No More 10 ft Stops?

[waterpirate]

Is anyboby even useing the navy tables for anything but disscussion on SB?
Eric

 

[ianr33]

My guess is that doing the 10' stop after teh 20 increases the off gassing rate.

No. It won't. Not on oxygen.

Tissue pressure of N2 is whatever it is.
pN2 in the breathing gas will be zero on 100% O2, no matter what the depth, so the pressure gradient is the same at any depth,so offgassing and hence length of deco stops should be the same.

Doing a final stop on O2 at 10 feet has the advantage that CNS loading will be lower,and less O2 will be used, but the total deco time should be the same.

---------- Post added March 2nd, 2013 at 09:59 AM ----------

Doesn't V-Planner use VPM? And aren't gradient factors (like 30/85) a Buhlmann thing?

Yes and Yes!

 

[Nemrod]

I agree. Ten foot stops are simply an annoyance in open ocean. Plus many people have been doing the 10 foot stop on 100%, so there is little benefit, compared with combining the times in a 20ft stop. The 20ft stop is just as effective, it is done below the 15 ft hang bar, below most of the swells, etc. The 20 ft stop is when most of us go to 100% anyway. Once am on 100%, I am not particularly concerned with additional ongassing.I suspect it has less to do with what's I vogue, and more to do with what works, and is functional.i doubt it has anything to do with fitness standards, or a specific scientific basis. It is just convenience. If a deco program shows me doing a 20 ft stop and a 10 ft stop on 100%, chances are I will combine them at 20 ft. In open ocean, the 20 ft stop makes sense. In other circumstances, the choice of a final depth depends on the environment. If I go to 40 Fathom, and there is a nice platform at 20 ft, where I can doze while doing my 20+ minute stop, without getting in someone's way, that's where I will do my deco. There's a 10 ft platform, too, but there is more traffic.

When a 10 ft stop might make more sense is when there is a limited gas supply concern.

I am pretty sure Dumpster was concerning himself with no-deco diving. You make good points that I would mostly agree with. Do you program VCRs too?

N

 

[PfcAJ]

Fwiw, GUE has been teaching "no 10ft stops" for quite a few years now during Tech 1 and Tech 2 classes.

Personally, for longer dives outside of the scope of T2, I've been dividing up the 20ft stops between 20', 15', and 10' with (so far) good results. Even though I think the CNS clock is bogus, I take oxygen very seriously. For short exposures (o2 times around 30mins or so), doing the entire thing at 20' followed by a slow ascent (~3fpm) is probably fine.

 

[NAM001]

I dont know, like i said i am not a deco guru, only suggesting pssible causes for difference in data.

Doesn't V-Planner use VPM? And aren't gradient factors (like 30/85) a Buhlmann thing?

 

[rossh]

The 10ft stop is needed in Air diving, to get the job of off gassing done in a reasonable amount of time. In Air diving, we have only the reducing ambient pressure to drive out the excess N2. If we stop at 20 only on Air, its takes a lot longer to finish.

This applies to 32% as well. On 50% its about even, with a small advantage to the 10 ft stop. On pure O2, we can do all the stop at 20, because the off gas gradient is the same on O2 at any depth. But with one item in mind - you will need to go to the surface eventually, slowly, and passing through 10 ft. So no harm in doing part of the stop at 10.

Here is a little more on this: Decompression myths and mistakes

 

[NAM001]

ROSSH

EVEN A DUMMY LIKE ME CAN UNDERSTAND THe majority of the link. thanks

---------- Post added March 3rd, 2013 at 05:12 PM ----------

Not even due to the larger differential presure? Wont you still have residual n2 in the lungs coming from the off gassing process for atleast say 5 min or a good portion of the 10 ft stop time. Not argung , just learning.

No. It won't. Not on oxygen.

Tissue pressure of N2 is whatever it is.
pN2 in the breathing gas will be zero on 100% O2, no matter what the depth, so the pressure gradient is the same at any depth,so offgassing and hence length of deco stops should be the same.

Doing a final stop on O2 at 10 feet has the advantage that CNS loading will be lower,and less O2 will be used, but the total deco time should be the same.

---------- Post added March 2nd, 2013 at 09:59 AM ----------




Yes and Yes!

 

[ianr33]

Wont you still have residual n2 in the lungs coming from the off gassing process for atleast say 5 min or a good portion of the 10 ft stop time. Not argung , just learning.

I think I see what you are saying. Yes, you will be offgassing nitrogen from your tissues into your lungs,thereby diluting the 100% O2 you are breathing. But, I think the amount of nitrogen is too small to worry about. (If it changes the 100% O2 to 99% O2 the difference would be lost in the noise)

Rebreather divers might have a better idea. I understand they need to flush the loop on deco at 20 feet every so often as the offgassing nitrogen reduces the pO2. Believe that takes a few minutes though at least.

Another thing to bear in mind is the body does not absorb much nitrogen. One fascinating fact I learned on Scubaboard is the body absorbs about 1 litre of N2, per atm of pressure at SATURATION. Dive to 100 feet for many hours and you will only absorb 3 litres of N2. (About HALF your lung volume Lung volumes - Wikipedia, the free encyclopedia Not very much is it? )

 

[Dive-aholic]

I must be dead or bent or toxed then

It's not a universalism IMO. I have not done a 10' stop in 7 years or so on a staged decompression dive. I do 3 (or longer for more significant exposures) minutes up from 20' at the end of a staged decompression dive. O2 clock is planned for.

If your O2 clock is planned for and you can do the entirety of your last stop at 20' then you're not doing the types of dives I'm talking about. The OTU table states no more than 45 minutes at 1.6 during a dive. The dives I'm referring to require more than 45 minutes more decompression once you hit 20'. Those are the dives I'm definitely going to 10' on. And I'm also doing breaks from the O2 every 20 minutes.

 

[PfcAJ]

Fwiw, you're at risk of oxygen toxicity on all these dives. Just because you haven't passed "100%" doesn't really mean much (you can tox below 100%), and passing 100% doesn't mean a whole lot, either.

Imo, oxygen is one of the biggest risks in technical diving, and it's also one of the biggest unknowns.