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Scuba Forum / General / August 2006Scientific Study of Nitrox and Air use
In an exhaustive study, lasting over 40 years and involving thousands of hours of diving, the relationship between air, nitrox and DCS is finally clarified. Study results are as follows: - Diving air, as air, within the limits of air tables, is completely safe. In thousands of test dives, at depths covering the entire range normally referred to as "recreational limits," absolutely no incidents of DCS were noted. - Diving air, as air, within the limits of pre gradient bubble computers is almost completely safe. In thousands of test dives, at depths covering the entire range normally referred to as "recreational limits," only one suspected incident of DCS was noted. Incidents aggregate less than one .05 percent (.0005), a statistically insignificant number of suspected incidents. It should be noted that the one suspected incident occurred at the extreme limit of recreational depths and at extreme limit of the computer's recommended profiles. In light of other results, it is likely that at least one, and perhaps more, manufacturers of early dive computers, failed to correctly identify the point at which some DCS risk occurs. - Diving air, as air, within the limits of more conservative modern computers, is completely safe. Absolutely no incidents of DCS were noted. It is further noted that the profile responsible for the one suspected incident of DCS experienced with an older computer, was not within profiles recommended by modern computers. It is likely that safeguards added to even the least conservative of modern computers have adequately addressed issues with older, less conservative models. - Diving nitrox, as nitrox, within the limits of modern nitrox capable computers, is completely safe. Absolutely no incidents of DCS were noted. Researcher's note: 1. No data is available for dives using nitrox, using nitrox tables. For information on this subject, users are directed to studies performed by other research groups including WKPP, GUE, DIR and Magilla. 2. Due to budget constraints, no data is available for diving nitrox as air. Since diving air as air and nitrox as nitrox, researchers concluded that there is no cost benefit to this practice. Rumors that the practice is "safer" or "more conservative" are made moot by the fact that it is simply not possible to be safer than 100% safe. Lee Bell 2006-08-04 > In an exhaustive study, lasting over 40 years and involving thousands of > hours of diving, the relationship between air, nitrox and DCS is finally > clarified. Study results are as follows: These data are interesting, but, you fail to mention what organization performed this scientific study... more info please. cheers, Chris >> In an exhaustive study, lasting over 40 years and involving thousands of >> hours of diving, the relationship between air, nitrox and DCS is finally >> clarified. Study results are as follows: > > These data are interesting, but, you fail to mention what organization > performed this scientific study... more info please. It was a government-funded study, no doubt. >> These data are interesting, but, you fail to mention what organization >> performed this scientific study... more info please. NAUI, SSI and TDI were represented. > It was a government-funded study, no doubt. Funded entirely with private funds, no advertising, endorsements or commercial contributions involved. Lee > NAUI, SSI and TDI were represented. > Funded entirely with private funds, no advertising, endorsements or > commercial contributions involved. Could you (or someone else) please provide an official source for this study? I mean no disrespect, nor do I question the validity of your statements - for my own reasons I'd very much like to have the actual document of this study, rather than what "some guy on the internet" said about some study. cheers, Chris >> NAUI, SSI and TDI were represented. >> Funded entirely with private funds, no advertising, endorsements or [quoted text clipped - 5 lines] > document of this study, rather than what "some guy on the internet" > said about some study. Yeah, like how do you know someone didn't just make it up? >>> NAUI, SSI and TDI were represented. >>> Funded entirely with private funds, no advertising, endorsements or [quoted text clipped - 5 lines] >> document of this study, rather than what "some guy on the internet" >> said about some study. > Yeah, like how do you know someone didn't just make it up? You read the official source. Perhaps you'd like to post the results of your own study. How many times have you been bent diving air as air? How many times diving nitrox as nitrox? How many times diving nitrox as air? Since you're positive that one is more dangerous than the other, surely you have something to back your position up . . . or was it, perhaps, something someone just made up? Lee >>>> NAUI, SSI and TDI were represented. >>>> Funded entirely with private funds, no advertising, endorsements or [quoted text clipped - 14 lines] > you have something to back your position up . . . or was it, perhaps, > something someone just made up? After a day of diving in Boynton Beach, Florida I once held a conch shell to my ear and could clearly hear the ocean.......though thinking about it I was standing on the beach at the time. LD. >>>NAUI, SSI and TDI were represented. >>>Funded entirely with private funds, no advertising, endorsements or [quoted text clipped - 7 lines] > > Yeah, like how do you know someone didn't just make it up? Actually, this whole argument boils down to one simple question: within the tables, is the risk curve flat or does it have a slope >0. The phenomenon of undeserved hits, which has been studied by many, always ends up being random, i.e. incidence without corelation to profile. There is therefore only one answer, that the curve is flat. some older studies, using older tables, did indeed show a cluster at the upper time/depth limits (where, btw, Lee got his hit) resulting in revised tables with the limits moved left of the increase in incidence. To my knowledge, there have been no table revisions from any source post WW II that were not based entirely on statistics, completly ignoring doppler studies, chamber studies, or any high tech scientific mishmash. (Yes, new tables have been developed, but they are either curiosities or developed for extreme profiles.) >Actually, this whole argument boils down to one simple question: >within the tables, is the risk curve flat or does it have a >slope >0. And that's your own problem in a nutshell. You've oversimplified the risk evaluation to meaningless noise. You're making the following unspoken assumptions: o The tables are good for everybody, regarless of any physiological or environmental conditions (e.g.: age, weight, fitness, pre- and post-dive exercise, dehydration, etc.) o In practice, people aren't adjusting their maximum limits due to the conditions above. o The idea that lack of an observable correlation to profile in decompression hits means that they're entirely random. You've completely neglected any external conditions that might make the normal profile a bad idea. o That "the tables" you speak of are all identical. o That people are diving the tables to near the limits (If they're not, then the limits of the tables are immaterial in terms of data gathering on bends). >To my knowledge, there have been no table revisions from any >source post WW II that were not based entirely on statistics, >completly ignoring doppler studies, chamber studies, or any high At least you have a disclaimer in the above. DCIEM tables were done with doppler studies. They tend to be more conservative than the NAUI/PADI/etc. tables. I've found the DCIEM tables to be readily available in the U.S. BTW: You keep claiming that it's more dangerous to dive air tables on Nitrox. There has never been a death due to oxygen toxicity during the entire history of recreational Nitrox use. By your own logic, that means that Nitrox does not add any danger.  