another gas mix question

[Mark Chase]

Originally Posted by Air Guzzler

Moz

It may not be an issue what i was trying to understand at first was the % / % thats people show

from what ive been taught is that if your not trained in a particular gas dont use it ? ( for example a member of anorther thread did his PADI deep diver cert in wast water on the way up they reached the 6mtr mark ans started there safety stop he was then handed a reg from a stage attatched to s shot line and proceeded to breath from it!!!! wtf is told him you could have breathed anything in the answer was the guy knew what was in the cylinder what was the problem) its the same for diver X did they now what was in the cylinder YES 25% o2 which now does not seem that bad

im not saying the people on board did not understand the potential risk as im sure they DID and would not have let person X try the gas.

I cannot comment if diver X was under any peir pressure as I 2 know the divers who where on the boat and cannot imagine them putting this person under any pressure knowingly but it does seem odd that this went on.

Yet you are, we asume, trained in the use of Nitrox but still messed up the calculation of PP02 on 30% @ 36m?

Official training resulting in a cert card is not everything.

You raise valid questions, but by implicating people without their concent, you do it badly.

ATB

Mark

[Miss Roxy Chablis]

30/30 is really a cave diving gas - primarily for long, difficult task loaded dives in the 30m range.
Andrew Georgitsis - the former GUE Training Director was an advocate of 25/25 as an ocean diving gas in the 30-40m range. For me it makes good sense in this range and I don't use 30/30 at all.
I've done enough diving with and without Helium in the 30-40m range to know that although the narcosis is only mild in this range - in UK conditions when viz can be poor with current and other complications - I'd rather be diving a gas that makes my life easier rather than harder.
Cost is a compelling arguement not to use it but as Garf says - if you took the cost out of the equation - what would be safer and better and mix is undoubtedly the answer - so I find it very hard to justify not using it when I have three young kids.
I did a dive that was at around 40m on the James Barrie up in Scapa Flow this year and the boat had run out of Helium - so I did it on weak Nitrox and if I'm honest - my judgement was seriously impaired and if we'd had a problem I wouldn't have been much use. It was a very pleasant feeling and i had a great dive - but not clever
Fully understand those who choose not to and don't criticise them in any way - what works for you works for you and a lot of it is finding where your own comfort level lies
The other thing is that the Helium molecule is about 2.7 times smaller than Nitrogen so it saturates and desaturates body tissues much more quickly than Nitrogen. From training and what works for me when deco diving - I believe if anything this lessens the deco obligation rather than increasing it. This tends to go against what some of the deco software will predict.
As Mark points out this quick desaturation means that potentially you could get more bent on a bad ascent with Helium mixes than Nitrogen mixes - but in reality should you be doing this type of diving if you can't control your buoyancy? I tend to use carefully structured deep stops and more deco in the mid range to handle this quicker offgassing and seem to get good results this way.
The real life implications of all this are that I generally feels much fresher, more energetic and "cleaner" after a Trimix dive than when I've dived weak Nitrox. Particularly if I've got a long drive home after a dive - I really appreciate this.
I know a lot of guys who dive CCR who just routinely dive quite rich Helium mixes all the time - even on shallower dives - cost is much less of an issue and its almost more hassle to switch to Nitrox for the shallow stuff - particularly if they've got it banked at home. The nature of CCR means that they're on a Helium right the way through the dive - including during deco and again people seem to report good results and prefer it.
Helium - great stuff - just expensive HTH

[Garf]

WARNING!

MARK CHASE DOES NOT READ POSTS BEFORE QUOTING THEM!!!!

OK Chasey, off we go mate

45mins at 30m on 30% gives you 18mins deco using GUE's own decoplanner software running 20/80GFs.

Add 30% Helium and it increases deco to 23mins

Doesn't sound a lot but its in fact increased your deco obligation by 28% Which is a lot

Sorry did I mention decoplanner? I believe I did say " In order to see this benefit you do have to be a little careful about which decompression model you choose, but it's defintiely there to take advantage of. "

Using VPMB on Vplanner you can make the gas choice of 30/30 work but Vplanner level 2 gives 23mins deco for 30% and 19mins for 30/30 so only a difference of 4mins or 17.5%

Right. so you're doing almost 20% less deco. Would we agree that 19 minutes is less than 23 minutes, becuase I've run it thorugh my bumber book of big mafs questions, and 19 keeps coming out as less. As withj the quote above, if you select the right decompression model, and follow the appropriate ascwent rates, you will have less deco to do. The point being there was an assumption from the original poster (before you and I waded in with our big gobs) that Helium would inevitably add to the decompression obligation - I would pointing out that this is not necessarily the case, and may indeed be the reverse in some cases.

