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Rod, Or be a semi-closed passive addition system which would have emptied the counterlung in this scenario, preventing hypoxic breathing---forcing the diver to surface well before a hypoxic blackout. Dan >Thanks. I thought that was what the report was saying. Every rebreather >should be equipped with an oxygen sensor at the scrubber exit and a >visual or audible warning of high or low pO2. No rebreather ought to be >permitted to be used unless it is equipped with pO2 monitoring, and >manufacturers and resellers of units lacking pO2 monitoring ought to >be shat upon until they die. Rod > >On Tue, 19 Mar 1996, richard soderberg wrote: > >> On Mon, 18 Mar 1996, rfarb wrote: >> >> > Would you please translate the coronor's report or whatever it is into >> > something that makes sense about how the rebreather killed him. Thanks. Rod >> >> First: a very simplified description of a rebreather: >> >> (My apologies to all who feel insulted by the basic level of explanation) >> >> A mouthpiece connected to a hose connected to a bag full of oxygen. >> >> This would be fine if the body did not produce carbon dioxide (CO2). >> CO2 would rapidly build up to unbearable concentrations in the bag. >> >> To remedy this we introduce a "scrubber" in the system, a device that >> will remove the CO2 from the system. This is usually a canister with a >> granular substance. >> >> Now, this rebreather would work fine except for the fact that after a >> while the oxygen would be used up. To fix this we take along a bottle of >> oxygen (O2) and connect it to the system. >> >> How fast should the oxygen be fed to the bag? >> >> There are several ways to decide this: >> >> 1.A constant mass flow valve (cmfv) will feed oxygen into the bag at a >> constant rate. If the flow is to great the bag will get bigger and bigger >> and the diver will have to adjust the filling rate. If the flow is too low >> the bag will eventually be drained of gas. Before this happens, however, >> the diver will note an increased resistance at the end of a deep breath >> and increase the flow. Keep this in mind in the following discussion! >> >> 2. A mechanical device sensing the bag volume will fill it when volume >> has decreased below a certain threshold. >> >> Now for a short inert gas digression: >> At sea level, a human will have approxemately 1.5 liters of Nitrogen >> (N2) dissolved in the body tissues. Why? Because air is mostly made up of >> N2. >> >> What happens if we start breathing pure oxygen? >> >> The body is saturated with N2 and there is no N2 in the gas we breathe. >> N2 will start to diffuse out of the tissues into the gas. If this gas is >> the O2 in the rebreather bag the O2 will be diluted by N2 because the >> scrubber will only remove CO2 and nothing else. Over time, the O2 will >> be diluted by N2. If the flow of O2 in the bag is impeded for some >> reason, (corroded valve, empty O2 bottle etc) the volume of the bag will >> *NOT* decrease, there will be no increase in resistance to signal the >> diver. Instead, the concentration of O2 will decrease until the diver >> becomes unconcious. Remember that lack of oxygen (hypoxia) is very >> insidious, the victim will hardly notice anything before (s)he passes out. >> >> (The same mechanism works in rebreathers that automatically sense the bag >> volume) >> The way to avoid this is to empty the bag of gas completely. When should >> this be done? After a while when N2 has begun accumulating in the bag. >> The procedure will have to be repeated at intervals. >> >> If we use more complex equipment for diving, we need more training, >> knowledge and awareness to dive safely. >> >> /RS >> >> (o o) >> +------------------------------oOO--(_)--OOo---------------------------+ >> | Richard Soderberg, MD, PADI DM | The Karolinska Institute | >> | Systems analyst | MIC-KIBIC | >> | Voice#: +46 8 728 80 00 | Library and | >> | Fax# : +46 8 33 04 81 | Medical Information Center | >> | Snail : PO Box 200 | Doktorsringen 21 C, | >> | S-171 77 Stockholm | S-104 01 Stockholm | >> | Email :richard.soderberg@mi*.ki*.se* | SWEDEN | >> +------------------------------------+---------------------------------+ >> | Diving Physician at Dykhuset/Scubahouse, Stockholm, Sweden | >> | URL:http://www.dykhuset.se | >> +----------------------------------------------------------------------+ >> >> -- >> Send mail for the `techdiver' mailing list to `techdiver@terra.net'. >> Send subscription/archive requests to `techdiver-request@terra.net'. >> >-- >Send mail for the `techdiver' mailing list to `techdiver@terra.net'. >Send subscription/archive requests to `techdiver-request@terra.net'. > > Dan Volker SOUTH FLORIDA DIVE JOURNAL "The Internet magazine for Underwater Photography and mpeg Video" http://www.florida.net/scuba/dive 407-683-3592
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