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No delta, it is either an absolute , like hitting the wrong gas, or a =
function of total exposure relative to the spike max. Repeated daily =
exposures or one long exposure have to be treated more carefully, but we =
never go over a 1.6 and even consider that way excessive deep, until we =
are either shallow or dry, and in general, we see the 1.4 range as =
safer. IE, at a 240 or 190 stop we are not 1.6 at all with the gas we =
use, more like <1.4, and we do not hit a 1.6 until 120 feet, but at that =
point may opt to move the bottle higher on a tough or mulitday exposure. =
Keep in mind we are also breaking to back gas every 209 form the =
beginning and generally go a big "clean up" break before we go to 50% or =
100%.
This is not an exact science, but dying is s permanent. We do not press =
the oxygen to beat deco weenery. Short exposures and single day diving =
allow for less concern over the s[pike issue, unless you have been =
exerting, ho have a co2 buildup, you have a headache, or you have any =
other physical stresses involved, in which case you get real =
conservative real fast.
-----Original Message-----
From: Marc Thompson <mbt@ti*.co*>
To: David Chamberlin <dwc@na*.co*>; Trey <trey@ne*.co*>
Cc: Tech Diver <techdiver@aquanaut.com>
Date: Friday, June 23, 2000 12:42 AM
Subject: PO2 spike limits (wasRe: Deco gas selection)
=20
=20
Have the WKPP or, anyone else for that matter, developed an =
acceptable or maximum delta in PO2 during a gas switch. As I understand =
it, many ox-tox incidents occur because of the momentary "spike" in PO2. =
Scott Hunsaker has addressed this to some degree but has not mentioned =
any numbers regarding an acceptable delta in PO2 or the relation to time =
and this sudden elivation in PO2.
----- Original Message -----=20
From: David Chamberlin=20
To: Trey=20
Cc: Tech Diver=20
Sent: Sunday, June 11, 2000 8:36 PM
Subject: Re: Deco gas selection
=20
=20
Trey wrote:
>=20
> What the fuck are you talking about? I never use trimix above =
21% Oxygen
> below 120 feet. It is stupid.
=20
That's what I would've thought, and that's why I asked the =
question.=20
The person who responded in private e-mail was someone I thought =
was
very knowledgeable about DIR SOP, so I wanted to go straight to =
the DIR
source and find out 1) if that was in fact the recommended gas =
and 2)
Why that would be selected. =20
=20
> The use of ONE gas for deco imples 50% - we
> have been over this,
=20
Sorry. I tried doing a search for this topic and the only =
responses I
came up with were the ones I posted earlier which didn't really =
cover
the "why's" of the choice of 50/50. So I was attempting to get =
more
information and clarification. As I said in my earlier post, =
I'm not
doubting what you are saying is correct - I just want to =
understand it
better. =20
=20
> Everyone else has been over
> this. Wake up.
=20
I'm sorry. As I said before, I tried to find earlier posts on =
this and
I only got some scattershot and very brief messages, which is =
why I
posted the question. So let me try an abbreviated form of my =
question.=20
I'm going to state what I think the rationale is for using 50/50 =
for a
one gas dive to depths <=3D50m with times <=3D30 min, in spite =
of what seems
to be contradictory information from the Baker's Dozen.
=20
1) The 50/50 let's you open your oxygen window earlier and thus =
you
clear out most of your deco earlier, so you don't have to do so =
much
"damage repair" at the shallower stops.
=20
2) The benefit of clearing out your deco earlier outweighs the =
fact that
deco on 50/50 will not be as beneficial at the shallower stops. =
And
since you cleared out most of your deco early, you don't need to =
be as
efficient at the shallower stops.
=20
3) The Baker's Dozen is comparing 80/20 at a depth of 30FSW, to =
100% at
a depth of 20FSW. The difference in depth between these two is =
not
significant enough to apply the reasoning of 1) and 2) to 80/20, =
and
thus 80/20 pretty much has all the downsides and none of the =
upsides.