SignatureRon (user ron in domain spamblocked.com) >>Actually, this whole argument boils down to one simple question: >>within the tables, is the risk curve flat or does it have a [quoted text clipped - 8 lines] > (e.g.: age, weight, fitness, pre- and post-dive > exercise, dehydration, etc.) Within the recreational tables, that's true. > o In practice, people aren't adjusting their maximum > limits due to the conditions above. And don't need to. > o The idea that lack of an observable correlation > to profile in decompression hits means that > they're entirely random. You've completely > neglected any external conditions that might make > the normal profile a bad idea. All external conditions are also random. > o That "the tables" you speak of are all identical. No, the recreational tables are nit identical. But they all are so conservative as to eliminate virtually all risk. > o That people are diving the tables to near the limits > (If they're not, then the limits of the tables are > immaterial in terms of data gathering on bends). As I said before, the limits have been moved so far to the left in modern recreational tables that "diving near the limits" is well within the actual limits. >>To my knowledge, there have been no table revisions from any >>source post WW II that were not based entirely on statistics, [quoted text clipped - 4 lines] > than the NAUI/PADI/etc. tables. I've found the DCIEM tables > to be readily available in the U.S. One of a few dozen tables, all of which are so far to the left as to be identical in practice. > BTW: You keep claiming that it's more dangerous to dive > air tables on Nitrox. There has never been a death due > to oxygen toxicity during the entire history of recreational > Nitrox use. By your own logic, that means that Nitrox > does not add any danger. Ahhhh, but the lifetime exposure is still in our futures. BTW, no one has ever died from oxtox. There have been quite a few that drowned as a result, however. > >>Actually, this whole argument boils down to one simple question: > >>within the tables, is the risk curve flat or does it have a > >>slope >0. > > > > And that's your own problem in a nutshell. You've oversimplified > > the risk evaluation to meaningless noise. Unfortunately, all of the "undeserved hits" incidences do indicate that there is indeed an element of noise within the activity risk. > > You're making the following unspoken assumptions: > > o The tables are good for everybody, regarless of [quoted text clipped - 3 lines] > > Within the recreational tables, that's true. Simply illustrations of some of the variables which might someday explain the incidences of 'undeserved' hits. > > o That "the tables" you speak of are all identical. > > No, the recreational tables are nit identical. But they all are > so conservative as to eliminate virtually all risk. Here's an example of how much the tables have changed: http://www.huntzinger.com/dive/old_PADI_dive_table.jpg Note that this table allows a no-stop profile to 100fsw for 25 minutes, and only requires a 3 minute stop at 10fsw for 30 minutes at 100fsw. BTW, this table uses a 90ft/min descent rate, a 60ft/min ascent rate, and bottom time is defined as start of dive to leaving the bottom (ie, the ascent time is not included). Finally, note which well-known recreational Agency's name is printed in the top right corner. > > o That people are diving the tables to near the limits > > (If they're not, then the limits of the tables are [quoted text clipped - 3 lines] > in modern recreational tables that "diving near the limits" is > well within the actual limits. As per the above table, versus what many dive computers use these days for their 100fsw no-stop limit and with the popular adoption of the 3-5 minute "safety" stop, I think it is safe to say that the evidence clearly shows that the popular 100fsw bottom time limit has been effectively reduced by (at least) roughly 50%. > > BTW: You keep claiming that it's more dangerous to dive > > air tables on Nitrox. There has never been a death due [quoted text clipped - 3 lines] > > Ahhhh, but the lifetime exposure is still in our futures. Plus, there have certainly been errors made by tank jockies in identifying the PPO2 content, both high and low. Do note that if a tank that's supposed to be (ie, marked) 32% or 36% but erroneously contains air (21%) and a diver then gets bent because he dived to Nitrox limits, this is indeed a Nitrox-attributable dive accident. > BTW, no one has ever died from oxtox. There have been quite a > few that drowned as a result, however. As well as injuries that were the result of erroneous PPO2 markings. -hh > Plus, there have certainly been errors made by tank jockies in > identifying the PPO2 content, both high and low. Not relevant. > Do note that if a tank that's supposed to be (ie, marked) 32% or 36% > but erroneously contains air (21%) and a diver then gets bent because > he dived to Nitrox limits, this is indeed a Nitrox-attributable dive > accident. If anything, it's an air attribuatable accident. In fact, however, it's neither. It's the fault of the diver who was taught to, and should have, checked his gas before he dove it. Having been involved in exactly that situation, it's fair for me to judge that it was my own damned fault. Lee > If anything, it's an air attribuatable accident. In fact, however, it's > neither. It's the fault of the diver who was taught to, and should have, > checked his gas before he dove it. Having been involved in exactly that > situation, it's fair for me to judge that it was my own damned fault. I couldnt begin to guess how much gas I have blended over the years, and it never ceases to amaze me that people who dive nitrox or trimix not only dont own an O2 analyzer and use it, but are willing to dive whatever it is I say they have, which makes me ultra paranoid. I calibrate the analyzer on air every time, even if I just filled three tanks simultaneously with the continuous blender, the analyzer gets calibrated to air in between each tank. 99% of the time, people dont even watch me analyze their gas, they just take my word for it, and go dive. I have had people bring in bottles and tell me that there is 32 in it, and to just "top it off with 32", and then pre-fill analysis tells me they had no idea what they were diving. Last week I analyzed one that was allegedly 32% that measured 42%. When I told the diver, he all but called me a liar. Only after I calibrated, measured two seperate bottles of air and nitrox, then his, did he believe me and understand that not only could he be dead, but that he should buy and use his own analyzer. No table in the known universe can accomodate stupidity or arrogance. >>If anything, it's an air attribuatable accident. In fact, however, it's >>neither. It's the fault of the diver who was taught to, and should have, [quoted text clipped - 23 lines] > > No table in the known universe can accomodate stupidity or arrogance. Amen. Scott wrote: >> No table in the known universe can accomodate stupidity or arrogance. Or complacency. You don't have to be stupid, or arrogant, to make a mistake like failing to check the gas you're breathing. You only have to be complacent. In my deserved hit, I looked right at an in line analyzer that read 32%, an analyzer that happened to be the same kind I own. Since I had tested the first couple of tanks and found them spot on (membrane system), I got complacent. I wasn't complacent enough not to look at all, but I was complacent enough not to test every tank myself, after the gas was in the tank. As you probably recall, I later noticed whips attached to tanks marked for air at the same time they were hooked to tanks marked for 32%. The in line gauge still read 32%, but it was not in line with the gas being pumped . . . air. The issue was not, however, whether I was breathing nitrox as air or nitrox as nitrox, but whether I followed the procedures for either. I didn't. Had I done so, the odds of getting bent would have been the same, breathing nitrox as air would not have gotten me bent. Breathing nitrox as nitrox, would not have gotten me bent. Breathing air as nitrox did. Lee > Scott wrote: > [quoted