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A lot of times, the diver feels the "impending doom" ( which is merely depleted brain chemisty) or just feels shitty, and goes off the oxygen only to tox. Otherwise, you need about ten minutes of a real low ppo2 before taking the risk of getting into the water from a dry space having been on oxyygen or any high PPO2. I addition if it is in the water deco ( or out ) you are also implying that the breaks are done properly anyway. When you are at or above 2.0 ( dry ), the uncertainty of the limits makes the big break mandatory. Where you really start looking for a problem is in the multiday exposures. This is why commercial lowers the ppo2's way below what recreational thinks is ok, and never spikes the PPO2 even a tiny bit. For instance, if you are working on a platform for hours and are running a resaonably high PPO2, but then just drop ten feet, that is enough to tox an overexposed diver. Translate that into recreational and what you have is the mutilday nitrox or deco diver who thinks he needs to juice his ppo2 for deco weenery prurposes, and dies. Kevin Connell wrote: > > Roger that, so it may just be "imminent" even though you've switched to low > po2 a few minutes before. > > At 04:03 PM 2/21/2000 -0500, trey@ne*.co* wrote: > >No, it does not - the reaction can take place quite some time after you > >are off the oxygen. This is whey we require a ten minute break in the > >troughs before entering the water after a long oxygen deco. > > > >That "off opxygen " crap was made up by the 80/20 strokes, like a PPO2 > >is not a PPO2. > > > >Kevin Connell wrote: > > > > > > Scott, can you (or anyone else) elaborate a bit on this. JJ discussed this > > > during tech3, about how studies showed that a *large* percentage of the > > > seizures (and maybe just symptoms too..) occurred after the switch to low > > > po2, in other words, it was the switch that precipitated the cns problem. > > > > > > At 07:36 PM 2/19/2000 -0600, Scott Hunsucker wrote: > > > >Hello, > > > > > > > >The infamous offgas effect. High PO2s cause biochemical changes in the > > > >Central Nervous System that may linger after the high PO2 has > > > >subsided. This may cause a seizure a few minutes after the diver has > > > >stopped breathing the hyperoxic mix. This is more likely to occur if the > > > >diver had experienced one of the "milder" symptoms of toxicity; however, > > > >toxicity can occur with no symptoms, so a watchful eye must still be > > > >employed. This possibility is greatly diminished after several minutes. > > > >How to avoid: Be extremely careful, avoid high PO2s. Very little is > > > >known about this. > > > > > > ---------------------------------- > > > Kevin Connell <kevin@nw*.co*> > > > > > > NW Labor Systems, Inc > > > http://www.nwls.com > > > > > > Res tantum valet quantum vendi potest. > > > > > > ---------------------------------- > > > > > > -- > > > Send mail for the `techdiver' mailing list to `techdiver@aq*.co*'. > > > Send subscribe/unsubscribe requests to `techdiver-request@aq*.co*'. > > ---------------------------------- > Kevin Connell <kevin@nw*.co*> > > NW Labor Systems, Inc > http://www.nwls.com > > Res tantum valet quantum vendi potest. > > ----------------------------------
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