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

[HolgerS]

Dear Scubaboard members,
I have watched the Dr. Deco list for a while and got the impression, that this list is real premium. You can find here superb knowledge and experience mixed with tolerance and discussion culture. Wonderful. Thanks! This encouraged me to sign on the list - and ask, what noone else could answer me so far.

I heard very often, that nitrogen inertgas saturation is much worse than Helium saturation in terms of oversaturation and decompression. GUE actively teaches this aspect and has a well known phrase for that: "Helium is your friend".

Unfortunately, noone could explain this issue to me properly ( I am a scientist, so phrases don´t convince me on the long run).

Yesterday, a friend asked my team for advice:
"I want to dive at a wonderful place at 45m (150ft) depth. To come to this dive site, I need to scooter to this location for about 45min. What is the best choice of gas for this scooter track, if I do that at 10m (or 33ft) depth. I recommended to take EAN50, but the majority of my group would do this with 21/35. The answer was, the "quality" of inertgas saturation is much better with 21/35 due to less "volume/mass/density" of inert gas saturation.

They also argued, that there was an article by - I believe - Brunce Wienke, who explained this issue. Unfortunately, noone has this article.

Could you explain the difference in "quality" of inertgas saturation between nitrogen and helium?

Best regards from Munich

HolgerS

 

[Dr Deco]

Readers:

Could someone help him out? My specialty is the physiological aspects of decompression and decompression sickness. This is a question on gas and dive technique. It is not “my bag.” [It sounds like something for the Tech Forum.]

Dr D.

 

[HolgerS]

Dear Dr. Deco,

thanks for the fast response.
May be there is a misunderstanding. I am interested in the difference in inertgas saturation in phyiological aspects. This is the only root for explanation I desire.

Safe diving
HolgerS

 

[BRW]

Hi HolgerS,

Great question that cuts to the quick, and focuses
on part of the evolution to revolution in diving. Helium mixes
are "your friend" and most tec diving ascribes to such today.

That's WKPP, C & C, NAUI Tec, and countless other ops.

The quick answer is that 21/35 tmix wins.

The details, stats, reasons, field testing, etc can be
found in a number of places, Wkshp proceedings, books.
The physical aspects, relating to gas transfer are detailed.
Also some physiological implications.

The article(s) that you reference by me are:

"Deep Stops And Deep Helium" and also "Deep RGBM"

They will be published in the Proceedings of The Deep Stops
and Modern Deco Strategies Wkshp.

I will be happy to post them here, but if you can't wait,
go to RGBMdiving.com and download them from the"
Tech RGBM subsection (with same names).

If you want a more complete story, check out a few
published books (Best Publishing by me):

"RGBM In Depth", or Technical Diving In Depth", or
"Basic Deco Theory And Application (2nd Edition)"

A long review paper is also being published in J Comp
Physics. And I will alert all.

Here at C & C Dive Ops, we seldom dive N2 mixes,
and we keep ppN2 at the absolute lowest minimum
possible (30 - 40 fsw narcotic potency maybe). So
does WKPP, NAUI Tec, and bunches of other groups
and individuals. And He is God's gas.

Physical/physiological factors making He better than N2 include,
He ingasses and offgases faster once you get pass mass
transport limits, has a greater MBD (minimum bends depth),
is just as deco fast when taken to the surface to pure O2
in the shallow zone (vs isobaric switches to nitrox), and
generally supports better diver vitality and health after
the dive (from all reports).

Also, He solubility in biomass is less than N2, so, consequently,
bubbles and micronuclei are hypothetically smaller, grow slower,
and can be washed out faster. Experiements in lab
substrates confirm such, with smaller but more numerous
He bubs vs N2 bubs. Cumulative bubble volumes have been
very close, though. In biomass, nothing has been done. Yet.

And it's taken a long time for this to happen. Just
like dual phase models.

Regards, and great He diving,

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

 

[100days-a-year]

There seems to be ample evidence that nitrogen and 02 both have negative affects on the body in increased PPs and hence are reactive gasses not inert.He does not have as many effects in the depths above 500'.HPNS is really the only thing I could find mention other than the gas loading aspect.N2 has a greater narcotic potential but I haven't found much else.02 has an effect on the pulmonary system,the blood,the CNS,vision and due to its effects on blood and the circulatory system has been implicated in bone damage.I used to believe that 02 was my friend,N2 was a pest and He was "as needed"I am rethinking this in spite of deco models that support this line of reasoning by not penalizing hi-02s or even moderately hi N2s.

 

[BRW]

Yo HolgerS,

Wanted to also note modern dual models,
with distinctions between He and N2, support
He, and show little advantages to N2 - -at
any ppN2s and for exposure times beyond the
mass transport limits (where He NDLs overtake
N2 NDLs).

