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Date: Sat, 11 Nov 2000 11:01:19 -0500
From: Wendell Grogan <wgrogan@dc*.ne*>=08
Subject: nitrogen elimination and oxygen
To pick up on an old thread I have been pondering-
Specifically, in a typical wreck dive, carrying slightly hypoxic bottom
mix (i.e.. in the 16% range), is there a way to predict, if you use your
bottom mix for air breaks, what the optimal length of the air break
should be?
Is the length of time on back gas based on how long it takes for the
vasoconstriction induced by the pure O2 to clear?
If so, is there a way of predicting how long that takes based on the
ppO2 or %O2?
Or is it just empiric based on personal experience with different mixes?
Thanks
Wendell G
--
It turns out, WG, that the 12 and 6 numbers correspond best to
the onset and clearing, but we concurrently arrived at those numbers
by experimentation. Since we are not at 1.6 for very long at other than=20
the 20 foot steps, the breaks below that are not as close together, and
converge on 12-6 only at that point.=20
=20
Our considerations for breaking deeper steps with lower =
overall ppo2's
was directed more out of concern for CNS tox than for decompression
reasons, and secondarily for obvious pulmonary reasons, which then=20
drove the 12-6 numbers as well. Results then alerted us to the efficacy
of this approach and we looked more closely into "why", and arrived at
the conclusions you stated.
=20
For deeper steps the stretch is longer , converging on 20-4
with what we call a 20 minute "clean up" break at about 50 feet on long=20
dives ( which conveniently coincides with switching from rebreathers to
open circuit ) and as always, we use our judgment to call breaks on=20
short dives, with the pulmonary consequences usually being the driver in =
those cases, i.e., if the whole deco is 20 minutes, no need to go off =
the
deco gas.
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<DIV><FONT size=3D4><B>Date:</B> Sat, 11 Nov 2000 11:01:19 =
-0500<BR><B>From:</B>=20
Wendell Grogan <A=20
href=3D"mailto:wgrogan@dc*.ne*"><wgrogan@dca.net>=08</A><BR><B>Su
bj=
ect:</B>=20
nitrogen elimination and oxygen</DIV><BR><PRE>To pick up on an old =
thread I have been pondering-
Specifically, in a typical wreck dive, carrying slightly hypoxic bottom
mix (i.e.. in the 16% range), is there a way to predict, if you use your
bottom mix for air breaks, what the optimal length of the air break
should be?
Is the length of time on back gas based on how long it takes for the
vasoconstriction induced by the pure O2 to clear?
If so, is there a way of predicting how long that takes based on the
ppO2 or %O2?
Or is it just empiric based on personal experience with different mixes?
Thanks
Wendell G
--
It turns out, WG, that the 12 and 6 numbers correspond best =
to</PRE><PRE>the onset and clearing, but we concurrently arrived at =
those numbers</PRE><PRE>by experimentation. Since we are not at 1.6 for =
very long at other than </PRE><PRE>the 20 foot steps, the breaks below =
that are not as close together, and</PRE><PRE>converge on 12-6 only at =
that point. </PRE><PRE> </PRE><PRE> Our
considerations for =
breaking deeper steps with lower overall ppo2's</PRE><PRE>was directed =
more out of concern for CNS tox than for =
decompression</PRE><PRE>reasons, and secondarily for obvious pulmonary =
reasons, which then </PRE><PRE>drove the 12-6 numbers as well. Results =
then alerted us to the efficacy</PRE><PRE>of this approach and we looked =
more closely into "why", and arrived at</PRE><PRE>the conclusions you =
stated.</PRE><PRE> </PRE><PRE> For deeper steps the =
stretch is longer , converging on 20-4</PRE><PRE>with what we call a 20 =
minute "clean up" break at about 50 feet on long </PRE><PRE>dives ( =
which conveniently coincides with switching from rebreathers =
to</PRE><PRE>open circuit ) and as always, we use our judgment to call =
breaks on </PRE><PRE>short dives, with the pulmonary consequences =
usually being the driver in </PRE><PRE>those cases, i.e., if the whole =
deco is 20 minutes, no need to go off the</PRE><PRE>deco =
gas.</PRE></FONT></BODY></HTML>
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