80% or O2 DECO

[Gene_Hobbs]

Well, I have now had three PM's asking my thoughts on this so I am going to wade into this one, against my better judgement. This should kill my signal to noise ratio on this list. :blinking:

<rant on>I love how this thread resembles the same threads that we used to see on this same topic almost ten years ago ( http://www.aquanaut.com/bin/mlist/aquanaut/techdiver/display?23150,from ) and almost every year since. <g> Simple fact of the matter is that the thread is predictable. Folks that like 80, will defend the use with "models" and "experience". The folks that like 100 will counter with more "models" and "experience". Eventually, it winds up with more trash talking than "models" and / or "experience". Then it will die for another 6 to 16 months when someone will "rise to the occasion" and ask it again. So, my question to the group is, have we learned anything? Does not appear so to me...

I am sorry that I don't have a clear cut answer for you. Hard data that I can post that we can all read and see that one is better than the other. Honestly, I feel like this argument is like the discussing the difference in pressure between decompression from 30 msw and 35 msw. Does it make a difference, probably not. Discussion of Oxygen Window, while interesting, does not really change that much between the gasses at these depths. Talk of models, VERY interesting, but all similar (time is relative...). Discussion of Trey, not worth the time to get into thoughts on how he has or has not motivated us, the sport, or just raw emotions, we are here to discuss gasses that don't seem to differ all that much remember.

So, in addition to wondering "if" we have learned anything, I am going to ask "why" we have not learned anything.

Hmm, dive research data... OK, so there is a ton of data supporting the use of 100%. US Navy, Canadian Navy, Royal Navy, and many other navies all have it on their standard gasses for their dive locker. Interesting, standard gasses, might need to come back to this one. Commercial divers? Yeap, they have 100% on site too. How about 80%... anecdotal... interesting... Operational? hmm... anecdotal... Wow... That's kind of fun... Still does not really tell us anything since we want the "right" answer with the gasses.

OK, since there is not much data on 80%, maybe we should be asking "why" again. Well, funding for diving research in the US has not really changed since the late 70's, early 80's and the number of diving researchers is also declining and new ones are not staying in the field (UHMS report to ONR, 2002). BTW - that is called a reference, it would be nice to see more of these on posts, especially when quoting people's previous work (feel free to use the techdiver post link above when quoting the "Baker's Dozen for not using 80/20"). So, if the funding is not going up and most of the researchers are either retiring or leaving the field, we might be on our own to answer this question of "what" is better.

More from the UHMS report is quoted here: http://rubicon-foundation.org/archive.html

Standardized gasses, interesting... Funny how the aviation and nuclear power industries have embraced human factors evaluations of procedures for everything from equipment to decision making. In medicine, we seem to be about 30 years behind aviation and making almost all of the same mistakes in the training they did back then. The Navy and Commercial divers have done proper evaluations on some things and don't seem to be quite that far behind. Where are we, the divers going out on weekends and every other chance we get to have just a few more minutes of bottom time? The Navy and Commercial divers have standardized gasses and procedures for everything. What do they really gain from this? Well, they are able to analyze things much easier when they go wrong... Accident Analysis... Seems like I heard about that in my cave training somewhere but it has been a long time... Seems like all their research reads the same too, Air, Nitrox, Trimix, Oxygen, wow... I'll bet if they use the same gasses every time, they might be able to learn something from their profiles. Is that called a probabilistic model? I could go on but then I would REALLY feel like I was wasting your time...

So, what can we do? DAN started a study several years ago. It was the second project I ever volunteered to help with there (yeap, I volunteered for a while before I begged for a job so I could do this full time ). Project Dive Exploration ( http://www.diversalertnetwork.org/research/projects/pde/index.asp) is a great project that has come a very long way. It is true that it is not what I had hoped but they are doing VERY good work and it may be the only chance "we" have at answering questions that are important to "us". You guys might want to consider giving profiles and standardizing the gasses on your dives. If we all use the same baseline gasses, we might even start getting dives and outcomes that can be used with each other. So, if I am diving and tweaking profiles based on my personal outcomes, and diver B is doing the same thing around the world, we might see similarities in the procedures or find something to make both more efficient... Wow, working together, safer dives, giving something useful back to the sport at the same time... I don't know this sounds like crazy talk to me.

Since I have wasted this much time to discuss the topic, I may as well voice my own practice. After that, I'll be back to commenting on things that do have real answers or just things I find interesting instead of pontificating over things that mean nothing without context.<rant off>

I use 100%. Why? In addition to the noted reasons above for standardization and consistency in my own data set (which includes ALL of my buddies since we ALL breathe the same gasses), I use it because I am only going to take a gas I can use for emergency to site. It is nice to have a bottle marked for Oxygen and actually have more than one use for it. I also don't like introducing more inert gas when I am already supersaturated at the end of the dive.

