Helium the Perfect Diver's Gas

[DCBC]

I'm curious...have you ever experienced HPNS yourself or witnessed someone else deal with it?

Yes, I've experienced HPNS and have seen others with it. But this is the exception rather than the rule. For me it has just been minor hand tremors which were a result of the descent rate being too fast (for me, at that time). It's really dependent upon the individual and this varies from one dive to another. Slow acclimatization is a big factor.

If HPNS symptoms are observed or reported operationally, the descent is stopped. If the problem persisted the dive would be scrubbed. It's resumed only when symptoms subside and the situation is stable.

There's no way to guarantee that HPNS is eliminated, but it can usually be avoided by either introducing nitrogen or hydrogen to the breathing gas (trimix / hydreliox). Sometimes it's preferred to keep the descent very slow (0.5 to 1 foot per minute) on deep dives (1000' +), with compression stops added to this.

 

[Kevrumbo]

Helium is superior to Nitrogen as a diver's gas in many ways. The size of the bubbles formed in Helium are smaller, it diffuses into and out of tissue faster, is less narcotic and leaves the diver feeling better after the dive, than other gases. The Helium minimum bends depth (MBD) is greater than those of Nitrogen, allowing for longer no-decompression times at depth.

Helium has been the mainstay of commercial diving for years, but its emergence into the technical field is more recent. No doubt cost is a factor, but is part of this a misconception about the gas itself?

I can't help but wonder why more of a push is not made for Heliox opposed to Nitrox (including air). It offers huge benefits in open-circuit and CCR diving at all depths. Why do you suppose that this hasn't been promoted by the diving industry more? Do you think this will be done in years to come or is the cost prohibitive?

Helium is not as utilitarian as you think for all recreational diving, other than the small subset of non-commercial non-military sport technical & rebreather diving . . . again, the point is it doesn't make economic sense for using Triox/Trimix for most common recreational NDL type dives and corresponding depths & times.

Helium and nitrogen trade off for NDLs depending
on depth and time. For most NDLs in the shallow
zone, nitrogen is better. For deeper exposures
helium is better. For deep and deco diving,
helium wins, especially when coupled to
strategic mix switching on the way up. Overall
nitrogen is not the divers friend, even though
it wins the recreational NDL contest. . .

For shallow and short exposures, slow diffusing
nitrogen allows longer NDLs (than helium).
While for longer and deeper exposures, rather
insoluble helium wins the NDL race (longer
NDLs than nitrogen)

http://www.scubaboard.com/forums/379457-post6.html

 

[DCBC]

Helium is not as utilitarian as you think for all recreational diving, other than the small subset of non-commercial non-military sport technical & rebreather diving . . . again, the point is it doesn't make economic sense for using Triox/Trimix for most common recreational NDL type dives and corresponding depths & times.

Yes, if you consider money to be a factor (as it is for most people, but not all).

When an 80\20 Heliox mixture is compared to an 80\20 Nitrox, the Heliox mixture allows additional no-decompression times of: 60m@40', 80m@50', 70m@60', 35m@70', 20m@80', 15m@90', 10m@100'-130', as an example.

 

[TSandM]

I'm probably one of those people . . . I pay about $35 for a 25/25 fill in my double 85s, and I can afford to do that, although I'd prefer NOT to do it for every dive. There's a point of diminishing returns for investment in a dive, and adding 80% helium to a tank to get a couple more minutes of no-deco time (on some models -- some penalize you for it!) probably falls into the poor return category. Shoot, a lot of people don't dive Nitrox because of the expense involved! And it's easier (at least around here) to find a shop that pumps Nitrox than one that pumps helium. And helium analyzers are very expensive.

I use helium because I honestly believe narcosis is downright dangerous, and begins before most people think it does. The decompression advantages of using it are a nice side effect.

 

[Blackwood]

When an 80\20 Heliox mixture is compared to an 80\20 Nitrox, the Heliox mixture allows additional no-decompression times of: 60m@40', 80m@50', 70m@60', 35m@70', 20m@80', 15m@90', 10m@100'-130', as an example.

That's a really odd progression. Why do you get more additional NDL at 50 and 60 feet than you get at 40 feet?

What algorithm are you using to develop NDLs with Heliox?

