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> THIS MESSAGE IS IN MIME FORMAT. Since your mail reader does not understand this format, some or all of this message may not be legible. --MS_Mac_OE_3015049960_5631795_MIME_Part Content-type: text/plain; charset="ISO-8859-1" Content-transfer-encoding: quoted-printable This message is posted on behalf of Olivier Isler A few Thoughts on Rebreathers In the last few years, rebreathers have been generating an ever increasing interest in the diving public. Users' motivations are very varied. For most, fun is the main motivator, hence the success of the Dolphin or th= e Rae from Draeger. Dives are limited in duration and depth and usually don't require decompression stops. Others, such as wreck divers, cave divers and scientific divers, are mostly interested in the autonomy provided by the units. Those long and deep dives require stops several hours long, and safety in autonomy must be looked at in a very different way. No (scuba or other) system can be considered 100% safe. One must therefore be able to react to any failure . In normal OC diving, a certain and variable amount of redundant systems is the norm: tanks, regulators =8A, and buddies. What about rebreathers? First, sharing a rebreather mouthpiece is much more difficult than on OC an= d must be attempted only as a last resort. That leaves only two possibilities= : redundant circuits, closed or open. A redundant open circuit is the solutio= n of choice for most rebreathers on the market today. There is even a complicated and bulky mouthpiece system available which allows switching from CC to OC without removing it. Is OC bailout a good solution? First, let's compare the respective performances of CC vs. OC. For the same tank capacity, there is a minimum ratio of 10:1 in favor of the least efficient rebreathers. In order to provide an equivalent OC redundancy, a great number of tanks exclusively dedicated to safety must be used. This means that they must be carried along or staged. What a waste of energy and resources! Further, form a "philosophical" point of view, isn't the reliance on OC for safety a confession of weakness, the glaring proof that, if rebreathers are very efficient systems (which we have known for the last 50 years!), they suffer from a chronic safety deficit? To use a comparison which is not that farfetched, what would airlines think of a plane designed with a single jet engine and requiring 2 or 3 zeppelins in tow for safety? The fact is, CC redundancy is possible, even though to my knowledge only tw= o systems offer it: le CIS-LUNAR in the USA and my own RI-2000 in Europe, which is still a prototype. If we take a hard look at the potential problems of deep wreck dives, doubl= e closed CC circuits are not a luxury. As for cave dives, my experience has convinced me that three independent circuits are an absolute minimum to undertake such dives with a minimum of serenity. But what about the bulk of redundant CC systems? With the limited means at my disposal, I was able to design, build and use = a separate redundant unit perfectly suitable for extreme diving, and I am convinced that a professional approach could lead to further miniaturizatio= n of a CC unit specifically designed for emergency use. In conclusion: Either, in a future that I hope is near, rebreathers will reach their maturity and offer for the safety of their users a minimum redundancy of 2 units, or divers wishing to make full use of their rebreather will need to practic= e some form of hybrid diving which will only tarnish the reputation of CC systems Olivier Isler --MS_Mac_OE_3015049960_5631795_MIME_Part Content-type: text/html; charset="ISO-8859-1" Content-transfer-encoding: quoted-printable <HTML> <HEAD> <TITLE>A Few Thoughts on Rebreathers</TITLE> </HEAD> <BODY BGCOLOR=3D"#FFFFFF"> <B>This message is posted on behalf of Olivier Isler<BR> <BR> </B>A few Thoughts on Rebreathers<BR> <BR> In the last few years, rebreathers have been generating an ever increasing = interest in the diving public.<BR> <BR> Users' motivations are very varied.<BR> <BR> For most, fun is the main motivator, hence the success of the Dolphin or th= e Rae from Draeger. Dives are limited in duration and depth and usually don'= t require decompression stops.<BR> <BR> Others, such as wreck divers, cave divers and scientific divers, are mostly= interested in the autonomy provided by the units. Those long and deep dives= require stops several hours long, and safety in autonomy must be looked at = in a very different way.<BR> <BR> No (scuba or other) system can be considered 100% safe. One must therefore = be able to react to any failure . In normal OC diving, a certain and variabl= e amount of redundant systems is the norm: tanks, regulators =8A, and buddies.= <BR> <BR> What about rebreathers?<BR> <BR> First, sharing a rebreather mouthpiece is much more difficult than on OC an= d must be attempted only as a last resort. That leaves only two possibilitie= s: redundant circuits, closed or open. A redundant open circuit is the solut= ion of choice for most rebreathers on the market today. There is even a comp= licated and bulky mouthpiece system available which allows switching from CC= to OC without removing it. Is OC bailout a good solution?<BR> <BR> First, let's compare the respective performances of CC vs. OC. For the same= tank capacity, there is a minimum ratio of 10:1 in favor of the least effic= ient rebreathers. In order to provide an equivalent OC redundancy, a great n= umber of tanks exclusively dedicated to safety must be used. This means that= they must be carried along or staged. What a waste of energy and resources!= <BR> <BR> Further, form a "philosophical" point of view, isn't the reliance= on OC for safety a confession of weakness, the glaring proof that, if rebre= athers are very efficient systems (which we have known for the last 50 years= !), they suffer from a chronic safety deficit? To use a comparison which is = not that farfetched, what would airlines think of a plane designed with a si= ngle jet engine and requiring 2 or 3 zeppelins in tow for safety?<BR> <BR> The fact is, CC redundancy is possible, even though to my knowledge only tw= o systems offer it: le CIS-LUNAR in the USA and my own RI-2000 in Europe, wh= ich is still a prototype.<BR> <BR> If we take a hard look at the potential problems of deep wreck dives, doubl= e closed CC circuits are not a luxury.<BR> <BR> As for cave dives, my experience has convinced me that three independent ci= rcuits are an absolute minimum to undertake such dives with a minimum of ser= enity.<BR> <BR> But what about the bulk of redundant CC systems?<BR> <BR> With the limited means at my disposal, I was able to design, build and use = a separate redundant unit perfectly suitable for extreme diving, and I am co= nvinced that a professional approach could lead to further miniaturization o= f a CC unit specifically designed for emergency use.<BR> <BR> In conclusion:<BR> <BR> Either, in a future that I hope is near, rebreathers will reach their matur= ity and offer for the safety of their users a minimum redundancy of 2 units,= <BR> <BR> or divers wishing to make full use of their rebreather will need to practic= e some form of hybrid diving which will only tarnish the reputation of CC sy= stems<BR> <BR> Olivier Isler<BR> <BR> <BR> <BR> <BR> <BR> <BR> </BODY> </HTML> --MS_Mac_OE_3015049960_5631795_MIME_Part-- -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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