=20
And finally, I'd like to reiterate one of my questions in my =
previous
post. You had said, "Most of my ocean dives are one gas dives - =
I do
not generally see the need for the oxygen at all on a short hop =
first
dive, and prefer not to take the
beating of using it for not reason." What is the beating you =
are
referring to? Have you found that these types of short =
exposures to
high (1.6) PO2s actually have longer-term effects? =20
=20
Thanks,
Dave
--
Send mail for the `techdiver' mailing list to =
`techdiver@aquanaut.com'.
Send subscribe/unsubscribe requests to =
`techdiver-request@aquanaut.com'.
--
Send mail for the `techdiver' mailing list to =
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Send subscribe/unsubscribe requests to =
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<DIV><FONT color=3D#000000 size=3D2>No delta, it is either an absolute , =
like=20
hitting the wrong gas, or a function of total exposure relative to the =
spike=20
max. Repeated daily exposures or one long exposure have to be treated =
more=20
carefully, but we never go over a 1.6 and even consider that way =
excessive deep,=20
until we are either shallow or dry, and in general, we see the 1.4 range =
as=20
safer. IE, at a 240 or 190 stop we are not 1.6 at all with the gas we =
use, more=20
like <1.4, and we do not hit a 1.6 until 120 feet, but at that point =
may opt=20
to move the bottle higher on a tough or mulitday exposure. Keep in mind =
we are=20
also breaking to back gas every 209 form the beginning and generally go =
a big=20
"clean up" break before we go to 50% or 100%.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>This is not an exact science, but dying is s =
permanent. We do=20
not press the oxygen to beat deco weenery. Short exposures and single =
day diving=20
allow for less concern over the s[pike issue, unless you have been =
exerting, ho=20
have a co2 buildup, you have a headache, or you have any other physical =
stresses=20
involved, in which case you get real conservative real =
fast.</FONT></DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 solid 2px; MARGIN-LEFT: 5px; PADDING-LEFT: =
5px">
<DIV><FONT face=3DArial size=3D2><B>-----Original =
Message-----</B><BR><B>From:=20
</B>Marc Thompson <<A=20
href=3D"mailto:mbt@ti*.co*">mbt@ticnet.com</A>><BR><B>To: =
</B>David=20
Chamberlin <<A =
href=3D"mailto:dwc@na*.co*">dwc@nautiboy.com</A>>;=20
Trey <<A =
href=3D"mailto:trey@ne*.co*">trey@netdor.com</A>><BR><B>Cc:=20
</B>Tech Diver <<A=20
=
href=3D"mailto:techdiver@aquanaut.com">techdiver@aquanaut.com</A>><BR>=
<B>Date:=20
</B>Friday, June 23, 2000 12:42 AM<BR><B>Subject: </B>PO2 spike
=
limits=20
(wasRe: Deco gas selection)<BR><BR></DIV></FONT>
<DIV><FONT face=3DArial size=3D2>Have the WKPP or, anyone else for =
that matter,=20
developed an acceptable or maximum delta in PO2 during a gas switch. =
As I=20
understand it, many ox-tox incidents occur because of the momentary=20
"spike" in PO2. Scott Hunsaker has addressed this to some =
degree=20
but has not mentioned any numbers regarding an acceptable =
delta in PO2=20
or the relation to time and this sudden elivation in =
PO2.</FONT></DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 solid 2px; MARGIN-LEFT: 5px; =
MARGIN-RIGHT: 0px; PADDING-LEFT: 5px; PADDING-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- =
</DIV>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A href=3D"mailto:dwc@na*.co*" =
title=3Ddwc@na*.co*>David=20
Chamberlin</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A=20
href=3D"mailto:trey@ne*.co*" title=3Dtrey@ne*.co*>Trey</A> =
</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Cc:</B> <A=20
href=3D"mailto:techdiver@aquanaut.com" =
