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Hi Sean, Interesting observation. This is another subject about which I can really talk with no authority. I was under the impression however, that one of the reasons that higher PP(O2)'s could be commonly used chambers was that an oxygen convulsion was not nearly as serious in a chamber as it would be in the water. Take care and dive safe, Scott In a message dated 8/21/00 9:40:46 PM, ststev@un*.co* writes: << Scott, I think you need to consider a fundamental issue with oxygen exposure. The NOAA "limits" are for a diver in the water, with a pressure differential across the lungs. Toxicity tolerances are much greater for a person in a gas space, with equal ambient pressure at all points. This is why you can tolerate PPO2's above 2.0 in a chamber, but on average, only 1.6 in the water. As I understand it, the relationship to the CNS "clock" is similar. Once I'm out of the water, I stop worrying about it. I don't breathe O2 on the way to my car, but that is only because I don't need spectators thinking I am dying or something. Whatever turns your crank. Pulmonary tox, on the other hand, would be an issue here if you were talking about that sort of exposure, but as you pointed out, we don't. -Sean On Sun, 20 Aug 2000 20:23:36 EDT, ScottBonis@ao*.co* wrote: >Hi Brock, > >You ask ... ><< A couple of my favorite sites (Oronogo, Lake Elmer Thomas) and some I've >yet >to visit (Cannonball Springs, Ribidoux Springs) require a hefty walk/climb >to a parking lot- easily 300 ft on a steep incline with no shade. I've >adopted Scott's recommendations and they seem to help. Over a >multi day visit (I've some training coming up)- do I place myself at some >danger doing this? >> > >From what I understand, in most cases I see no real problem with breathing >oxygen or a high oxygen mix on the surface if it makes you feel better. The >max PP(O2) you'll get is 1.0 ATA from the pure oxygen and 0.5 ATA from EAN >50. So you use up the oxygen clock at around 0.3 %/min. at 1.0 ATA and 0.1 >%/min. at 0.5 ATA. So if it takes you 30 minutes to get your stuff to the >car, you have added around an extra 10% to the CNS oxygen clock by breathing >pure oxygen and around 3% for EAN50. You need to decide if that's important. > >By the way, the previous numbers are based on the NOAA limit of 5 hours >allowed for the CNS oxygen clock for a PP(O2) of 1.0 ATA. But have you ever >been in the burn ward of a hospital? You may see people in oxygen tents >breathing pure oxygen for two weeks in a row. You make up your own mind on >the level of conservatism that you want to accept. > >Pulminary oxygen toxicity almost never comes into play for the type of diving >you're doing. > >And always remember, that the advice you recieve from me is worth what you're >paying for it. > >Take care and dive safe, Scott -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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