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Scuba Forum / General / August 2005Help a guy out?
Sorry if this is the wrong place to post this, but I've been looking for something the last couple of days and it's driving me to distraction. I few years ago, I saw a little blurb on TV (Discovery Channel, I think?) about what was then a 'new' thing for people who wanted something a little more then snorkling but not quite SCUBA. It was a small mouthpiece (or maybe a mouth piece and a mask) that had an air canister on either saide of the mask (looked like an over-sized CO2 cylinder for a BB gun). The cylinders were replacealbe, not refillable, and would let you swin underwater for a half hour or so, and wouldn't let you go very deep (~20 feet?). If anyone knows what I'm talking about, I'd sure appreciate knowing what I'm talking about! Thanks, Aaron > Sorry if this is the wrong place to post this, but I've been looking for > something the last couple of days and it's driving me to distraction. I few [quoted text clipped - 6 lines] > hour or so, and wouldn't let you go very deep (~20 feet?). If anyone knows > what I'm talking about, I'd sure appreciate knowing what I'm talking about! Was that the one put out by Kevorkian enterprizes? > Sorry if this is the wrong place to post this, but I've been looking for > something the last couple of days and it's driving me to distraction. I few [quoted text clipped - 10 lines] > > Aaron It was probably the Japanese recreational re-breather shown on Beyond 2000. The entire body was merely a ribbed hose that went around your back meeting at a co2 scrubber cartridge. It was only good to 30' and apparantly never caught on with the small ox bottles being very expensive by western standards. Maybe: OHBA by Nippon Sanso Inc > It was probably the Japanese recreational re-breather shown on Beyond > 2000. [quoted text clipped - 5 lines] > > Maybe: OHBA by Nippon Sanso Inc Yup, that was it. My waife said something about how cool it would be to stay under water for a while without having to go through all the SCUBA classes (which we're both going to do once we get some cashflow...), and it made me think of that. Guess it's not gonna happen, though. Ah well, was worth a thought. >>It was probably the Japanese recreational re-breather shown on Beyond >>2000. [quoted text clipped - 11 lines] > made me think of that. Guess it's not gonna happen, though. Ah well, was > worth a thought. Not a good idea to use these things without knowing about pressure and atmospheres the greatest pressure change is in the depths that are very shallow > Not a good idea to use these things without knowing about pressure and > atmospheres the greatest pressure change is in the depths that are very > shallow If I remember the show, they showed it in use with the commentary saying as it got closer to 30', it became more difficult to breath as a warning. I can see photographers having one aboard in the event they need that one shallow shot of a critter that bubbles keep spooking, without the higher cost of some of the more traditional death boxes. >> Not a good idea to use these things without knowing about pressure and >> atmospheres the greatest pressure change is in the depths that are very [quoted text clipped - 7 lines] >one shallow shot of a critter that bubbles keep spooking, without the >higher cost of some of the more traditional death boxes. I might be tempted to carry one on the boat (wind) to unfoul the prop or pry off the barnacles.  Signaturedillon Linux, it's not just an OS, it's a way of life. And a damn fine one, at that. > >If I remember the show, they showed it in use with the commentary > >saying as it got closer to 30', it became more difficult to breath as a [quoted text clipped - 9 lines] > -- > dillon Don't forget to get Spishaks underwater electric barnacle scraper. > Not a good idea to use these things without knowing about pressure and > atmospheres the greatest pressure change is in the depths that are > very shallow I'm sure you meant to say "volume" instead of "pressure," right? John Eells > > Not a good idea to use these things without knowing about pressure and > > atmospheres the greatest pressure change is in the depths that are [quoted text clipped - 3 lines] > > John Eells no, he meant to say the greatest percent pressure change... >> > Not a good idea to use these things without knowing about pressure and >> > atmospheres the greatest pressure change is in the depths that are >> > very shallow >> I'm sure you meant to say "volume" instead of "pressure," right? > no, he meant to say the greatest percent pressure change... Volume change works too. > >> > Not a good idea to use these things without knowing about pressure and > >> > atmospheres the greatest pressure change is in the depths that are [quoted text clipped - 5 lines] > > Volume change works too. Yes, but not quite as well as pressure. The two are obviously closely intertwined; however, I'd say that changing depth changes pressure which, in turn, has an effect on volume (depending on the container). >> Not a good idea to use these things without knowing about pressure and >> atmospheres the greatest pressure change is in the depths that are [quoted text clipped - 3 lines] > > John Eells no I meant pressure >>> Not a good idea to use these things without knowing about pressure >>> and atmospheres the greatest pressure change is in the depths that [quoted text clipped - 5 lines] > > no I meant pressure Pressure varies in a linear fashion with depth, though. Every foot of salt water yields an additionaly 1/33 ATA, no matter whether you're talking about the first foot or the 250th. Volume, on the other hand, halves with the first 33 fsw, and then again at 99 fsw. This is why buoyancy control is easier the deeper you go--the buoyancy change is predominently volume- (not pressure-) related. The combined gas law is PV=nRT, where P is pressure, V is volume, n is the number of moles of gas, R is the gas constant, and T is temperature. You can derive all the other gas laws with algebra. John Eells >>Sorry if this is the wrong place to post this, but I've been looking for >>something the last couple of days and it's driving me to distraction. I few [quoted text clipped - 20 lines] > > Maybe: OHBA by Nippon Sanso Inc Maybe it didn't catch on because it is deadly? The big problem with rebreathers is that your body only gets a signal to breath from CO2 buildup. If the CO2 is being scrubbed then you would not notice the O2 cylinders being empty and would simply pass out