text clipped - 19 lines] > nitrox as air would not have gotten me bent. Breathing nitrox as nitrox, > would not have gotten me bent. Breathing air as nitrox did. Dont get me wrong, I am not calling you any name whatsoever. If you really want to see the death rate of complacency, just look at rebreather fatalities. > Dont get me wrong, I am not calling you any name whatsoever. You've never called me a name I didn't deserve. > If you really want to see the death rate of complacency, just look at > rebreather fatalities. Precisely why I don't use a rebreather. I had a long discussion about rebreathers in a UK forum, where people actually wish to own and dive the Yellow Box of Death (Buddy Inspiration). When it was all said and done, my conclusion was that UK divers are more cautious about their diving than I'm ever likely to be and that, if I could not be consistent and careful, anal if you prefer, I should not be using a closed circuit, computer controlled rebreather. So far, so good. Speaking of which, I'll never forget the post about the guy who, when his inspiration gave him a predive alarm, banged the computer module on something hard to get it to stop. I learned from his mistake. He didn't get a chance to. Lee rec.scuba's resident pussy "Scott" <pugetsounddiver@gmail.com> whined: > I couldnt begin to guess how much gas I have blended over the > years, That's because you're too lazy, sloppy, and stupid to properly maintain records. SignaturePosted via a free Usenet account from http://www.teranews.com >No table in the known universe can accomodate stupidity or arrogance. Darwins table. in only two parts. either in the gene pool or out of the gene pool. >> If anything, it's an air attribuatable accident. In fact, however, it's >> neither. It's the fault of the diver who was taught to, and should have, [quoted text clipped - 11 lines] > continuous blender, the analyzer gets calibrated to air in between each > tank. If I don't recalibrate the analyzer I use every time, I'd get different readings every time, I'm sure. Don't have enough experience with analyzers to know if that's normal, or if it's because it's a well used dive shop owned analyzer.....but even after mixing my own gas, I always recalibrate and check it twice. > 99% of the time, people dont even watch me analyze their gas, they just > take [quoted text clipped - 12 lines] > > No table in the known universe can accomodate stupidity or arrogance. Here, here. LD. > If I don't recalibrate the analyzer I use every time, I'd get different > readings every time, I'm sure. Don't have enough experience with analyzers > to know if that's normal, or if it's because it's a well used dive shop > owned analyzer.....but even after mixing my own gas, I always recalibrate > and check it twice. O2 analyzers are basically oxygen powered batteries. An analyzer simply reads the voltage produced by the analyzer; the more O2, the more voltage, and displays the result as a percent rather than a voltage. They are sensitive to temperature, humidity and length of exposure to O2. Every now and then, I expose ours to pure he and pure O2 to see what the swing is, and to see the degredation of the cell. Teledyne R22D's are as good as they get, with thermistors and hydrophobic membranes, but they still vary a great deal with length of exposure to O2, temperature and humidity. >> If I don't recalibrate the analyzer I use every time, I'd get different >> readings every time, I'm sure. Don't have enough experience with [quoted text clipped - 17 lines] > membranes, but they still vary a great deal with length of exposure to O2, > temperature and humidity. Hmmm, good to know. I only get by there on Mondays but I'll make a point to see if I get 100% on the O2 bottle after I calibrate it to 21%. Speaking of, all this now has me wondering how close it is, since I usually just calibrate by using ambient air in the shop.....of course the doors are usually open but it is inside a fill station after all. Still, I'm sure it's not a significant difference than outside air. The nitrox tanks are drained outside before being brought in. LD. > > Plus, there have certainly been errors made by tank jockies in > > identifying the PPO2 content, both high and low. > > Not relevant. No? Incorrectly high PPO2 increases OxTox risks. Incorrectly low PPO2 increases (Narcosis and) DCS risks. > > Do note that if a tank that's supposed to be (ie, marked) 32% or 36% > > but erroneously contains air (21%) and a diver then gets bent because [quoted text clipped - 5 lines] > checked his gas before he dove it. Having been involved in exactly that > situation, it's fair for me to judge that it was my own damned fault. Yes, it was basic human error, but my point was that the only reason that the error could only have existed was because there is "mucking around" with the PPO2 content via Nitrox, whereas PPO2 manipulatioin isn't done when diving Plain Old Air (POA), so its harder to get it wrong. Any time there is a process step added, there is the potential for it to be done wrong, which results in increased risks. Redundent checks are one way to offset some, but its always hard to beat KISS. -hh >> > Plus, there have certainly been errors made by tank jockies in >> > identifying the PPO2 content, both high and low. >> Not relevant. > No? No. If standard procedure is to check your gas, which it is, then what the tank jockey does is not relevant. The mistake was not a nitrox related one but, rather, a failure by the diver himself. This thread, which has not morphed yet, is about the relative risks, or benefits, of breathing nitrox as if it were air. I think it's important to keep that separated from the risks of the diver's failure to follow procedures he/she knows are important, like checking the gas. The failure of the diver to check the gas he's breathing is no more a nitrox issue than the failure of a diver to ensure his tank is full at the start of his dive. > Yes, it was basic human error, but my point was that the only reason that > the error could only have existed was because there is > "mucking around" with the PPO2 content via Nitrox, whereas PPO2 > manipulatioin isn't done when diving Plain Old Air (POA), > so its harder to get it wrong. By this logic, all diving accidents are compressor errors since, without compressors mucking around with gas pressure, there would be no diving accidents. Ok, so this is a bit extreme, but it illustrates the point. Taking someone else's word for what you're breathing, is a mistake that the diver, himself, could have and should have controlled. Failing to check is exactly the same mistake whether you're breathing nitrox as air or as nitrox. If you'd like to start a new thead called "risk of assuming your gas is air/nitrox/trimis without testing it" I'm game, but it ought to be a really short discussion. > Any time there is a process step added, there is the potential for it to > be done wrong, which results in increased risks. You bet, but we're talking about risks directly related to breathing nitrox as air versus breathing nitrox as nitrox. Other risks aren't relevant to that particular issue. > Redundent checks are one way to offset some, but its always hard to beat > KISS. Which would be to stay out of the water altogether. Anything else requires certain fundamental elements to be safe. Lee > >> > Plus, there have certainly been errors made by tank jockies in > >> > identifying the PPO2 content, both high and low. [quoted text clipped - 6 lines] > tank jockey does is not relevant. The mistake was not a nitrox related one > but, rather, a failure by the diver himself. With air, the gas check is for Pressure. With Nitrox, the gas check is both Pressure and PPO2. Hence, more opportunities for error, thus, greater risk even when absolutely all other risks are absolutely equal. > ... The failure of the diver to check the gas > he's breathing is no more a nitrox issue than the failure of a diver to > ensure his tank is full at the start of his dive. >From a holistic system approach, every possible {risk/failure mode} has to be accounted for, and typically then organized into