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A short fat well off crap cave diver. Likes wrecks
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Makes a change from getting his teeth into me. Nice one Scott


I have added a bit on the end so maby he will have a go >


Mark Chase
 

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Fear not my young apprentice - his powers are useless here!
 

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Hi guys, guess I got more than I bargained for when I posted that. Apart from my glaring error about using 80% (what a f***wit),there was some good debate, but can anyone tell me more about this "Bakers Dozen"?
Also what are your opinions about the free deco software available. I like GAP and Vplan but found DDlan a bit less user freindly. Any thoughts...?
Stu.
 

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Stu

Here is the so called "bakers dozen" reasons why not to use 80/20:

I particularly like #13

1) This gas was introduced in an effort to overcome the inability of unqualified student "tech" divers to control their buoyancy in open water, and is as such is yet one more concession to doing things in a convoluted fashion to offset a self- inflicted set of problems brought on by the "doing it wrong" thinking that pervades diving today.

2) A heavy sea is not a problem for a deco stop if it is not posing a lung-loading problem. Look at your depth gauge in a heavy sea and "see" for yourself what the changes are - insignificant, and if they are not, you should either not have been diving or incurring a decompression liability of this magnitude in the first place. In the event of a change in conditions during the dive, see below where the 80/20 becomes a liability rather than an asset.

3) In the interest of using a standardized set of gases for which you can permanently mark your bottles , it is a poor concession to inability to sacrifice the benefits of pure O2 to accommodate a real or perceived lack of skill - learn to dive before taking up tech diving.

4) In this same interest you will find that when you graduate to real diving, as in caves, you will not want to accelerate your PPO2 at lower depths while still being faced with a long decompression at shallower depths, and making bizarre mixes to do this is a dangerous mistake (just like the fantasy of holding an accelerated PPO2 on a rebreather throughout a deco). I am anticipating the thinking that the 80/20 crowd would then go to an additional oxygen in cave without accounting for total exposure, and subject themselves to the risk of tox in the final deco steps. Tox you do not get out of - bends you do.

5) 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. The gas mixing in your lungs has already lowered the effective PPO2 enough to prevent spiking at 20 feet anyway with the use of pure oxygen - in other words, we are dealing with a simplistic misunderstanding here, or "old wives tale" that is typical in diving.

6) If 100% oxygen is a perceived buoyancy control risk at 20 feet, then why is the same PPO2 (intended) not a risk at 30 feet? This shows the total lack of reasonable logic involved in the decision to use this gas, as well as a lack of understanding of the whole picture ( see the rest of this discussion).

7) Along those lines, all we hear is howling about "oxygen cleaning" above 40% mixtures, and dive shop proprietors on here complaining about scuba tanks with oxygen in them being filled in their shops. With a pure oxygen system, the tank only ever gets filled with oxygen from oxygen tanks, not from every dive shop compressor it sees. Again , this shows the total inconsistency of agency thinking, and reveals that the true reason for this gas is to pretend to lower liability for teaching incompetents to dive, which is bull, and to attempt to accrue some inventive accomplishments to the dive agency pundits who themselves prove that they do no real diving by making this recommendation in the first place. This is like the colored regs, the stages on either side, the quick-release buckle, and the poodle jacket: nonsense of the most obvious nature developed through one-dimensional thinking by those whose universe of understanding is not only severely limited, but blinded by the hubris of not being the "inventor" of the techniques that work.

8) 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. To make matters worse, you can not get out from your 30 foot stop in an emergency (not doing the other stops) on the 80/20 mix without really risking a type 2 hit.

9) This is a dangerous method to achieve a greater total volume of gas for the bad breathers (another obvious reason the gas is in vogue), who should not be incurring these decos, and even that benefit of having more gas is lost since it is breathed at 30 feet, and then has to last for the other stops. The fact is that gas is effectively saved by using the lower deco gas up to this point, relying on the pressure gradient to both achieve the deco and provide a break from high the previous gas's higher PPO2 prior to going to pure oxygen where the spike could be a problem on an extreme exposure without an adequate low PPO2 break (again this shows that the 80% user is a neophyte diver with no real experience or understanding of the true risks of these dives) .