title=3Dtechdiver@aquanaut.com>Tech=20
Diver</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Sunday, June 11, =
2000 8:36=20
PM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> Re: Deco gas=20
selection</DIV>
<DIV><BR></DIV>Trey wrote:<BR>> <BR>> What the
fuck are =
you=20
talking about? I never use trimix above 21% Oxygen<BR>> below =
120=20
feet. It is stupid.<BR><BR>That's what I would've thought, and =
that's=20
why I asked the question. <BR>The person who responded in =
private e-mail=20
was someone I thought was<BR>very knowledgeable about DIR SOP, =
so I=20
wanted to go straight to the DIR<BR>source and find out 1) if =
that was=20
in fact the recommended gas and 2)<BR>Why that would be =
selected. =20
<BR><BR>> The use of ONE gas for deco imples 50% -
we<BR>> =
have=20
been over this,<BR><BR>Sorry. I tried doing a search for =
this=20
topic and the only responses I<BR>came up with were the ones I =
posted=20
earlier which didn't really cover<BR>the "why's" of =
the choice=20
of 50/50. So I was attempting to get more<BR>information =
and=20
clarification. As I said in my earlier post, I'm =
not<BR>doubting=20
what you are saying is correct - I just want to understand=20
it<BR>better. <BR><BR>> Everyone else has been =
over<BR>>=20
this. Wake up.<BR><BR>I'm sorry. As I said before, I tried =
to find=20
earlier posts on this and<BR>I only got some scattershot and =
very brief=20
messages, which is why I<BR>posted the question. So let me =
try an=20
abbreviated form of my question. <BR>I'm going to state what I =
think the=20
rationale is for using 50/50 for a<BR>one gas dive to depths =
<=3D50m=20
with times <=3D30 min, in spite of what seems<BR>to be =
contradictory=20
information from the Baker's Dozen.<BR><BR>1) The 50/50 let's =
you open=20
your oxygen window earlier and thus you<BR>clear out most of =
your deco=20
earlier, so you don't have to do so much<BR>"damage =
repair" at=20
the shallower stops.<BR><BR>2) The benefit of clearing out your =
deco=20
earlier outweighs the fact that<BR>deco on 50/50 will not be as=20
beneficial at the shallower stops. And<BR>since you =
cleared out=20
most of your deco early, you don't need to be as<BR>efficient at =
the=20
shallower stops.<BR><BR>3) The Baker's Dozen is comparing 80/20 =
at a=20
depth of 30FSW, to 100% at<BR>a depth of 20FSW. The difference =
in depth=20
between these two is not<BR>significant enough to apply the =
reasoning of=20
1) and 2) to 80/20, and<BR>thus 80/20 pretty much has all the =
downsides=20
and none of the upsides.<BR><BR>And finally, I'd like to =
reiterate one=20
of my questions in my previous<BR>post. You had said, =
"Most=20
of my ocean dives are one gas dives - I do<BR>not generally see =
the need=20
for the oxygen at all on a short hop first<BR>dive, and prefer =
not to=20
take the<BR>beating of using it for not reason." What =
is the=20
beating you are<BR>referring to? Have you found that these =
types=20
of short exposures to<BR>high (1.6) PO2s actually have =
longer-term=20
effects? <BR><BR>Thanks,<BR>Dave<BR>--<BR>Send
mail for =
the=20
`techdiver' mailing list to `<A=20
=
href=3D"mailto:techdiver@aquanaut.com'">techdiver@aquanaut.com'</A>.<BR>S=
end=20
subscribe/unsubscribe requests to `<A=20
=
href=3D"mailto:techdiver-request@aquanaut.com'">techdiver-request@aquanau=
t.com'</A>.<BR>--<BR>Send=20
mail for the `techdiver' mailing list to `<A=20
=
href=3D"mailto:techdiver@aquanaut.com'">techdiver@aquanaut.com'</A>.<BR>S=
end=20
subscribe/unsubscribe requests to `<A=20
=
href=3D"mailto:techdiver-request@aquanaut.com'">techdiver-request@aquanau=
t.com'</A>.<BR></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>
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