one of the catagorical "bins". Since diving with air never really had to check PPO2, why should it be put into the "air" bin? > By this logic, all diving accidents are compressor errors since, without > compressors mucking around with gas pressure, there would be no diving > accidents. Ok, so this is a bit extreme, but it illustrates the point. It does, for in a Root Cause analysis there's a lot of options for organizing your risk/failure nodes, and thus, what ends up where. However, what they all have in common is that in the end, every possible option has to go *somewhere* in each and every one of them. > Taking someone else's word for what you're breathing, is a mistake that the > diver, himself, could have and should have controlled. Failing to check is > exactly the same mistake whether you're breathing nitrox as air or as > nitrox. Particularly true when we're receiving gas from a station that's capable of pumping both. And while an air/Nitrox station is increasingly common today, it wasn't always so: we don't really have to go back all that many years to when the Rec choices for gas were "just air" and the only question was contamination. It was from this historical perspective that I chose to "bin" the PPO2 content error risk as being Nitrox-attributable, versus what had traditionally been the "air-only" Recreational diving risks. > > Any time there is a process step added, there is the potential for it to > > be done wrong, which results in increased risks. > > You bet, but we're talking about risks directly related to breathing nitrox > as air versus breathing nitrox as nitrox. Other risks aren't relevant to > that particular issue. Depends on your altitude: there's risks at the tank jockey fill station from possible exposure to high pressure, high-PP Oxygen, such as an Oxygen fire. These have to be "binned" someplace too, plus we need to answer the question of risk transfers between participants. For an example of risk transfer, if we were to come up with some "magic mix" that reduces diver fatalities by 30 per year, but the fatality rate of diveshop tank jockeys goes up by 30 per year, has "diving" become more or less dangerous? The answer kind of depends on if you're a diver, a tank jockey, or an outside industry observer. > > Redundent checks are one way to offset some, but its always hard to beat > > KISS. > > Which would be to stay out of the water altogether. Anything else requires > certain fundamental elements to be safe. Another one from Appalachia: "Mother, may I go out to swim?" "Yes, my darling daughter, But hang your clothes on a hickory limb, And don't go near the water." -hh > With air, the gas check is for Pressure. > With Nitrox, the gas check is both Pressure and PPO2. I purchase my gas at a shop that will tell you quite clearly that they don't do air fills. They do, however, do 21% fills. I test every tank of gas I use for both pressure and O2 content. If you look back only a few days, you'll find that I'm not the only one that checks 21% fills. > Hence, more opportunities for error, thus, greater risk even when > absolutely all other risks are absolutely equal. For shops that bank 21% and other nitrox and trimix, the error mechanism is the same regardless of the gas you ask for and the need to test is the same. Air fills are only lower risk when obtained from shops that are not equipped to do other types of fills. >>From a holistic system approach, every possible {risk/failure mode} has > to be accounted for, and typically then organized into one of the > catagorical "bins". Since diving with air never really had to check > PPO2, why should it be put into the "air" bin? I agree that all risks need to be considered. See my comments above regarding why the same risks apply to most air fills as apply to most nitrox fills. Also, please understand that the only point I've tried to make is that the use of nitrox according to air standards is no safer, from a DCS standpoint, than using nitrox as nitrox provided you abide by all the standards of whichever gas you are using. Mistakes unrelated to that specific issue certainly can cause problems, but that's true no matter what you breathe, no matter how you breathe it. >> By this logic, all diving accidents are compressor errors since, without >> compressors mucking around with gas pressure, there would be no diving >> accidents. Ok, so this is a bit extreme, but it illustrates the point. > It does, for in a Root Cause analysis there's a lot of options for > organizing your risk/failure nodes, and thus, what ends up where. > However, what they all have in common is that in the end, every > possible option has to go *somewhere* in each and every one of them. Only in the holistic approach. We, at least I, am still talking about a single issue, the relative safety of nitrox breathed as air versus nitrox breathed as nitrox. Originally, I was even willing to forget about the OxTox issue, at least until one of the proponents of the safety of using nitrox that way demonstrated that he didn't know the MOD of the gases he was discussing. >> Taking someone else's word for what you're breathing, is a mistake that >> the >> diver, himself, could have and should have controlled. Failing to check >> is >> exactly the same mistake whether you're breathing nitrox as air or as >> nitrox. > Particularly true when we're receiving gas from a station that's > capable of pumping both. If I'd seen this earlier, I'd have saved some typing time. > And while an air/Nitrox station is increasingly common today, it wasn't > always so: we don't really have to go back all that many years to when > the Rec choices for gas were "just air" and the only question was > contamination. It was from this historical perspective that I chose to > "bin" the PPO2 content error risk as being Nitrox-attributable, versus > what had traditionally been the "air-only" Recreational diving risks. >> > Any time there is a process step added, there is the potential for it >> > to >> > be done wrong, which results in increased risks. >> You bet, but we're talking about risks directly related to breathing >> nitrox >> as air versus breathing nitrox as nitrox. Other risks aren't relevant to >> that particular issue. > Depends on your altitude: there's risks at the tank jockey fill > station from possible exposure to high pressure, high-PP Oxygen, such > as an Oxygen fire. These have to be "binned" someplace too, plus we > need to answer the question of risk transfers between participants. They need to be considered in an overall study of diving related risks. They don't need to be considered in this discussion. > For an example of risk transfer, if we were to come up with some "magic > mix" that reduces diver fatalities by 30 per year, but the fatality > rate of diveshop tank jockeys goes up by 30 per year, has "diving" > become more or less dangerous? The answer kind of depends on if you're > a diver, a tank jockey, or an outside industry observer. Not unless the tank jockeys were diving at the time they died. Lee > Taking someone else's word for what you're breathing, is a mistake that > the diver, himself, could have and should have controlled. Failing to > check is exactly the same mistake whether you're breathing nitrox as air > or as nitrox. What proportion of "air" tanks have you checked with an O2 meter? >> Taking someone else's word for what you're breathing, is a mistake that >> the diver, himself, could have and should have controlled. Failing to >> check is exactly the same mistake whether you're breathing nitrox as air >> or as nitrox. > What proportion of "air" tanks have you checked with an O2 meter? Back when I used air exclusively, I didn't check any of them. These days, most of my dives are done on nitrox and the few that aren't are filled by a shop that specializes in nitrox and trimix. Since the chance for error at the shop I frequent is the same for air as it is for any other gas purchased there, I check them too. It's just as easy to check all my tanks as some of them. I didn't used to check my air fills. The shops I used in the past did partial pressure fills and my tanks