Trimix ICD gas switches

[Scubakevdm]

The deepest I have been in travis was 170 feet.

For cave diving carrying a 3rd deco gas is no biggie, I drop it at the start of the dive.

I like to talk about these types of subjects because I want to know more, and its hard to find people that have nitty gritty detail level knowledge of this stuff.

Of course remember too these are all models and theories, and a good example of how these therioes have flaws is saw tooth profiles will bend you but your computer won't tell you that, it's model is not accurate enought to deal with that, it proves our lack of knowledge of what is really going on, all these numbers, m vlaues, its all smoke and mirrors in an attempt to try to understand what is happening.

Maybe, but it's fun to think about. I don't have alot of nit or grit, but your observations seem logical to me.

 

[The Chad]

Wait a minute now. Are we talking just deep tech diving or cave diving? Cave diving I would assume you would have alot of sawtooth profiles and depending upon what computer you are using and what mode it is in you will get different results. The guys I know have to keep theirs in Bulh as VPM blows the computers mind with all the ups and downs. Back to topic...I would not want to be doing all this stuff in a cave

 

[FIXXERVI6]

Wait a minute now. Are we talking just deep tech diving or cave diving? Cave diving I would assume you would have alot of sawtooth profiles and depending upon what computer you are using and what mode it is in you will get different results. The guys I know have to keep theirs in Bulh as VPM blows the computers mind with all the ups and downs. Back to topic...I would not want to be doing all this stuff in a cave

Doesn't matter, cave or deep ow sawtooth will still get you, none of my computers ever complained about saw tooth, I did some profiles in caves that were so saw toothed I flet like crap after the dive even with extended shallow stops.

I dove my VR3 in VPM mode only and it never got pissy with any of my profiles.

I know the Vytec will throw a hissy but all it does is punish you, I don't think its really adjusting for your bodys gas load so much as the computer knows enough that its "bad" and it will punish you try try to make up for what it can't model.

 

[The Chad]

Good topic guys....if I ever end up moving to Austin maybe we can do a dive. Did I mention I have a boat? take it easy

 

[ianr33]

You have a can of coke, I don't know how much stuff they put in it but lets say its under 3 ata of Co2 pressure, let it sit long enough the disolved gas inside the coke itself could be cald 3 ata of pressure inside the fluid, but this is not the same as pressure of pushing against something its gas disloved in a fluid.

Open the coke, the ambient pressure drops to 1 ata of different gases, co2 comes out fast coke fizzes, if you opened the coke up to 1 ata of Co2 it would not come out as fast because the difference in pressure between the disolved gas (3ata) and ambient (1ata) is only 2 ata difference, with air its 3 ata difference.

I dont think that is correct.Suppose you replaced the gaseous CO2 with nitrogen at 3 ATM pressure.By your argument it would fizz wildly due to the 3 ATM difference in the CO2 pressure,but in reality it would not fizz at all as the pressure has not changed. What would happen is that the net rate of diffusion of the CO2 out of the liquid would increase. (It diffuses out at a set rate but no CO2 will be diffusing in to replace it)

This is analogous to switching to pure O2 when breathing air.You WILL NOT get rapid fizzing of N2 bubbles when you switch (Thankfully!) What will happen is that the net rate of diffusion of N2 out of the body will increase (Because no N2 is diffusing in)

There are 2 processes going on here. One is gasses diffusing out of a liquid from the surface (eliminating inert gas from the lungs) and the other is bubbles being formed by supersaturation (DCS) when the net pressure is reduced.

I think we are getting the 2 mixed up . Dive to 200 feet on air for an hour,large N2 loading. Imagine that O2 is not toxic and switch to 100% (still at 200 feet) You wont get any bubbling as the pressure has not changed (ignoring partial pressure vacancy/oxygen window stuff) but the rate of outgassing of N2 would be maximised.
Kind of a shame you cant actually do that,would make diving really easy!

 

[amascuba]

I have read to that inner ear hits may actually be spinal tissue hits in the areas that affect inner ear function and such, this would make sense to me as the spinal tissue I believe is the fastest tissue group.

