Physics of diving question...

[arcFlash]

JointVentureDive - I don't need to be told to go to the surface. That's kind of insulting.

If you reread, it's before ooa. Say I have 20 minutes supply and 28 minutes deco. Can I affect how I may get bent (if at all) by adhoc modification of my ascent profile. Skip deep stops or shallow stops?

I've read a bunch of docs from
Some are old but many are worth a read. They can be very dry reads.


Disputes females are more likely to get DCS under similar dives. Three studied from 87 and 88 are available.

[JointVentureDive]

Arcflash.   First I apologize if you think my post was intended to insult you.  If you knew me,  you would know that I would never try to insult you or anyone.   I have been around divers for over 12 years or slightly more than half my life.    I been on lots of dive trips, and boats, with great divers and “jerks.”

I’ve had plenty of times where I could have insulted someone for just cause and did not.    I have never been told that I have tried to insult any diver.  If anything, I am one of the most complimentary and congenial persons you will meet. Hopefully over time you too will agree.  So before I go off and cry, I think I will post the following:

I must admit the key argument in your dispute, is that I missed the word BEFORE  OOA.    I had just read a complex string of comments herein, from Smith and Dectorguy.   

HOWEVER, your scenario led me in a different and to me perhaps a logical and sequential set of an assumptive path that  I would have taken, and done. 

Let me explain.  In the scenario , when you indicated that you "know you are going to have to violate a compartment"  which is what you said.....

and I understand that you indicated under NORMAL conditions you know your rate of Consumption of air. BUT.. MOST PEOPLE WOULD REACT TO THE 20 MIN.of air Estimate,  28 MIN DECO TIME DIFFERENTLY. Chances are your entire situation and breathing RATE by default, will soon change for the worst.
Nevertheless,
IT TELLS ME THAT YOU ARE ASSUMING YOU ARE GOING TO BE OUT OF AIR, Because what else should I assume, if you know one of the two compartments that you listed are going to cause a decompression hit.   OTHERWISE, you would not have to be considering the scenario you did.  IE..   
Just for example.
Quick to 30ft then very slow - bend arm
very slow to 30, then quick - bend spinego up fast, 
[/quote]

In either case, if you are going to violate anything, arm,spin, etc.  whatever,   YOU ARE VIOLATING EVERYTHING   that was not planned.  It doesn't matter what compartment.  You don’t have enough gas to offgas, and as such, you are OOA.   
Basically, the scenario described is not your planned dive.   
The safest alternative is  to stay at 15 feet for as long as you can. Almost deplete all air, and Surface and get help with or from another diver.  Which is what I posted. 

In an ideal emergency (if you can call it that)  you may be able to get some  air with another diver get back into the water with a rescue diver together, and off gas to proper deco.   Of course, if you have to surface,  suck on O2;  get 911 going;   pure O2deal works wonders.
That’s all I was trying to say.  Hope your still my friend.  Also, my gills are cold  : but they still can't make  O2.    Milk shakes anyone!
Nicki.

[arcFlash]

I read John's post as wanting to know what part of the body correlated to what tissue compartment. That made me wonder if it's useful outside of academics. So the logical question is, given the chance, can I effectively alter my decompression to limit the risk of getting bent in a really bad place? I can live with a bad elbow, knee... but getting bent in the spine and being paralyzed isn't. So, it sounds like no. The tissue group that limits the NDL is likely to be the control on the entire dive including the planned decompression component.

I would have interpreted the model to say the NDL is limited by the fastest compartment but the slow(er) control the decompressing times. That said, the spine is likely slow being it's closed off by the meninges. If I want to avoid a bent to that body part, do I have any options, theoretical as they may be?

Biology is a messy thing but it's not random.

My former manager got a spine bend on a repetitive 60 ft dive for 30min on air. lost her legs, had 5 chamber rides and still has issues walking. She had a pfo and didn't know it.

John,
This doc from 2000 talks about the original model and how half times were created and by whom.

Note: this document describes lab testing of animals resulting in death.
"Haldane
calculated these half lives to represent what happened in
the body. Moir’s data gave him his 20 minute half time.
Haldane used Hill and Greenwood’s3 data of nitrogen
excretion to provide his 5 minute half time. That is based
on the nitrogen content of urine. Hill and Greenwood
considered that as the kidneys are very well perfused in life
they represented what we now call a fast tissue. They
experimented on themselves in a chamber under pressure
where they passed urine every 5 minutes or so. The urine
was passed out of the chamber and the nitrogen content
measured. JS Haldane’s experiments on goats gave a 75
minute half life. From his mathematical calculations he
showed that, if the body had an equal perfusion, then this
would represent a 10 minute half time. I have not been able
to find the origin of his 40 minute half time."