have always been filled while I watched. It would be hard to fail to notice someone first putting oxygen in them and then topping them off with air. I felt relatively comfortable that they were, in fact, filled with air. These days, I'm a bit more careful than that, particularly since the only times I use air any more is when I'm planning a dive beyond the depths where nitrox is practical and/or safe. FWIW, I get my tanks filled and tested by the shop I buy my gas from. I test them using the shop's analyzer. If my test and theirs don't agree, we resolve the difference before I leave the shop. When I get the tanks home, I check the pressure, which has stabilized by that point, and the O2 content, and replace the shop's contents sticker with my own. I use yellow duct tape and a black marker. When I'm ready to go diving, I look for those yellow tanks. Any tank that does not have my label on it, gets tested for both pressure and O2 percentage before it, even those that I think contain air. When I set up for a dive, one of the first things I do is remove that duct tape. Because I have 12 tank that may contain anything from 21 to 50% oxygen, I make a real effort to ensure I know what is in the one I plan on using that day. Lee >>> Taking someone else's word for what you're breathing, is a mistake that >>> the diver, himself, could have and should have controlled. Failing to >>> check is exactly the same mistake whether you're breathing nitrox as air >>> or as nitrox. > >> What proportion of "air" tanks have you checked with an O2 meter? > Back when I used air exclusively, I didn't check any of them. > I didn't used to check my air fills. The short answer is: You don't know. > >>> Taking someone else's word for what you're breathing, is a mistake that > >>> the diver, himself, could have and should have controlled. Failing to [quoted text clipped - 8 lines] > > The short answer is: You don't know. And the accurate answer is what he gave. Dennis. >>>> Taking someone else's word for what you're breathing, is a mistake that >>>> the diver, himself, could have and should have controlled. Failing to [quoted text clipped - 9 lines] > > The short answer is: You don't know. Only if you can't read. I'm about to go to bed. Tomorrow through Thursday, I'll be out diving nitrox, as nitrox . . . a lot. I'll be using nitrox because it lets me do the number of dives I want each day. I'm a lot more worried about sharks that want my catch and the 5-7 foot waves NOAA is predicting than I am about the risk of DCS, at least now that I've learned that I need to check every tank I use to be sure I know what is in it before I breathe it. My final word, at least for now, is that it's good to be conservative, but best to understand what the real costs and benefits of what you chose are. If you were to chose to cut your dive short by a few minutes, no problem. If you were to chose, as I do, to do multiple deep stops, slow your ascent and extend your safety stop, no problem. I just think that cutting a dive you could do safely on nitrox roughly in half by using it as though it is air is just plain crazy. YMMV Lee PS: My Oceanic computer allows 24 minutes at 90 feet on air and 46 minutes at 90 feet on 36%. > PS: My Oceanic computer allows 24 minutes at 90 feet on air and 46 > minutes at 90 feet on 36%. Suunto allows me 22 min on air, 38 min on 36%. It gives me 6 min at 150' on air. > If you'd like to start a new thead called "risk of assuming your gas is > air/nitrox/trimis without testing it" I'm game, but it ought to be a > really short discussion. Yup, and it was almost discussed last time I checked in when somebody was mentioning the death of Audry Mestre. If you don't check the contents of yer own tanks for scuba, meaning pressures *and* mixes, then I'm afraid you gets whats ya gets. LD. >BTW, no one has ever died from oxtox. There have been quite a >few that drowned as a result, however. I hadn't heard about that. Any pointers to reports? SignatureRon > >BTW, no one has ever died from oxtox. There have been quite a > >few that drowned as a result, however. > > I hadn't heard about that. Any pointers to reports? You are kidding, right? Drowning is the cause of death in almost all SCUBA related fatal oxtox events. Convulsions make you spit out your reg and aspirate water. A few divers have survived the convulsions, and smoe due to wearing a FFM. > At least you have a disclaimer in the above. DCIEM tables were > done with doppler studies. They tend to be more conservative > than the NAUI/PADI/etc. tables. I've found the DCIEM tables > to be readily available in the U.S. According to Peter Bennett, studies done on divers using the DCIEM tables produced exactly the same rate of DCS as the PADI tables - aprroximately 0.04%, leading him to believe that the tables are as safe as they can be, and that the unexplained DCS was perhaps related to the ascent rate. I don't know how the later studies on that went. > The phenomenon of undeserved hits, which has been studied by > many, always ends up being random, i.e. incidence without > corelation to profile. There is therefore only one answer, that > the curve is flat. Are you saying the Lee Bell Curve is flat? JF >>The phenomenon of undeserved hits, which has been studied by >>many, always ends up being random, i.e. incidence without [quoted text clipped - 4 lines] > > JF Yes. > >>The phenomenon of undeserved hits, which has been studied by > >>many, always ends up being random, i.e. incidence without > >>corelation to profile. There is therefore only one answer, that > >>the curve is flat. > > > > Are you saying the Lee Bell Curve is flat? > Yes. So much for a break on the mark then. JF >> NAUI, SSI and TDI were represented. >> Funded entirely with private funds, no advertising, endorsements or >> commercial contributions involved. > Could you (or someone else) please provide an official source for this > study? I mean no disrespect, nor do I question the validity of your > statements - for my own reasons I'd very much like to have the actual > document of this study, rather than what "some guy on the internet" > said about some study. You read the original. It wasn't something said by someone about some study, it was the direct results of the study conducted by the person that presented it. Lee > You read the original. It wasn't something said by someone about some > study, it was the direct results of the study conducted by the person that > presented it. Oh, OK. That's a horse of a different color then. The way this material was presented, I thought this was a real scientific study, not simply the results of one diver over the course of time. While I'm sure these data are correct for the unknown diver that presented the material to you, the scientific method of this study cannot be documented and therefor it would be improper and dangerous for me (or anyone else) to extrapolate these data to apply to themselves. Thanks for the clarification. cheers, Chris > Oh, OK. That's a horse of a different color then. The way this material > was presented, I thought this was a real scientific study, not simply > the results of one diver over the course of time. It was a real scientific study. It was a test of the specific conditions under discussion, enough times to be statistically significant, carefully controlled and even more carefully observed. Just because you don't recognize, or know about, my scientific credentials, does not make the study any less scientific. > While I'm sure these data are correct for the unknown diver that presented > the material to you, the scientific method of this study > cannot be documented and therefor it would be improper and dangerous for > me (or anyone else) to extrapolate these data to > apply to themselves. Let's try this again. I'm the guy that did the thousands of hours of dives over more than 40 years. I'm the guy that had the tanks filled, knows what was in them, planned the dives and measured the depths and times. This is not guesswork, it's specific, detailed, scientific and accurate, right down to the single case of DCS at the limits of one of the old style