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comment=First off, there were no accidents, incidents or any other nature of problem with any Odyssey at any time. If you would like more information on the Odyssey, send me your snail mail address and I'll get it to you. To summarize how the Odyssey works: Exhalation goes into a compound bellows at two points. On inhalation the smaller portion is discharged while the larger compartment is rebreathed after "cleansing" in the scrubber. This cleaned gas is augmented by an appropriate amount of new gas after the scrubber operation. The amount added will depend on two factors: respiratory minute volume and depth (with the compound portion of the bellows compensating in size with depth through use of Boyle's Law). There certainly is less likelihood of single point failure in this case because there aren't any small orifices or other friction points (like regulators in the addition mechanism) which can sometimes malfunction like those found on a Draeger. A couple of mushroom valves are really the only friction points in the Odyssey addition mechanism. Let's face facts though. Anything can fail. The relevant question here is will the diver know it with appropriate warning so he can do something about it? In the Odyssey system the diver will notice changes in the breathing characteristics within a couple breaths because the mechanism is keyed to respiration. The mechanism is so reliable (since it relies on physical laws of nature, not man-made devices,If its not working the volume of gas will reduce proportionately to the breaths and let the diver know that it's time to bailout. That's not necessarily so with a system like the Draeger. Burping can be a reliable indicator of a properly functioning addition mechanism if a diver maintains a linear depth profile but how many do that and how many divers would notice a change in off-gassing quickly even if they did? Some, but all? So in a best case scenario the best divers may get to bailout. What of other scenarios? If a diver ascends with an active addition system like the Draeger and there perchance is a failure in the addition mechanism the diver would not know something is wrong. This is because the unit will continue to burp due to gas expansion in the bag. If the diver descends then the increasing ambient pressure would not allow for burping but the breathing will seem the same to the diver until a large enough depth change occurs so that the bag volume is insufficient to supply lung volume. So the result could well be hypoxia in these two cases AND without advance warning. This would be more likely on any ascent because of dropping partial pressures due to the ascent. Dave. >>I just got done reading the long rebreather info (commercial? 8-) that was >>posted recently. It specifically mentions that the Odyssey works around the >>single point of failure I mentioned in the Draeger unit by making the bag >>demand fed and flushing 20% (or so) of the exhailed air for each breath. >>But it doesn't say anything about how this flushing is done. Does anyone >>know the mechanics behind this device? Can you explain how it works? >> >>Seems to me you've just substituted one single point of failure for another. >>If this valve they have doesn't work to it's full 20% it won't be getting >>out the right amount of bad air and, therefore, you won't get as much good >>air. I guess it depends on whether you trust the Draeger (and others) feed >>system or the Odyssey exhaust system more. Comments? >> >>Devon > >I'm not familiar with the Odyssey, but "The Physiology and Medicine of >Diving" by Bennet and Elliot describe a French rebreather that expells a >portion of the breathing gas with every breath. This system uses a large >bellows with a smaller bellows located inside it. When the large bellow >expands (diver exhales) the smaller bellow also expands creating a vacuum >that pulls gas in through a one way valve. When the large bellows contract >(diver inhales) the smaller bellow forces the gas that is trapped inside it >out through a one way valve and into the water. > >However, it is my understanding that the Odyssey is more complicated. The >amount of gas exhaled is also determined by the depth. > > WATER > Valve > ---------------^^^^--------------- > < < > > > > > < Small < > Large Bellows < < > Bellows > > --> > > < <--- < > < < > > > ---^^^^-------^^^^^------vvvv----- > [ Valve Valve Valve ] > [ Gas In ] Gas out ] > >OK, so I'm not an artist. I would like to read more about the Odyssey, >especially the accident if one did occur. > > >Mark Pansing NSS 26348 >markp@co*.co* > > >-- >Send mail for the `techdiver' mailing list to `techdiver@terra.net'. >Send subscription/archive requests to `techdiver-request@terra.net'.
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