 

[DCBC]

That's a really odd progression. Why do you get more additional NDL at 50 and 60 feet than you get at 40 feet?

What algorithm are you using to develop NDLs with Heliox?

These profiles were generated with the RGBM (Abyss Software Package). The deeper you go the percentage of the NDLs of Nitrox increase with Helium. At 40' you have a Helium NDL of 260 mins with 200 mins for Nitrox. At 50' it's 180 (He) and 100 (N) and at 60', 130 (He) and 60 (N). As you get shallower, the percentage advantage decreases.

 

[Kevrumbo]

Helium is superior to Nitrogen as a diver's gas in many ways. The size of the bubbles formed in Helium are smaller, it diffuses into and out of tissue faster, is less narcotic and leaves the diver feeling better after the dive, than other gases. The Helium minimum bends depth (MBD) is greater than those of Nitrogen, allowing for longer no-decompression times at depth.

Helium has been the mainstay of commercial diving for years, but its emergence into the technical field is more recent. No doubt cost is a factor, but is part of this a misconception about the gas itself?

I can't help but wonder why more of a push is not made for Heliox opposed to Nitrox (including air). It offers huge benefits in open-circuit and CCR diving at all depths. Why do you suppose that this hasn't been promoted by the diving industry more? Do you think this will be done in years to come or is the cost prohibitive?

DCBC, here's the thesis behind your OP topic "Helium, The Perfect Diver's Gas"

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. [i.e. The Perfect Diver'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

http://www.scubaboard.com/forums/427265-post4.html

And with regard to your argument for 80/20 heliox NDL's (a pure helium-oxygen mix that's not even listed in NAUI-tec's textbook RGBM Deco Tables, nor have I heard of anyone using it in the sport technical diving field):

When an 80\20 Heliox mixture is compared to an 80\20 Nitrox, the Heliox mixture allows additional no-decompression times of: 60m@40', 80m@50', 70m@60', 35m@70', 20m@80', 15m@90', 10m@100'-130', as an example. These profiles were generated with the RGBM (Abyss Software Package). The deeper you go the percentage of the NDLs of Nitrox increase with Helium. At 40' you have a Helium NDL of 260 mins with 200 mins for Nitrox. At 50' it's 180 (He) and 100 (N) and at 60', 130 (He) and 60 (N). As you get shallower, the percentage advantage decreases.

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 [longer] 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 [As a general rule of thumb . . .
two hours bottom time is roughly the point where
the slower diffusivity/higher solubility of N2 becomes
the determining factor over the faster diffusivity/lower
solubility of Helium (Powell, Deco for Divers p.182)]
. . .To quantify this exactly, you would
need RGBM (code) to delineate comparisons.
And it shows up easily doing A mix to B mix
comparisons. . .

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

http://www.scubaboard.com/forums/427565-post9.html

Again --other than for academic discussion-- for all practical purposes, for the non-commercial/non-military sport diver:

All,

Tec and rec diving come at the question of nitrox vs
helitrox vs heliox from different vantage points . . .
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
cases other than single, no-deco penetrations. . .

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.

. . .

Try RGBM In Depth to cover the bases.


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

http://www.scubaboard.com/forums/429780-post14.html

 

[DCBC]

DCBC, here's the thesis behind your OP topic "Helium, The Perfect Diver's Gas"

Thanks for your links to other discussions surrounding Helium. Outside of the cost and availability issues, Helium has several advantages. Your links highlight some of these benefits.

a pure helium-oxygen mix that's not even listed in NAUI-tec's textbook RGBM Deco Tables, nor have I heard of anyone using it in the sport technical diving field.

Sport technical diving is in its infancy. I'm sure we'll see quite a few things change in time.

 

[Kevrumbo]

Helium Triox mixes in the recreational range like 30/30, 25/25 or NAUI 26/14 are not the perfect gas or most convenient choice of gas for me however. Even staying within shortened NDLs with proper ascent & safety stops on breathing Triox only, I still suffered "the chokes" (shortness-of-breath) after two repetitive dives with a 90min SIT in between because of residual fine helium bubbles clogging my lungs' alveolar bed.

I now utilize a deco bottle of oxygen to help clean-up during the last repetitive dive of the day, for any set of recreational depth type dives using Triox (haven't had problems with the chokes since). . .