I would like to thank our moderator for his brilliant use of the word "theoretical" and a reference to go along with his post. Makes that "one" of 100 worth reading.

Take care,
G

 

[Rick Murchison]

I also don't like introducing more inert gas when I am already supersaturated at the end of the dive.

"More" than what? 20% is less inert gas than anything you're breathing before the switch, yes? And at a partial pressure less than any tissue loading, since you likely started the entire event with about .8 ATA and intend to eventually get back to that, yes? So the use of 80% isn't "introducing more" inert gas, but is in fact, introducing less. (Can you tell this "introducing more inert gas" is one of those little "red flag" statements for me? )
---
However... reading through your "rant" I hadn't intended to be in disagreement with anything you had in it until I ran across that little nit near the end... because your points on standardization are well taken and solid. And I also agree with you when you say "Does it make a difference, probably not."
So if it probably doesn't make much difference, what other real-world considerations might have weight in selecting which gas to use?
Standardization: In the broader world of overall research and accident analysis standardization on 100% would ease the task in both, true. But within a particular dive team standardization needn't cater to the broader world; it can be based on team preference, and team preference can be based on lots of things, from "what's handy," to money, to whim. It doesn't really matter much so long as the choices are safe and standardized within the team, so a team can standardize on 80% just as easily as they can 100%, if they want to.
Why might they want to?
First, as several have already mentioned, for "typical" normoxic or hypoxic dives, when using a single deco gas, 80% will get you out of the water sooner. For wimps like me who hate shaking through those last two minutes, this can be a pretty big factor. (As I've already said, in an earlier post, if the plan calls for two bottles I prefer 100% as the final gas, for the same reason.)
Secondly, I've been around 100% oxygen for four decades now, and I've seen enough that I'm really anal about handling pure oxygen at high pressures. I mix my own gasses, and I do not like Haskeling O2 all the way to 3000 psi if I can avoid it and still get enough gas in the bottle to have a decent load for deco (I will do it, but I don't like it ) - so I typically will only charge my O2 bottle to about 2200 psi - and that by transfilling if possible. I can take that same 2200 and top it up with EAN32 (which we have banked) for a full bottle of 80%.
For my money, (for the kind of diving we do) if I had only a single deco bottle, and dove with a group that agrees, I'd use 80%. If I had two deco bottles and planned to use both from time to time, I'd dedicate one of 'em to 100% and the other to something 50% or more, depending on the profiles typical to the team and what the team wants to standardize on. Ideally, own three deco bottles, standardize on 50%, 80% and 100%. Use 80% when the team's using a single deco gas, 50% and 100% when using two. (I'm assuming normoxic or hypoxic bottom gas here)
I should also mention that if you're typically diving Nitrox I or II, or travelling on it, then the decrease in deco time from using 80% is minimal, if any at all, so if you're satisfied that the offgassing gradient difference is important - and especially if you're typically making single or two stop dives only, then 100% should be your deco gas of choice.
The bottom line here is that standardization is important. Whether one of your standardized gasses is 80% or not depends...
I like options...
And, oh, yeah, I mustn't forget that 80% helps compensate for my sorry buoyancy control, right?
Rick

 

[Gene_Hobbs]

So the use of 80% isn't "introducing more" inert gas, but is in fact, introducing less. (Can you tell this "introducing more inert gas" is one of those little "red flag" statements for me? )

and I can appreciate the comment but it can also be safe to "assume" that some of us might like heliox on deco because it is "easy" (I really don't feel like a debate on my meaning of "more" in terms of A or a). A debate was and is a waste of time. As are "assumptions" so I appreciate your question of what I meant.

So if it probably doesn't make much difference, what other real-world considerations might have weight in selecting which gas to use?

You will notice that I did not make any assumptions about when, why, or how anyone uses gas. Simple fact is I just don't care.

It doesn't really matter much so long as the choices are safe and standardized within the team, so a team can standardize on 80% just as easily as they can 100%, if they want to.

Again, I just don't care what you or anyone else decides to use. Simple fact is that there is data to support use of standardization and there is data published on Oxygen that motivates my decision.

The bottom line here is that standardization is important. Whether one of your standardized gasses is 80% or not depends...

