Is there a Nitrogen Loading Equilibrium Point?

[Thalassamania]

Please permit me to clean up a few items:

At 100 fsw we are nitrogen loading. At 15 fsw we are off gassing nitrogen. My question - what is the depth of equilibium where we are neither absorbing or off gassing, and are there variable factors that have relevance. Can this depth be incorporated for planning in extended diving i.e. liveaboards where doing 5 tanks in a day isn't unheard of.-Thanks

See Bob's excellent answer.

Some could say that it's 33 fsw. Because that is where the pressure gradient is at a 2:1 ratio, and there is no - NDL for less than 33 feet. However. Offgassing will occur at deeper depths, depending on how much nitrogen you've accumulated, and the depths at which you've accumulated them.

However... I think what you're asking is - is it safe to do 5 dives a day on air? In short. Yeah. You can do that no problem. Do you have a dive computer?

The authorities will say 24 feet is the deepest that you can saturate and return directly to the surface.

Here's a discussion point for you all (not sure I agree with the story, but here's what I heard):

The dive captain / instructer on the Molokini trip I did in Hawaii said that when he was a DM in the Virgin Islands, he knew of an instructor that got bent in 20 feet of water, due to the fact he conducted five OW check out classes in one day with several students each class. I asked him why, and he said it was because of the numerous ascents made with each student when the did the CESA at the end of each class with each student.

I found it hard to believe, but I suppose that it will put a strain on your body to some degree.

I don't know the details, but I assume that he was underwater pretty much all day long (four to five hours bottom time with minimal SI?), which is not unheard of with resort instructors. Proves that you definitely ongas at very shallow depths. Maybe the depth was minimized for the story - maybe he was in closer to 25 to 30 feet, but still, that is an interesting story.

This is not classic DCS, this is bubble pumping, it is quite possible, but it has more in common with AGE.

Is it possible to get bent in 20 ft of water? Yes - in fact if you look at the RDP, the most "dangerous" pressure groups for a single dive are shallow dives for long periods of time - hence the WXYZ rules for mimimum surface intervals. This is because the so called "slow" compartments take on gas very slowly, but also release it very slowly also - hence repetetive shallow dives for extended periods of time can be misleadingly believed to be "safe". In theory, you are still on-gassing even whilst making a safety stop at 5 metres after a sixty minute dive.

While I do know of two diagnosed cases of DCS that resulted from saturation between 20 and 24 feet, that is most unusual. You are right to respect long shallow exposures (especially before flying), but the PADI tables were never designed to have any bearing on saturation exposures, they were designed ONLY to model typical recreational dives.

An article I read from Suunto suggested 6 CESAs from 9 metres (45 ft) is enough to significantly increase a person's pre-dispostion to DCS. A number of rapid ascents caused during training dives could easily have led the instructor in this case to get bent.

Given that most instructors in resort areas can be spending 3 or more hours a day in the water - and longer in some cases - their risk of DCS becomes more significant.

Again, that's bubble pumping, not DCS and one CESA followed by a descent and reascent ... that's enough to do it.

I also know of one case where a girl got bent during a Discover Scuba Diving experience (max depth of 6 metres) due to a Patent Foramen Ovale (hole in the heart) - a medical condition with potential problems for divers (I won't go into it here).

Again, PFOs do not result in DCS, they result in AGE.

Full sat diving is not for the faint of heart and, as a number of wheelchair-bound full-sat oil rig divers from the 70s are finding out, not especially good for your health.

Happy decompressing,

C.

Saturation diving on air at 24 feet is relatively risk-free and can be done by recreational divers at Jules Undersea Lodge in Key Largo.

I am not sure I get the point of the OP question but as fisheater pointed out equilibrium or saturation is based on time at a particular depth whatever that depth may be and usually is considered to be 24 hours. If you stay at 100 feet for 24 hours you are at equilibrium for 100 feet. Descend to 150 feet you are ongassing until you reach equilibrium at 150 feet after another 24 hours. The same happens in reverse when moving to a shallower depth.

Exactly.

 

[Don Burke]

I spent some time fiddling with various deco software and a dive computer simulator and found that they all said I was unbendable at 12 feet on air. It took a really long time to get bent shallower than 20 feet, but it can be done.

 

[Thalassamania]

Despite what your simulations might say, people have spent 60 days at 24 feet and come directly to the surface with no ill effects.

 

[Don Burke]

Despite what your simulations might say, people have spent 60 days at 24 feet and come directly to the surface with no ill effects.

If we are swapping anectdotes, people have been bent after eight hours at 20 feet.

Your mileage may vary. May cause airsickness in diabetic pregnant chickens.

 

[Thalassamania]

If we are swapping anectdotes, people have been bent after eight hours at 20 feet.

Your mileage may vary. May cause airsickness in diabetic pregnant chickens.

Would you mind detailing three? I only know of two ... and those are questionable.

 

[Don Burke]

Would you mind detailing three? I only know of two ... and those are questionable.

Sorry, I do not walk around with a file of everything I have ever read.


There were two people in the same incident that I can recall right off. An STG and a tech rep were working in a pressurized SONAR sphere on a destroyer and got themselves bent. It was in one of the Navy safety pubs, probably in the late 1980s.

Those things are not pressed to more than 20 FSW.

There is always the possibility that alcohol the night before could have been a factor.

The pub made a big deal out of them never getting wet.

 

[H2Andy]

what is the depth of equilibium where we are neither absorbing or off gassing, and are there variable factors that have relevance.

this is a really difficult thing to calculate

it's all relative. it depends at which depth you absorbed the nitrogen into your system, how much time you spent at that depth or lower, and how fast you make your ascent

of course, it's not that simple, because then you get into partially filled tissue, and the different absorption and release rates for the various kinds of tissues and so on ...

also, depending on how hydrated and/or fatigued you are, or how much lactic acid you have on your muscles, or how old you are, these rates change so ...

hmmm ... sorry, i guess the answer is, beats me

 

[cks44diver]

oh my, out of all of these answers there are only a couple that actually make since and are even close to correct

 

[captain]

oh my, out of all of these answers there are only a couple that actually make since and are even close to correct

Please enlighten us with the correct answer.

 

[Thalassamania]

Please ...