10) The 20-30% longer 30 foot time on the lower PPO2 is not only overcome on the pure oxygen at the next stops, the breaks do not come into play until the initial good dose of pure oxygen has been absorbed, since you are not spiking from a high previous dose without a break that is effectively achieved on the previous gas. These things need to be understood and taught by the agencies, not some superficial convolution that is designed to obfuscate the problem rather than openly acknowledge and deal with it in a responsible fashion.

11) In an emergency situation, getting onto the pure O2 for 20 minutes or so (for long dives something approximating the bottom time or a any decent interval) would give you a real good shot at getting out of the water having missed the rest of your deco and living through it with pain hits only. You have to think these things all the way though, not go for the transparent superficial thinking of those who merely are trying to "make their mark" with some "great" idea they can call their own. The acid test is, as always, is the caliber of the divers who adopt these practices.

12) If there is some problem with your deco or you otherwise develop symptoms and need oxygen either on the surface or back in the water, it is silly to have not had it there all along. 80/20 is a joke for that purpose, unless you have asthma, in which case any accelerated oxygen mix would be a nightmare. This is again part of the "thinking it all the way through" philosophy which is obviously missing from the 80/20 argument.

13) Only a card-carrying stroke would do something like this, and showing up with 80/20 is no different than wearing a sign on your back saying "I am a stroke, and have the papers to prove it". It announces to all the world that you have no clue, kind of like wearing clip-on suspenders or having dog dirt on your shoes.
 

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</span>
[b said:
Quote[/b] ]Here is the so called "bakers dozen" reasons why not to use 80/20:
<span =''>
Thanks for reminding us what an incoherent ramble much of the "Bakers dozen" is. There are perhaps 2 or 3 reasonable, but arguable, points in there; the rest is opinion and bluster, exemplified by point 13.

Ian W
 

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A short fat well off crap cave diver. Likes wrecks
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Thats the final confermation then.

I dive a bungied wing
I have my long hose off the left post
I sling my stages one each side
I dont use a spool
I dive with almost any one
I use 85/15 for deco coz I am concerned about holding 6m in the English Chanel in a force 6.

I AM A STROKE

I like the bit where he said if you arive at 6m and find conditions are too rough for you to hold the stop you shouldent have done the dive. WHAT? Do the write that on your grave stone or somthing.

How bout putting it like this: If you arive at the dive site and conditions are a bit rough (ie 50% of UK dives 80% in the winter/spring months)Then all the divers on 100% stay on the boat and all the 85% strokes get to do the dive



Surley you can deco off of any thing. I have seen good divers doing 50m stuff and using 50% all the way up from 21m. You can deco off air if you like it just takes a long time. I did a 45min deco on air after a deep dive once as there was no access to deco gas on the islend. I spent it pootling up and down the reef and was quite happy to do it. I just wouldent do it hanging in green soup in the UK.  

Also the point on presure of fills. Getting a good 100% fill is often hard. I like 200bar plus in my 7ltr rich deco tank and often have 250. Getting this with 100% is not easy. OK I come up with 100+ bar of deco gas but if somthing goes wrong on the dive I might need that one day. I also use that 100 bar on the next few shallow dives as a on boat safety tank. I dont see how breathing 85% can be worse for you than not breathing 02 at all after an incident.

But hey what the #### do I know. I am a Stroke


Just to make sure can any one tell me where to get some good split fins?

Mark Chase  
 

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I'm impressed that, despite there being postings from both Mole & Vic, on the subject of Nitrox mixes, there's been no mention of "Just get a rebreather" yet ;)
 

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A short fat well off crap cave diver. Likes wrecks
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Sorry Rob your not getting away with that M8

The yellow box squad are Strokes by default. That GI3 bloke (or GIT as I like to think of him) thinks they are the spawn of satin.