Did I ever say there was NEVER a need for 80? If I did, please tell me where so I can make sure I don't trip your defensive mechanisms again. It is not in my nature to question an operation I am not a part of and knowing what your mix training is, no need to question you. I have similar experience to karstdvr in that locations existed where the cave told me a stop at 30 would be better than stops at 20 or 10.

I like options...

What is your point, divers need to think? What a concept, you mean there is no magic bullet? Damn, and I hoped I could stop all this data collection because there was a real answer out there somewhere.

My argument was simply that decisions have to be made and that it is funny how we don't seem to learn anything as we go along. If we had, more information would be available now than there was in 1997. Oddly enough, that's about the same time that Project Dive Exploration, then Project Dive Safety, was first starting. Sad that their dive numbers are not bigger... Guess we have spent to much time talking about these gasses, defending use when it is not called into question, and not diving rather than trying to actually add to the scientific knowledge base.

I do appreciate your thoughts and comments in another thread "in" another board. Without more people submitting dives, outcomes, and getting everyone on similar gasses, the scientific community may not ever have much to offer. The Navy and Commercial divers make the advances they do because they do the same thing every time. Sure would be nice to see an organized effort from our community and bigger numbers to draw better conclusions. We are working on better tools that can be put in a divers hands but funding is holding back a bunch of real work...

Thanks,
G

 

[Dan Gibson]

Yes, but the length of stops required help determine if the curve needs reshaping.

If one is doing 1,1,1,1,1 or some other short stops then there is likely not much of a difference. Once those stops become longer (I have no idea where to define that point), then I would think wasting time deeper than one needs to be is counter productive.

I have heard the same thing, the premise being that doing a linear ascent (i.e. from 70 to 30) is simpler than reshaping. I have done linear acsents in that depth range on 50% and noticed zero difference from a S-shaped deco.

 

[Rick Murchison]

What is your point, divers need to think?

Yep... I reckon that's pretty much it
I'm all for the "cheery 'aye, aye, sir'" when the team leader makes his/her decision on what the standards are for the team, what with me being flexible, responsive & enthusiastic & all - but I want both the team leader and the team members to have a real good sound understanding of what went into the decision, good enough to abide with the decision because it will work rather than "because I say so."
Your points on settling on 100% to improve the quality of the data points available are strong; compelling. Should I have an opportunity to contribute some day I'll gladly leave my bottle of 80% in the garage.
I think we're on common ground - sort of a "grass is green" vs "sky is blue" discussion mostly.

Rick

 

[rjack321]

Yes, but the length of stops required help determine if the curve needs reshaping.

If one is doing 1,1,1,1,1 or some other short stops then there is likely not much of a difference. Once those stops become longer (I have no idea where to define that point), then I would think wasting time deeper than one needs to be is counter productive.

In my case is was 20 mins of deco on 50%. So the profile went: 2,2,2,2,2,6,4
vs a reshaped profile like this 3,3,1,1,2,6,4

As I imagine is the case in many circumstances, moving a couple of minutes around didn't make the slightest difference.

I don't use 80% as a single deco gas, 50% allows me to use more bottom gas before reaching "rock bottom". Also avoids protracted stops on backgas from 60 (approx) up to the switch.

 

[Benthic]

Should I have an opportunity to contribute some day...

Actually the opportunity is here. And it's a great opportunity for those using 100%, or 80%, or 50%, or NDL diving, or any other kind of diving for that matter.

Brian

 

[Dan Gibson]

Under that deco, I think it's safe to say that shaving a little here and adding a little there in the 70-30 range isn't going to result in that big a change, so linear for simplicity may be a good thing. I wonder if the thinking changes on the longer stops. One would think it would have to.

In my case is was 20 mins of deco on 50%. So the profile went: 2,2,2,2,2,6,4
vs a reshaped profile like this 3,3,1,1,2,6,4

As I imagine is the case in many circumstances, moving a couple of minutes around didn't make the slightest difference.

I don't use 80% as a single deco gas, 50% allows me to use more bottom gas before reaching "rock bottom". Also avoids protracted stops on backgas from 60 (approx) up to the switch.

 

[limeyx]

Under that deco, I think it's safe to say that shaving a little here and adding a little there in the 70-30 range isn't going to result in that big a change, so linear for simplicity may be a good thing. I wonder if the thinking changes on the longer stops. One would think it would have to.

I think there was an example with 4,4,4 etc. in it too, which seems like It might have more of an effect

 

[SparticleBrane]

Well, they are able to analyze things much easier when they go wrong... Accident Analysis... Seems like I heard about that in my cave training somewhere but it has been a long time...

I'm pretty certain Coach Brown might have mentioned it...:14:
Thanks Gene for a great post.