Counterdiffusion discussion

[And]

Originally Posted by Brian Donaghy

I'll give Ellyat one thing, he has far more experience of DCI that most people.

LOL.

What he says is in contradiction to everything the WKPP and EKPP do, and they do it for much longer bottom times and therefore longer decos. Bruce Wienke dislikes nitrogen in ANY dive gas, and he has written and couple of books on the subject and done a bit of testing with his RGBM model.

It might work for depth record bounce dives (sorry, it has worked once, as he got bent on the others), but personally, I'm not about to go and do one, so I'll disregard what he says for now until a proper diver does it on a real dive, a dive I can at least relate to.

Andy

[Janos]

Originally Posted by Mark Elliot

Dry suit’s pose an interesting complication for decompression divers. If you inflate drysuits with mixes containing helium then this will speed diver cooling. The cooling is not due to heat loss because of helium’s presence in the suit solely (a function of its poor insulating properties). As helium de pressurises and expands (Joules Thompson effect) much faster than air or argon, it enters the dry suit much colder and has a noticeable chilling effect.

I'm sorry but I don't believe this at all. A quick recap of some physics (apologies if you know all this already).

The energy of a gas depends purely on it's temperature. The mean energy of a gas molecule is (3/2 kT) where k is the Boltzman constant.

The energy of a gas molecule is also equal to 1/2 mv2 (ie 1/2 mass * velocity squared).

So 1/2 mv2 = 3/2 kT

So gases with a small mass (like Helium) must have a high v to compensate. At the same temperature, heavier gases have a smaller v. Ie Helium is small and wizzes around. A molecule of N2 is much larger, wizzes around much slower, but still has the same energy (and temperature). This explains Helium is a better thermal conductor because it's molecules move around more quickly than N2.

The reason that gases cool on expansion is from the ideal gas law (PV = nRT) and so when volume doubles, the Temperature (in degrees Kelvin) halves. This is completely independent of the gas used (assuming we're in the ideal gas region below 250bar)

I suppose it could be vaguely possible that the Helium gets through your first stage quicker, allowing you to remove squeeze that little bit quicker, and so you notice it more, but the overall energy (and hence temperature) of the gas has in your suit is going to be the same, maybe you notice the change most with He, but I can't really see it myself.

Originally Posted by Mark Elliot

You must keep the nitrogen % constant or dropping....

I'm afraid I don't see this. I understand why heavy to light is bad, as the Nitrogen goes out more slowly than the He goes in, meaning that the total partial pressure of inert gas in your cells might go over the limit, but I can't see the mechanism for heavy to light. The amount of N2 on-gassed through your skin would be very small compared to the amount off-gassed through your lungs. I can't see it being a problem.

Originally Posted by Mark Chase

I dont post these because I think he has the one true path, I only post them as a point of comparison for other theories.

I'm with Bruce Wienke on this one.

And of course on the YBOD it makes no difference to you as your ratio of He to Nitrogen is going to be pretty much constant anyway.... Lucly sod.

Laters,
Janos (once again, talking the talk, but not walking the walk in aany way shape or form I think everyone mentioned / posting on this thread has done stops deeper than my deepest dives...

[Brian Donaghy]

Originally Posted by And

Bruce Wienke dislikes nitrogen in ANY dive gas, and he has written and couple of books on the subject and done a bit of testing with his RGBM model.

Yes, but his tables where you ride back gas up to 6m and switch to O2 are useless to me. I'm happy to dive RGBM with sensible gasses though.

Originally Posted by And

It might work for depth record bounce dives (sorry, it has worked once, as he got bent on the others)

No, if you read his telling of the story in Diver he got bent on that one as well. Just less bent, he didn't need the support divers to hold his semi-unconscious body in place during his deco on that one. A real triumph.

[Mark Chase]

Originally Posted by Brian Donaghy

I'll give Ellyat one thing, he has far more experience of DCI that most people.

*The Jools Holland effect is where you make a TV music program featuring worthy and often excellent bands, but when you sit through a whole show the overall effect is that you are left cold.

LOL Jules Holland effect


Your not giving him credit for his development work. I seem to remember GI3 saying he used conventional deco profiles and got 'F*cked up big time' (His words) then he developed his own system / developed Pyles work (depending on your point of view)

Mark Ellyat did a big dive to 280m I think using conventional decompression theory. He got bent big time.

