HELIOX where to find information?

jaap

Yes maybe, but I think those computations are a littel too simple. Not taking into consideration transient events and several linked compartments.

The thing I think can be dangerous with a switch to a much higher pHe is that it will go in som much faster than the N2 is going out.

Found an old article:
Prlonged bubble production by transient isobaric counter-equilibration of helium against nitrogen.

Its about animals subjected to saturation at 132 and 198 ft on N2 (PO2 0.3)
followed by a sudden isobaric gas switch from saturation on N2 to He.

Bubbles occurred.

The final sentence of the abstract:
"Gas switches from a more soluble to a less soluble and/or more rapidly diffusing gas should therefore be avoided until physiological limits are well worked out."

The abstract of the article:
http://www.ncbi.nlm.nih.gov/entrez/q...=pubmed_docsum

Sorry if this is considered off topic in this thread...

J. V.

I use an HS Explorer O on nominal RGBM, my PpO2 is around 1.1/1.2 at depth and 1.3 during deco (kiss-like rebreather). Bailout tables are cut with RGBM or VPM.

No. Heliox USN tables use 0.7 PpO2, it's probably secure, but means very long deco obligations, more than I want to do (specially in cold alpin lakes!), and it's not "deep stops" tables.

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Drmike

The USN tables I provided the link for are for 1.3 ppo2. But you are right about the deep stops.

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J. V.

Oh, scuze me, I've not seen this link. They are more usable than 0.7 one, but shallow stop are long, too long for me

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Mikel-Deko

[quote=J. V.]I use an HS Explorer O on nominal RGBM, my PpO2 is around 1.1/1.2 at depth and 1.3 during deco (kiss-like rebreather). Bailout tables are cut with RGBM or VPM.

But, do you said to your computer that you are breathing trimix or Heliox? Do you clear your computer?

Thanks
Mikel-Deko

J. V.

I give computer the right gas. During normal dive, diluant is 10/90 , computer is on 10/90 and use info of the O2 cell to calculate deco.
(I use 10/90 for all dive, deep or shallow, that don't change anything for the computer but it's more easy for me to calculate PpO2 after a flush. )
If I need to go on OC bailout, I put the computer on OC gas ; 5 are available in the computer .

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Jacques
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Mdemon

From a link by Saturation on the "Treat with O2" thread...

However, in dry surroundings, it seems that the N2 diffuses out faster than He diffuses in.

So maybe heliox is less risky than going from trimix to heliox. How big is the risk of the bubble-enlarging effect though?

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The question Mdemon raises of swapping from Trimix diluent to Heliox for ascent seems a typical example of a question regarding ICD, given that I am confused and wish to understand I will lay out my thinking so that I may be understood and guided… Please appreciate that I am a NOVICE and am seeking advice/stimulate discussion not trying to give advice it so please bear with me and my example:

Ignoring compleities of gas solubility but looking only at the pp of individual gases:

Using Aldo (bubnotbub)s thin diluent mix as an example. 8/64 with a dive to 100m for 30 mins using a SP of 1.2 in combination with Mdemon’s suggestion of swapping the diluent to Heliox for ascent I want to see if ICD is a serious concern.

At 100m I have the following pp of gases O2=1.2, He=6.82, N2=2.98 in the loop.

To get the advantage that is sought for shortening the decompression obligation I need to remove the N2 component you have to switch to Heliox diluent and flush the loop for ascent.

I have no idea how efficiently I would be able to remove the N2 from the loop, but the most extreme case is that I am 100% effective so I will assume that this is achieved within 1 minute.

The ∆ppN2 = 2.98, remembering that at the surface the ppN2 is 0.79 so I cannot say that this change is equivalent to going to the surface.

But:

If it was the same as going to the surface then given Equivalent Air Depth for the N2 component = 27.75m I have effectively gone to the surface from the N2s perspective, breathing air at 27.5m for 30mins (ignoring decent) will I get a bend? well it is certainly looking like a high risk maneuver surfacing from 27.5m in a minute after being there for 30 minutes!

Above we assuming an ascent to the surface where the pp N2 would still be 0.79 so as I am moving to 100m from 100m(isobaric) where there is no N2 in the loop, I think that I should add the 0.79 to the 2.98 = 3.772 ∆ppN2 which is an EAD of 37.7m and 30mins at 37.7m with an ascent to the surface in 1 min seems very likely to cause an N2 bend!

Whilst simplistic are either of my calculations valid? And if so which one?

Other thoughts that I have kept out of this are that
1) if I was to swap diluent and not flush there would be a negligible change in ppN2
2) a partially successful flush would result in an unknown mix which would be better from an ICD perspective
3) I can reduce the N2 component of the mix and hence any ∆ppN2 if I reduce ∆ppN2 so that it is within NDL equivalence then I should be ok.
4) gas solubility is way to complex for a long armed idiot to consider.

The conclusion I draw is that there is no guaranteed safe ∆ppN2 so people who are diving Heliox are doing the right thing!

I have reached the end of my concentration span - coffee required.

J. V.

In this case, dive is deep, exposure long and change is in the way for ICD (heavy gaz -tmx- to light gaz -heliox), so ICD is a concern.
But something I don't understand : why take an heliox after a trimix 8/64 ? To offgas N2 more quickly? Why not, but you'll charge more and more helium. Deco obligation will be egal or longest. If I dive with 8/64, I probably stay on this diluant all the way. If I want absolutly change dil, I take a gas where N2 not raise too much and He fall, something like a 20/30 around 60 meters, or a nitrox where narcosis is not an issue, Nx 40 at 30 meters.

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Drmike

The way I figure it (at the moment) for my deep dives is;

1) My primary aim is to get out the water unbent
2) How long it takes for me to get out the water is not anywhere-anywhere near as important as 1)
3) Long deco doesnt necessarily mean more risk if the deco is easier to model
4) Deep dive deco modeling is hard/unreliable enough without adding any additional complication/unknowns/risk factors to the deco that existing models just dont really cover or that we dont know enough about - such as ICD


So to me at the moment I'm favoring a single dilutent up and down. I may incur more deco - but I believe I'm incurring less risk of the deco schedule not being sufficient because that deco is easier to model. KISS.

__________________
Cave diving is a sport
Wreck diving is a sport
Diving in general is a sport

'Rebreather diving' is not a sport
its the delusional obsession with a highly dangerous and often inappropriate piece of equipment