Calculating deco and mix

[Bismark]

Sometimes you can actually here it snap shut if you listen carefully........

 

[JeffG]

Sometimes you can actually here it snap shut if you listen carefully........

Yes...much better than giving an answer.

 

[Bismark]

after 3 mins? sounds like BS to me.


gee...why do we do 12/6 with 100% @ 20 ft then.

At first glance I would tend to agree but with all the drahk I have been reading in the last 24 hours about this, it looks like the we are accomplishing a couple of different things with 02, only one of which is using the 02 window. The more regular understood process concerning diffusion and partial pressures works regardless of the 02 window, hence the effectiveness of extended 02 (with breaks) at 20'. Would probably work deeper also but for the risk of higher pp02's. Check back in on monday for my summary......for whatever it's worth.

 

[Bismark]

Yes...much better than giving an answer.

Thank you. Even people from Edmonton appear to have a sense of humour. I lived in Cold Lake, pretty much the only way to get through the winter..........

 

[Bismark]

Please explain this window open, closed thing. Is it sometimes open then suddenly shuts?

Dave, were you really asking or just joking? (serious question) My understanding is that the 02 window loses it ultility at a certain point due to the vasoconstrictive effects of 02. At that point, the diver benefits more from the diffusion aspects of higher pp02 in conjunction with increased pressure gradients. In that aspect, the 02 window effectively "closes" (at least past the point of utility) until it "re opens" again. I believe the backgas break at 30' might be what constitutes the time for the vasoconstriction to reduce to the point where the effects of the 02 window again become worthwhile when you go on 100% 02 again at 20'. I am finding it easier to conceptualize the 02 window as a time frame rather than as an opening. More like a window of opportunity versus an opening or a door. Might be why we don't call it the 02 door........

 

[limeyx]

Too Funny...that last bit.

My understanding is the latest GUE take on the 70' stop is that vasoconstriction significantly reduces the effectiveness of the 02 window after 3 minutes and at that point you benefit more from an increased gradient. I am pretty sure this might just apply to Tech I level stuff because otherwise if you need longer times at 70' to shape the curve, how do you justify cutting it short?

I've not heard that, but then it's been a couple of years.
More important than losing a bit of benefit @ 70 to me is keeping a consistent way to calculate stops so we all agree on the plan. However, I believe GUE has also changed that to linear stops at tech1 now (which may be why 3 mins seems to be the upper limit at 70 feet because thats what you get with liner stops on a 30 min deco which is kind of the max recommended for T1)

 

[Bismark]

I've not heard that, but then it's been a couple of years.
More important than losing a bit of benefit @ 70 to me is keeping a consistent way to calculate stops so we all agree on the plan. However, I believe GUE has also changed that to linear stops at tech1 now (which may be why 3 mins seems to be the upper limit at 70 feet because thats what you get with liner stops on a 30 min deco which is kind of the max recommended for T1)

Yep, this was tech I stuff and I think you hit the nail on the head. On a Tech I dive with a GUE tech instructor last fall, I was surprised that on a 160 for 25 dive (I think that was it) One of the first things we did was lock in the 3 min at 70' stop even though I had previously been taught something different. Previous to that I had been instructed differently and most of the time we ended up with 4 or even 5 minutes in the tech I range. I think this might have something to do with the AG-postAG RD stuff but I can't say for sure. My previous instruction (pre GUE Tech I) was definitely Ag stuff so who knows. I like the fact that generally speaking, GUE keeps moving forward so maybe there are some real good reasons for this change. I will get back to you on this also.

 

[limeyx]

Yep, this was tech I stuff and I think you hit the nail on the head. On a Tech I dive with a GUE tech instructor last fall, I was surprised that on a 160 for 25 dive (I think that was it) One of the first things we did was lock in the 3 min at 70' stop even though I had previously been taught something different. Previous to that I had been instructed differently and most of the time we ended up with 4 or even 5 minutes in the tech I range. I think this might have something to do with the AG-postAG RD stuff but I can't say for sure. My previous instruction (pre GUE Tech I) was definitely Ag stuff so who knows. I like the fact that generally speaking, GUE keeps moving forward so maybe there are some real good reasons for this change. I will get back to you on this also.

Well, I heard that the reason for the change was to make it "easier" for people, esp on deeper dives and that the S-curve benefit was not that great, but I am not convinced that's why. Who knows. I stick to my original plan as does everyone around here.

 

[JeffG]

Well, I heard that the reason for the change was to make it "easier" for people, esp on deeper dives and that the S-curve benefit was not that great, but I am not convinced that's why. Who knows. I stick to my original plan as does everyone around here.

Thats what I heard as well. (and what Richard Lundgren posted)

 

[wedivebc]

Dave, were you really asking or just joking? (serious question) My understanding is that the 02 window loses it ultility at a certain point due to the vasoconstrictive effects of 02. At that point, the diver benefits more from the diffusion aspects of higher pp02 in conjunction with increased pressure gradients. In that aspect, the 02 window effectively "closes" (at least past the point of utility) until it "re opens" again. I believe the backgas break at 30' might be what constitutes the time for the vasoconstriction to reduce to the point where the effects of the 02 window again become worthwhile when you go on 100% 02 again at 20'. I am finding it easier to conceptualize the 02 window as a time frame rather than as an opening. More like a window of opportunity versus an opening or a door. Might be why we don't call it the 02 door........

I am quite serious. As far as I know GUE has the exclusive on this concept of open and shut oxygen windows. I understand the concept as far as creating a higher gradient by adusting the gas you are breathing. I also understand that by reducing inerts as far as possible you increase the gradient to its maximum. I also believe that vasocontriction can impede gas tranfer although I don't know where the concept is incorporated in decompression models other than GUE's RD.
Please explain this to me in simple non-GUE terms so I can understand it.
How do you know when the window is open and when it is closed?