Overshooting NDL and mandatory deco stops

[The Chairman]

When I was less experienced than I am today, I believed that some lethargy and sleepiness was quite normal after a dive or two.

Yep, in my experience the Nitrogen Nap is a real thing.

After a DAN lecture with Dan Orr, it was obvious to me that I needed a longer safety stop. Neural fluid has about the same half time as blood at around five minutes. Making them 5 minutes has eliminated the need to take a nap afterwards. Those two extra minutes really make a difference.

 

[Storker]

US Navy tables are said to have a DCS risk of approx. 2%

According to our country's perhaps leading clinical hyperbaric physician, who has been the first author of roughly the last half dozen revisions of our national tables:

Revision 7 of the USN decompression tables has an estimated risk of DCS of between 2 and 6% depending on depth, bottom time and decompression procedure

(my translation)
Ref: Risberg J, Møllerløkken A, Eftedal O, Norske dykke- og behandlingstabeller (Norwegian diving and DCS treatment tables), 2017, http://www.dykketabeller.no

 

[Mike1967]

SWAGs (Scientific Wild-A** Guesses)

Lol

 

[taimen]

SWAGs (Scientific Wild-A** Guesses)

My guesses are definitely only WAGs but I am surprised that there aren't more educated guestimates on dsc risk with different gf:s.
Does your Norwegian authority have any estimate how your tables compare to usn tables riskwise?

 

[RayfromTX]

The difficulty in accurately determining actual risks through scientific testing is multifaceted.

At a bare minimum testing is made difficult by the fact that you are testing for actual DCS hits which means you must test until you harm your test subjects which has obvious ethical implications.

On top of that, it appears that the variability of risk between individuals is actually quite high and because of the first problem it is difficult to accurately access with certainty a method for accessing the risk tolerance of any specific individual.

To make it even worse, the risk within particular individuals seems to vary depending on ill-defined variables that may include dehydration, diet, rest and other factors.

This is a simplified explanation of why it is impossible for decompression studies to conclusively state what our actual risks are with accurate specificity.

Bottom line is play it safe by backing away from the edge, consider your current health and the stress you have accrued by the frequency of your diving and any other factors you feel important and make adjustments to the conservancy you use on your dives.

If you are unwilling or unable to do more than just follow the computer on your wrist then set the conservancy to high or medium based on your tolerance to risk and your age and health. Don't push it because we don't and can't know where the edge exactly is for a given person on a given day in a given diving environment

 

[Storker]

Does your Norwegian authority have any estimate how your tables compare to usn tables riskwise

In fact he has more than that. He has proper statistics:

During [the ten year period from 1993 to 2003], 220,000 dive hours were logged [by the Norwegian Contractors Association]. The statistics showed an incidence of DCS of about 0.05 ‰ per hour; i.e. one incidence per 20,000 hours. [...] Diving at Kalstø showed a particularly high incidence (9259 dives, DCI incidence 0.18%). Among the other dives (52352) the incidence was 0.04%. Several studies show, however, that some divers experience symptoms after decompression, but don't consult a physician for "untreated DCI". [...] The amount of this unofficial treatment is probably fairly small.

again, my translation.
Ref: ibid, p. 2

 

[BRT]

Not aimed at you specifically, I see this comment a lot. Just something to bear in mind, although a CESA from 15' is not a major deal on a VERY benign dive, when you are inert loaded, that is the worst place to do a fast ascent. the pressure change gradient there is the steepest and it is where, in my tech training, the emphasis on a slow ascent rate has been the highest. The so-called "champagne phase"

I understand and agree. My gauges are mine and I trust them. But if there is no air with the SPG reading 150# I'll share or go up. Rather than saying 500# is the minimum and not taking the long safety stop.

 

[Rooster59]

Can anyone make an educated guess how many additional dsc cases (statistically) can be expected when changing from 40/85 to 45/95.
On other words, how large is that difference in terms of relative risk.

Oh man, now you're going to be studying US Navy Thalmann:

http://archive.rubicon-foundation.o...le/123456789/4820/NEDU_1985_08.pdf?sequence=1

 

[PfcAJ]

The difficulty in accurately determining actual risks through scientific testing is multifaceted.

At a bare minimum testing is made difficult by the fact that you are testing for actual DCS hits which means you must test until you harm your test subjects which has obvious ethical implications.

On top of that, it appears that the variability of risk between individuals is actually quite high and because of the first problem it is difficult to accurately access with certainty a method for accessing the risk tolerance of any specific individual.

To make it even worse, the risk within particular individuals seems to vary depending on ill-defined variables that may include dehydration, diet, rest and other factors.

This is a simplified explanation of why it is impossible for decompression studies to conclusively state what our actual risks are with accurate specificity.

Bottom line is play it safe by backing away from the edge, consider your current health and the stress you have accrued by the frequency of your diving and any other factors you feel important and make adjustments to the conservancy you use on your dives.

If you are unwilling or unable to do more than just follow the computer on your wrist then set the conservancy to high or medium based on your tolerance to risk and your age and health. Don't push it because we don't and can't know where the edge exactly is for a given person on a given day in a given diving environment

The NEDU man-tests decompression profiles to establish quantified risk.

 

[lv2dive]

While I agree with you, I don’t think your statement is mutually exclusive with Ray’s.

The NEDU man-tests decompression profiles to establish quantified risk.