Mailing List Archive Mailing List Archive
George Thanks for the information on the gasswitching and when the flushes are made. That waa the kind of information i was curious about. I wasnt referring to a "design flaw", rather a phenomenum that applies to all rebreathers, that the loop gas will expand on ascent. The RB80 design works by, lets call it, pumping out, part of the loop gas with each respiration until the lung "bottoms out" and purges in new gas via the second stages at the top of the lung assembly. So, as you point out below, on a normal "deco" ascent then the ventilation works due to that the pumping effect is greater than the gas expansion due to the ascent. The lung will bottom out periodically and new gas will be added. -But at what ascent rate do you actually risk "out-running" the units own ventilation, providing you do not flush. (Just to make it clear. I am not really interested in the accident, It just sparked my interest in how the RB80 is dived, RB80 diving protocols if you like, therefore my questions. I can take them offline if you want.) Best regards /esbjörn ----- Original Message ----- From: "George Irvine" <girvine@be*.ne*> To: "Esbjörn" <esbjorn@no*.co*>; <techdiver@aquanaut.com> Sent: Saturday, September 14, 2002 2:29 AM Subject: RE: Halcyon RB 80 Accident > There is no "design flaw" in the RB 80 - the thing vents itself when you > ascend , and with any rebreather, you need to expect the ppo2 to drop as > you ascend unless you replace the gas in a mechanical RB or oxygen is > added in the case of the CCRs. The idea of flushing the loop on ascending > deco at each new step is to take advantage of the ppo2 inherent in that > step. The shape of the ppo2 at any given step with any venting or not > venting is predictable bases on the behavior of offgassing and the nature > of the equipment. > > Conversely, what I actually do in practice is NOT immediately flush the > loop when I switch gases so as to not spike the ppo2, but let it rise more > slowly for a while, and then I start flushing it out periodically to > overcome the drop in effective oxygen content caused by the offgassing of > inerts, the water vapor, etc, which diminishes as the step progresses, and > I flush it out when I change depths. > > I will remind all of you who incurs the most massive decompression > obligations in technical diving and who executes them most effectively - me > - and I do them without incident of any kind on the Halcyon rebreather as > well as open circuit. What other people do who refuse to recognize or > believe that we have this worked out is none of my concern, but I will not > sit here while people speculate about things that are clearly not well > understood by them and hold no significance in and of themselves. > > As far as the question that somebody asked ( directed at me) about constant > ppo2 deco, see the WKPP.org website regarding deco procedures. In a > nutshell, you need to "toggle" on and off the high ppo2s. Constant ppo2 > only works for dives where no real deco is required in the first place - in > other words, it is not the correct way to decompress. > > I am still waiting for somebody to try to live through one of my > decompressions on a constant ppo2 - any takers? > > > > > -----Original Message----- > From: Esbjörn [mailto:esbjorn@no*.co*] > Sent: Thursday, September 12, 2002 4:20 PM > To: techdiver@aquanaut.com > Subject: Re: Halcyon RB 80 Accident > > > Having read a translation of the report, (which accuracy i can in no way > check) the following grabs me. > > "> Both divers said they forgot to flush the RB80' Loop before ascenting > till arrive at the first stop (change mix) at 66m. They also said they do > not remember what happened during this part of the dive and that sometimes > breathing became ¨heavy¨. Arriving at 40m , Luiz Toledo said he was having > difficulties to coordinate movements of his bellow members. " > > Basically the only achilles heel of the RB80/DC55 design is the need to > flush the loop continuesly when ascending. Not suprising breathing became > "heavy" or that they do not remember that part of the dive when hypoxic. > > Would this have been the starting point of the chain of unfortunate events > or I am completely out on the wrong limb here ? > > regards /e > > > -- > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. > > -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]