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Thanks for posting this again. I seem to have misplaced my previous copy. Could you explane the term poodle jacketed second stages. This term is not used up here. Thanks Tim Ross -----Original Message----- From: Bill Mee <wwm@sa*.ne*> To: cavers@ca*.co* <cavers@ca*.co*> Cc: techdiver@aquanaut.com <techdiver@aquanaut.com> Date: Wednesday, May 13, 1998 3:20 PM Subject: Baker's Dozen Revisited >Fellow Divers, > >Once again the subject of 80/20 rears it's ugly head. We are now told >that the use of this peculiar gas mix is somehow or the other possibly >an unwritten defacto IANTD teaching standard. Let me remind you that the >WKPP does not use this gas mixture for anything and if you made the >mistake of showing up with this stuff you would never get out of the >parking lot. For those who may forget the past and possibly repeat it I >reiterate the famous "Baker's Dozen" reasons why we do not use this gas. > >If you think reason #12 is a joke may I point out that the dive boat >which carried, the now late, Tai Wilkerson on his final fatal dive had >no oxygen on board. They did however have 80/20. > >One of the reasons for carrying pure oxygen as a deco gas is that it >will be immediately available in an emergency. The administration of >pure oxygen is SOP in the aftermath of almost all forms of diving >related accidents. This may prove to be an issue in subsequent wrongful >death litigation in that having "no pure oxygen" is essentially >indefensible and could be considered negligent. > >Using some homebrew dive table program to justify the use of 80/20 is >not reasonable inasmuch as the Buhlmann algorithm (upon which almost all >of these programs are based) is a diffusion based compartmental model >which does take into consideration micro-physiological issues. > >PLEASE REREAD the Baker's dozen and take this seriously. > >Regards, > >Bill Mee > > >> >> ---------------------------------------------------------------------- >> A (BAKER'S) DOZEN REASONS WHY WE DO NOT USE 80/20 (By George Irvine) >> >> 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 guage 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 techdiving. >> >> 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 pervious 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 somethng 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. >> >> George Irvine >> Director, WKPP >> "Do It Right" (or don't do it at all) >> ------------------------------------------------------------------------- ---- >> Bill Mee's post: >> >> George, >> >> Thank you for exhaustively laying the reasons why we or anyone else >> should not use 80/20. The only thing missing from this discussion is >> the Q.E.D. at the end. >> >> Reason #8, reiterated here for discussion purposes is perhaps the >> soundest reason, among many very cogent ones, as to why this practice >> should be avoided: >> >> " 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. " >> >> The rush to embrace this practice, recommended by technical diving >> diving opinion leaders, was widespread and in retrospect, irrational and >> poorly thought out, like so many of the "trial balloons" in this field >> of endeavor. It seemed to many, at first glance, to be a simple means of >> increasing one's supply of deco gas while eliminating its bothersome >> volume and mass. In fact, the perceived benefits transform into >> liabilities when subjected to a thoughtful analysis. When you view >> decompression as a two pronged challenge: to progressively widen the >> oxygen window and increase the diffusion gradient to maximize passive >> transport of dissolved inert gas, it becomes clear that the 80/20 >> solution falls short on both requirements at a critical point in the >> decompression profile. >> >> Section 11 emphasizes a very compelling argument for those who are >> concerned with managing dive related crises. When diving in the open >> ocean divers and boat operators should always be prepared to "scram" the >> deco at any time. This could be for any number of reasons, not the >> least of which might be a sudden change in the sea conditions or >> unscheduled events such as dive accidents or impending ship collisions. >> Just follow the Whitefish Point thread for an excellent example of why a >> deco may require being aborted (or never started in the first place). >> >> Most unfortunately the "80/20 problem" bears a strikingly resemblance to >> several other ad hoc technical contrivances mentioned in this same >> article (section 7) i.e. dual bcs, colored regulators, bilateral stage >> bottle positioning, poodle jacketed second stages and harness quick >> releases. All of these ideas, while seemingly reasonable, become >> tainted when subjected to thoughtful review. >> >> Good show Director Irvine. >> >> Bill Mee > -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. 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