Also I dont see many CCR lads doing 100% 02 deco either. They turn pale at the thaught of using all that gas


Let me see 1.4 ppo2 at 6m thats equivilent to, Errrr let me think, Oh yes I know 87% (Te He)

Mark Chase
 

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Aharr - George Irvine hates Inspirations with a ferocity bordering on the fanatical.  Trouble is, most of his beefs against the unit are very poorly thought out and he's far too arrogant ever to admit he's wrong on much of the shite he spouts about it.  So we all laugh at him, which pisses him off no end.

BTW, most of the CCR lads I know (inc me) flush the loop with 100% when we get to 6m and ramp the PO2 up to 1.6.  Doesn't make a whole lot of difference though.  I've done the maths on doing OC with 50% and 80% (85%, whatever) and 100% and running the box at 1.3 for the working phase of the dive and 1.5 for deco.  There's only minutes in it.  I've dived with OC guys who came out of the water at the same time or before me cos the back/deco gas they'd chosen was ideal for the dive we were on.
A few % here and there makes sod-all difference on deco times in real time, so why all the fuss?  
I don't subscribe to the mantra of oxygen windows, I want a well-developed, tried and trusted algorithm with a shitload of 'fudge factor' built in, so that I can do the dives I want to do without constant stress about how close to the envelope I am.  Blimey, fell of the fence again.

BTW.... LOVE the spawn of satin remark.  You're a mate, I love you dearly, I do understand your dyslexia and everything, but THAT is getting printed on the lid of my unit.  Spawn of Satin.  Everybody'll think I'm a pimp.  Wonder if I should redecorate the hoses with a bit of leopardskin.  I'LL PAINT IT PINK AND PUT FINS ON THE BACK!!

Yip yip
Rob
 

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Whoops {:0

Major embaresment factor 10 /10

Hey Mr Moderator

How bout a spell check on the new web site?

No?

Oh Bugger. Oh well at lest it gets the odd laugh.

All the best

Mark Chase
 

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Quote: from Rob Evans
Wonder if I should redecorate the hoses with a bit of leopardskin.  I'LL PAINT IT PINK AND PUT FINS ON THE BACK!!

Please do it after the Mull trip, we don`t want them up there to get the wrong impression of us down here.
Mind you it`ll match my daughter Becky`s dry suit.
 

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No, that was just a mad, babycham-and-curry inspired rant.  I'm far too sensible for that sort of nonsense.  However I do have lots of rufty tufty double hard gouges hacked out of the lid of the unit. I maintain this is all down to extreme-diving-type-stylee wreck penetration.  The guys I dive with reckon it's cos I spend lonely nights in front of the antiques roadshow wielding a rough file.  They are -of course- liars, fools and vagabonds.

A leopardskin drysuit you say?  Hmmm.. I might have to spend the trip strapped to the roof of your Discovery.  I'll only be a nuisance if left to my own devices inside the car.
 

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<font color='#000080'>Does this make any sense?

George Irvine argues that decompression should be completed with 100% O2. His arguments, presented as a "Baker's Dozen", boil down to just a half dozen points:

1. Decompression with mixes less than 100% is inefficient.

2. Decompression with 80/20 simply allows divers to compensate for poor buoyancy control and generates longer decompression times.

3. The 80/20 mix is inadequate for depths above 9 M as it provides a maximum pO2 of 1.52 bar.

4. The 80/20 mix provides a pO2 of only 1.28 at 6 M and 1.04 at 3 M, which he claims is "worthless for decompression."

5. In a diving emergency that causes decompression to be shortened, 80/20 does not provide as large a safety margin as 100% O2.

6. If buoyancy control is a problem at 6 M, why isn't it a problem at 9 M?

In response to arguments that breathing pure O2 has measurable negative effects on the lungs one can take occasional breaks by breathing a little backgas. This argument appears to negate the principal argument as breathing backgas provides a return dose of nitrogen.

I do not believe that there is a right answer to the question as posed. During decompression one must find a balance between efficent offgassing by minimising pN2 (by maximising pO2) and preventing bubble growth.

