100 % O2 breathing at safety stop

[fins wake]

I enjoyed the course and would recommend it. However I have not taken the equivalent course from another agency so I cannot compare them.

I, however, have. What's more, with the same instructor.

On a general level, I've trained with TDI, IANTD, DSAT and other agency instructors. I like them all and I'm not afraid of comparing agencies. In this case, however, the main point was that two of the agencies do not allow 100% O2 on their initial Advanced Nitrox or equivalent (Apprentice Tec) course. I expressed no views on the relative merits, pros and cons of this.

On the WKPP:

If you look at their profiles, you'll see that they far exceed the recommended O2 allowance. How do they do it?

In general terms, I do not find Mr Irvine's opinions as uncontroversial as so many people on this board (and this side of the pond) seem to do. I admire and respect George Irvine's and the WKPP:s accomplishments, but for recreational decompression practices I would definitely stick with the NOAA advice.

The current PO2 limits are based on very thin research...

This must surely be one of the most common urban legends in recreational/semi-technical/technical diving today. I disagree completely. Current PO2 limits are based on very extensive research dating back to WWII - some of it highly debatable from an ethical point of view - on empirical evidence from many of the world's navies and commercial outfits since then, on anecdotal evidence from the sports diving community and on general concensus from the November 2000 DAN workshop.

I would NOT do any of this without taking a class. Blowing it with high PO2's will kill you faster than you can say "Bob's your uncle".

On this I agree entirely.

 

[leadweight]

The term "recreational decompression" sounds like an oxymoron to me. The idea of brething pure O2 at a safety stop sounds a bit odd also. Are we really talking about a deco stop?

 

[Braunbehrens]

leadweight once bubbled...
The term "recreational decompression" sounds like an oxymoron to me. The idea of brething pure O2 at a safety stop sounds a bit odd also. Are we really talking about a deco stop?

I should put the following in my macro list " all dives are deco dives " ;-)

I think O2 is only warrented for long stops. Breathing it for a couple minutes isn't worth the hassle of bringing it, IMO.

If you have a couple minutes of stops and want to increase the safety, just double your stop time and/or do more stops.

 

[Dr Deco]

Dear Readers:

Oxygen Toxicity and Early Research

In actuality, as indicated by “fins wake,” there has been considerable research in this subject. Research during the 1940s centered on exercise and DCS, a field that was largely forgotten for 40 years after. During the 1950s, considerable work was performed on oxygen, especially for treatment of DCS.

One of the major researchers prior to WW II was JBS Haldane, the son of John Scot Haldane. During the war, much work was done by Donald.

Carbon Dioxide

The problem seems to be related, in part, to carbon dioxide, at least, that is the hypothesis. Carbon dioxide is a vasodilator (= opens blood vessels) and increases the blood flow. Blood then carries more oxygen into the brain tissue than can be metabolized and the partial pressure of dissolved oxygen increases. Various deleterious biochemical reactions follow as the oxygen scavenging defenses of brain tissue are overwhelmed.

Carbon dioxide is normally exchanged at the lungs and concentrations in arterial blood are controlled. The problem, as determined by early researchers, is that some individuals sometimes retain carbon dioxide in the arterial system. Apparently the exchange to the lungs is less than optimal and some people are classified as “carbon dioxide retainers.” Who they are and why they do this is not known; the effect can vary from day to day. For this reason, blanket rules concerning oxygen usage are necessary.

Early Research During the War

During the war years, some research was performed that would not be done today. A “shooting war” puts things in a different perspective. This was true of studies on DCS and exercise, also.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[kraken]

Personally I would suggest just diving the correct mix of nitrox on the dive instead of the hassle of stage bottle.

Just my .03

 

[Braunbehrens]

Dr Deco once bubbled...
Dear Readers:

Oxygen Toxicity and Early Research

In actuality, as indicated by ?fins wake,? there has been considerable research in this subject.

I think you mention this later, and please correct me if I'm wrong, but isn't it the case that the variability for toxing is HUGE? One guy toxes after 90 seconds, the next one goes until they stop the test an hour later?

Also, isn't it true that by taking frequent low PO2 breaks, one can extend the toxicity clock massively?

If I'm wrong on any of this, please let me know.

