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You wrote: > >>On 2/10 Michel Therrien wrote: >>>>You should consider taking five minutes air-breaks every 20 or 25 >>minutes.<< >> > >Jesse wrote: > >>I wonder why this is being suggested. Most people would say "to back the CNS >>clock down," but I am not sure this is valid. Current thinking, as I >understand >>it, is that the %CNS clock "decays" or resets at a half life (or better, >>half-time) of 90 minutes. In other words, if you were at 100 %, after 90 >>minutes you would be at 50% and after 180 minutes you would be at 25 % and so >>on. If you are decoing at 20 feet on pure O2, and are at, for example, 100% of >>your CNS clock, five minutes will bring you down to something like 97.25% >>(somebody check my math). > >I checked your math and it would be 96.2223836894%. > >Seriously, this mathematical approach to determine the CNS clock is very >practical for us, but math. formula should not replace common sense. I'm >not sure of the origin of that method of determining residual CNS toxicity, >but I believe it comes from the technical diving community (probably by Dr. >Hamilton for IANTD). My belief is that the exponential decay formula was >created only by using the NOAA assumption that after 12 hours the CNS clock >is reset. I am sure that Tom Mount could correct me on that one. > >The procedure of taking air-breaks every 20-25 minutes does not depend on >the %CNS. I don't know what is the origin for the procedure. However, we >can read about it in many sources. That procedure is specified in the DCIEM >Diving Manual. I also remember reading about it in AquaCorps (Volume 3, >page 32). > >Michel Therrien >m.therrien@ne*.qc*.ca* > >-- >Send mail for the `techdiver' mailing list to `techdiver@terra.net'. >Send subscription/archive requests to `techdiver-request@terra.net'. > The resetting of the clock in 12 h with a t1/2 of 90 min does not follow, assuming that it takes 6 t1/2 to reach 98+% desaturation, as is the assumption with N2 offgassing. One would expect that a 9 h desaturation would be required to reset with t1/2 = 90. Comments? Esat Atikkan
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