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

[jadairiii]

Nobody's missed the point. ....

Actually you missed it completely. But I will talk slow so you understand. It had nothing to do with the actual use of 80/20 vs O2. The side point (if you read it) was software getting divers out of the water faster on 80/20. The POINT is was making was that the software does a lot of weird things and that I would, personally, not trust that completely. I can tweak DECOM and get tables identical to VPlanner yet they claim to be different "models".

Now do you understand?

 

[lowviz]

... But I will talk slow so you understand. ... The POINT is was making was that the software does a lot of weird things and that I would, personally, not trust that completely.

Good, an argument based on facts, science, outcomes and not religion. I think that I follow your analysis, but how do you factor in reserve capacity?

 

[Dr. Lecter]

Actually you missed it completely. But I will talk slow so you understand. It had nothing to do with the actual use of 80/20 vs O2. The side point (if you read it) was software getting divers out of the water faster on 80/20. The POINT is was making was that the software does a lot of weird things and that I would, personally, not trust that completely. I can tweak DECOM and get tables identical to VPlanner yet they claim to be different "models".

Now do you understand?

OMG, you mean if you give each one different variables and/or alter the constants employed by the model itself, you can make two different sets of calculations provide roughly the same result?! Someone call Snopes, that's just crazy!

I understand your original post referenced software specifically failing to give credit for extended stops at gas switches, and therefore being obviously wrong…and I correctly pointed out that you don't understand whether that makes the software right, wrong, or if it's totally irrelevant any more than the guy on a subway platform at 3AM ranting about government mind control can provide an factually indisputable history of the Kennedy assassination.

DIR divers do a lot of weird things and I would, personally, not trust any of them completely. I'll say it again: if whatever hare-brained approach to deco you've been using has worked for you thus far, huzzah for you. Just don't confuse that with either you being an authority on what is/isn't the optimal approach to deco, or, being able to speak authoritatively as to whether you or a given model are correct where you and it differ.

Good, an argument based on facts, science, outcomes and not religion. I think that I follow your analysis, but how do you factor in reserve capacity?

Anecdote != science. Other than that, no concerns.

 

[jadairiii]

.......

What is your area of practice?

 

[boulderjohn]

Actually you missed it completely. But I will talk slow so you understand. It had nothing to do with the actual use of 80/20 vs O2. The side point (if you read it) was software getting divers out of the water faster on 80/20. The POINT is was making was that the software does a lot of weird things and that I would, personally, not trust that completely. I can tweak DECOM and get tables identical to VPlanner yet they claim to be different "models".

What do you mean by "weird things"? Are you saying that you have a personal algorithm that is superior to the ones used by the different software makers? If so, how was it derived? How was it tested?

BTW, I do know someone who has and teaches a personal algorithm. When he teaches it, he says he derived it by his own experiences, and he knows it is superior to software algorithms because he uses it and does OK. He also says it is OK to tweak it yourself based on your own experiences. So it would not be out of reason for you to have developed your own algorithm. It would just not be my choice to do so.

 

[Errol Kalayci]

Taking advice from anyone on the internet is only slightly worse than listening to what is said in a typical dive shop. It is called decompression theory not fact, I do not give decompression advice to anyone. I have done some decompression diving and have done it the way the same way for over 20 years except that I am not as aggressive anymore as I have aged and taken on more responsibility but have a very solid idea of what works for me. I use helium in my 70' bottle and oxygen when needed from 20' up. I use 30/30 and treat it like Nitrox when I catch lobster on the 100' ledge- that is just me and I am not advising anyone to do anything.

