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OK, I have deliberately held off replying to this, in the hopes that either a) someone else would, or, barring that, b) I could be more restrained. Unfortunately, as no one else has taken ANDI to task for their shit-for-brains 50/50 bailout, I will. But, first things first: Stuart Masch sez: > A personal observation to the two individuals who made the remarks: [...] > You could have been a little more forthright and mentioned that you are both > certified ANDI instructors. I hope that you are not reffering to me as being one of the two people: I am not an ANDI instructor, never have been one, and have no desire to become one. (If you are reffering to me, that would explain a lot: how can you keep track of advanced concepts like O2tox, etc, when you can't even keep track of your instructors?) > A final comment. I suggest each of us be very careful about our postings. > Making publicly libelous or slanderous statements about individuals or > organizations might find one the subject of legal or other actions as those > targeted protect their rights and reputations. Ohhhh, I'm so nervous! Big threats from such a little man! Stuart, why don't you put your money where your mouth is? (On second thought, please don't: it's not nice to defecate on genuine US currency.) Your little threat actually does more to bolster my position that ANDI is nothing more than a greedy marketing driven entity than you could ever know. An organization actually dedicated to furthering diving and dive safety would be more than happy to encourage thorough discussion of all aspects of diving. Just a final note on this subject: should you decide that you really want to take the legal approach to solving your problems, remember that US courts, and particularly NY courts, are rather harsh on nuisance suits. It would be a big mistake on your part to pursue this further. ---------------------------------------------------------------------- And now, without further ado, on to Remedial Nitrox 101: the course for those who are too stupid to realize the dangers of a bailout mix with a ppO2 of 2.0. First, we begin with some quotes from _The Application of Enriched Air Mixtures_ by Ed Betts (billed as The Complete Users [sic] Guide [to SafeAir(tm), ANDI's trademarked name for nitrox] by ANDI): > Page 37 of The Application of Enriched Air Mixtures, the textbook for ANDI's > Complete SafeAirR User program describes the ranges of differing levels of > oxygen dosage: > 1.60 - Maximum dosage for normal dives or "open-water" > decompression only 45 minutes single dive exposure as the limit > > 1.60+ - CNS toxicity becomes a very likely occurrence - Paul Bert > effect. Dosages in this range are very dependent upon time and CO2 loading > > 2.0 - 100% oxygen at two ATA (optimize out gassing of nitrogen) > For "at rest" only situations - Hyperbaric therapy. > Page 42: > The U.S. Navy and NOAA: > The U.S. Navy and the other large commercial diving enterprises > backed the exposure limit of oxygen down to 1.6 ATA partial pressure. > Page 43: > > Carbon dioxide is the prime catalyst for CNS type oxygen toxicity. It is > imperative to realize that high workload dives must be accompanied with more > conservative dosages of oxygen. Note that this passage really ought to read "...is *a* prime...", but the important aspect is the dirrect correlation between CO2 retention (or buildup) and O2 toxicity. What about CO2 causes problems with O2? One major factor is that CO2 buildup increases the carbonic acid in the bloodstream (a primary CO2 transport pathway), and taxes the blood buffer system. It is critical to realize that the cause of CO2 buildup (or, more to the point, acidosis) does not matter: your body does not care and can not tell the difference between working hard, skip breathing, panting, swimming hard, or wacking off. The effect is the same in all cases: a buildup of CO2, increased acidosis, and, as the Betts' book points out, increased susceptability to CNS O2 toxicity. Now, let us take what we have just learned and apply it to the situation of bailout gases. Again, we begin with some readings from the Betts' book: > >From page 48 of the text: > > A bailout gas is a gas > breathed during emergency ascent. It is not acceptable for horizontal escape > (ie. cave or wreck penetration.) It is recommended that the PO2 contained in a > bailout gas should never exceed 2.0 ata PO2 (SafeAirC 50 as a bailout gas has a > maximum operational depth limit of 100 FSW (30 MSW.) > Application 7 from the Instructor's manual: > > For horizontal escape from an overhead environment do not exceed 1.6 ata > PO2 dosage. For vertical ascents in MOD based upon 2.0 ata may be used as the > gas would be breathed for extremely brief exposures. We will limit this discussion to non-overhead environments, and focus our discussion on the appropriateness of a ppO2 of 2.0 ata for a bailout gas. Now we see a rather strange dichotomy: 1.6 ata ppO2 is OK for ordinary situations, but 2.0 ata ppO2 is acceptable for a bailout situation. And, note, Betts is not saying that a 2.0 bailout is a last resort -- he is saying *ACTUALLY PLAN YOUR DIVE WITH A 2.0 BAILOUT*. Lets think a little about when a bailout gas is actually used; a