100% O2 for DECO Stops

[NITROXDIVER]

Do any of you use pure O2 for your Decompression stops(@ 20')? I've heard that it helps increase the rate of off-gassing. I've tried it on some dives and it does leave me feeling more energetic when i get back on the boat. Any comments pro or con?

 

[Waterlover]

are you trolling?

 

[Uncle Pug]

Originally posted by Waterlover
are you trolling?

Let me be the first to ask...
Why would you think he is tolling?

 

[The Iceni]

Hi Nitroxdiver,

Many divers routinely employ high concentrations of oxygen, including 100% O2 in their deco mixes when undertaking "accelerated decompression".

The theory is very neat.

If the inhaled gasses contain little or no nitrogen, the nitrogen pressure gradient from blood to alveoli is much greater and therefore so is nitrogen off-gassing. For example when decompressing on air at 6 M the opposing nitrogen pressure is 0.79 x 1.6 or 1.26 bar, 1.26 bar greater than when decopressing on 100% oxygen at that depth as then the opposing nitrogen pressure is (close to) zero and decompression much more rapid!

To my mind there are two major disadvantages.

The first problem is the anxiety over the use of high partial pressures of this "devil gas" because of the real risks of CNS oxygen toxicity when the inspiratory pp O2 exceeds 1.6 bar. (Can you guarantee to keep station at 6 M and not to mistake the O2 reg for another at depth?)

The second is the effects such a high inspiratory pp O2 has on the the theoretical CNS oxygen clock. Most agencies recognise an accumulative effect of high exposures of oxygen on the CNS, while I do not have the figures to hand, a reasonable period of exposure to a pp O2 of 1.6 bar during such a stop can clock up more CNS exposure than the rest of the dive put together. This could completely mess up any planned second dive that day!

(As an aside a Heliox deco mix could THEORETICALLY be used following a nitrox dive for the same reason, but this is not really practical)

I have used 100% Oxygen at 3 M but suggest you ought do a little more research before adopting pure oxygen routinely for the 6 M stop.

A CNS hit at 6 or 8 M is just as catastrophic as one a depth so the UK jury is still out.

Most report a feeling of euophoria or "fizzing".

Take care! : =-)

 

[Uncle Pug]

Originally posted by Dr Paul Thomas
(Can you guarantee to keep station at 6 M and not to mistake the O2 reg for another at depth?)

while I do not have the figures to hand, a reasonable period of exposure to a pp O2 of 1.6 bar during such a stop can clock up more CNS exposure than the rest of the dive put together. This could completely mess up any planned second dive that day!

Hi Paul,
First point we'll let ride... training being the key...

Second point... here in the US the NOAA limits are 45 minutes at PO2 1.6 per single exposure and 150 minutes per 24 hr. exposure...

 

[BILLB]

This can be said about that. WKPP divers used 100% oxygen and found it to be so good (meaning zero DCS hits) that it is now the deco mix of choice.

Toxic hits when going below a 1.6 partial pressure is NOT a problem for experienced divers. And, by all definitions, the use of 100% oxygen as the final deco stage gas is for experienced divers.

The other mix (80/20) that was in wide use gave the deco stop some leeway but it still has nitrogen in it thus, you are still ongassing even at the shallow depth of 15-20 feet.

Helium and oxygen (or even tri mix) are not deco gases. Yes you can deco on them but the time spent in the water becomes way too long IF that is the only gas you have. Helium has other deco problems that are usually resolved by using a Nitrox mixes at deeper depths.

Using 100% oxygen for recreational diving does allow more nitrogen offgassing and therefore a diver (in theory) has less "silent bubbles". Using Nitrox has been reported to be a "magic" gas with all concerned "feeling better" after a dive. Feeling better after 100% O2 should be no different. The theory on this on is that on deep and long recreational dives, we may be subject an in-between region now called sub-clinical DCS.

I am not a tech diver but I do try to keep current on these subjects because it has applications for recreational divers and for us who teach the sport.

 

[newton]

Originally posted by BILLB
The other mix (80/20) that was in wide use gave the deco stop some leeway but it still has nitrogen in it thus, you are still ongassing even at the shallow depth of 15-20 feet.

Close, but not quite. You're not really on-gassing, since the percentage of nitrogen is still less than what you'll have at the surface (both in terms of Partial pressure as well as N2 percentage). However, using 100% O2 increases the gradient by 25%, and thus decreases off-gassing of N2 (and potentially He in technical diving) that much more.

Using 100% oxygen for recreational diving does allow more nitrogen offgassing and therefore a diver (in theory) has less "silent bubbles". Using Nitrox has been reported to be a "magic" gas with all concerned "feeling better" after a dive. Feeling better after 100% O2 should be no different.

Except that becaise of O2 toxicity, using 100% makes for very shallow recreational dives. ;-)

For recreational diving, 100% O2 is never a necessity, since recreational diving never involves deco (at least, in my world it doesn't.) The only use for 100% O2 in recreational situations is out of the water DCS treatment, which we all hope to avoid.




Nate

 

[BILLB]

Hey, That is what this board is for. To keep the inaccuracies and mis-information at a minimum. I should have chosen my words more carefully.

In other words, the deco diver using 80/20 is off-gassing a net lost of N2. It is quite obvious that the diver will NOT be in the water long enough to equalize his /her body to the 80/20 mix.

As far as recreational "style" diving, I do envision using 02 as a safety stop gas. This is even more practical if the recreational community adopts heliox for deep dives.

Lastly, for those of us advancing in years, a 100% O2 safety stop is already a reality where I dive (East Coast).

 

[rcohn]

I heard a talk by Dr. Bill Hamilton at the beginning of April. He said he believes in doing what works. He also said (among other things) that both 80/20 and 100% O2 work.

Ralph

 

[The Iceni]

Bill B said

"Helium and oxygen (or even tri mix) are not deco gases. . . "

Well spotted Bill! Now could you explain why? (Purely for theorterical/discussion purposes you understand)

If helium has not been used in the bottom gas and is only used in heliox during shallow deco (in order to minimise the risks of oxtox) there will be minimal on-gassing of helium (with a partial pressure of around 0.5 bar for less than 15 minutes). Would this really pose an unacceptable additional risk? (Forgetting about the costs.)


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 as a lot of recreational UK divers uses it regularly!