GUE & Isobaric Counter transport/diffusion

[plfaasen]

Hallo All

Just for interest sake, i was wondering, what the GUE stance on isobaric counter diffusion is? I watched the new GUE dvd, but it was not refered to.
I am both GUE & NAUI trained. During tech, deco dives, the GUE-way is to switch to EAN50 at 21m, but NAUI sees this as dangerous in terms of Isobaric Counter Diffusion (ICD). NAUI advocates using backgas all the way to the 6m stop and then to switch to 100% O2.

Any thoughts on this issue?

[Martin Burnard]

I have not got a clue, but I look forward to the replies.

[Ahmed Adly, Marlin Inn DC]

Quote: (Originally Posted by plfaasen)

Hallo All

Just for interest sake, i was wondering, what the GUE stance on isobaric counter diffusion is? I watched the new GUE dvd, but it was not refered to.
I am both GUE & NAUI trained. During tech, deco dives, the GUE-way is to switch to EAN50 at 21m, but NAUI sees this as dangerous in terms of Isobaric Counter Diffusion (ICD). NAUI advocates using backgas all the way to the 6m stop and then to switch to 100% O2.

Any thoughts on this issue?

Use the force

[caverkevin]

Quote: (Originally Posted by plfaasen)

Any thoughts on this issue?

Yeah!! Don't make any hard switches from a bunch of helium to a bunch or nitrogen. It sucks and hurts!!

Cheers!!

Kevin

[Mark Powell]

I'm not sure of the current official line from GUE but George Irving has been very dismissive of ICD in the past.

I think there is something to ICD but that it's not something that is going to affect you in the Tech 1 or even Tech 2 range. In addition I think GUE standard gases are pretty good at minimizing the risks of ICD.

If you want more information then take a look at;
http://www.dive-tech.co.uk/resources... Diffusion.pdf

And if you really want to know more about deco theory then this might be of interest;
http://www.dive-tech.co.uk/decompres...y%20course.htm

[Alastair]

As I understand it ICD is a risk if you spike the Partial pressure of nitrogen during deco. With the standard gases this isn't a big risk as the jump is all quite minor:

e.g. 18/45 at 21m on back gas:
PPN2 1.15

switch to 50%
PPN2 1.55

So the PPN2 does spike a little but not in the same way it does if you say switch to 32% at 36m

18/45
PPN2 1.7

32%
PPN2 3.13

This is still quite conservative compared to switching from trimix to air at 60m as people used to do. So stick to standard gases and the problem shouldn't occur (insert phrase about santa claus and the easter bunny).

Cheers
Al

[Ahmed Adly, Marlin Inn DC]

What about 10/70 to 50 @ 21m
PN2=0.62 to 1.55!!!

I would have been fried a long time ago.

[Chris B]

Quote: (Originally Posted by Alastair)

As I understand it ICD is a risk if you spike the Partial pressure of nitrogen during deco. With the standard gases this isn't a big risk as the jump is all quite minor:

e.g. 18/45 at 21m on back gas:
PPN2 1.15

switch to 50%
PPN2 1.55

So the PPN2 does spike a little but not in the same way it does if you say switch to 32% at 36m

18/45
PPN2 1.7

32%
PPN2 3.13

This is still quite conservative compared to switching from trimix to air at 60m as people used to do. So stick to standard gases and the problem shouldn't occur (insert phrase about santa claus and the easter bunny).

Cheers
Al

Bang on in my view, it is a recognized problem as it can happen....if you create the conditions for it to exist!

I think this is why GI3 took his usual 'not on the fence' view; it is only a problem if you make it one/allow it to exist!

[caverkevin]

Well this very thing was something I was trying to wrap my brain around after a 100m dive back in April. The dive was with 12/60, 18/45, 50 and O2. I got a mild type one hit in my right elbow. I felt the hit about the middle of the O2 stop, while still in the water. I figure I wacked myself switching from all the helium to straight 50. So take that for what it is worth.

Cheers!!

Kevin

[Ahmed Adly, Marlin Inn DC]

I bet you bumped your funny bone one the way up the ladder or something