NOAA Nitrox 32 No-Decompression Table Questions

[2airishuman]

LOL. 99.99% is more like it, according to the studies done..

I realize you know this stuff better than I do. Still.

I believe that, for about 99% of divers, the tables "work" in the sense that 99% of divers can regularly dive the tables to the NDLs over a long period of time without having clinical symptoms. I don't believe that 99.99% of divers can do that.

 

[boulderjohn]

I realize you know this stuff better than I do. Still.

I believe that, for about 99% of divers, the tables "work" in the sense that 99% of divers can regularly dive the tables to the NDLs over a long period of time without having clinical symptoms. I don't believe that 99.99% of divers can do that.

The 99.99% figure is the percentage of dives with no DCS. It is a rare event. The statistics include all dives, including those violating limits. I have heard that roughly half of DCS cases occur on dives on which the diver did not violate limits, meaning that the other half include violations. That means people following the limits are even less likely than those numbers indicate.

Here is a further complication--how do we know the people who were diagnosed with DCS actually had it? Many diagnoses are difficult, and they will frequently put the diver in the chamber when they are not sure. We had a thread a few years ago dealing with DAN's arguments with some chamber operators, and someone posted some documents related to it. In one interesting letter, DAN was talking about the need to have a properly trained physician making the diagnoses, because they believed many people who were being treated did not have DCS. They listed a number of maladies that are often misdiagnosed as DCS. Some of them not only present as DCS, the patient recovers in about the same amount of time someone would spend in the chamber, thus making it appear as if the chamber was the cure.

 

[tursiops]

The 99.99% figure is the percentage of dives with no DCS. It is a rare event. The statistics include all dives, including those violating limits. I have heard that roughly half of DCS cases occur on dives on which the diver did not violate limits, meaning that the other half include violations. That means people following the limits are even less likely than those numbers indicate.

- What is the risk of DCI?
Look for the "unexpected" rates.....they really are 99.99%.

 

[boulderjohn]

- What is the risk of DCI?
Look for the "unexpected" rates.....they really are 99.99%.

Very interesting--note that it includes some of my points--statistics often include issues other than DCS in their totals, and there are misdiagnoses in the totals as well.

 

[KeithG]

It would also be interesting to understand how often and under what condtions "skin bends" occur. I did a quick search for "skin" in the above link and did not get a hit (unintended pun, sorry...).

The most mInor form of skin bends presents as a rash and the literature claims it is often ignored as a sunburn.

edit: so my point is: how many minor cases of bends go unreported?

 

[2airishuman]

The 99.99% figure is the percentage of dives with no DCS. It is a rare event. The statistics include all dives, including those violating limits. I have heard that roughly half of DCS cases occur on dives on which the diver did not violate limits, meaning that the other half include violations. That means people following the limits are even less likely than those numbers indicate.

Here is a further complication--how do we know the people who were diagnosed with DCS actually had it? Many diagnoses are difficult, and they will frequently put the diver in the chamber when they are not sure. We had a thread a few years ago dealing with DAN's arguments with some chamber operators, and someone posted some documents related to it. In one interesting letter, DAN was talking about the need to have a properly trained physician making the diagnoses, because they believed many people who were being treated did not have DCS. They listed a number of maladies that are often misdiagnosed as DCS. Some of them not only present as DCS, the patient recovers in about the same amount of time someone would spend in the chamber, thus making it appear as if the chamber was the cure.

I agree with all that.

On the other hand, the vast majority of dives have a duration nowhere near the no-stop limit. I suppose it depends on experience level, and where and how you dive, but I would imagine there are many divers who rarely if ever are on a dive where they reached the no-stop limits.

 

[KeithG]

I agree with all that.

On the other hand, the vast majority of dives have a duration nowhere near the no-stop limit. I suppose it depends on experience level, and where and how you dive, but I would imagine there are many divers who rarely if ever are on a dive where they reached the no-stop limits.

Interesting comment. My personal experience leads me to the opposite conclusion.

I think most divers either do a "trust me" group dive (and get surprised by NDL or gas) or ride their computer NDL (see post #19). But I have no hard evidence to support my theory.

This is based upon my experience with low current, high viz Caribbean vacation dives where it is very easy not to suck yur tank dry. But you make me nosey. Next LOB I will pry into my fellow divers gas reserves...

 

[Saniflush]

I kept an eye on the remaining bottom time & ascent whenever it got down to 1-2 minutes left and didn't feel fatigued after the dives. I just felt a bit shakened up when a diver in front of me who, I "ass-u-me", had similar dive profiles, got bent & had to be dragged out of the water. That made me wonder whether I had also pushed my limit without realizing it.

This is self realization I would contend a very good thing. If you are able to ask this question about your own profile and be honest with the data you find, then you are way ahead of the game.

 

[100days-a-year]

1.Without any regard for algorithm, gas,depth or time at depth some people are more resistant and some are more susceptible to DCS.

2.Tables are not computers,computers are not tables.

3.Safety is relative and subjective, what I consider safe you may not.What you consider aggressive I may not.

4.It is "Decompression theory " not "Decompression fact"

5.There is tendency in some divers to ascribe every ache and pain they feel to DCS,either hypochondria,ignorance,machismo or some other mental quirk may be driving this.

6.There are some divers who will ascribe DCS symptoms to any other possibler cause for the same reasons.

7.SB is not PubMed,much of the info here is well intended but mostly anecdotal or second hand and even when illustrious decompression specialists give advice it comes with a caveat as many of them have changed beliefs over their career as better science has become available.

 

[Neilwood]

I kept an eye on the remaining bottom time & ascent whenever it got down to 1-2 minutes left and didn't feel fatigued after the dives. I just felt a bit shakened up when a diver in front of me who, I "ass-u-me", had similar dive profiles, got bent & had to be dragged out of the water. That made me wonder whether I had also pushed my limit without realizing it.

The important thing to do is think about your physique, conditions etc when deciding how conservative you want to be.

What a dive computer can't do is know exactly how your body is reacting to the decompression stress. The best they can do is give a mathematical line in the sand where statistical analysis has confirmed there are an "acceptable level" of DCS hits. It doesn't know how YOU are doing, but how statistics suggest an average person will probably do.

What you as a diver have to do is look impartially at yourself and your potential dive and decide do I have any risk factors such as overweight, unfit, poor circulation, lack of hydration, cold weather, strong currents (which suggest a lot of strong kicking might be required) etc. If you do see risks there, increase your conservatism. If you get out unusually tired, it could well be subclinical DCS.

An oft quoted phrase here - new divers comment that they know very little about DCS, experienced divers comment about bubble formation, gas permeability, compartment types etc and scientists and professionals who study diving physiology comment that they know very little about DCS.