Very deep dives inflation gas choice - risk of skin bends for Rebreather dives

Drmike

Ok I know squat about this subject and am trying to get my head around it.

If anyone has any knowledge on this Im all ears.

My question related to Drysuit infation gas and risk of skin bends on CCR dives in the 150-200m range

I have read (see below) that some view argon or even air (if your on high He mix or Heliox) as a potential problem for suit inflation at these depths

"A complication with Argon is, as you are unlikely to be breathing it, there is a large pressure gradient between inert gases in both your skin and other tissue. This causes skin bends minimally, on larger dives."


My question is - is this true? If there is a need to keep the suit inflation gas the same as the breathing mix that would be hard to achieve with a ccr where the breathing mix changes with depth.


Or is the Argon molecule too big to defuse through the skin making this a non issue?

Is Nitrogen also too big to diffuse? making air acceptable?

Agron is not readily available in some of the remote sites Im diving so would air be ok for suit inflation when doing high He or Heliox dives in 150-200m range?


Cheers
Mike

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GuyW

Dr Mike

there is supposed to be a counterdiffusion issue with breathing a slowly diffusing has (e.g. Air) whilst in a quickly diffusing atmosphere (e.g. Helium). From Bennet and Elliot's book:

COUNTERDIFFUSION: RELATION TO DECOMPRESSION
‘Counterdiffusion’ is the term used to describe the
physiologic effects of an individual’s being exposed to
two inert gases of very different diffusion properties. It
relates to decompression in two ways. First, the
symptoms of the two ‘gas lesion diseases’ – DCS and
counterdiffusion sickness – are similar and the etiology
is apparently the same – bubbles in the skin or gas
emboli elsewhere. Second, counterdiffusion situations
can complicate decompression or can aid it, and
counterdiffusion lesions can happen with or without
pressure changes. There are two categories of inert gas
counterdiffusion as defined by Lambertsen, a ‘superficial’
condition and a ‘deep tissue’ condition (Lambertsen
1989).
Superficial counterdiffusion
Superficial counterdiffusion occurs through body surfaces
when a heavy or slowly diffusing gas is breathed (e.g.
N2 or Ne) and the external environment is a lighter,
more rapidly diffusing gas (e.g. He). A net inward flux
of the lighter gas into the skin causes subcutaneous
supersaturation and extravascular bubble formation,
which can occur without pressure change. In human
exposures at elevated pressure, intense itching was
accompanied by hard, raised, bloodless lesions and severe
vestibular dysfunction (Harvey & Lambertsen 1978,
Lambertsen et al 1977).
An opposite effect occurs when the switch is from
helium to nitrogen as the background gas. If a diver
breathes helium–oxygen at depth and changes to air
during decompression, helium leaves his tissues faster
than nitrogen enters and the resulting undersaturation
appears to allow accelerated decompression, does not
appear to cause counterdiffusion problems, and is a
well-established practice for most deep helium–oxygen
bounce diving (Hamilton 1976).

If you are in an Argon or Air atmosphere your are ok. Generally this is not a big issue as people generally don't use helium in their drysuits. You would freeze your nuts off.

Guy

Drmike

cheers,

So if I understand that correctly if Im using air as a suit inflation this shoudnt be an issue as Nitrogen from the suit diffuses slower into the body than the trimix Im breathing during the dive diffuses out. The net effect is the tissue tensions will be dropping faster than Nitrogen can uptake. The ascent ceiling is goverend by the fastest diffusing gas which will be the breathing gas....does that sound about right?

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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

cys

Here is a link to an old thread from the nwdesigns rebreather list that discusses argon:

www.metacut.com/rbarchive/1998/1755.html.gz

GuyW

Yes. You actually have to do a few things wrong to get effected in this way (via the skin). It is to do with the difference in solubility versus permeability ratios with helium versus nitrogen (or Argon) I think. The helium can go in faster than the nitrogen goes out and over pressures the tissue.

There is a more problematic counterdiffusion issue with inner ear bends when flushing to air from a helium diluent. This is not what you were asking about, but is an issue for big dives.

http://www.rebreatherworld.com/dive-...mpression.html

Guy

DrJM

Ur right Mike, Argon is "maybe" a good idea but a pain to find middle of nowhere (aka middle of France ) and not breathable if shit happen and if you still have 200m to exit the cave !

In fact having Air for bcd/suit inflation saved the life of one of my mate 4-5 month ago: he exited the cave breathing/sucking his 2 lit air suit inflator via his bcd

Back to deep dives, I dropped argon a long time ago, and I'm survivng with air and
Xerotherm artic 4th Element
DUI 400gr Thinsulate
Typhoon heating jacket

No skin bends (yet)

Good day

Jerome

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Drmike

Thanks Jerome, was hoping you would be able to offer some 1st hand experience. Just been adding up the number of stage tanks for bailout, Im up to 14. .....Maybe I should stage my MK15.5 in the cave for bailout!


PM sent.

__________________
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

Simon Mitchell

Mike,

Guy's interpretation is correct. You are fine with air or argon in your suit.

With regard to the efficacy of argon as a drysuit inflation gas, the only study which examined the issue in a blinded and objective fashion (including thermistors on the skin surface and up the divers bums) found no subjective or objective benefit (tested vs air during drysuit diving in very cold water).

I would definitely not go to the bother of carrying an extra cylinder of non-respirable gas.

See:

Risberg J, Hope A. Thermal insulation properties of argon used as a dry suit inflation gas. Undersea Hyperbaric Med 2001;28:137-43

Regards,

Simon M.

DrJM

[quote=DrmikeMaybe I should stage my MK15.5 in the cave for bailout!
[/quote]

If I still had mine I would, simple reason if shit happen you'll be happy not to breath those noisy/cold/consumming stage tanks !!!

And if DCI out of the water you can go back IWR straight away with 12h of new scrubber

Ok enough encouraging you doing dangerous things

Jerome

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DrJM

oups last one about inflating dry suit (ex clx450 or tls350):

3 lit 300b was never enough for me down to -180m, mainly if the profile of the cave is a little bit up and down

so nowadays

7 lit (S40) 230b, much more comfy


Ask Mario M. to tell you his story about St Sauveur 2005 -163m


May the force be with you young DrMike apprentice

Jerome

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