do this), I should point out that when I had my unfortunate incident I was at a stage in my life where I was in hindsight drinking a bit too much (4 pints pre dive evening)
 
Is the original question for your own understanding or something more official? It might help,
 
I can also place the other extreme with no chance of survival - think U-869/The last dive or a diver skipping 2 hours of deco after a 100 meter dive.
U869 sits in 240ft, 73m.

This is the beginning of a rabbit hole on pDCS

And another
 
https://www.shearwater.com/products/perdix-ai/

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