computers, a computer I still have. If you can't draw conclusions from the information, that's you're problem. The data is accurate and reflects on exactly the issues being addressed. Unless you have comparable experience or information to the contrary, information as easily traced to its source as mine is, I suggest you think twice about denying the validity of its results. Lee >> Oh, OK. That's a horse of a different color then. The way this material >> was presented, I thought this was a real scientific study, not simply [quoted text clipped - 24 lines] > information as easily traced to its source as mine is, I suggest you think > twice about denying the validity of its results. Try to publish it in a reviewed journal if you want to see how credible it is. > Try to publish it in a reviewed journal if you want to see how credible it > is. I already know how credible it is. I live it. >> Try to publish it in a reviewed journal if you want to see how credible it >> is. > > I already know how credible it is. If so, how does it generalise? > If so, how does it generalise? It generalizes about as well as any other study involving thousands of hours or testing. At some point, you either conclude that the lack of a problem event means your tables are good enough or you don't. If you do, then enjoy your diving. If you don't, find another hobby. If you can't trust the tables and an exceptionally long history of testing, then you have no basis for accepting any combination of gas, depth and time as safe. Lee I think DAN would disagree.... I have read dozens of stories in the DAN magazine about people getting bent while following the tables, computers, etc. We all know the risks, mitigate them to meet our risk profile and hopefully live to dive another day. Myself, I dive a very conservative Nitrox computer... I also carry an air computer in case I have to go to the PONY and also as a backup.(Never needed it yet) I may go to the limits of my current Nitrox Mix but I try to mitigate my risk by following the deco stops of my air computer. To conservative?? maybe...but it has worked for me since computers were cheap enough to own several. >>If so, how does it generalise? > [quoted text clipped - 8 lines] > > Lee > I think DAN would disagree.... I have read dozens of stories in the DAN > magazine about people getting bent while following the tables, computers, > etc. Then you need to think again. First, DAN wasn't there for any of the reported dives. Second, they have a vested interest in having you believe that you're likely to get bent even if abide by the tables. How much insurance do you think they would sell if everyone knew that all they had to do to stay safe is stay within the tables? Before you say it, no, I'm not suggesting DAN is lying. I'm suggesting that DAN simply choses not to question what they're told by others. Finally, nobody said that there aren't unexplained hits. What we said is that they really are unexplained and that they are, as near as anyone can tell, the same no matter what gas, or gas tables are being used. > We all know the risks . . . Actually, it's pretty clear we don't all know the risks. At least one person here did not know what the MOD was for various gases that he was advocating be used like air. At least one other person here stated that there had never been an OxTox death, something that is only true if you somehow decide that drowning during OxTox convulsions is not OxTox related. Nobody here has spoken against diving conservatively. Nobody here has spoken against cutting your dive short because you feel safer, even on nitrox, if you don't dive it to the limit. All we've said is, no matter how conservative you chose to be, dive air like air, nitrox like nitrox, heliox like heliox and trimix like trimix. > Myself, I dive a very conservative Nitrox computer... I also carry an air > computer in case I have to go to the PONY and also as a backup.(Never > needed it yet) Your air computer is a complete waste. It backs up nothing. It can't account for the nitrox you were breathing at the beginning of the dive. If you want to carry a backup for a nitrox computer, carry a second nitrox computer. > I may go to the limits of my current Nitrox Mix but I try to mitigate my > risk by following the deco stops of my air computer. To conservative?? > maybe...but it has worked for me since computers were cheap enough to own > several. Not too conservative. More like too ignorant. Ignorance can be cured. You can't dive nitrox to the limit if you follow the deco stops of your air computer. The concepts are mutually exclusive. Lee >Nobody here has spoken against diving conservatively. Nobody here has >spoken against cutting your dive short because you feel safer, even on >nitrox, if you don't dive it to the limit. All we've said is, no matter how >conservative you chose to be, dive air like air, nitrox like nitrox, heliox >like heliox and trimix like trimix. Although, it strikes me as ironic. The very thing you're counseling against (diving nitrox, within the MOD, using air tables for extra conservatism) would have prevented your bends incident. Diving nitrox on air tables is safe, as there is no instance where the air table specifies less time than the nitrox table. That's not true for all profiles when you're using heliox or trimix. SignatureRon (user ron in domain spamblocked.com) > Although, it strikes me as ironic. The very thing you're > counseling against (diving nitrox, within the MOD, using > air tables for extra conservatism) would have prevented > your bends incident. I would not be so confident. There have been people who have gotten DCS hits on profiles as rediculously "safe" as 20 minutes @ 20fsw. > Diving nitrox on air tables is safe, as there is no instance > where the air table specifies less time than the nitrox table. When you only look at half of a question, you only get half of the answer. Here, DCS risk is only 'half the question'. Consider a dive on that old PADI table that I already posted: it allows depths to 140fsw. On 36% Nitrox, that would be a 1.9 PPO2. Still feeling that DCS is the >only< risk to worry about? Note that old table also permits bottom times of up to 20 minutes at 140fsw on air. After 6 minutes @ 10ft, you surfaced as an "I" (old lettering system) Residual Nitrogen level for planning repetitive dives. -hh I'm gone for two weeks. Someone hold up my end, please. >Consider a dive on that old PADI table that I already posted: it >allows depths to 140fsw. On 36% Nitrox, that would be a 1.9 PPO2. > >Still feeling that DCS is the >only< risk to worry about? Have you stopped beating your wife? I never said or felt that DCS is the *only* risk to be concerned with. In fact, I said, and you quoted: "(diving nitrox, WITHIN THE MOD, using air tables for extra conservatism)" Emphasis added, so that maybe you can notice it this time. SignatureRon (user ron in domain spamblocked.com) > I never said or felt that DCS is the *only* risk to be > concerned with. In fact, I said, and you quoted: > "(diving nitrox, WITHIN THE MOD, using > air tables for extra conservatism)" > Emphasis added, so that maybe you can notice it this time. You first wrote: "Although, it strikes me as ironic. The very thing you're counseling against (diving nitrox, within the MOD, using air tables for extra conservatism) would have prevented your bends incident." ...which was in context of the profiles that Lee did, and got bent on. After a <CR> to end the paragraph, you then went on to make a much more broad statement: "Diving nitrox on air tables is safe, as there is no instance where the air table specifies less time than the nitrox table." Note the absence of any other qualifiers here than "on air tables". Perhaps you intended for this statement to have more qualifiers such as the MOD but it was not what you wrote. And this would appear to be even more clear when you went on to say: "That's not true for all profiles when you're using heliox or trimix." ...which we all know are mixes suited for deep diving. But the air table is deep enough. Plus, there is the little problem of people well within the limits