Why not 60% O2 for prof during OW?

[suprasteve]

I would not flirt with the edge of the O2 sword without a good reason. And merely to reduce N2 (all day long) is not adequate justification.

I was hoping someone would finally point this out. I for one, and I believe I'm not alone here, would much rather deal with DCS than Oxygen toxicity (of course I would like to never encounter either...). But seriously, your choices in the situation you've presented are:
A) higher nitrogen loading, correlating fatigue and greater chance of DCS symptoms or
B) Oxygen toxicity at depth, and convulsing with your reg out of your mouth in front of a group of students, none of which would have the slightest idea how to help you
Given the choice of the two, the lesser evil is certainly A

 

[don Francisco]

Hello all,
Why not use 60% O2 for professionals during OW? ---- What are the drawbacks of diving less nitrogen as a professional?

You're asking the wrong question, and approaching it backwards. before considering why not do something, first consider why you'd do it in the first place, and what the benefits might be, if any.

With little reason to do so (if any), I can't imagine why you'd even consider fooling with a rich special mix, and the new problems and added costs it introduces.

There's lots of things you might do if so inclined, especially if you get creative, but unless there's a compelling reason not to, you generally do best by keeping things simple.

 

[JonKranhouse]

Follow the money.

Published research, outside the cozy DAN / UHMS / for-profit insurance-underwriting schema, shows a high incidence of brain lesions and bone necrosis among professional divers. Example? 25% of dive instructors in one recently published study had bone necrosis (and none had a history of any DCS hits).

PUBLISHED STUDY (December 2007):
Dive computer algorithms that may cause long-term harm. This was published in Aviation, Space, and Environmental Medicine. This is a peer-reviewed medical journal from the highly regarded Aerospace Medical Association (AsMA), which has no financial interest in the recreational dive industry.

Whereas the UHMS journal does not generally publish research that is disruptive to the profit-stream of the recreational dive industry. Sometimes they'll print just the abstracts. Mainstream dive industry publications further abbreviate these abstracts in a few column-inches, typically buried among lots of other news. Doing so protects the industry from a lack-of-disclosure claim that plaintiff lawyers might argue.

But ONLY ScubaBoard provides a forum where such hard-won information can be re-introduced and BROADLY understood.

These risks can be greatly mitigated with smart protocols, like extended safety stops. Conversely, studies of groups of retired Navy divers, who's thousands of career dives adhered to strict protocols, have almost no incidents of bone necrosis and brain lesions.

The long-term health impacts from hyperbaric exposure is probably one of the reasons that NOAA, and other science divers, are strongly discouraged, and often forbidden, from using air on shallow dives.

That said, EAN-60 is not a good idea for the reasons mentioned in earlier posts of this thread. But mainstream EAN 32 / 36 / 40 should help mitigate long-term health issues.

In light of many international peer-reviewed studies revealing potential harms from long-term hyperbaric exposure, albeit not promulgated by DAN / UHMS, I believe it should be mandatory for instructors to use enriched air in the scenario suggested by the OP. The only reason not to require this is a slight additional cost. Non-nitrox shops have had years to play catch-up. Other arguments are just sophistry with a profit motive.

 

[lefemme36]

Are you asking in abstract why instructors don't always dive "best mix?" If so, that would have been a much easier way to word it

sorry
yes
thanks

 

[John_B]

These risks can be greatly mitigated with smart protocols, like extended safety stops. Conversely, studies of groups of retired Navy divers, who's thousands of career dives adhered to strict protocols, have almost no incidents of bone necrosis and brain lesions.

The long-term health impacts from hyperbaric exposure is probably one of the reasons that NOAA, and other science divers, are strongly discouraged, and often forbidden, from using air on shallow dives.

That said, EAN-60 is not a good idea for the reasons mentioned in earlier posts of this thread. But mainstream EAN 32 / 36 / 40 should help mitigate long-term health issues.

Did the AsMA study differentiate between EAN 32/36/40 and air? Or just tables vs. computers? If its concentrating on instructors, shouldn't they be more concerned with all the ups and downs and the CESA drills with students?

 

[JonKranhouse]

John,

It's worth taking the time to read the whole study published by AsMA.

Participants were both instructors and guides, and had to have at least 500 career dives. "Just" recreational divers with >500 dives were not included in the study.

You're right, repetitious up/down CESA activity may aggravate this condition. Maybe. There's no research to prove that, but it's a reasonable suggestion.

But it is highly dubious that DAN / UHMS would want to fund any such comparative study (dive instructors vs. 100% recreational divers), fearing that results could create the basis for class-action litigation against training agencies, computer manufacturers, and themselves for failing their "duty to warn."

But maybe the results of frequent ups / downs have less impact vs. "simple" cumulative impact of time at depth. Nobody knows.

The best way to mitigate risks is to not buy into the concept of a "more liberal" computer. By analogy, some people like to zoom down the highway on a motorcycle without a helmet (where state laws allow). My full-face Shoei saved my life, when something entirely unpredictable and unavoidable occurred.

A study from France published just a few weeks ago finds that "pre-breathing" normobaric oxygen for 30-minutes before diving greatly reduces bubble formation in multi-day repetitive diving scenarios. Such pre-breathing has been done for decades by U-2 and SR-71 pilots, and astronauts.

 

[John_B]

LOL! I had to look up "normobaric" oxygen... You are saying they breath 100% O₂ at the surface for a half hour prior to diving?

 

[UCFKnightDiver]

Im curious Ronzo why the hell would you post a question, and then go onto say "this question is somewhat rhetorical", you dont seem to be listening to what anyone else has to say, and it seems that everyone is in pretty much unanimous agreement. Why post at all your obviously set in your ways and thinking. Real silly in my opinion.

 

[boulderjohn]

There is a part of the study for which I would like more information.

It notes that there was no problem with navy divers, and points out that they are very disciplined and follow their tables carefully. It then contrasts that with instructors and divemasters, suggesting that these divers are less disciplined in following their computers.

I don't see any evidence that they considered the difference between the navy tables and the Buhlmann-based computers of the instructor test group. U.S. Navy procedures are different from Buhlmann. Did they consider the possibility that the difference in the algorithm might have had something to do with it?

What is interesting is that much of the technical diving community scoffs at the Navy tables and refuses to follow them, saying they create a "bend 'em and fix 'em" profile.

By the way, I am offering no argument here--just a piqued interest.

 

[DwayneJ]

Im curious Ronzo why the hell would you post a question, and then go onto say "this question is somewhat rhetorical", you dont seem to be listening to what anyone else has to say, and it seems that everyone is in pretty much unanimous agreement. Why post at all your obviously set in your ways and thinking. Real silly in my opinion.

IMHO Ronzo has always been an intelligent contributer to this forum and certainly I see no issue with throwing the question out here for discussion. This thread has generated some good information for me. A thanks for RonzoTheGreat!

Personally I believe EAN60 is too high as there is minimal theoretical PPO2 wriggle room if a student wanders into deeper water and you have to go fetch them.

Dwayne