If not, then I think it makes sense to keep the bottom po2's as low as possible and to take frequent low pO2 breaks during high PO2 deco in the shallows. Running a high po2 on the bottom is asking for trouble.

 

[Dr Deco]

Braunbehrens:

You are certainly correct that the CNS toxicity limit is quite variable (it can be a factor of several fold for the same individual). I personally would be very cautious with high oxygen partial pressures if I were using only a mouthpiece as do SCUBA divers.

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[fins wake]

The term "recreational decompression" sounds like an oxymoron to me. The idea of brething pure O2 at a safety stop sounds a bit odd also. Are we really talking about a deco stop?

Yes, we are. Recreational decompression diving is by definition not done in the United States or by US training agencies.

In Europe, however, the situation is different. Recreational decompression diving is allowed by many national federations, however, the procedures and philosophy vary greatly. BSAC allows limited decompression diving, with a maximum hang time of 21 minutes. FFESSM - which has rigorous training - allows very advanced decompression diving for its CMAS*** divers, with hang times beyond an hour! (That's for long deep air dives down to 60 metres, BTW. No further comments ... )

Incidentally, the FFESSM also allows decompression on pure oxygen. If the deco time exceeds five minutes, one is allowed to cut decompression time by a third (i.e. use two thirds of designated deco time).

Now, French scuba diver training is extremely rigorous, perhaps even the best in the world for recreational divers, but personally I'm still happier with the US system: Recreational training and limits for recreational divers, solid technical training for technical divers.

I agree with Leadweight that breathing pure oxygen at a safety stop, i.e. after an NDL dive, would be odd to say the least ... can you guys imagine how the oxtox cases would shoot into the sky for recreational OW divers?

So I'd go with Kraken's nitrox suggestion anyday. For dives requiring long stops, get the required technical training. Or go to France ...

EDIT: "minutes" to "metres" in second paragraph.

 

[100days-a-year]

Uh...O2 at 15' isn't 1.6 it's 1.5 if you round up.Also have to consider this concerns multiple dives in a day .Multiple dives increase your DCS chances more than an 02 hang at 15' increase your oxtox chances.Using the 02 as an insurance against DCS is going to become more common.A 15' hang bottle or deco bar would be an example to me of a well thought out plan for multi-day/multi-dive trips.Can anyone come up with credible evidence that oxtox incidents have actually happened in similar instances or is this like PADIs stance 10-15 yrs ago about nitrox? The sky ain't fallen yet.

 

[Braunbehrens]

100days-a-year once bubbled...
Uh...O2 at 15' isn't 1.6 it's 1.5 if you round up.Also have to consider this concerns multiple dives in a day .Multiple dives increase your DCS chances more than an 02 hang at 15' increase your oxtox chances.Using the 02 as an insurance against DCS is going to become more common.A 15' hang bottle or deco bar would be an example to me of a well thought out plan for multi-day/multi-dive trips.Can anyone come up with credible evidence that oxtox incidents have actually happened in similar instances or is this like PADIs stance 10-15 yrs ago about nitrox? The sky ain't fallen yet.

Far be it from me to exxagerate the dangers of breathing O2. I do it on most dives. However, you have to weigh the risks. First of all, yes, hanging a bottle of O2 off the boat at 15 fsw may not be a bad idea....but it would probably be safer to hang a bottle of 50%. Who knows how experienced the guy breathing it is going to be. However, this could save someone's b|_|tt if they have really blown it.

As far as what to do as a more general principle to reduce the chance of dcs...that is a different story, IMO.

I think in this situation you are better off accepting that all dives are deco dives, and dive them accordingly, doing the proper stops.

Trading DCS for OxTox is IMO a mistake. Most people are scared shirtless of DCS. What they really should be scared of is OxTox.

Compare diving to riding a mountain bike. If you ride enough, you'll eventually fall. You might bruise something, or even break something. That's part of the sport, and you'll heal and you'll be ok. However, taking the helmet off so you can see better, is not such a good idea.

Of course some dives are better done with O2. But not for 5 mn at the safety stop...

BTW, I think it takes 5 mn for you blood to go "once around". So doing anything like breathing O2 for 5 mn or less may not do much at all.