If you had to choose, 80% or 100% for deco gas and why.

[lowviz]

DIR thinking is to think things through and understand.

Not all that hard for you, your thinking has been done for you by the DIR brass. And I'll be the first to admit that they are damn good at creating a generic product. You should look into how they got that way, no rules were ever broken no "unreachable areas" were ever explored and mapped.

...//... Kwinter states that he has a PFO and thinks that continuing to decompression dive is a good idea. Hmmm, I will go with thinking things through.

Quick think for you. He can't dive, no generic recipe exists for him. End of story.

On the other hand, he could easily and safely do saturation diving as long as he found an ascent procedure that allows for his recirculated nitrogen burden. At a fundamental level, he is no different than you. Come up too fast and both of you will bubble on the arterial side.

Keep thinking...

 

[TONY CHANEY]

Someone mentioned filling O2 to 4500psi which prompted the comment.
Most of the shops I have seen bank and fill to 3,000psi which would give 40cft in an Al40. Does filling to 3,000psi generate the same issues as filling to 4,500psi? Why would you need to ever fill higher pressure? I would only fill an al 40 to 3,000psi to get the 40cft, otherwise I bring a diff cylinder and no need to pump it that high. Then again, I sometimes exceed the speed limit but don't speed when it appears risk outweighs the benefit. I do not drink and drive, ever. Maybe my logic is flawed but there you have it.

I guess that there really is something to being a little bit pregnant.

I also wonder just how much better is 100% in being at 1.6 but having to take back gas breaks where the O2 might be 21%. There really is a reason for not breathing 100% O2 for a prolonged amount of time for a reason. But Hel!, I am only a RRT, what do I know.

 

[Dr. Lecter]

are the 80% folks breathing it at 20'? or do you breathe it at 30'?

Yes - hence the O2 exposure and deco efficiency differences. This is not rocket science, nor is there anything magical about 20% of a slow-loading inert gas in your shallow mix. Adding a fast-loading gas like helium to a midwater mix like 50%, like Kalayci mentioned, strikes me as a much stupider thing to do from a deco efficiency standpoint. But I try not to question whatever little voodoo rituals make people feel better about poorly understood stuff like IBCD or CNS.

 

[LiteHedded]

Guys (aj has a bit of personal experience with this he's mentioned) have proven for years that 100% o2 is fine for huge exposures so I stick with the zero inert deco gas. But whatever floats your boat.

 

[kwinter]

Kwinter states that he has a PFO and thinks that continuing to decompression dive is a good idea. Hmmm, I will go with thinking things through.

My small PFO has been discussed with the medical staff at DAN as well as the chief of diving medicine at a major medical university. I have studied the research and adjusted my ascent profiles accordingly. I carry a Doppler and check myself. But if you think I should ignore all of them and listen to you and the Kool Aid clowns instead, then I guess I should rethink my whole diving paradigm.


iPhone. iTypo. iApologize.

 

[mathauck0814]

This conversation again? Jesus, who cares? The best ascent plan is the one that gets you home in time to argue with the wife about all the chores you neglected while you were out tech diving with your friends (somewhat muted when she came with you, but still).

On open circuit or closed, I'll use whatever I happen to have and adjust accordingly. Per the OP's question, we're talking about a dive with only one deco gas, so you're barely talking about doing deco at all. If you're only bringing one bottle, you're not exactly pushing the envelope. We know how to do those dives. Just go dive and do whatever deco your gas requires.

 

[jadairiii]

Not all that hard for you, your thinking has been done for you by the DIR brass. ...

I always enjoy it when someone posts on a subject they know nothing about. Errol was teaching "DIR" before there was a GUE and was there at the beginning of GUE. You would be surprised who's c-cards throughout the world has his signature on them. Very surprised.

But don't let ignorance of a subject stop you from posting, please continue.

 

[lowviz]

I always enjoy it when someone posts on a subject they know nothing about.

Please point out my ignorance using specifics, not broad inferences.

... Errol was teaching "DIR" before there was a GUE and was there at the beginning of GUE. You would be surprised who's c-cards throughout the world has his signature on them. Very surprised.

I am not that naive, I did my homework before posting. I'm quite aware that I'm alone in a minefield. The rules haven't changed, challenge one and you get the entire organization. That is, after all, part of the attraction of DIR for all the semi-skilled, self-conscious wannabes.

The part that keeps me going is that your organization does indeed have many fine people that I both respect and admire immensely. I would never name them as it would just do them an undeserved disservice. I agonized for several years if GUE was right for me, a lot of that can still be found on the web. It appears that you can't see shades of gray, just black and white.

On a similar note, I've just changed doctors. I've also become old enough to understand that age is only worth so much in terms of either deference or current skills.

... But don't let ignorance of a subject stop you from posting, please continue.

Just correct my mistakes as you identify them and we can both coexist quite peacefully. I am a student of diving and have a lot to learn. In addition, please remember that many more than you and I are reading this and the Internet has a powerful memory.

 

[PfcAJ]

The 90s called. They want their thread back.

 

[Dr. Lecter]

Someone mentioned filling O2 to 4500psi which prompted the comment.

My comment was directed at someone saying they dove with 4,500+psi of oxygen.

If that was in this thread, I’ve missed it…could you point me to it? If you were looking at my reference to keeping a large HP tank full of 100% either around topside or hung at 20’, rest assured the fill pressure on such a tank is 3442psi…just like the numerous HP3L CCR O2 bottles that get boosted up to ~3500psi around the world every single day.

I’d also be interested to hear the logic behind why a system sufficiently O2 clean to handle 3000psi of O2 couldn’t safely boost O2 to 4,500psi assuming a true HP tank such as may be found more commonly in Europe. Which is not to say you’re wrong about whether the extra 1500psi of pressure makes O2 significantly more dangerous — merely that you’ve concluded something is “crazy” without bothering to show your work. Which leads me to my next, and last, point on this thread’s topic.

DIR thinking is to think things through and understand.

Perhaps that’s true, but nobody reading your or GI3’s words about 80% vs. 100% would rationally reach that conclusion. What we see instead is a constant stream of bald conclusions about deco gases and CNS loading measures that are loudly stated as points of fact, apparently in hopes that readers are unfamiliar with the concept of conclusions that flow logically from a series of stated premises. The following are the antithesis of “thinking things through”, rather than examples of someone who “understands” facts and can explain how they support his claims:

The 80/20 mix is in fact totally useless and contraindicated as a deco gas. At thirty feet it is only a 1.52 ppo2 ( the real 1.6 ppo2 gas would be 84/16) and as such does not either provide the right oxygen window, nor does it does it work as well as pure oxygen without an inert gas at any depth.

Any perceived decompression benefit of using a higher ppo2 at 30 feet with 80/20 is then given back by the lowered ppo2 at 20 feet, not to mention the fact that the presence of the inert gas in the breathing mixture defeats the purpose of using oxygen in the first place ( see the Physiology and Medicine of Diving). The ppo2 of 80/20 at 20 feet is 1.28, not much of an oxygen window, and at 10 feet it is 1.04 - useless for deco.

That’s funny, because relative efficiency numbers for 80% and 100% show an extremely small difference between the two mixes. And anyone invoking the “oxygen window” may as well cite 100%’s greater toxicity to the tiny demons that live in inspired inert gas and afflict ascending divers...one might say using the term is like hanging a “stroke” sign around one’s neck, but that would be rude.

There is simply no justifiable reason to dive 80%, ever.

Conclusory nature self-explanatory.

I’ll now let you get back to thinking you’re the only one doing ocean dives deep enough and long enough to rack up major deco time.