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12 on 6 off or else we feel like we have a severe chest cold for says afterwards. By way of comparison, the usdct "divers" did 20 -30 minute of oxygen in their chamber and 5 minute breaks, but then they were sick as dogs for says afterwards, bent, had slobitis, and some of them stayed sick for the full three months, but then Bill Stone and his large cast of "advisors" all think the know better than me how to run a diving operation. Terry, even the 1.6 of 20 feet will give you a fit in the damage department, and in fact pure oxygen at any partial pressure seems to have that effect, it just happens faster and more decisively at the higher partials, meaning you feel the damage on the spot whereas the lower partials take until the next day to realize you "burnt" your lungs. -----Original Message----- From: Terry Michael [mailto:terry-1@ly*.co*] Sent: Sunday, November 12, 2000 8:16 PM To: Wendell Grogan; Trey Cc: Techdiver@Aquanaut.Com Subject: Re: re nitrogen elimination and oxygen How does the 1.9 stuff in the habitat and lung degradation fit into all of this? Thanks -- On Sat, 11 Nov 2000 15:20:36 Trey wrote: > > >Date: Sat, 11 Nov 2000 11:01:19 -0500 >From: Wendell Grogan <wgrogan@dc*.ne*> >Subject: nitrogen elimination and oxygen > > >To pick up on an old thread I have been pondering- > >Specifically, in a typical wreck dive, carrying slightly hypoxic bottom >mix (i.e.. in the 16% range), is there a way to predict, if you use your >bottom mix for air breaks, what the optimal length of the air break >should be? >Is the length of time on back gas based on how long it takes for the >vasoconstriction induced by the pure O2 to clear? >If so, is there a way of predicting how long that takes based on the >ppO2 or %O2? >Or is it just empiric based on personal experience with different mixes? > >Thanks >Wendell G > >-- > It turns out, WG, that the 12 and 6 numbers correspond best to >the onset and clearing, but we concurrently arrived at those numbers >by experimentation. Since we are not at 1.6 for very long at other than >the 20 foot steps, the breaks below that are not as close together, and >converge on 12-6 only at that point. > > Our considerations for breaking deeper steps with lower overall ppo2's >was directed more out of concern for CNS tox than for decompression >reasons, and secondarily for obvious pulmonary reasons, which then >drove the 12-6 numbers as well. Results then alerted us to the efficacy >of this approach and we looked more closely into "why", and arrived at >the conclusions you stated. > > For deeper steps the stretch is longer , converging on 20-4 >with what we call a 20 minute "clean up" break at about 50 feet on long >dives ( which conveniently coincides with switching from rebreathers to >open circuit ) and as always, we use our judgment to call breaks on >short dives, with the pulmonary consequences usually being the driver in >those cases, i.e., if the whole deco is 20 minutes, no need to go off the >deco gas. > > Get FREE Email/Voicemail with 15MB at Lycos Communications at http://comm.lycos.com -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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