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Carl Heinzl wrote:
>
> The different deco models alone could easily account for *any*
> differences, but, ok, this is the type of information that I
> wanted to hear about. Can you site the source of your data?
>
My data source was simple observation on two different occassions on a dive
boat. Explanation: A friend owns/operates a high-tech diving supply business
that markets a popular brand of doppler bubble detector. Last year he began
using the detector to validate the tables he generates. Of course, everybody
else on the boat wanted to be "dopplered" too. The two occassions I mentioned
involved air divers flying their computers and decompressing on EAN50. They
had some bubbling - nothing severe, but they didn't come up "clean".
POINT: I began to wonder about the supposedly comparable decompression
efficiency of EAN50 after two divers showed minor bubbling following
a single 20 minute air dive to 180 FSW using reasonable decompression
tools (monitor2, I think) and EAN50 for added decompression efficiency.
FURTHER:
Would the bubbling have been more severe if these divers had chosen an
accelerated schedule rather than the air schedule on their D/Cs?
DISCLAIMER:
This is just incidental data - nothing official or even controlled.
All I can say is that it made an impression on me.
> ... one of their points was that by decompressing on 50% O2, you get many of
> the benefits of decompressing on pure O2 (i.e. deco times were pretty close)
> with a gas that you can use as deep as 70' and none of the hassles and/or
> dangers involved ...
>
I agree with most of what you're saying, but I see now that we're making
different points:
I believe you are trying to point out that with EAN50 you can get off your
bottom gas sooner, and keep PO2's lower during decompression, which should
translate to greater decompression safety, and similar efficiency. Both are
good points.
My issue is with the phrase "none of the hassles and/or dangers involved".
You can seize/drown on air, EAN50, or O2 - they're all equally dangerous.
Divers have seized on high FO2 gasses outside their MOD after inadvertently
switching to them at depth. Divers have died on air and high FO2 gasses
WITHIN their MOD on repetitve dives because they exceeded the recommended
oxygen limits OR had unanticipated/unplanned risk factors, such as stress,
exertion, hypothermia, etc.
We can probably agree that in some ways EAN50 may be SAFER than O2, but
both gases still have significant use hazards.
> Granted OTUs must be accounted for and MOD is an issue, *but*
> MOD is, like most things we deal with, not some magical line
> that you cross over and *wham* you're toast.
>
Divers are *usually* more concerned with their CNS O2 clocks, rather than
the pulmonary O2 clock. Also, on *long* O2 decompression (1.5 hours or more)
it's possible that drifting down below 20 FSW for only a few seconds can
produce symptoms of oxtox. Air breaks can reduce this risk somewhat, but a
1.5 hour or longer O2 decompression pulled completely at 20 FSW is a hazardous
undertaking.
> Also, in an *extreme* emergency, I'd rather have to take a couple
> of hits of EAN50 at depth than pure O2...
>
Me too - especially if it meant the difference between getting to my next
stop or bottle of gas or not getting their.
regards,
GregD
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