BRW
Contributor
Somebody out there asked about optimal gas switching
strategies, but had some misconceptions about dissolved
gas transfer. At any rate, the simple answer these days
to the former is solid, tested, validated, recorded data, and
backed up by real diving, in the real world. And phase models
(RGBM) concur on first principles (which is very nice too):
1) dive helium based mixes for deco, extended range,
deep, and tech diving. Avoid air and nitrogen rich
mixes. Tech divers also report "feeling" better on
same upon surfacing -- a qualitative statement of
course, but one made around the world
2) adjust mix for something like 1.4 atm ppO2 at
bottom, and nitrogen (if using trimix) to a narcotic
depth of something like 100 fsw, and the rest helium.
3) ride helium rich botom mix, or deco mix, to 20 fsw
and switch pure O2, OR
4) make isobaric switch to EAN50 at 70 fsw, and
then switch to pure O2 at 20 fsw
Riding a helium rich mix to 20 fsw and switching to
pure O2 only incurs a few more minutes deco penalty
time over an isobaric switch to EAN50 at 70 fsw. In fact,
by progressively decreasing He and increasing O2, in same
proportion, while keeping N2 constant (if there is N2), differences
are kept really minimal.
You will not see this unless you invoke deep stops
(ad hoc or model-wise), use helium rich bottom mixes,
and modern deco theory -- not Haldane stuff (USN, ZHL,
DCIEM, M-values, etc) which doesn't work.
In other words, this is real world skinny, not theory
nor field testing alone. Data for this is recorded, and will
be made available at the RGBM Data Bank (RGBMdiving.com).
See TDID, RGBM In Depth (book coming out), NAUI Deep Stops
And Modern Deco Strategies Wkshp Proceed (when available),
RGBMdiving.com for more of same.
Best to all,
Bruce Wienke
Program Manager Computational Physics
C&C Dive Team Ldr
strategies, but had some misconceptions about dissolved
gas transfer. At any rate, the simple answer these days
to the former is solid, tested, validated, recorded data, and
backed up by real diving, in the real world. And phase models
(RGBM) concur on first principles (which is very nice too):
1) dive helium based mixes for deco, extended range,
deep, and tech diving. Avoid air and nitrogen rich
mixes. Tech divers also report "feeling" better on
same upon surfacing -- a qualitative statement of
course, but one made around the world
2) adjust mix for something like 1.4 atm ppO2 at
bottom, and nitrogen (if using trimix) to a narcotic
depth of something like 100 fsw, and the rest helium.
3) ride helium rich botom mix, or deco mix, to 20 fsw
and switch pure O2, OR
4) make isobaric switch to EAN50 at 70 fsw, and
then switch to pure O2 at 20 fsw
Riding a helium rich mix to 20 fsw and switching to
pure O2 only incurs a few more minutes deco penalty
time over an isobaric switch to EAN50 at 70 fsw. In fact,
by progressively decreasing He and increasing O2, in same
proportion, while keeping N2 constant (if there is N2), differences
are kept really minimal.
You will not see this unless you invoke deep stops
(ad hoc or model-wise), use helium rich bottom mixes,
and modern deco theory -- not Haldane stuff (USN, ZHL,
DCIEM, M-values, etc) which doesn't work.
In other words, this is real world skinny, not theory
nor field testing alone. Data for this is recorded, and will
be made available at the RGBM Data Bank (RGBMdiving.com).
See TDID, RGBM In Depth (book coming out), NAUI Deep Stops
And Modern Deco Strategies Wkshp Proceed (when available),
RGBMdiving.com for more of same.
Best to all,
Bruce Wienke
Program Manager Computational Physics
C&C Dive Team Ldr