Earlier Stuff

Great question that cuts to the quick, and focuses
on part of the evolution to revolution in diving. Helium mixes
are "your friend" and most tec diving ascribes to such today.



The quick answer is that 21/35 tmix wins.

The details, stats, reasons, field testing, etc can be
found in a number of places, Wkshp proceedings, books.
The physical aspects, relating to gas transfer are detailed.
Also some physiological implications.

The article(s) that you reference by me are:

"Deep Stops And Deep Helium" and also "Deep RGBM"

They will be published in the Proceedings of The Deep Stops
and Modern Deco Strategies Wkshp.

I will be happy to post them here, but if you can't wait,
go to RGBMdiving.com and download them from the"
Tech RGBM subsection (with same names).

If you want a more complete story, check out a few
published books (Best Publishing by me):

"RGBM In Depth", or Technical Diving In Depth", or
"Basic Deco Theory And Application (2nd Edition)"

A long review paper is also being published in J Comp
Physics. And I will alert all.

Here at C & C Dive Ops, we seldom dive N2 mixes,
and we keep ppN2 at the absolute lowest minimum
possible (30 - 40 fsw narcotic potency maybe). So
does WKPP, NAUI Tec, and bunches of other groups
and individuals. And He is God's gas.

Physical/physiological factors making He better than N2 include,
He ingasses and offgases faster once you get pass mass
transport limits, has a greater MBD (minimum bends depth),
is just as deco fast when taken to the surface to pure O2
in the shallow zone (vs isobaric switches to nitrox), and
generally supports better diver vitality and health after
the dive (from all reports).

Also, He solubility in biomass is less than N2, so, consequently,
bubbles and micronuclei are hypothetically smaller, grow slower,
and can be washed out faster. Experiements in lab
substrates confirm such, with smaller but more numerous
He bubs vs N2 bubs. Cumulative bubble volumes have been
very close, though. In biomass, nothing has been done. Yet.

 

[flw]

100days-a-year once bubbled...
I used to believe that 02 was my friend,N2 was a pest and He was "as needed"I am rethinking this in spite of deco models that support this line of reasoning by not penalizing hi-02s or even moderately hi N2s.

I used to be the same, however, partly due to switching over to a ccr, so it is feasible, I like most others I know now use 10/50 diluents for all dives down to 80ishm regardless of how shallow they are, and then stay on the same diluent from surface back up to 6m. It's subjective, but I do notice how much better I feel afterwards - on occasion I've done drills bailing out to a 50% on ascent, and its yucky ( technical term) in comparison.
I've recently been playing around with 16/70 as a diluent, and like that better, though its not as convenient to blend quickly
F

 

[Charlie99]

BRW once bubbled...
Yo HolgerS,

Wanted to also note modern dual models,
with distinctions between He and N2, support
He, and show little advantages to N2 - -at
any ppN2s and for exposure times beyond the
mass transport limits (where He NDLs overtake
N2 NDLs).

Please explain the phrase "mass transport limits" a bit.

I'm interested in the relative desireability of He in the gray zone between rec and tech ---- 100-140', with bottom times within or just a bit beyond NDLs.

TIA,

Charlie Allen

 

[BRW]

Yo Charlie,

Real pertinent question for mixed gas divers.

Mass transport of inert gases into biomass
depends on the product of gas solubility times
diffusivity. Helium has faster diffusivity,
and N2 has higher solubility relative to each
other (like 1/2.8 and 4.2 roughly). For short,
shallow exposures, the slower diffusivity
of N2 results in less total gas buildup in bulk
tissue, and hence shorter NDLs than He. For
longer and deeper exposures, He wins because
of its lower solubility. The point where
He and N2 NDLs meet, or cross over, is called
the "mass transport boundary".

This limit point changes with depth, exposure
time, and mix. See the NAUI Trimix Manual
for nitty gritty guidelines we pass onto
students. To quantify this exactly, you would
need RGBM (code) to delineate comparisons.
And it show up easily doing A mix to B mix
comparisons.

But I can pass this onto you because we have
tested it, constructed Tables, and used it
advantageously on C & C, and at NAUI Tec for
training beaucoup tec divers and instructors.
And the statements are general too here.

In the region 100 -140 fsw, and beyond air
NDLs, the use of HELITROX (enriched heliair)
is really advantageous from the point of view
of staging, repets, and hang time. In that
regime, you are past the mass transport limit
point for N2, and optimizing deco with He.
Everybody, especially on repets, feels better
on helitrox than nitrox. And nitrox loses
on other counts too.

See TDID, RGGM In Depth, and/or Basic Deco
And Apps for comparisons, data, etc. Plus
global reports from He divers on RGBM

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

 

[pipedope]

Is it better to have both He and N2 in the mix over He and O2 only?

I am not considering cost in this question as I am thinking in terms of CCR. Is HeO2 or HeliAir better as diluent?

thanks