He then did his record attempt dive using his own decompression theory to 312m and didn’t get bent.

This is what I found interesting when I first looked at his work. I was interested in Pyle and GI3 for the same reasons.

ATB

Mark Chase

[Brian Donaghy]

Originally Posted by Janos

The reason that gases cool on expansion is from the ideal gas law (PV = nRT) and so when volume doubles, the Temperature (in degrees Kelvin) halves. This is completely independent of the gas used (assuming we're in the ideal gas region below 250bar)

Yes but even with real gas effects (Joule-Thompson) I don't believe He behaves as he describes. He's got it backwards.

Originally Posted by Mark Chase

Your not giving him credit for his development work. I seem to remember GI3 saying he used conventional deco profiles and got 'F*cked up big time' (His words) then he developed his own system / developed Pyles work (depending on your point of view)

I think a lot of the older WKPP profiles came from Bill Hamilton. I've no idea where Ellyat's come from and I really can't see their application to real world SCUBA diving or 99.99999% of it.

Originally Posted by Mark Chase

Mark Ellyat did a big dive to 280m I think using conventional decompression theory. He got bent big time.

I think he used Abyss/RGBM on that one.

Originally Posted by Mark Chase

He then did his record attempt dive using his own decompression theory to 312m and didn’t get bent.

Like I said above, he did get bent.

[Drmike]

Originally Posted by And

I'll disregard what he says for now until a proper diver does it on a real dive

Andy

So mark isnt a 'proper diver'?

What do you mean by this?

Just curious.

Cheers
Mike

[And]

Hi

What I mean is that Mark is somewhat controversial in his views and these are based on one off record chasing bounce dives, with very limited success. That kind of diving I am not interested in and personally I don't count it as 'proper' diving.

Andy

[Mark Chase]

Originally Posted by And

Hi

What I mean is that Mark is somewhat controversial in his views and these are based on one off record chasing bounce dives, with very limited success. That kind of diving I am not interested in and personally I don't count it as 'proper' diving.

Andy

Mark Elliot also holds the record for the most number of dives carried out below 150m and the deepest wreck dive and was involved with test dives on RGBM.

I am reasonably confident he didn’t just jump in the water and drop to 312m one day because he felt like it. He is also an accomplished cave diver and current world record holder of the deepest air cave dive at 130m that’s if you’re referring to scootering through holes in the ground and seeing how much string you can lay down as 'proper diving'

You guys are letting dive club loyalty get in the way of research. Have you ever tried simulating a dive on his system? His argument is that only in the extremes of diving can we test the model seems fair. I agree some of his ideas are hard to come to terms with but that’s true of errrr other schools of diving isn’t it.

Strange thing is that Mark is one of the few people who actually support and agree with a lot of the DIR decompression theory that the main stream diving establishment thinks is dangerous rubbish. You appear to be slagging off a fellow believer in He deco.

ATB

Mark Chase

[Mark Chase]

I think a lot of the older WKPP profiles came from Bill Hamilton. I've no idea where Ellyat's come from and I really can't see their application to real world SCUBA diving or 99.99999% of it.

Quote from Marks web site:

The DecoChek Dive analyser was developed as a training tool for mixed gas students wishing to understand decompression theory. The designer, Stephen Burton has been a keen follower of decompression theories for over 20 years.

Since its inception 6 years ago, DecoChek has evolved into the first complete decompression plan analyser. The program compares your dive plan against an enormous data base of successful and failed dives. The program displays decompression violations as warnings. These warnings can be removed by increasing stop time or making adjustments elsewhere in the dive plan.

I think he used Abyss/RGBM on that one.

True

Like I said above, he did get bent

Yes but your exaggerating what happened. He completed the dive and got out of the water and four hours later suffered a nagging pain in his arm which was successfully treated with surface breathed 02.

This was after shaving 5 hours off the accepted deco time for his dive plan and in a diver who had previously suffered a big bend??

Pretty impressive stuff if you ask me.

ATB

Mark Chase

[And]

I'm not slagging him off, I said that I am disregarding his comments until a diver I trust starts saying the same thing.

I said not to turn this into a chestbeating affair, so I won't continue anymore. Its not worth it and not productive.

Andy