15-20' dives

[CBulla]

I said it jokingly, and maybe this is my technical inexperience shining like a new penny, but would a shallow dive of 15-20' be something like a long deco stop? Would you just be a constant off gassing (not of the chili induced variety) thus the reasoning behind people stating "dive all day at that depth!"??

See.. my joke phrase of "one looooong deco stop" has peaked my curiosity into the tech of that situation

 

[mwilding]

What would you be off gassing - your burrito lunch?

 

[Karl_in_Calif]

20 ft is indeed one long deco stop. Works well for air, works better with nitrox, and the ideal diffusion rate occurs with pure oxygen.

The NOAA Diving Manual tells you that you can stay there as long as you like, on air, and then surface (to sea level) any time. NOAA has other limitations for EANx however.

The recreational dive tables tell you to round up to 40 ft, but that conceals the benefit of final stops at 20, 15, and or 10 ft.

20/33 + 1 = 1.6 ATAs

There is something magical about 1.6

25/33 + 1 = 1.76

The magic all goes away by the time you get to 25 ft already, based on the empirical findings.

20 ft on pure oxygen is even more magical, provided you take air breaks every 15 minutes of about 5 mins each. If you remember kinetic gas theory from college chemistry, the diffusion will tend to be from richer to leaner diffusions of gas. Pure oxygen has no N2 diffused in it at all, allowing maximum transport across the diffusing membrane (the avioli in our case).

Science does not really understand the magic, although there are several working mathematical models for it. The most modern is Dr Bruce Wienke's own RGBM. Reduced Gradient Bubble Model, I think.

 

[DocVikingo]

As yours is an inquiry "concerning the scientific aspects of decompression," the focus of the Ask Dr Decompression forum, rather than a medical one I have taken the liberty of moving it here.

Best regards.

DocVikingo

 

[baenglish73]

I'm new too.

FWIW, It seems to me your tissue would equalize with the partial pressure of inert gasses at 1.6 ATA . But that leads me to more questions.

If I was on oxygen at 20' for a looooong time after starting at the surface (and I'm immune to O2 toxicity) would I outgas the nitrogen that was in my tissue at 1 ATA? Do intubated people on pure O2 in the hospital outgas their nitrogen?

hmmm

 

[Dr Deco]

Dear Scuba Board Readers:

Shallow Dives

You cannot get DCS from shallow dives because you have not taken in a sufficient dose of nitrogen to form a sufficient volume of gas bubbles in the critical tissue (probably tendon and ligament). It is not a decompression stop because you are not eliminating dissolved gas from a deeper depth. You are on gassing an insufficient (for DCS) amount at 20 feet. The time limit at any given depth is the NDL.

Oxygen Breathing

Whenever you are breathing oxygen, you are exchanging it for whatever gas(es) are in your body. In fact, breathing any gas will exchange the gases at the partial pressure of the breathing gas for whatever gasses are in your body. This can be done at any depth.

Yes, on the surface, breathing oxygen, you can washout the dissolved nitrogen. If you were to then go diving, this would confer upon you a slight decompression advantage. In general, this advantage is not worth the effort.

Dr Deco :doctor:

 

[pipedope]

"Yes, on the surface, breathing oxygen, you can washout the dissolved nitrogen. If you were to then go diving, this would confer upon you a slight decompression advantage. In general, this advantage is not worth the effort. " Dr Deco


The other problem is that you are using up your OTUs.

I do LOTS of dives to 10-15', many times with lots of bounces and outrageous ascent rates. It is part of the job sometimes. No problems, no symptoms, just another day at the office.
The big risk in this is expansion injuries, not DCI.

 

[RichLockyer]

baenglish73 once bubbled...
If I was on oxygen at 20' for a looooong time after starting at the surface (and I'm immune to O2 toxicity) would I outgas the nitrogen that was in my tissue at 1 ATA? Do intubated people on pure O2 in the hospital outgas their nitrogen?

Yes.
Fighter pilots and astronauts pre-breathe pure O2 prior to their missions to eliminate nitrogen to avoid getting bent.

 

[BRW]

You would need a chamber at reduced pressure, or go
to an altitude of roughly 18,000 ft, to drop ppO2 below .5 atm
on pure O2.

You need drop ppO2 below .5 atm on average to beat
full body and/or CNS oxtox over long times while offgassing
N2 indefinitely.

Depending on ambient pressure, you would then offgas N2
slowly down to inherent saturation limit points for humans
breathing pure O2 (given initial N2 loadings)

Bruce Wienke
Program Manager Computational Physics
C & C Dive Team Ldr

 

[CBulla]

Thanks for the move DocViking!

Thanks to Dr Deco and for everyone else thats replied! Fortunately I have a diverse enough background to have understood the basis of the answers.. If you come across information that relates to this or other information for shallow dives, please feel free to share with me PM as it seems that my dives tend to be shallow. I also enjoy learning and reading.. anything to stimulate the grey matter.