An ideal deco mix is one that gives a safe maximum pp O2 of around  1.6 bar with a different diluent from that used in the bottom gas, one with a heavier molecular weight. A 50:50 and 80:20 mix of Oxygen: Xenon have been proposed but Xenon is highly narcotic and causes unconsciousness at atmospheric pressure! Clearly Nitrox mixes are ideal for decompression following heliox dives because nitrogen diffuses much slower than helium so the problems of isometric counterdiffusion are absent and the nitrogen content of the deco gas is largely irrelevant following a dive where there has been no nitrogen loading from the bottom gas;- so get you cheque books out!

In the case of oxygen as a "diluent" there are toxicity concerns. Ideally one would breath as much O2 as possible throughout the decompression, and that is exactly what rebreather divers do. For the lung tissue concerns it isn't a question of the fraction of oxygen, but of the partial pressure of oxygen breathed - the limit is reached deeper for 80% than 100%.  

Either approach will work, but one point to consider is what happens if a diver were forced to breath his O2 on ascent after a catastrophic loss of breathing gas. At 20 M on pure O2 your pO2 is 3.0 bar, while on 80% it is 2.4. Both are dangerous but 3.0 is very dangerous, and almost guaranteed to cause fitting. Here a little inert gas goes a long way, which is why I always carried Nitrox 50 for the deeper stops when needed.

Also for point 6, Boyle's law is why buoyancy control is worse at 6 M than 9 M. I have seen divers gain buoyancy as their tanks empty, becoming uncontrollably buoyant when they reach the shallows leading to a runaway ascent.

Surface oxygen

A very important point to consider, and one that is almost always overlooked, is the ever present formation of micronuclei during the climb up the ladder onto a boat or over rocks. If 100% oxygen is used during this phase none of the resulatant newly formed micronuclei will contain any nitrogen so rapidly disappear due to metabolism. Not so if any nitrogen is present in the arterial blood. Indeed I used 100% surface oxygen as an added "hidden stop" on many dives for this reason alone.

With surface 80% Nitrox, nitrogen is present with a counter pressure of 0.2 bar, while air has a counter pressure of 0.8 bar.

I firmly believe post-dive isometric exertion is a common cause of subsequent unexpected DCI and a sadly neglected phenomenon.  

Decompression does not stop when you leave the water!

(with acknowledgements to Dr Micheal Powell)
 

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<font color='#0000FF'>hi all.


ermmmmmmmmmm what you lads mean when saying , " HE IS A STROKE "  
?


ANdy
 

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[b said:
Quote[/b] ]1. Decompression with mixes less than 100% is inefficient.
Anyone know enough about the topic to confirm or deny that, since Oxygen is a vasoconstrictor, breathing pure Oxygen will slow down offgassing and therefore NOT be as efficient as you might think?

[b said:
Quote[/b] ]2. Decompression with 80/20 simply allows divers to compensate for poor buoyancy control and generates longer decompression times.
Isn't that the same as point 6?


[b said:
Quote[/b] ]5. In a diving emergency that causes decompression to be shortened, 80/20 does not provide as large a safety margin as 100% O2.
Isn't that why we keep Oxygen on the boats..?

P.S. A stroke originally mean a deliberately unsafe diver, ie one that had been shown a safer way to dive but stuck with the dangerous way as it was more "macho". Original term was "ego-stroker" then just "stroker" and finally "stroke".
These days, calling someone a stroke basically translates to "You're not 100% DIR so you're a crap diver"
 

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[b said:
Quote[/b] ]1. Decompression with mixes less than 100% is inefficient.
You need to consider the 100% question in context of the hole dive. Ie using O2 below 6 or 9m (habitat) is generally unsafe. Also "air" breaks need to be considered to avoid CNS & Pulmonary toxicity effects that may impinge on efficient off gasing via diffusion and perfusion methods.