It is hard for me to believe that anyone teaches 80% anymore as it was initially used to solve training issues. I was dive buddies with the heads of the early agencies and the concerns were that divers could not hold stops and were hoovers while booster pumps were not in place then. The solution of course is to learn buoyancy and stability while getting fit and comfortable so you use less gas and are not fighting to hold your stops. I left in the late 90's and helped start an agency that teaches the way we dive. I stopped teaching for a long time and started again to try and give back to the activity that I am passionate about.
These days with boosters you can always get oxygen at 3,000psi, pumping O2 higher is crazy talk. If you are diving in the ocean, you would have already used 50/50 or 50/15 like me before you would switch to oxygen. How deep and long of dive are you doing where you are on Oxygen for longer than 20-30' in the Ocean with more than one gas switch? I would suggest not many people are doing that unless they are following some very, very conservative tables. The ones that are use Oxygen. In a cave of course you are on Oxygen and taking back gas breaks. You should be using a dpv for any deep dive or most any dive in the ocean, after 20-30 minutes you will be bored on a wreck having made multiple loops and explored the interior of the wreck, unless you then scooter off and do flying deco over shallower wrecks and reefs like we do There is simply no justifiable reason to dive 80%, ever. People justify poor choices all the dive, there is no place for poor choices in technical diving. Think through everything and Do it Right. If an instructor is unable to explain why he recommends something, run! If it sounds convoluted, run! You can play with software and make it say whatever you want for the most part, but why? Using the standard gasses allow you to see patterns and adjust decompression on the fly when you need to do so. Using different mixes for back gas and deco complicates the dive as you have to remember many variables and harder to modify when needed on the dive. Instead of posting or reading post on dive forums seek out the best and learn from them. That is what I do and have done when it comes to diving, sport and business-works for me. Do it Right....or play golf

 

[Diver0001]

Interested to hear the different perspectives on this and to see if the reasons are similar to my own. If you respond, please stay on topic with which of the two (and only two) options, and why. Please don't list a bunch of other deco gases you use, or tell me it depends. Humor me, pick one, and give me the reason.

Thanks,

Mike

It really depends on the dive.

Normally... and I must stress that this is the normal MO for only me an my buddies, we use 50% because (a) it's cheap and (b) it strikes a good balance between deco times, the costs involved and ease of logistics.

I don't think we've ever managed our deco times based on minimizing hang time. It's always a combination of hang time and the hassle involved. We do 50+ deco dives a year and only a hand full of them are planned to minimize hang times.

R..

 

[Errol Kalayci]

Does anyone realize the reason for 80% was because they could only fill to 2400psi O2 and then top up with air which made 80% to give them more volume? Otherwise why not 70% or 65% or 85%? Deco tables can accommodate any combination you want as they are math models but you need to use your brain. 80% was not used because it was better in any way other than divers wanted more gas than they could get before boosters and the agencies liked it because they thought it better for unskilled divers. Unfortunately, those agencies still promote higher bottom PO2's than I am comfortable with see Kenneth Donald's book Oxygen and the Diver for more information. 80% reminds me of a story I heard where every year at Thanksgiving the wife carefully cuts off both ends of turkey so it is exactly 20" explaining her grandmother was an amazing chef and that is how she did it. One year old grandmom comes over and is horrified when she sees the granddaughter doing this. But grandmom I watched you do this everyyear and your turkey was amazing! Grandma says but dear, I had to do it since that was the size of my oven yours in 36" silly

 

[kwinter]

There is simply no justifiable reason to dive 80%, ever. People justify poor choices all the dive, there is no place for poor choices in technical diving. Think through everything and Do it Right. If an instructor is unable to explain why he recommends something, run!

And there you have it. Opinionated, inflexible a-holes like you are the reason I will never have anything to do with DIR, GUE, UTD, etc. It is those instructors that have always regaled me with the "we do it this way just because we all do it the same" rather than having a justification.

I ran schedules and posted them either in this thread or another. Using 100% for deco instead of 80% was marginally more efficient and reduced deco time by something like 4%. But it increased O2 exposure by over 20%. Shallow stops are a mixed bag. Reducing DCS risk is at the expense of increasing OxTox risk. Deco stress comes from many things, and it is an individual decision of how to balance those risks. Even with my PFO, I would rather increase my DCS risk and reduce my OxTox risk. Oxygen induced seizures can occur with little or no warning signs and at pO2 of only 1.3. If it happens under water, you are dead. End of story. You won't get bent until you've been on the surface a while, if at all. There will be oxygen, personnel, and transportation assistance available. I do long deco dives at constant pO2. And even though the O2 clock and OTUs are not perfect, they are a gauge. So let me make the risk balancing decision for myself and keep your GI3 and JJ inflexible BS to yourself. I'll stick with 80% because I'm not too lazy to blend it and I have a brain that works.



iPhone. iTypo. iApologize.

 

[LiteHedded]

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