quick taxonomy will help: 1) If the primary gas supply is exhausted a) due to "operator error" (e.g.: not watching the contents guage, not properly planning the gas requirements for the dive, etc.) b) unexpected difficulty at depth (e.g.: entanglement, rescue operations, silt out, etc.) 2) Loss of primary gas supply because of equipment failure Situation 1a should never happen. But the diver-type who experiences 1a should not be diving nitrox at all, as they are unable to even follow the basic rules of diving. (In fact, nitrox probably puts them at greater risk, as these are the same type of people who have a problem following depth limits -- "I went how deep???" -- and nitrox simply adds the risk of O2 toxicity to an already risky situation.) Situation 1b concerns the diver who suffers an unexpected difficulty which forces him to overstay his wellcome, so to speak. However, while our diver does not have a "real" overhead environment (the bounds of our discussion), we have a sort of virtual overhead environment, in that our diver may not yet be untangled, the silt may not have cleared, etc, so he may not yet be free to leave for the surface. The role of the bailout gas in this case is to buy some more time, give our diver an extra chance for survival. Of course, our diver will be under a great deal of stress at this point; we certainly do not want to introduce additional risk factors! Situation 2 concerns an unexpected equipment failure, which does not place our diver in an overhead situation, but certainly does increase his stress load. So again, we do not want to introduce any additional risk factors. Now, what effect does stress have, and how will anticipated stress affect our bailout gas planning? Stress causes many changes to take place, but the simplest to think about is potential problems with -- you guessed it -- CO2 and acidosis. Try this simple experiment: start panting with rapid, shallow breaths right now. (Be sure to stop!) You begin to feel a buring sensation and some diziness -- exactly the same symptoms as holding your breath. What happened was your shallow breathing caused you body to be unable to unload the CO2 in you bloodstream (and a host of other things, but we won't go into more detail here), and the resulting CO2 buildup caused the symptoms. What if we were at depth, and experienced a stressful situation, as in situations 1b and 2? A skilled diver should, of course, control the stress response, and remain calm. But that is a lot to ask, and do we really want to place ourselves in a situation where we deliberately penalize ourselves for a stress reaction and jepordize our survival? Of course, the answer is NO! Naturally, what this shows is that any bailout gas, whether for an overhead environment, a virtual overhead environment, or a free swimming dive, should follow the same mix recomendations as our primary gas. Put another way, a backup gas supply is just that: a backup of the primary gas supply. It is not a bailout/deco supply, it is not a "breathe this, feel great super mix"! There is one other major concern with the approach ANDI takes towards teaching the 50/50 bailout: regulator identification. (Perhaps this has been revised, so perhaps the issue is now covered; when I took the course a few years ago, it wasn't.) If you plan your dive with a max ppO2 of 1.X ata, and plan a bailout gas of 2.0 ppO2 ata, you have now created a situation where a regulator mixup is no longer just a surprise inconvenience, but is rather a potentially life-threatening situation. If a diver were to inadvertantly begin the dive on their bailout regulator, there is a very real chance (see the quoted ANDI text, above!) of an underwater convulsion. All of a sudden, we can no longer be at all casual about regulator marking, placement, etc. But the ANDI course makes no mention of this! Rec divers, especially new rec divers, routinely mixup regulators; its a fact of life. True, it should not happen, and with experience it does not, but why kill someone just because they mixed up two regulators? In tec diving, with multiple gas mixes, the penalty is, perhaps, unavoidable. But in a tec situation, much attention is given to this issue. Here we have less experienced divers who are not being given any advance warning of the severity of the situation they are getting themselves into. (If anyone wants to discuss lawsuits, this sounds absolutely criminal to me. Anyone need an expert witness?) --------------------------------------------------------------------- Remember, ppO2 of 2.0 ata is dumb for diving, and even dumber for bailout. So don't do it. OK, class dismissed. To ANDI: take your heads out of your collective butts, and stop thinking like a marketing-driven entity. If you would spend less time worrying about trademarking, advertising, etc, and more time worrying about diver safety, brain-dead schemes like 50/50 bailout/deco would not come up. > Stuart Masch, Chief Operating Officer > American Nitrox Divers International -frank -- fhd@in*.ne* | People who brook no compromise in programming 1 212 559 5534 | languages should program in lambda calculus or 1 917 992 2248 | machine language, depending. 1 718 746 7061 | -- Andrew Koenig
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