MUCH more importantly, Helium is far less forgiving of poor buoyancy control than Nitrogen. Suffer a rapid ascent on 30/30 and your far more likely to seriously hurt your self than you are on 30%.

Can I refer in my post to where I said you have to fuck up the ascent. What I did say was "Now we have to be a little careful here, but when you take the 30/30 standard gas IN LINE with the other DIR protocols - the standard minimum gas ascent rates". I think that's a pretty clear warming that, like everything in DIR, it just doesn't work to do a bit of it, you have to look at the bigger pictire, and the bigger picture is that you have to be able to hold your stops and ascent at the appropriate rate. I would agree 100% that Helium is less forgiving when you fuck up, but think I qualified my post well enough. As a point of interest, from a DIR perspective, I believe people should be capable of doing ascents like this LONG before they go near trimix anyway, however I hope you'll agree I qualified my post with a comment about suitable ascent rates.


I won't pick you up on your comments about complexity becuase I did read your laster posts, and as you say it clouded the message you were trying to put across. I don't disagree with much of what you say here Mark, it's just I think you're picking up more than you need to when I am already qualifiying what I say.

If you and Andrew did this and got bent three times, you can't turn that around at claim its the bloody helium's fault, it's down to the knowledge and skillset you had at the time. You then went away and learnt about it. Diving without knowledge of what you are doing is inherantly dangerous, regardless of whether you are breathing mix or not. Yes, mix is less forgiving, which is why I said we have to be more careful, we have to select an appropriate decompression plan, we have to follow specific ascent rates. Given those three variables, which point did you disagree with again??????

[Mark Chase]

[quote]

Originally Posted by Garf

WARNING!

MARK CHASE DOES NOT READ POSTS BEFORE QUOTING THEM!!!!

OK Chasey, off we go mate



Sorry did I mention decoplanner? I believe I did say " In order to see this benefit you do have to be a little careful about which decompression model you choose, but it's defintiely there to take advantage of. "

Yes I do, and it read badly so it needed clarification.


GUE is DIR and GUE's decompression planner was Decoplanner. When I first got into GUE deco schedules they were running 30/90GF with modified deep stops in order to plan and compare DOTF profiles.

Last year Decoplanner was updated with the OPTION of VPMB and so for the first time you could say VPM was at least associated with GUEs public face of decompression planning

VPMB level 2 somehow became the "normal" setting but its widely slated as being very aggressive. A lot of dives carried out on VPM are in no way pushing the system. When you get to the more extreme ends of decompression the general consensus is move up to level 3 or even four and on dives past 100m add the Buhlman shallow stops typical of VPMBE

So planning a big dive on Decoplanner 20/85GF like 30mins at 100m running 10/70 21/35 50% and 100% you end up with 202mins deco

Run the same profile on Vplanner Level 3 VPMBE and you end up with 215mins


Now you can look at this and say that quite rightly bigger dives the margin for error is increased or you can look at this and say on smaller dives we take more risks. Its a half empty half full situation.

Right. so you're doing almost 20% less deco. Would we agree that 19 minutes is less than 23 minutes, because I've run it through my bumber book of big mafs questions, and 19 keeps coming out as less. As withj the quote above, if you select the right decompression model, and follow the appropriate ascwent rates, you will have less deco to do. The point being there was an assumption from the original poster (before you and I waded in with our big gobs) that Helium would inevitably add to the decompression obligation - I would pointing out that this is not necessarily the case, and may indeed be the reverse in some cases.

Correct, so your thread advocates 20% less deco than the standard Buhlman profile run by most people. VR3s for example run profiles on zero safety that come in at around the same runs at GF 20/85

Question? is your VPM deco aggressive?

How does the safety factor of VPMB level 2 compair with 20/85GF?


Id be fascinated to know because i cant figure it out. What I can tell you is i have run GF aggressive deco and got sub clinical. I could easily get the GF deco down to 19mins by altering the level of aggression to 20/90 but I accept its more aggressive. All your post is saying to me is, "run more aggressive deco and you get out of the water quicker".

