Are there any entry tech courses that include Trimix?

[amascuba]

I would say that helium is more unforgiving than nitrogen if you do a typical ascent that is taught in an open water class. (The bend and mend ascent, as my GUE instructor puts it) However, if you do a proper ascent with deep stop, to control the free phase off gassing, then helium is no more unforgiving than nitrogen. That is where proper buoyancy comes in and again if you can't control your buoyancy then you shouldn't be conducting dives with mandatory decompression.

 

[Meng_Tze]

I would say that helium is more unforgiving than nitrogen if you do a typical ascent that is taught in an open water class. (The bend and mend ascent, as my GUE instructor puts it) However, if you do a proper ascent with deep stop, to control the free phase off gassing, then helium is no more unforgiving than nitrogen. That is where proper buoyancy comes in and again if you can't control your buoyancy then you shouldn't be conducting dives with mandatory decompression.

And this is the crutch of this entire thread (well, after it swayed off anyway).

I dont think we are doubting/questioning the positive effects He has on decompression itself, but how it behaves during that decompression.

He is more unforgiving in terms of mistakes made on ascend (this includes the actual ascend profile), but it is your friend in terms of the time spent doing that ascend. Dr Wienke confirmed what TSandM is saying below, empirical testing has shown that WKPP benefited dramatically. (Chapters 6.5 and 6.6 of Basic Decompression Theory and Application)

The insertion of deepstops does make for a better offgassing profile, but the fact remains that IF you make a mistake, He is less forgiving that Nitrogen since it dissipates faster. With nitrogen you have a little time to correct since it takes time for the nitrogen to react (dissipate) to the gradient change, He does that 2.7 times faster........

 

[wedivebc]

I'd be interested to see any hard evidence to back up that point of view.
Or is it just "conjecture and gut feel" coupled with what instructors have told you?

Agreed on the stops, but I dont see that as any different on nitrox or 30/30 -- same thing applies (except I wouldn't be doing mandatory deco dives on 32% generally -- certainly not deeper than 100 feet)

I very seldom take things people tell me at face value, especially scuba instructors.
My feeling is that, and I don't claim to be an expert on decompression but helium is a smaller molecule and it is well know that it moves in and out of saturation faster than nitrogen.
Since fast tissue is the first to reach saturation helum would only hasten that effect. Considering that highy perfused tissue is expected to take on inert gas faster than slower less perfused tissue and that one really fast compartment is spinal and brain tissue it seems the likelyhood of receiving a hit that would result in type II DCS is higher when using a gas that goes into and out of solution faster.

So following Peronnes logic from the earlier post, do that dive on nitrox and you'll probably get a skin or pain hit. Do that dive on 30/30 and you may need a wheelchair.

 

[amascuba]

So following Peronnes logic from the earlier post, do that dive on nitrox and you'll probably get a skin or pain hit. Do that dive on 30/30 and you may need a wheelchair.

100feet for 90minutes is three times the limit for NDL/MDL. It's likely that Nitrox would give you a type II hit as well.

 

[rjack321]

But Weinke has demonstrated that bubble size is inversely related to solubility. So He bubbles are smaller. And therefore more likely to make it back to the lungs from a capilary bed and get off-gassed. Other than Buhlmann's empirically derived safety factor for He (and the merit this model is inherently debatable), I see little actual evidence that He is less forgiving.

 

[PerroneFord]

Wedivebc, that is exactly where I was going.

Look up this guy: Dr David Doolette

That is who was in my class. He taught a seminar at the GUE conference last year. Very sharp guy, and I enjoyed learning from him during class.

 

[limeyx]

I very seldom take things people tell me at face value, especially scuba instructors.
My feeling is that, and I don't claim to be an expert on decompression but helium is a smaller molecule and it is well know that it moves in and out of saturation faster than nitrogen.
Since fast tissue is the first to reach saturation helum would only hasten that effect. Considering that highy perfused tissue is expected to take on inert gas faster than slower less perfused tissue and that one really fast compartment is spinal and brain tissue it seems the likelyhood of receiving a hit that would result in type II DCS is higher when using a gas that goes into and out of solution faster.

So following Peronnes logic from the earlier post, do that dive on nitrox and you'll probably get a skin or pain hit. Do that dive on 30/30 and you may need a wheelchair.

Well, I would like something somewhat better than "It would seem" because often things that are "logical" or should be that way because of this and that factor, often aren't.

 

[limeyx]

100feet for 90minutes is three times the limit for NDL/MDL. It's likely that Nitrox would give you a type II hit as well.

yes, you will need your wheelchair for either dive.

if it had been a 100 foot for 30 mins, then we might (might) have something to talk about but unless anyone has any hard data, it will all be conjecture.

 

[PerroneFord]

Limeyx, The gentleman that I mentioned is conducting HUMAN trials on Navy Divers at NEDU in Panama City. I don't know if there are published papers or not. But that is what this guy does for a living. When he had something to say about decompression, I listened. Closely.

 

[rjack321]

Limeyx, The gentleman that I mentioned is conducting HUMAN trials on Navy Divers at NEDU in Panama City. I don't know if there are published papers or not. But that is what this guy does for a living. When he had something to say about decompression, I listened. Closely.

Type II is bad all around. I don't care whether a He bubble caused it or an N2 bubble. The profile you posted is way beyond "entry level deco" by any standard. You don't want to F^&k that ascent up period. Missing roughly an hour of deco is likely to leave you beyond the wheelchair and halfway into the coffin.