[b said:
Quote[/b] ]2. Decompression with 80/20 simply allows divers to compensate for poor buoyancy control and generates longer decompression times.
Thats one of the reasons why the industry moved away from the 1.6 bar @ 6m stop. Afterall if you can only hold a stop to +/- 0.5m then at 6m you'll go from 1.65 to 1.55 bar ppO2. Might be enough to push you over the edge. So rather than turn away a cheque from a unready cash cow .. oops sorry meant diver... they came up with 80%.  Shifts the higher exposure down to 9m where its easier to hold a stop and the effects of poor buoyancy are less significant regarding O2 spikes.

[b said:
Quote[/b] ]3. The 80/20 mix is inadequate for depths above 9 M as it provides a maximum pO2 of 1.52 bar.
4. The 80/20 mix provides a pO2 of only 1.28 at 6 M and 1.04 at 3 M, which he claims is "worthless for decompression."
The oxygen window concept behind the WKPP deco model and its subsequent deco gas choices is that more gas is removed the higher the O2 pressure (not forgetting upper limits due to tox problems) 1.6 (1.9) bar is generally the best obtainable underwater. Once a gas switch is made and you ascend from the optimum depth the ppO2 will drop, the benefit from this high ppO2 will therefore drop. Once it drops to approx 1 bar the effect is minimal so a switch to a higher FO2 gas is made. The obvious corollary is that you should switch at every depth to a gas to maintain the ppO2 at 1.6 bar- this leads to the constant ppO2 RB argument.

This is why the deco gas FO2  are what they are:

<6m 100%
21m - 9m 50% 1.6bar - 1bar
and then 35% for vary deep deco gas the switch is not made at 1.6 to minimise tox exposure and risk.

[b said:
Quote[/b] ]In response to arguments that breathing pure O2 has measurable negative effects on the lungs one can take occasional breaks by breathing a little backgas. This argument appears to negate the principal argument as breathing backgas provides a return dose of nitrogen.
First off there is mounting evidence that adding He to deco mixes eg 50/25 increases deco efficieny allowing for shorter cleaner deco. Though these benefits have only been experienced on dives with significant BT. I mention that to show that life isn't simple and the Art of Deco is often a balence of conflicting forces. Using 100% does max out the pressure gradient to allow the max off gassing in both diffused and bubble forms. But cos you have to control your O2 exposure you have to balence the effect you want with protocols to minimise effects you don't wont. C'est la vie

[b said:
Quote[/b] ]Also for point 6, Boyle's law is why buoyancy control is worse at 6 M than 9 M. I have seen divers gain buoyancy as their tanks empty, becoming uncontrollably buoyant when they reach the shallows leading to a runaway ascent.
Do the maths at 9m on 80% ppO2 = 1.52 bar a +/-0.5m varience on stop depth will alter ppO2 from 1.56 - 1.48 bar cf 100% @ 6m where the range is 1.65 - 1.55 bar so at 9m the absolutes values are lower and the range is smaller. Thus allowing a diver who cant hold a stop a larger margin of error at  9m than at 6m. As for divers who cant hold a stop WTF should I alter the way I dive cos of the incompetance of others.

[b said:
Quote[/b] ]A very important point to consider, and one that is almost always overlooked, is the ever present formation of micronuclei during the climb up the ladder onto a boat or over rocks. If 100% oxygen is used during this phase none of the resulatant newly formed micronuclei will contain any nitrogen so rapidly disappear due to metabolism. Not so if any nitrogen is present in the arterial blood.
Not sure that your right when you say that any micronuclei are composed soley of 100%. As there will be plenty of diluent still being diffused out of the body as well as coming out in bubble form. Afterall if breathing 100% would protect from post dive exercise triggered DCS then a lot of bends could be avoided.

[b said:
Quote[/b] ]I firmly believe post-dive isometric exertion is a common cause of subsequent unexpected DCI and a sadly neglected phenomenon.  
Decompression does not stop when you leave the water!
Any rpt any form of exercise during deco causes a significant increase in risk. After all thats what DR Powell talke about at the recent workshop in Tampa.

[b said:
Quote[/b] ]Decompression does not stop when you leave the water!
Worth repeating.

Scotty
 
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