VPM apparently handles Helium better than Buhlman and so we see the advantage in the deco time. GUE will point to their success in diving and thousands of hours of empirical data and claim it all works. However id point you toward the big daddy of Helium Decompression research Comex. They have done far far more research than GUE could ever dream of and their deco schedules are considerably longer than 20/80GF on the equivalent dive

On bigger dives I have run 20/100 and felt bent after the dive so when I look at VPM profiles with similar in water times I get all twitchy. Thats not to say they wont work for every one. I am sure there are people doing big dives on pure VPM and feeling great after.

The most important point for me is I did the SAME profiles on "trimix all the way out" as i did with out issues on "Nitrox to finish" and on the "trimix all the way" dives, I got bent. So my empirical data suggests 30% is a better choice than 30/30.

The whole point of my retort is that YOU ARE NOT making the dive safer in terms of deco running 30/30 You are INCREASING the risk of injury and INCREASING the demands on the diver.

Using VPM theory to justify this is playing a very dangerous game in my book. It may well work but you need to build up gradually to it not jump in with both feet thinking your actually being more conservative than the diver doing 20/80GF and running 30%

Can I refer in my post to where I said you have to fuck up the ascent. What I did say was "Now we have to be a little careful here, but when you take the 30/30 standard gas IN LINE with the other DIR protocols - the standard minimum gas ascent rates". I think that's a pretty clear warming that, like everything in DIR, it just doesn't work to do a bit of it, you have to look at the bigger picture, and the bigger picture is that you have to be able to hold your stops and ascent at the appropriate rate. I would agree 100% that Helium is less forgiving when you fuck up, but think I qualified my post well enough. As a point of interest, from a DIR perspective, I believe people should be capable of doing ascents like this LONG before they go near trimix anyway, however I hope you'll agree I qualified my post with a comment about suitable ascent rates.

WAYYYYYYYY to ambiguous

In line with other DIR protocols???? WTF does that mean to the un initiated

DIR protocols are totally not relevant to the discussion. Accurate stop holding and ascent rates are not DIR protocols, they are normal decompression procedures protocols WE ALL USE. The margin for error is not reduced greatly by using helium in the mix all the way out of the water.

QED its more dangerous DIVER BEWARE

I won't pick you up on your comments about complexity because I did read your laster posts, and as you say it clouded the message you were trying to put across. I don't disagree with much of what you say here Mark, it's just I think you're picking up more than you need to when I am already qualifiying what I say.

I felt your thread did not adequately identify the risks and did a poor job of explaining the additional precautions required to execute the dive. If something is safer it should be easier and have a greater margin for error, not harder to use with a reduced margin for error.

The overall impression I got from your thread was 30/30 is the safer more sensible gas. You may feel you put in adequate Caveats to protect the uninitiated on an open forum but i didn't, hence my clarification/warning.

As I said before, getting away with it is not the same as it actually being a better method.

Have you seen this?

Maybe all the deco advantage the GUE boys believe they have gained from fiddling with the stops is nothing more than taking advantage of the physics of horizontal ascents.

Rubicon Research Repository: Item 123456789/5050





ATB

Mark

[Air Guzzler]

It is possible i miss read my table

[Rovingshark]

Originally Posted by Mark Chase

Not to 46m surely? PP02 1.76?
Even i think thats a little daft

I'm not very clever/experienced, but:
46m= 5.6 ats.
5.6 ats x 21% = 1.176 PPO2.
x 25%= 1.4 PPO2

RS

[MixedUp]

Originally Posted by Rovingshark

I'm not very clever/experienced, but:
46m= 5.6 ats.
5.6 ats x 21% = 1.176 PPO2.
x 25%= 1.4 PPO2

RS

I thought he was referring to 32%. OK if so it should have been 1.79. (So close that it makes no difference)

Or it would have been 1.76 at 45 metres.

Steve

[Mark Chase]

Originally Posted by Rovingshark

I'm not very clever/experienced, but:
46m= 5.6 ats.
5.6 ats x 21% = 1.176 PPO2.
x 25%= 1.4 PPO2

RS

Your maths are spot on, only the gas was wrong

ATB

Mark

[Rovingshark]

Originally Posted by Mark Chase

Your maths are spot on, only the gas was wrong

The gas referred to was 25/25. I'm not the world's greatest diver but I'm good at this reading lark.

RS