underwater. Personally, I think you be safer using scuba kit without training than this thing. > Maybe it didn't catch on because it is deadly? The big problem with > rebreathers is that your body only gets a signal to breath from CO2 > buildup. If the CO2 is being scrubbed then you would not notice the O2 > cylinders being empty and would simply pass out underwater. Personally, I > think you be safer using scuba kit without training than this thing. Sorry Barry, but you're way off base. While it is correct that CO2 is the primary trigger for taking the next breath, it's the CO2 in your body, not what is in the gas you breathe. Still, your conclusion wasn't bad. Rebreathers can be deadly, particularly one that uses pure oxygen, which comments suggest this one did, used below 20 feet (a PPO2 1.6 for pure O2). At 20 feet, you're up to a PPO2 of almost 2.0, something not recommended even for trained scuba divers, let alone untrained ones. Lee > > Maybe it didn't catch on because it is deadly? The big problem with > > rebreathers is that your body only gets a signal to breath from CO2 [quoted text clipped - 5 lines] > primary trigger for taking the next breath, it's the CO2 in your body, not > what is in the gas you breathe. In an O2 RB, if the O2 injection fails, the volume of gas in the loop will drop with each breath, and eventually, breathing resistance will go up. Depending upon starting loop volume, this may only take a few breaths. But if there's another (non-CO2) gas in the loop, the volume of gas might "bottom out", at a level that still feels OK WRT breathing resistance. You end up breathing normally, but the gas isn't supplying any O2. You pass out, and you're dead - from drowning, if you let go the mouthpiece, or from hypoxia, if you don't. > Still, your conclusion wasn't bad. Rebreathers can be deadly, particularly > one that uses pure oxygen, which comments suggest this one did, used below > 20 feet (a PPO2 1.6 for pure O2). At 20 feet, you're up to a PPO2 of > almost 2.0, something not recommended even for trained scuba divers, let > alone untrained ones. You must have meant at 30 feet, PPO2 will be almost 2ATA. SignatureArt Greenberg artg AT eclipse (remove this) DOT net >> Still, your conclusion wasn't bad. Rebreathers can be deadly, >> particularly [quoted text clipped - 5 lines] > > You must have meant at 30 feet, PPO2 will be almost 2ATA. I did. Thanks. At 30 feet, you're up to a PPO2 of almost 2.0. Lee >>Maybe it didn't catch on because it is deadly? The big problem with >>rebreathers is that your body only gets a signal to breath from CO2 [quoted text clipped - 5 lines] > primary trigger for taking the next breath, it's the CO2 in your body, not > what is in the gas you breathe. Yes, but that's the point - this thing could still be happily allowing you to expel CO2 from your body even if there was 100% nitrogen in the loop - your body would not get a signal that the O2 level in the rebreather was dropping. Of course, if the thing works on 100% O2 then you would get increased breathing resistance but if there's 80% nitrogen in the loop this may not happen if the tube can squeeze and once PPO2 falls below about 0.11 you will go unconscious. Again, the problem with rebreathers (apart from the high PPO2 one you mention) is that if the O2 injection fails buy the CO2 scrubbing goes on then you run out of O2 without your body getting a warning signal. > Still, your conclusion wasn't bad. Rebreathers can be deadly, particularly > one that uses pure oxygen, which comments suggest this one did, used below [quoted text clipped - 3 lines] > > Lee >>>Maybe it didn't catch on because it is deadly? The big problem with >>>rebreathers is that your body only gets a signal to breath from CO2 [quoted text clipped - 5 lines] >> the primary trigger for taking the next breath, it's the CO2 in your >> body, not what is in the gas you breathe. > Yes, but that's the point - this thing could still be happily allowing you > to expel CO2 from your body even if there was 100% nitrogen in the loop - > your body would not get a signal that the O2 level in the rebreather was > dropping. Whether your body gets the signal that the O2 level in the rebreather is dropping or not has nothing to do with the CO2 issue. That's what was off base about your comment. Your body creates CO2. You'll still have an urge to breathe whether you are breathing pure O2, air, pure nitrogen, or anything else. > Again, the problem with rebreathers (apart from the high PPO2 one you > mention) is that if the O2 injection fails buy the CO2 scrubbing goes on > then you run out of O2 without your body getting a warning signal. The same thing happens when your tank goes empty. >>>>Maybe it didn't catch on because it is deadly? The big problem with >>>>rebreathers is that your body only gets a signal to breath from CO2 [quoted text clipped - 16 lines] > to breathe whether you are breathing pure O2, air, pure nitrogen, or > anything else. Sure you'll have an urge to breathe, but only to a normal extent - but you'll get no warning that you are beginning to breath a dangerously low percentage O2 mix. >>Again, the problem with rebreathers (apart from the high PPO2 one you >>mention) is that if the O2 injection fails buy the CO2 scrubbing goes on >>then you run out of O2 without your body getting a warning signal. > > The same thing happens when your tank goes empty. But then you have no other gas to breathe in and out of your lungs, which can carry away your body's CO2 with it. > Sure you'll have an urge to breathe, but only to a normal extent - but > you'll get no warning that you are beginning to breath a dangerously low > percentage O2 mix. Actually, you probably will, but it may not be enough to save your life. I seem to recall reading, somewhere, that, while the presence of elevated levels of CO2 are the primary breathing trigger, the absence of sufficient O2, while much weaker, is a trigger too. Either way, we have no argument except about whether the risk to the rebreather is the lack of CO2 in the counterlung. Lee >>Sure you'll have an urge to breathe, but only to a normal extent - but >>you'll get no warning that you are beginning to breath a dangerously low [quoted text clipped - 6 lines] > except about whether the risk to the rebreather is the lack of CO2 in the > counterlung. There's an interesting (if partially fictionalised) analysis of this you might want to read at: http://www.scubadiving.com/training/lessons_for_life/the_deep_sleep/ |
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