100 % O2 breathing at safety stop

[fins wake]

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.

Absolutely, in fact I wouldn't mind an O2 hang bottle or bar at 6 metres. I agree with 100days-a-year that people are too caught up on oxtox risks based on pure ppO2:s of 1,5-1,6 at safe depths, particularly after low O2 load nitrox or air dives.

The way you're describing it above is how things are done for Bikini wreck diving (80% EANX) and many places in France (O2). It would certainly appear to me to be a good idea on many multiday-multidive trips, yes.

However, this assumes that it's a bar or fixed bottle at safe depth, not something you're carrying yourself!

It's the latter I'm thinking of when pondering the myriads of OW divers who suddenly breathe out of their O2 bottle at 30 metres, or donate the wrong reg to an out-of-air buddy or whatever. This would happen! For sure.

Also, as far as the bar is concerned, I'd personally want the dive operator to demonstrate to me (or measure myself) the O2 fraction of the gas mix. If they say it's pure O2 and I'm calculating on it, and it turns out to be say EANX87, I'd be rather miffed ...

 

[Braunbehrens]

Hanging bottles in open ocean is a bad idea, if you're going to rely on them, IMO. This has been the cause of fatalities in the past. What if you don't find your way back?

I always carry my gas. Hanging a SAFETY bottle is another matter.

 

[Pez de Diablo]

Braunbehrens once bubbled...
Hanging bottles in open ocean is a bad idea, if you're going to rely on them, IMO. This has been the cause of fatalities in the past. What if you don't find your way back?

I always carry my gas. Hanging a SAFETY bottle is another matter.

And carrying deco bottles to depth and switching to the wrong gas has caused fatalities in the past. Pros and cons to each scenario. Plan your dive according to the conditions, what may work this time won't the next time.

 

[pufferfish]

I was at a DCI talk last year by Dr. Peter Bennett of DAN fame and he was asked what changes to recreational dive procedures he could foresee so as to lower the rate of Type 2 DCS injuries which has not changed at all despite the introduction of computers, better equipment, training, etc. over the last twenty years (ok lets leave out training)

His three answer were:

1) Ascent rates slowed down to 30 ft/min or slower

2) Deep 'safety' stops on deep recreational air dives (i.e. 100-130 ft) especially on those square profiles in cold water. He suggested a stop at half the deep depth and then the traditional 15 foot stop as well.

3) Using the "Queen of gases, oxygen" on the safety stop and/or on the surface interval. We have oxygen bars in New York so why not on the surface interval for recreational air divers?

That is how we will finally lower the incidence of Type 2 DCS injuries in recreational divers. I don't think using O2 on the safety stop is such a way out idea.

 

[Dr Deco]

Dear Readers:

Nuclei Formation

Readers familiar with my concepts as written for SCUBA BOARD will know that I would not agree with the ideas proposed by Dr Bennett. He is a wonderful fellow, but we do not see eye to eye on most decompression issues.

I am a firm believer in the idea of micronuclei and stress-assisted nucleation as the cause of most problems in decompression. Naturally this must be coupled with some over saturation. (You can lift weights all you want in a gym, but you will not get DCS – no over saturation is present.) Sharp-eyed readers will also note that I have often commented that my replies are my opinions supported (and interpreted) by my research, but they are not necessarily shared by the entirety of the barophysiology research community.
Most researchers find it difficult to believe that nuclei can be created and controlled by the individual. The concept of nuclei is accepted and is 60 years old, but it is thought of as a vast abstraction. It is not considered a part of everyday life. Many will ascent to the idea of bubbles playing a role in ascent rates but that is about as far as it will go. It is academic beyond that. :book2:

Neurological DCS

Neurological DCS has not been reproduced in the laboratory with any degree of consistency. Unlike joint-pain DCS (the bends) it does not appear to be directly linked to gas loading. Certainly techniques such as “double diving” and “dive and recompress” will produce neurological problems but this is probably an epiphenomenon [of the excessive gas loads].

Neurological problems have their origin, I believe,

• in the autochthonous nuclei in the moveable spine or
• arterialization for loss of pulmonary filtration, or
• rebound flow arising from Valsalva-like maneuvers.

While it is certainly true that tissue desaturation by oxygen breathing is a good idea, the washout times are slow. I believe that they are too slow as contrasted with problems issuing from stress-assisted nucleation. Slow scent rates will help to be sure, but they will fail, too divers haul all that gear around while on the surface.

Long decompressions in the water (by tech divers) are probably helped by the adynamia in the water the same as we see in astronauts during EVA. This needs to be tested in the laboratory, but the question will probably outlast me. Retirement is coming up – along with the lack of research funds (which fosters my plans to retire).

Dr Deco :doctor:

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

 

[fins wake]

Hanging bottles in open ocean is a bad idea, if you're going to rely on them, IMO. This has been the cause of fatalities in the past. What if you don't find your way back?

If you rely on them, it's not recreational diving anymore. One should always have a choice: Do I want to do my safety stop (not compulsory deco stop!) on oxygen, or do I want to do it on whatever I'm breathing now, and have 50 bars left of (classic recreational diver rule)?

Sharp-eyed readers will also note that I have often commented that my replies are my opinions supported (and interpreted) by my research, but they are not necessarily shared by the entirety of the barophysiology research community.

I buy it, though. Checks to be sent to ... nah, just joking!

Seriously, it makes a lot of sense! I find that the whole idea of stress-assisted nucleation (particularly beyond certain depths, temperatures, body 'moods' & times) explains a h*ll of a lot of "weird" anecdotal decompression data ...

How can you go from 156 metres to the surface on air in one (1) minute and still survive unscathed (infamous accident)? How can you do aggressive semi-saturation diving in Florida caves unscathed when the minions do the stage collecting, and then end up bent when handling the tanks yourself just this once, albeit only from 6 metres to the surface and onto the trolley?

I really have to save up for that decompression class in September! Anyone know a good bank to rob? Or whatever?