It was explained to me by my GUE instructor that joint pain associated with DCS is actually a bubble on the spine that is affecting the nervous system in the region of where ever the joint pain is at, rather than a bubble in the joints.

 

[FIXXERVI6]

I dont think that is correct.Suppose you replaced the gaseous CO2 with nitrogen at 3 ATM pressure.By your argument it would fizz wildly due to the 3 ATM difference in the CO2 pressure,but in reality it would not fizz at all as the pressure has not changed. What would happen is that the net rate of diffusion of the CO2 out of the liquid would increase. (It diffuses out at a set rate but no CO2 will be diffusing in to replace it) I agree with this so I guess I didnt' say it right or my brain was straying from what I was trying to communicate, it wouldn't fizz wildly but there would be rapid gas exchange

This is analogous to switching to pure O2 when breathing air.You WILL NOT get rapid fizzing of N2 bubbles when you switch (Thankfully!) What will happen is that the net rate of diffusion of N2 out of the body will increase (Because no N2 is diffusing in) Your dealing with a single inert gas so yes when you go to pure o2 you do not fizz, pure o2 also opens up "slots" for nitrogen to be carried out so the rapid diffusion of N2 out of the tissue has a place to go, it just won't bubble out.

There are 2 processes going on here. One is gasses diffusing out of a liquid from the surface (eliminating inert gas from the lungs) and the other is bubbles being formed by supersaturation (DCS) when the net pressure is reduced.

I think we are getting the 2 mixed up . Dive to 200 feet on air for an hour,large N2 loading. Imagine that O2 is not toxic and switch to 100% (still at 200 feet) You wont get any bubbling as the pressure has not changed (ignoring partial pressure vacancy/oxygen window stuff) but the rate of outgassing of N2 would be maximised.
Kind of a shame you cant actually do that,would make diving really easy! Oxygen isn't a second inert gas so it behaves differently so I agree, but do the same thing with heliox on the bottom and switch to air, game chanes with a second inert gas

no argument from me

 

[ianr33]

Wow,everybody in agreement. Where is the fun in that ?

Only thing I might question is <<it wouldn't fizz wildly but there would be rapid gas exchange>>

I dont think it would be rapid,It would take hours,maybe even days to come to equilibrium,same as it takes hours/days to eliminate all nitrogen after a deep dive.

Now for the real question? What is the best way to mount my nitrox spare air on a Halcyon backplate??

 

[Scubakevdm]

I dont think that is correct.Suppose you replaced the gaseous CO2 with nitrogen at 3 ATM pressure.By your argument it would fizz wildly due to the 3 ATM difference in the CO2 pressure,but in reality it would not fizz at all as the pressure has not changed. What would happen is that the net rate of diffusion of the CO2 out of the liquid would increase. (It diffuses out at a set rate but no CO2 will be diffusing in to replace it)

This is analogous to switching to pure O2 when breathing air.You WILL NOT get rapid fizzing of N2 bubbles when you switch (Thankfully!) What will happen is that the net rate of diffusion of N2 out of the body will increase (Because no N2 is diffusing in)

There are 2 processes going on here. One is gasses diffusing out of a liquid from the surface (eliminating inert gas from the lungs) and the other is bubbles being formed by supersaturation (DCS) when the net pressure is reduced.

I think we are getting the 2 mixed up . Dive to 200 feet on air for an hour,large N2 loading. Imagine that O2 is not toxic and switch to 100% (still at 200 feet) You wont get any bubbling as the pressure has not changed (ignoring partial pressure vacancy/oxygen window stuff) but the rate of outgassing of N2 would be maximised.
Kind of a shame you cant actually do that,would make diving really easy!

Makes sense.

 

[The Chad]

Wow,everybody in agreement. Where is the fun in that ?

Only thing I might question is <<it wouldn't fizz wildly but there would be rapid gas exchange>>

I dont think it would be rapid,It would take hours,maybe even days to come to equilibrium,same as it takes hours/days to eliminate all nitrogen after a deep dive.

Now for the real question? What is the best way to mount my nitrox spare air on a Halcyon backplate??

LMAO agreed that does seem like a problem. I think you should open a new thread and get some input. Remember you should be redundant, so figure out where to get the manifold and isolator for your trimix.nitrox spareair