Differences in "quality" of inert gas saturation - He vs. N2

[BRW]

PD,

Just a quicky guideline.

For CCRs it doesn't make a big difference on
heliox vs helitrox at the mass transport limit
points. Beyond 150 fsw, for longer deco
exposures, heliox sails, especially in the
higher ppO2 regime (like .9 atm and above)

So heliox for deep and extended deco, helitrox
for shallow, nominal deco.

And all on RGBM, of course.

Bruce Wienke
Program Manager Computational Physics
C & C Dive Team Ldr

 

[HolgerS]

Thanks Bruce,
that was THE (start) of answer, I hoped to receive

Unfortunately, I need to spend some time for business so I can afford my favority hobby - that means I also need some time to work through your recommended readings.

Could you help us through your published articles/books - you mentioned 5 of them each being of high "value"
# Could you send me by PM the outline of the books
# Are there overlaps in your books/articles
# Which one should I focus on if I am most interested in
- the latest state of the art deco theory (should be practical also, not just formulas (hobby!)
- practical guide for real diving

A very short question in advance: Is it really state-of-the-art to move from high O2 mixes to high H2 mixes. That means Nitrox is "old" for recreational diving, Trimix is old for Texch-divers. The new mixes will be Helitrox for Recs and Heliox for Tecs?

Is this feasible? Are there no compromises - diving must also be afforded by the amateurs?

THANKS for your expert knowledge


HolgerS

 

[Dr Deco]

Dear SCUBA SOURCE Readers:

Recreational Mixes

I would personally believe that air and nitrox would work well for the recreational diver for a long time to come. This is mainly a cost factor.

The dual phase models are very nice “road maps” for deep diving but begin to converge with the Haldane-derived algorithms where recreational scuba is involved. This is because we are in the range where a few microbubbles (nuclei) in the tissue do not make a great deal of problems.

Avoidance of DCS

If one wishes to be able to perform dives safely in the recreational world, I believe the answer lies in nucleation-formation control rather than gas-loading control. That is my personal view, and it involves avoiding those post-dive activities that will lead to nuclei formation, viz, climbing boat ladders with your gear on, lifting heavy gear, running and jumping or playing volleyball, etc. :lifter:

My research experience indicates that it is these activities that will lead to DCS more than simply the nitrogen supersaturation limits. For technical divers, helium is a part of the game.

Dr Deco :doctor:

 

[BRW]

All,

Tec and rec diving come at the question of nitrox vs
helitrox vs heliox from different vantage points, as Dr D
noted in his post. It's economics, not optimality of
mixes. And availability.

But on the optimality side, consider the following.

In the 90 -140 fsw range, helitrox wins especially with
repets. Beyond that, heliox wins especially on RBs for
long(er) exposures. Trimx with high He is great, too, especially
with pure O2 washout in the shallow zones. The latter is
widespread across tec diving from all reports. So is pure
O2 in the shallow zone with deco on just about any mix
or diluent. The above are deco efficient, but maybe more
important is the fact that divers report feeling better after
He rich dives vs N2 rich dives, especially deco repets. And
caes other than single, no-deco penetrations.

TDID and RGBM In Depth have a bunch of A to B comparisons,
if interested.

For recreational diving, because of cost and availability,
air and nitrox will be around for a long time. My choice
for recreational divers is always nitrox if available --
less N2 and more bottom time inside the 130 fsw rec limit.

HolgerS,

Try RGBM In Depth to cover the bases.


Bruce Wienke
Program Manager Computational Physics
C & C Dive Team Ldr

 

[HolgerS]

Thanks Dr. Deco, thanks Bruce!

What I am still interested in - but what you maybe can´t tell us here in the short - what are the implications for me as diver, if I want to optimize
# risk
# bottom time?

When is the break-even in mass transport limit?

I do agree with Dr. Deco who says there are basically two fundamental strategies:
1) nucleation-formation control
2) gas-loading control

I currently dive according rule #1. According rule #2, I make some compromises (Air and Nitrox in "Rec", Tx in Tec.)

How far can I reduce my risk OR lengthen my bottom time if I dive with even higher´He-rates.

Bruce, could you please tell us, what your "standard mixes" are in the depth range 10m (33ft) to 120m (400ft)?

I was trained at my GUE course:
<30m EAN32
30m-45m 21/35
45m-70m 15/60
70m-120m 10/80

A lot of other GUE trained people take:
<30m EAN32
30m-45m 21/35
45m-60m 18/45 !
60m-75m 15/55 !
70m-120m 10/70 !

You see, there are absolute different "standard" mixes out there.

If I understood you correctly, Bruce, your team takes mixes with an N2-narcotic potential of less than 9m-12m (30-40ft). This rule is quite progressive. So I am eager to get to know your mixes...

Thanks a lot & allways SAFE DIVING
HolgerS

 

[HolgerS]

Oh, Bruce, yes, I will invest time in reading your publications. Hopefully, I will understand them

HolgerS

 

[chrisch]

I've read this with interest as I am booked up to do my IANTD Rec Trimix course after Xmas. As the original question was about diving to 45m - this is the area that I intend to use this gas so the responses are very important to me.
Firstly the IANTD course only gives me a EAN50 as deco mix - is it worth doing another course (TDI Adv EAN) to get 100% O2 ??
Second, a lot of the stuff on He I found hard to understand. The basics are easy - less N2 less narcosis. Clearly also He has lower propensity to bubble nuclei formation from what has been said.
So - how much He is required? I have read that 30% He is the point at which there is a "benefit" - is this true or is it about partial pressure rather than the fraction of He?
There is also a widespread view that He is a "moneyspinner" for the diving industry. Personally I do not mind the little extra for some He over Nitrox for the few dives that I do beyond 35m so I disagree.
I am sure Trimix will gain in popularity and I hope to be part of that so I am already "converted", but when other people ask me about it I need a better explanation than Bruce's view it is "God's gas" (what???).

Chris

 

[BRW]

Chrisch,

Try NAUI Tec on your further training -- Nauitec@aol.com.
can refer you to NAUI Tec Instructors in the UK. Dick Lucas
in the Netherlands can also help.

Helium is the mainliner in NAUI Tec training. And deco training
really then starts beyond rec diving and in the 150 fsw range.
And on He based mixes for efficiency, safety, and repet
activity

EAN50/50 doesn't take you past 70 fsw for deco training
if you limit ppO2 to 1.4 atm. That's rec diving to many.

It's of course up to you on Agencies -- just some
background info on NAUI Tec for your digestion.

The advantages of He are as posted. Plus tec divers all
report feeling better on He dives then on dives with
lots of N2 or deep switches to nitrox.

Another good point is that DCS risk goes up with ppN2 --
reported at Wkshps (Repet Wkshp, Reverse Profiles Wkshp).
That's why we keep ppN2 as low as possible -- 40 - 60 fsw
in our mixes when we dive anything with N2

This, plus the earlier posts cover the bases on He.

The way to dial mix is pretty simple for tec/deco diving and
helium.

First dial O2 percentage to depth for desired ppO2 (like
1.4 atm). Then dial N2 (if N2 is in mix) to something below
60 - 80 fsw (and less as exposure time increases),
and the rest with He. Then switch to pure O2 in 20 fsw.
Isobaric switches to lesser He mixes often help, as
can nitrox above 70 fsw. But the switch nitrox mix depends
on the bottom mix and should not have N2 above N2
levels in bottom mix.

TDID has much more on this, plus mix to mix comparisons,
stats, and related info.

Bruce Wienke
Program Manager Computational Physics
C & C Dive Team Ldr