who have gotten "undeserved hits", with air or nitrox. This is not the first time that this topic has been discussed. From past conversations, we know that Peter Bennett, developer of the DCIEM tables found that the DCS risk profile tailed out into a flat line at 0.04% incidence. Supposedly, it made him a bit perturbed :-) Bennett was previously known to been doing a study at UNC to see if he could lower this apparently profile independent (ie, 'flat') 0.04% incidence risk rate, through slower ascent rates. Not sure if he found anything or if it has been published yet. FWIW, my personal opinion is that it is likely a manifestation of the uncontrolled risk from PFO's. If you look at the following paper from Bennet et al, http://www.smw.ch/docs/pdf200x/2001/25/smw-09706.pdf ...which states: "Some divers try to decrease the amount of nitrogen load by using special nitrogen-oxygen mixtures ("nitrox"), with 40% oxygen and 60% nitrogen as typical example. The reduced nitrogen content compared to air decreases the probability of bubble formation, but 40% oxygen in the breathing gas carries the double risk of oxygen toxicity. These are all but theoretical considerations, and no prospective clinical trial has ever been conducted to establish their utility in daily routine for the prevention of decompression events in the presence of a cardiac right-to-left shunt." Emphasis on the "....no prospective clinical trial has ever been conducted to establish their utility..." statement. PFO's occur in ~25% of the Adult population. Since most people don't even know that they have one, their presence is generally independent of the dive profile. As such, it is a quite plausible causal attribute to the "flat" 0.04% incidence rate of 'undeserved' hits. You also might want to try finding the USN's Statistically based Decompression Tables (Weathersby, P.K., S.S. Survanshi, R.Y. Nishi and E.D. Thalmann. "Statistically Bases Decompression Tables VII: Selection and Treatment of Primary Air and N2-O2 Data". Joint Report NSMRL (#1182) and NMRI (#92-85), US Navy, 18 September 1992), which will tell you what each of the lines represent on this chart: http://www.huntzinger.com/dive/usn_risk.pdf -hh > http://www.smw.ch/docs/pdf200x/2001/25/smw-09706.pdf > > ...which states: In the Summary: "The use of special nitrogen-oxygen mixtures ("nitrox", 60% nitrogen and 40% oxygen as the typical example) decreases the probability of nitrogen narcosis and probably bubble formation, at the cost of increased risk of oxygen toxicity." For dives with a hard bottom less than the MOD of the nitrox mix, there's practically a zero risk of oxygen toxicity when diving recreational profiles. Diving nitrox on air tables for these divers is certainly safer than diving air. Oxygen toxicity for recreational dives on deeper water sites is only a concern for inattentive divers. Those same divers are just as likely to run a deco obligation and get into trouble with DCS as well. The threat of oxygen toxicity as compared with the dangers of DCS for recreational profiles by attentive divers is a red herring. > For dives with a hard bottom less than the MOD of the nitrox mix, there's > practically a zero risk of oxygen toxicity when diving recreational > profiles. Diving nitrox on air tables for these divers is certainly safer > than diving air. Did someone say you're a lawyer? Diving nitrox on air tables (.0004 probability of DCS) is certainly safer than diving air (.0004 probability of DCS)? Can you give us just a rough estimate of how much less .0004 is than .0004? Dive Brooklyn, the birthplace of scuba. > Did someone say you're a lawyer? I know when to assert the 5th. > Diving nitrox on air tables (.0004 probability of DCS) is certainly > safer than diving air (.0004 probability of DCS)? .0004 may be the probability of DCS for the general population. Individual subpopulations may bear a higher risk and that risk is doubtlessly reduced by diving nitrox to air tables. For instance, the birth control pill might have an overall efficacy rate of 99%, but it's 100% certain I won't get pregnant. > Can you give us just a rough estimate of how much less .0004 is than > .0004? > > Dive Brooklyn, the birthplace of scuba. Dive L.A., the birthplace of scuba instruction. [someone had to start teaching it after all the Brooklynese started dropping like flies on a NY summer day] > .0004 may be the probability of DCS for the general population. > Individual subpopulations may bear a higher risk and that risk is > doubtlessly reduced by diving nitrox to air tables. You'd probably make them half happy by just saying use the damn Nitrox tables, and back off the NDLs. Same thing, in reality. Then ask them if getting comatose drunk is what you're trying to avoid, is just getting plastered on a regular basis without passing out healthy? Oops, sorry, bad example, wrong crowd <evil grin>. Curtis > Then ask them if getting comatose drunk is what you're trying to avoid, > is just getting plastered on a regular basis without passing out healthy? You can't get bent if you don't get wet, but look at all the fun you're missing by staying dry. >> Then ask them if getting comatose drunk is what you're trying to >> avoid, is just getting plastered on a regular basis without passing out >> healthy? > > You can't get bent if you don't get wet, but look at all the fun you're > missing by staying dry. And just who is staying dry? Damn Greg, I'd have thought the lawyer would have caught the real analogy. ;-) Curtis >>Dive Brooklyn, the birthplace of scuba. > > Dive L.A., the birthplace of scuba instruction. LA was kinda late. Le Prieur was teaching scuba in the '20s. > For dives with a hard bottom less than the MOD of the nitrox mix, there's > practically a zero risk of oxygen toxicity when diving recreational > profiles. Yes, and for divers having similarly good practices and staying within the No-Deco limits, there's also practically a zero risk of DCS when diving recreational profiles...approx 0.04% So in a nutshell the question is if "half of zero" really is better than "zero". > The threat of oxygen toxicity as compared with the dangers of > DCS for recreational profiles by attentive divers is a red herring. Any time you try to divide something by zero, you're going to get dramatic-looking answers which are fundamentally misleading: when two risks are very small, examining the ratio between them is the red herring. So do all the 'Herring Halving' you wish ... you're not really changing the risks. And the pragmatic question is even if it did achieve "half a zero", is it significant enough to be worth paying an extra $8/tank for? -hh > Yes, and for divers having similarly good practices and staying within > the No-Deco limits, there's also practically a zero risk of DCS when > diving recreational profiles...approx 0.04% > > So in a nutshell the question is if "half of zero" really is better > than "zero". I think the better question is whether 0.04% is really zero. If 0.04% is zero, 0.08% is twice zero and would still be zero. However, that defense won't work very well, say, in a DUI case when you try to convince the judge that you're not really drunk because you only blew a 0.08% on the Breathalyzer and that's really just zero because it's merely twice zero. > And the pragmatic question is even if it did achieve "half a zero", is > it significant enough to be worth paying an extra $8/tank for? What price to put on the all saved lives? I dunno. Ask Ford. Ask Firestone. If I had my way, I'd sue whoever invented air for product liability. Maybe we can sue the dive shops for continuing to carry the crap. It's like selling unfiltered cigarettes. Plus you have all the collateral benefits, some real, some imaginary. There may be less narcosis, if oxygen isn't as or more narcotic than nitrogen. You may experience less fatigue, possibly due to reduced microbubble formation, possibly from the oxygen "high". At the least, there's a placebo effect. On liveaboard trips when I'm diving unlimited nitrox, I always stay up later than anyone diving air and manage to metabolize more alcohol as well, and still manage to