I would like to be open-minded and try to extract any useful information contained in this text, focusing on the substance, rather than the form. Let me see whether I understand it correctly, by restating each point in (hopefully) a simpler, more verbose, and less offensive language, with some additional comments in parentheses. I am not aiming here for a literal translation, but rather trying to capture the author's intent, while filtering irrelevant content, and avoiding redundancy. Is this accurate? In a few cases, marked in red, I felt that citations were required, and I would appreciate some help with links to the relevant sources with concrete data. Disclaimer: I am not trying to project an opinion, or express any judgment, whether positive or negative, and I have no agenda other than trying to fully understand and appreciate this person's perspective... I did not find all of these claims equally convincing or consistent, but I did my best to draw out the key insights nevertheless... I realize that given my limited experience, in many cases, I probably misunderstood or misrepresented something, and I would be grateful for pointing that out. This being said, if there are subtleties that I missed, I think it would benefit the wider audience to explicitly draw them out, and illustrate them with concrete examples, citations, and data...
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.
Translation: Beginning tech divers sometimes choose EAN80 over pure O2 as a deco gas because EAN80 is more forgiving to small changes in buoyancy, and they want to avoid the risk of O2 toxicity while they are still working on maintaining precise depth during shallow stops (note: 1.5 ppO2 @ 30 fsw for EAN80, as compared to 1.6 ppO2 @ 20fsw for EAN100). The problem is that many divers get used to having this additional margin of safety, and continue to use EAN80 well past their basic training. As a result, they might be less determined to continue improving their buoyancy skills. A good tech diver should not consider their training to be complete until they get to the point where they can safely maintain a 20fsw deco stop on pure O2 without concern for O2 toxicity. Once they reach that point, O2 toxicity should no longer be a major factor in the diver's decision between EAN80 and O2 as a deco gas.
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 assett.
Translation: A good diver should carefully assess the ocean conditions, and not enter the water if heavy seas are expected, whether carrying EAN80, or pure O2 as a deco gas, because of other risks involved in such scenarios. In particular, if water movement were so strong that the resulting pressure fluctuations would affect the safety of decompression, it would also affect the diver's ability to breathe comfortably (note: breathing is driven by pressure gradient, and rapid changes in water pressure would disrupt this process). The problem is that the use of EAN80, in this context, is a reactive strategy devised to cope with the potential problem scenario once it unfolds, and this might give a diver a false sense of security that could lead to complacency and a subconscious downplaying of the dangers of diving in heavy seas. Ideally, a diver's focus should be on preventing such scenarios in the first place. When a diver is carrying pure O2 as a deco gas, they are likely to stay more conservative.
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 benfits of pure O2 to accomodate a real or percived lack of skill - learn to dive before taking up techdiving.
Translation: There are concrete benefits in having a very small, standardized set of deco gases (note: this includes, e.g., the ease of mixing, planning, computing deco profiles on the fly during the dive using methods like ratio deco, or sharing deco gases between divers in case of an emergency). Some of the benefits are, to a degree, dependent on all divers in the group using the same mixes. As explained below, there are also benefits of pure O2 in terms of decompression efficiency
(note: citations needed; after running a number of profiles with 30-60 min. bottom times @ 100-200 fsw on air as well as on standardized Trimix mixes using deco software with Buhlmann GF 30/80, it seems that EAN80 compared to O2, whether accompanied by EAN50 or not, seems to be consistently giving run times shorter by a few minutes). The problem is that adding EAN80 to the set of standard mixes introduces complexity, and potentially undermines these benefits. Given this, and the fact that, as stated earlier, the perceived need for EAN80 could be addressed by additional training or more conservatism, it stands to reason that in the longer term, and in broader perspective, the overall impact of some divers in the group using EAN80 is negative. A better strategy is to begin with the end in mind, and aim for O2 as the last deco gas.
4) In this same interest you will find that when you graduate to real diving, as in caves, you will not want to accellerate 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 accellerated 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.
