In message <Pine.SOL.3.92.960610173344.17771A-100000@hs*.us*.ed*>,
"Peter N.R. Heseltine" <heseltin@hs*.us*.ed*> writes

Peter
>
>Bret says:
>
>"If you don't like the exposures that I have detailed, I suggest you take
>your case to the US Navy and NOAA from which my notes were derived. Oxygen
>exposures are "dose" related, not simply partial pressure, as anyone with
>a shred of experience understands. And you can exceed a dose limit at 1.3
>ATA just as easily as you can at 1.6 or any other setting you might
>choose."
>
>By this, and our telephone conversation, I infer that he means dose *and
>time*. i.e., that a certain minimum time at the dose must pass (e.g., 45
>mins at 1.6 ATA for a single exposure) in order for toxicity to occur. Are
>you concerned that O2 "hits" are possible in persons who have not exceeded
>their CNS clock at pO2s between 1.3 and 1.6 ATA?

In essence what he says is correct, I.e the possibility of a CNS hit is
a funtion of partial pressure and exposure time.As to wether there
should be concern regarding the liklehood of a hit for persons inside
the clock is a mute point. I, personally do not, if I did I would have
stopped this thing before I started. There are other pre-disposing
factors that will influence the likelehood, as I am sure you are aware.
If you need some data on subjective testing you should try and read
'Oxygen and the Diver' by Kenneth Donald - ISBN 1-85421-176-5.

>
>Bret also says:
>
>"The flow rates on the (Atlantis I) mechanical injection of nitrox gas
>considerably exceed any conceivable metabolic consumption of even the most
>conditioned high performance athlete."

Brave words!.

>
>The manual (Joe Odom, 1995, rev 1, 3/96) used by TDI in training/
>certifying divers for the Atlantis I indicates that the currently
>available 7.6 L/min constant mass flow valve using (recommended) EAN50 on
>the unit delivers an FiO2 of 32% at a VO2 of 2.0 L/min and an FiO2 of 35%
>at a VO2 of 1.75 L/min, using the standard equation.

Interesting! - I have the Draeger manual, which quotes 7.2 L/min.

Drager quote an FiO2 of 34.7% for a VO2 of 1.5 litre/min. Some
discrepancies I suggest!!!!!!. Perhaps the equation TDI are using is not
so 'standard'.?

>
>But, as noted in a previous post by Bernie Woolfrey:
>
>"Diving and Subaquatic Medicine", quotes O2 metabolic rates (VO2)
>as ranging from between 0.8 L/min to over 3 L/min, with rates of over
>2 L/min "quite common" (these are based on swimming tests, breathing O/C air).
>        The book goes on to say that:
>        Typical gas consumption rates for a "slow swim" 0.5kt, a diver
>would be breathing about 20 L/min of air, with an O2 consumption of
>about 0.8 L/min, and
>
>  0.8 Knots     =       30 L/min air breathed =  1.4 L/min O2 consumed
>  1.2 Knots     =       50 L/min air breathed =  3 L/min O2 consumed.
>
>This is an FiO2 of 17% at 3 L/min and an FiO2 of 13.6% at 3.2 L/min. Do
>you consider that VO2s in this latter range and higher are likely to be
>reached by a high performance athlete?

Draeger state that : - 'The equipment was designed for maximal use of
2.5 L/min of oxygen.If the diver consistently uses 2.5 L/min of oxygen
then the oxygen level being circulated will be at a minimum of 17% by
volume.'

Hope this is of some use

Regards

Chris
Chris Hellas

e-mail:- chris@de*.de*.co*.uk*
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