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Dan, I have some comments about your post on RBC rebreather. At 11:29 PM 6/2/96 -0500, you wrote: > 1. Some people have been touting one of the constant flow semi-closed > (active addition) units as a way to obtain longer >no-decompression dives. It is a bit narrow mind to consider constant flow to be the only active addition system. There are other ways to have an active addition even with a gas addition keyed to your RMV. Let not consider an active addition system systematically as a constant flow semi-closed unit. Then we should not apply the disadvantages of constant flow system to other active addition systems. > In my opinion, the most responsible approach that I >have seen to date for this type of unit appears to be Grand Bleu with the >"Fieno". This is a limited depth and duration unit that is very light and >compact, has an innovative mouthpiece that shuts off automatically if >dropped from the diver's mouth and has a prepacked 45 minute scrubber insert > that is very easy to load. In addition, the limited duration supply gas >cylinder must be exchanged for another precharged and tested cylinder, thus >reducing the possibility of incorrect mixtures. They have attempted to >reduce the possibility of hypoxia inherent to this type of rig through training. I heard that the fieno is not yet commercialized. One of the reasons would be that the gas injection rate is not sufficient to avoid hypoxia when the O2 metabolizing rate is high (3L/min). So it could be only used by a young japanese lady (Who is nice on all fieno pictures, my french point of view only...) with a low O2 consumption rate. > b. RMV regulated (passive addition) semi-closed units. > > The only unit of this type currently available to the >civilian market is the RBC "Odyssey". This type of rebreather is less likely >to cause hypoxia than the active addition units because, should the >addition fail for any reason, the diver is immediately warned by shorter >and shorter inhalations. In fact, ANY failure on this unit will result in >an immediate and recognizable change in breathing characteristics. These >changes are designed to be the warning system, and do not require the diver >to monitor anything. I still not understand why a failure on the purging system (which activate the passive addition) will not conduct to an hypoxia? Do not tell me that such a failure is not possible, I think we should consider the same risk of failure on the purging system than on a active addition system. Now, I accept that the design allowed the detection of a purging system failure but it is also true for any well designed active addition system (not only constant flow injection) Also one of the major characteristics of a semi closed rebreather is the O2 percentage evolution as function of depth for low workload (O2 metabolizing rate=0.5L/min or more) and extreme workload (O2 metabolizing rate=3L/min or more). Such a graph should be produced for the RBC for different supply gas, Why not?. Even if the addition mechanism is keyed to respiratory minute volume there is still a O2% variation. The quality of a semi-closed rebreather (active or passive addition) will be the capability of the system to reduce the O2% variation and to have the O2% independent of the depth (which I believe is the case on the RBC as the purging ratio is depth compensated). To conclude this post, I should say that I have nothing against the RBC. But I expect that the system will prove its efficiency without masking some aspects. The marketing approach for the Odyssey seems to me unfair as some truth about the Odyssey and other system are not mentioned but misinformation is used. There are always alternatives to a problem, the articles by Jack Kellon are biased and are presented as the Truth (with a big T). This is Misinformation (with a big M) and should be said to the Tek diving community. Now I have expressed my opinion, I feel better. My therapist will be happy isn't it? Frederic ------------------------------------------------------------------------------ Frederic BADIER Dowell Schlumberger Schlumberger Riboud Product Centre 26 rue de la cavee (BP 202); 92142 Clamart Cedex, France Tel : (33) 1 45 37 20 00 Switchboard Tel : (33) 1 45 37 20 41 Direct Line Fax : (33) 1 45 37 25 13 Sinet : badier@cl*.do*.sl*.co* (or DSA::BADIER) ------------------------------------------------------------------------------
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