Translation: Although using a larger number of custom mixes to maintain a higher ppO2 can slightly shorten the total decompression time, it can also increase the total %CNS load, which might lead to problems given the widespread tendency among divers to downplay the dangers of O2 tocixity.
(note: citations needed; after running a number of profiles, as noted above, it seems that EAN80 compared to O2 seems to often be giving significantly lower total %CNS, especially if it is the only deco gas available, which seems to fly in the face of the above statement).
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 lowerd the effective ppo2 enough to prevent spiking at 20 feet anyway with the use of pure oxygen - in other words, we aer dealing with a simplisitc misunderstanding here, or "old wives tale" that is typical in diving.
Translation: Oxygen permits more effective decompression at 1.6 ppO2 at the shallowest stops
(note: this does not seem to translate into shorter run times, and it appears to justify the use of higher ppO2, which contradicts the position adopted earlier, of minimizing the risk of CNS toxicity).
6) If 100% oxygen is a percieved 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).
Translation: There is little difference in the CNS risk due to small buoyancy fluctuations between 1.5 and 1.6 ppO2
(note: clarification needed, since at the face of it, this does not seem to be true... the single-dive %CNS/min. limit increases rapidly from 0.83 @ 1.5 ppO2, to 2.22 @ 1.6 ppO2).
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 accomplishemts to the dive agency pundits who themseleves 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 developped through one-dimesional thinking by those whose universe of understanding is not only severly limited, but blinded by the hubris of not being the "inventor" of the techniques that work.
Translation: Since no mixing is required with O2, the process simpler, and there is less risk of combustion, or breathing a contaminated gas.
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.
Translation: Limiting decompression in the last stops to 1.5 ppO2 or lower, as compared to 1.6 ppO2 achievable at 20 fsw with pure O2, does not leave enough Oxygen window to make it effective
(note: clarification needed; while I don't own that text, according to the books I do own, e.g., Mark Powell's "Deco for Divers", even though this form of Oxygen window allegedly reduces the chances of bubble formation, it does not make offgassing faster, and can even slow it down due to vasoconstriction). In case of an emergency, with O2 there are fewer deco stops to skip, which translates into a lower risk of a type 2 hit
(note: citations needed, since at the face of it, this seems counterituitive; a diver with EAN80 can offgas faster earlier, and therefore has the option of ascending to shallower depths sooner than a diver who only has O2 at her disposal).
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 effecively 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 neopyte diver with no real experience or understanding of the true risks of these dives) .
Translation: Carrying multiple custom mixes such as EAN80 means that the same amount of bottom gas is used during a shorter portion of the dive, which leaves more back gas, and can tempt some divers to increase their bottom times, so they can use up all the available volume of their doubles. The resulting higher decompression obligation can, in turn, lead to a more aggressive use of deco gases with high ppO2 in the attempt to make up for the increased runtime, and that may leave less room for low-ppO2 breaks, resulting in an increased risk of a CNS hit when the ppO2 is increased to 1.5...1.6 in the final stops.
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.
Translation: The established way of tracking O2 toxicity does not accurately reflect the risk of a CNS hit; a conservative dive plan needs to not only track %CNS exposure, but also create room for low ppO2 breaks
(note: citations needed).
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 accellerated oxygen mix would be a nightmare. This is again part of the "thinking it all the way through" phiosophy which is obviously mising from the 80/20 argument.
Translation: If pure O2 is used as a deco gas, likely much more of it will be available for surface O2 treatment in case of a suspected DCS hit or shortened decompression because each diver will carry an abundant supply of it, with an appropriate safety margin.
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.
Translation: A diver's education does not end the moment she receives a C-card; rather than blindly following the procedures taught by her instructor, and habits developed during her training, a good diver should seek an in-depth understanding of the detailed rationale behind any procedures she has been taught, and be prepared to question and reevaluate these procedures in the light of new theories, recent data, and the experiences of other divers.