be one of the first up in the morning. At home, when I breathe mere air, I can never keep up that sort of behavior for long. > > So in a nutshell the question is if "half of zero" really is > > better than "zero". > > I think the better question is whether 0.04% is really zero. We currently can't lower the risk below 0.04%. That's what makes it effectively zero. And considering that we know that 25% of the Adult population has a PFO which IIRC has roughly 4x the DCS risk, this means that we're aware of a subpopulation with roughly a 0.20% risk, yet because no Rec Agency requires a diving candidate to undergo a PFO screening test as part of their pre-certification medical, the "Accepted Industry Practice" is choosing to ignore this demonstrably higher risk. YMMV on if you agree with them, but DAN has stated that this PFO-attributable condition is an acceptably "small" (relative) risk in diving. > If 0.04% is zero, 0.08% is twice zero and would still be zero. However, > that defense won't work very well, say, in a DUI case when you try to > convince the judge that you're not really drunk because you only blew a > 0.08% on the Breathalyzer and that's really just zero because it's merely > twice zero. The fallacy in this example is twofold. First, we're talking about trying to reduce risk, not increasing it. Second, in the case of alcohol, it is possible to consume some small amount and have a blood alcohol that's below 0.04%, but with diving, if we proverbially even stick a toe in the water, its a step function to an activity risk floor of 0.04%. We aren't (yet) capable of reducing this "background noise" without effectively total cessation of diving activity, whereas even an alcoholic can safely eat a vanilla cupcake, and "zero" DWI's are due to the driver's consumption of 2 TSP/4hrs of cough syrup. > > And the pragmatic question is even if it did achieve "half > > a zero", is it significant enough to be worth paying an > > extra $8/tank for? > > What price to put on the all saved lives? I dunno. Cross that bridge once we come to it, for the road we're on might not even lead us there. > If I had my way, I'd sue whoever invented air for product liability. Don't worry, you'll get to meet Him, eventually, to plead your case: we pretty well know that air is toxic to human life, although it has a half-life of 74 years (as per most life insurance companies :-) > Plus you have all the collateral benefits, some real, some imaginary. You should have said collateral "effects", for they're not all necessarily beneficial: if nothing else, spending the extra money for Nitrox means less cash remaining for booze :-) And yes, the effects encompass both the physiological and psychological realms, which in Humans can be very difficult to quantitatively partition, particularly when the test subject's motivation levels are an uncontrolled variable. -hh > You should have said collateral "effects", for they're not all > necessarily beneficial: if nothing else, spending the extra money for > Nitrox means less cash remaining for booze :-) That's why I love Aggressors: $100 for unlimited nitrox and the booze is free. >> You should have said collateral "effects", for they're not all >> necessarily beneficial: if nothing else, spending the extra money for >> Nitrox means less cash remaining for booze :-) > > That's why I love Aggressors: $100 for unlimited nitrox and the booze is > free. Dayum, why have they been keeping this kind of intel from ME? LD. > > That's why I love Aggressors: $100 for unlimited nitrox and the booze is > > free. > > > Dayum, why have they been keeping this kind of intel from ME? > > LD. Probably because they're hoping to be able to stay in business. >> > That's why I love Aggressors: $100 for unlimited nitrox and the booze > is [quoted text clipped - 3 lines] > > Probably because they're hoping to be able to stay in business. Chris, you're on to me! LD. Ron wrote: > Although, it strikes me as ironic. The very thing you're > counseling against (diving nitrox, within the MOD, using > air tables for extra conservatism) would have prevented > your bends incident. Yes, but not for the reasons you think. I could not have done the dive safely on air. I would have avoided getting bent because I would have been sitting on the boat instead of diving. By the way, I'm not counseling against anything. I'm simply saying that those that use nitrox based on air tables get a poor return on their money. They neither get the increased dive time/shorter surface interval I get, nor the increased safety they believe they are getting. > Diving nitrox on air tables is safe, as there is no instance > where the air table specifies less time than the nitrox table. There are, however, both depths and times (separately) that air tables allow that nitrox tables don't.. Lee > I'm simply saying that those that use nitrox based on air >tables get a poor return on their money. They neither get the increased >dive time/shorter surface interval I get, nor the increased safety they >believe they are getting. Maybe so. Or maybe it helps to avoid long-term problems. Reports of cognitive dysfunction and damage to the liver, retina, and heart of the diver with no history of decompression sickness are now emerging. Because these symptoms may occur gradually and away from the dive site, prudent physicians should be aware of the signs and symptoms related to adverse events of diving in order to minimize the morbidity and mortality they can cause. http://www.scuba-doc.com/LTE.htm Whether extra conservatism can address the long-term problem remains speculative, since I'm aware of no good scientific studies on this. SignatureRon (user ron in domain spamblocked.com) > Whether extra conservatism can address the > long-term problem remains speculative, since > I'm aware of no good scientific studies on this. Other than DAN and NEDU, I don't have any either. >> Whether extra conservatism can address the >> long-term problem remains speculative, since >> I'm aware of no good scientific studies on this. > > Other than DAN and NEDU, I don't have any either. And, of course, DCIEM, but they're Canadian. >> If so, how does it generalise? > > It generalizes about as well as any other study involving thousands of hours > or testing. Let's not confuse Lee with Science; _cience is his game. > Try to publish it in a reviewed journal if you want to see how credible it > is. One needs not to fully understand the studies, findings, results, and recommendations published on rec.scuba before knowing with absolute certainty where such studies, findings, results, and recommendations belong. Credibility is credibility - this is rec.scuba. Lla qindi qawdihaw "ben bradlee" <NoWay@Way.Bite.Me>, dawghattlxhasi: > Credibility is credibility - this is rec.scuba. IOW, no credibility. SignaturePosted via a free Usenet account from http://www.teranews.com > Lla qindi qawdihaw "ben bradlee" <NoWay@Way.Bite.Me>, > dawghattlxhasi: > >> Credibility is credibility - this is rec.scuba. > > IOW, no credibility. It's one man's opinion. It was apparent to me that Lee's post was a story. Maybe it's a true story. Maybe it current memories clouded by the shades of time. Maybe it's strung together aspirations. It's of little importance what it is, but it was a cute story. The problem with much (I claim most) of what you read on rec.scuba is that is just opinion. Three or four guys agree and it becomes fact. If one stepping into rec.scuba doesn't know that the bullshit is flying, he or she could very well believe what is said and get hurt. Let me explain it another way. There are things that people know. Your knowledge, 2 + 2 = 4, etc. There are things that people don't know. You say, "I don't know" because it's the truth. Then there is a third category: Things we don't know we don't know. Here you're confronted with, or providing, information about a subject that you don't know enough to determine you don't know. Most of rec.scuba is don't know we don't know. People providing buckets of information from a thimble full of reserves. This is rec.scuba. |
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