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> Date sent: Sun, 14 Jan 1996 11:42:30 -0500 > To: techdiver@terra.net > From: s_lindblom@co*.co* (Steven Lindblom) > Subject: Re: How to use a O2 rebreather? > > > > >> My understanding is that emptying the breathing bag 2 or 3 times by exhaling > >> through the nose should work, > > > > My understanding is that purging n times wastes n bagfuls and n lungfuls of > >oxygen and grossly shortens the dive. I see no need for more than: empty bag > >and your lungs as far as you can, then start breathing from the set, then > >purge once. > > > Am I the only one this makes nervous? We've got someone who apparently has > a rebreather they have neither directions or training for, and two levels > of "I gather" type notions to guide him in how to use it. Or is this just a > troll? Anyhow, I'll bite.... > > My copy of BASIC SCUBA DIVING, circa 1964 (and surely one of the last > introductory SCUBA texts to give full directions for rebreather use!) > recommends purging three or four cycles. An older US Navy dive manual says > to do it until the bag is completely flat, then every hour and before > beginning an ascent. > This is for a plain jane manually operated straight 02 rig. There are a lot > of newer ones offering one degree or another of automation, mixture > control, or gas mix options, each of which requires specialized techniques > and training. > > Exhaling during the purge cycles, "I gather" is not just a matter of > exhaling through the nose, since any exhaled gasses that make it back into > the bag defeat the process - it's necessary to have either a three way > valve that allows blocking the flow back to the bag, or else to crimp the > hose with your fingers to block it off. I've been using an old Pirelli (looks like it was made during WW2) for just that purpose. I plug in at 8 metres, and purge via nose every 15 minutes. I purge the bag at the surface before diving to get rid of the ambient nitrogen. The bag is made from really thick neoprene, and hasnt cut or torn yet! BTW, I use the oxygen deco usually as my safety factor, i.e. schedule as for air. Unless of course it is a long and/or really deep dive, where the oxygen is part of the deco. But then we usually have a tree to breathe off, and the rebreather is backup. > > Has anyone else had any experience using a rebreather just for decom use? > It doesn't seem like an optimum use at all, because of the chances of water > getting into the bag while the outfit is hanging (doubly a problem with any > rebreather not made specifically for diving and using absorbents like > caustics and hyperoxides which are intolerant of water), and the difficulty > of effectively doing an effective initial purge underwater. It would also > probably be a good idea to purge more often, in decom use, since one would > be outgassing significant amounts of nitrogen. > > Experienced, trained rebreather divers still manage to die using > rebreathers, and the record is much worse for rebreathers not specifically > designed for diving (like the mine gas masks common in the USA after WW2, > or the surplus Soviet ones turning up on the surplus market now). Anyone > considering using one should be very sure of the accuracy of their > information and their understanding of the subtleties involved. > >-- > > > -- > Send mail for the `techdiver' mailing list to `techdiver@terra.net'. > Send subscription/archive requests to `techdiver-request@terra.net'. > Greetings Prof JG van der Walt Head: Dept. Physiology Veterinary Science University of Pretoria Onderstepoort 0110 Republic of South Africa Tel # + 27 12 529-8025 Fax # + 27 12 529-8305
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