100% O2 for DECO Stops

[Uncle Pug]

Originally posted by Dr Paul Thomas
I am not at all convinced that there is such a thing as a CNS oxygen clock (as it is an all-or-nothing event) but will happily accept a safe limit of 45 mins at 1.6 bar pp O2.

So 100% O2 is safe and beneficial.

Just as well because a lot of recreational UK divers uses it regularly!

Hi Paul...
AFAIK the O2 clock refers to whole body toxicity (pulmonary)....
The single exposure rule deals with CNS hits...

100% is beneficial but not intrinsically safe... it must be used correctly or it is deadly... taking along an extra cylinder that could be used at the wrong depth is not *safe*... training & discipline are necessary to mitigate the hazzard of having O2 along on a dive.

So back to your first point that I let ride:
1) The ability to control buoyancy in the 6m/20 ft range is critical to *safe* usage.
2) Training in when and how to deploy and use O2 as well as how to even carry it on the dive are critical to *safe* usage.
3) Understanding and implementing the concept of *toggling* is critical to *safe* and efficient usage.

 

[BILLB]

The sole advantage of helium is to reduce narcosis from nitrogen. Helium being a "lighter" gas is absorbed by human tissues at a faster rate than N2. It also off gasses faster too. This in theory suggest it can have applications for the non deco recreational dives. The down side is it is expensive and if you do get a DCS hit it is more difficult to recover (and I have heard more painful) from with hyperbaric treatment.

Again O2 safety stop after a non deco dive has similar benefits with heliox as with nitrox/air.

CNS and the 24 hour O2 clock is not well understood but until this migrates from theory to fact it pays for us as divers to heed this restriction when using high O2 mixes.

 

[Uncle Pug]

Originally posted by BILLB
The sole advantage of helium is to reduce narcosis from nitrogen.

Nope... not the sole adavantage:

A chief advantage of He is decreased WOB with consequent reduction in CO2 retention and all the bad things that go with that...

Plus He is easier to deco from than nitrogen...

Plus He lets you talk funny on the surface

 

[BILLB]

Dear Uncle Pug,

The bad thing I have heard is that helium removes heat from the body faster. Then, upon reading this "myth" explained by Dr. Julie Bookspan it is only the sensation of being cooler. She gave a rather in depth explanation and concludes that helium is not that much different from other gasses with thermal exchange in our bodies.

Help me here. What is WOB? How does this help with CO2 retention?

Thanks!

 

[Munin]

and if you do get a DCS hit [helium] is more difficult to recover (and I have heard more painful) from with hyperbaric treatment.

Many people are saying the that it's not these days. George Irvine swears that it is the exact opposite.

I don't know his reasons for it, but it makes sense to me. Since helium is a faster gas, it should diffuse faster after a hit and be more responsive to oxygen treatment. That's just a guess though.

Does anyone here have anymore information about this? What are the reasons for claiming that helium is worse or better than nitrogen?

 

[Uncle Pug]

Originally posted by BILLB
Help me here. What is WOB? How does this help with CO2 retention?

Dear Bill,
WOB = work of breathing and greatly contributes to CO2 build up which is just a really bad scene...

 

[The Iceni]

Hi Bill,

Helium has several useful and not so useful properties. One of it greatest beneficial properties is its lightness.

I think we may have gone a bit off track.

If there is no nitrogen in the deco gas, decompression of dissolved nitrogen is accelerated. Thus Heliox 50 will be just as efficient, if not more so, than 100% oxygen and could be used for the deeper stops - after Nitrox or air dives only - to boot.

In the UK I see many divers doing staged deco with up to three cylinders for deco from 21 M, when IN THEORY one light cylinder of Heliox 50% would do for all stops. (oxygen is more than twice as heavy as helium)

OK there is the cost. As for heat loss. Helium is more conductive than air but has lowewr thermal capacity. In any case thermal conductivity is not really a problem for shortish recreational dives - particularly if helium is only used for deco!

I must be missing something.

Or is it that no-one has thought of this before. I am pretty sure that cannot be the case!

 

[Uncle Pug]

Originally posted by Dr Paul Thomas
I must be missing something.

Or is it that no-one has thought of this before. I am pretty sure that cannot be the case!

Shoot and me having to run out the door this second...

 

[Dr Deco]

Dear Readers:

There actually is an “oxygen clock” for both pulmonary and CNS forms of oxygen toxicity. The progression of the pulmonary form is slow and the regression is slow. In the CNS case, the presentation comes on rapidly.

The problem with this second form is that it is extremely variable as to the length of the safe interval. It is even highly variable from day to day in the same individual. In fact, oxygen toxicity tests are no longer performed, at least in the Royal Navy.

Dr Deco
:doctor:

 

[Uncle Pug]

Originally posted by Dr Deco
The problem with this second form is that it is extremely variable as to the length of the safe interval. It is even highly variable from day to day in the same individual.

Was there any understanding that came out of the tests done... any thing the was consistent across the boards???