Another stupid question

James Appel

I was wondering (and no I havent taken any tri-mix classes as evident perhaps by this question), but why don't people use a 79% helium 21% oxygen mixture as regular normal air diluent getting rid of the nitrogen completely, removing all nitrogen from the loop? And if your doing deep dives and using a diluent with less oxy, WHY use nitrogen at all?


Stupid is as stupid does...........

Gibbon

Some people do it is called Heliox, the disadvantages are

1) that it costs more as some "waste" is inevitable and you need compatible bailout mixes as well.
2) The deco is longer than with trimix/heliair as you off gas both the gases at the same time...
3) You dont get narked
4) There is possibly more likelyhood of OxTox as there is no narcosis buffer against it
5) Requires a booster pump to achieve high pressure He fills

I have not yet done anything that 10/50 was not appropriate for, however there are plenty of people here who have been way deeper.

If you use Heliox, like using heliair, you dont need a trimix analyser to do top ups, other advantages would be that cylinders dont get exposed to nasty compressor oil, and I supppose the gas density in the loop would be even lower so the WOB would be less.

Have to wait for a proper madman to come along and give you a more detailed answer!

wedivebc

Could you explain that one please?

__________________
Cheers,

Dave....

Man is the only animal burdened with the knowledge he will eventually die

6Gill

There have been studies that suggest that the presence of nitrogen in a mix versus he and o2 alone helps to buffer oxtox up to a point. I'm sure we have someone online that could give a proper technical explanation.

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"It's a shame ignorance isn't painful!"

Gibbon

in simple terms (as I am no expert in this area), Oxtox is the CNS getting over active, narcosis has the opposite effect, this is generally belived to be the reason why some deep air dives have not resulted in Oxtox.

Barrie Law

Hi James,

Not a stupid question at all, I have been using Heliox for a couple of years and Nitrogen free diving does have it's advantage's.

Current decompression algorithms will give greatly increased run-times for Heliox as against Trimix although with Heliox there is only one inert gas to be decompressed unlike the two (Helium-Nitrogen) in Trimix.

Those who use Heliox would be more likely to be using much less than 21% oxygen due to PPO2 limitations at depth. A 10/90 mix would give a MOD of 130 mtrs and they would be diving a CCR unit, diving this mix on open circuit would not be an option due to gas cost and body temperature problems Helium takes heat from the diver much faster than Nitrogen does and would be a real problem for deeper diving.

For CCR use Heliox offers a number of problems;

* No current proven Algorithm.

* Depth limited by HPNS (Helium equivalent of Nitrogen Narcosis)

* Nitrox Bailout gasses are not suitable due to IEDCS.


Heliox also has some benefits;

* 0 EAND on all dives.

* Practically removes possibility of IEDCS

* Decompression stops can be concentrated at deeper depth's giving shorter run-times when compared to Trimix.

* Loop volume can be used for an indication of off-gassing along with visual monitoring of the over-pressure valve dumping, it is much faster and more noticeable with Heliox than with Trimix.

* Bailout ascent's can be done using the same 10/90 Heliox.

The above brief comments are my own opinion based on my experience using Heliox, this is still a work in progress and although others worlwide are also using Heliox although it is generally not openly discussed because of the closed minds of many individuals that assume the current thinking regarding Trimix is Gospel despite the number of bent divers who have appropriately followed accepted Trimix dive plans.

Part of the problem is no agency or body is actively researching this area and information that is offered comes from studies like mine that are conducted at my own expense and therefore limited and time consuming.

I will be visiting the UK to dive a quarry early in 2007 for a weekend of Heliox decompression research to be based on data taken from dives to approx 100 mts with 30 minute bottom times and individuals with an interest in Heliox diving are most welcome to attend.

Regards

__________________
Barrie Law
Rebreather World Store
Supplying the Rebreather World

Tel:US +19548403892 Fax:US+19543333792
Tel:EU+442071930496 Fax:EU+442077606344
Mobile+353876880628 Skype:barrielaw
Email: barrie@rebreatherworldstore.com

gtzavelas

very interesting
any chance of publishing / posting the results for the people who cant attend?

Barrie Law

The documented results obtained over the weekends diving will be published along with my findings over the past 2 years.

A comparative study between divers one using Heliox and one using Trimix will be carried out and then repeated over 3 days with gas sampling taken at 30 points during each dive.

The gas samples will be analysed and the data can then be used to compare the different dive profiles followed and there effectiveness relating to decompression.

The winter months are a problem in this part of the world and with the absence of a 100mtr deep heated pool a quarry will suffice when it reaches 10 degrees as a minimum temperature for diver comfort and also dexterity.

Regards

__________________
Barrie Law
Rebreather World Store
Supplying the Rebreather World

Tel:US +19548403892 Fax:US+19543333792
Tel:EU+442071930496 Fax:EU+442077606344
Mobile+353876880628 Skype:barrielaw
Email: barrie@rebreatherworldstore.com

Brad_Horn

Barrie et al

With regard to "For CCR use Heliox offers a number of problems;

* No current proven Algorithm"

For published tables for heliox look in the RN/RAN/USN mixed gas diving manuals as that is all they use and significantly more research has likely gone into the use of Heliox as a diluent then the entire amount of Trimix research OC & CC.

Sure its fixed setpoint stuff either 0.7 or more recently 1.3 but the money has been spent on the data.

Regards
Brad

dave t

Barrie

any signs of HPNS this side of 100m?


<<<Loop volume can be used for an indication of off-gassing along with visual monitoring of the over-pressure valve dumping, it is much faster and more noticeable with Heliox than with Trimix.>>>

any idea how much gas is actually offgassed (in terms of litres/mililitres)

thanks

Dave