Best Nitrox Mix/ Profile at 100'

[Instructor_Tom]

When diving a 32% mix using a AL 80 @ 3100 psi diving between 85-115' I get about 22-25 min before I start getting into caution zone on my computer. With a 3 min safety stop I surface with about 1200 -1400 psi.My dive partner usually does a little better than me.we're leaving a good bit of gas in our tanks.

Since running out of gas isn't the problem, how can we increase our bottom time? We would like to increase our depth too, 122-130'.

Any pointers?

Doug

your question is actually 2.

1. you have 1200 PSI in your tanks and want to use more of your gas. you need to get some advanced training and learn decompression diving. this will require 2 things 1 moving from AL to Steel tank with increased capacity and the use of an AL30 or AL40 for accelerated deco.

2. bottom mix calculation. personally I always allow a margin of error for my bottom mix of at least 10+ft while maintaining a 1.4 PPO2. for a 130ft a with a 1.4 target an EAN 28% would be the ideal mix at 1.38 PPO2, I would dive an EAN 26%. also remember that as you go deeper you have to be aware of higher levels of Narcosis so the PO2 level is just one part of the equation at depths of 130+ you should look at getting Trimix certified and add Helium to your mix. for a 130 dive I would use a 26/15 mix for 2 reasons. 1 the helium will cut the Narcosis and have me clear headed at depth to better deal with issues and to remember the dive better and 2 the addition of Helium will extend my NDL since Helium is not an absorbed gas like Nitrogen.

in a nutshell it sounds like you are ready to extend your diving into a more technical realm and the correct way to do this is to find a good qualified instructor and do it safely.

hope this helps

T


Sent from my iPad using Tapatalk HD

 

[dumpsterDiver]

your question is actually 2.

1. you have 1200 PSI in your tanks and want to use more of your gas. you need to get some advanced training and learn decompression diving. this will require 2 things 1 moving from AL to Steel tank with increased capacity and the use of an AL30 or AL40 for accelerated deco.

2. bottom mix calculation. personally I always allow a margin of error for my bottom mix of at least 10+ft while maintaining a 1.4 PPO2. for a 130ft a with a 1.4 target an EAN 28% would be the ideal mix at 1.38 PPO2, I would dive an EAN 26%. also remember that as you go deeper you have to be aware of higher levels of Narcosis so the PO2 level is just one part of the equation at depths of 130+ you should look at getting Trimix certified and add Helium to your mix. for a 130 dive I would use a 26/15 mix for 2 reasons. 1 the helium will cut the Narcosis and have me clear headed at depth to better deal with issues and to remember the dive better and 2 the addition of Helium will extend my NDL since Helium is not an absorbed gas like Nitrogen.

in a nutshell it sounds like you are ready to extend your diving into a more technical realm and the correct way to do this is to find a good qualified instructor and do it safely.

hope this helps

T


Sent from my iPad using Tapatalk HD

I did not know that helium is not absorbed during a dive. I learn a lot on this board!

 

[bap]

your question is actually 2.

1. you have 1200 PSI in your tanks and want to use more of your gas. you need to get some advanced training and learn decompression diving. this will require 2 things 1 moving from AL to Steel tank with increased capacity and the use of an AL30 or AL40 for accelerated deco.

2. bottom mix calculation. personally I always allow a margin of error for my bottom mix of at least 10+ft while maintaining a 1.4 PPO2. for a 130ft a with a 1.4 target an EAN 28% would be the ideal mix at 1.38 PPO2, I would dive an EAN 26%. also remember that as you go deeper you have to be aware of higher levels of Narcosis so the PO2 level is just one part of the equation at depths of 130+ you should look at getting Trimix certified and add Helium to your mix. for a 130 dive I would use a 26/15 mix for 2 reasons. 1 the helium will cut the Narcosis and have me clear headed at depth to better deal with issues and to remember the dive better and 2 the addition of Helium will extend my NDL since Helium is not an absorbed gas like Nitrogen.

in a nutshell it sounds like you are ready to extend your diving into a more technical realm and the correct way to do this is to find a good qualified instructor and do it safely.

hope this helps

T


Sent from my iPad using Tapatalk HD

Perhaps you meant that helium is an inert gas?

Helium diffuses in and out of tissues much faster than nitrogen since the molecules are smaller and that means it has a much faster half-time rate than nitrogen.

[-]Helium also is not going to directly influence (decrease or increase) your NDL time.[/-]You use helium to reduce the nitrogen percentage to reduce narcosis.

 

[Kevrumbo]

Perhaps you meant that helium is an inert gas?

Helium diffuses in and out of tissues much faster than nitrogen since the molecules are smaller and that means it has a much faster half-time rate than nitrogen.

Helium also is not going to directly influence (decrease or increase) your NDL time.

No . . . Not quite:
From Bruce Wienke, Technical Diving in Depth, Reduced Gradient Bubble Model (RGBM) In Depth:

Helium NDLs are actually shorter than nitrogen for shallow exposures . . . Reasons for this stem from kinetic versus solubility properties of helium and nitrogen, and go away as exposures extend beyond 150 fsw, and times extend beyond 40 min or so.

Helium ingasses and outgasses 2.7 times faster than nitrogen, but nitrogen is 1.5 to 3.3 times more soluble in body aqueous and lipid tissue than helium. For short exposures (bounce and shallow), the faster diffusion rate of helium is more important in gas buildup than solubility, and shorter NDLs than nitrogen result. For long bottom times (deco and extended range), the lesser solubility of helium is a dominant factor in gas buildup, and helium outperforms nitrogen for staging. Thus, deep implies helium bottom and stage gas. Said another way, transient diving favors nitrogen while steady state diving favors helium as a breathing gas.
http://www.scubaboard.com/forums/ask-dr-decompression/32090-helium-offgassing-rate-2.html

Translating BRW's conceptual take on why shallow Helium has shorter NDL's than Air or Eanx 32 into practical and proper decompression profiles is not difficult: the NAUI RGBM Deco Tables have been out since 2003. Below (linked) are the comparative NDL's for Ean 32 and Helitrox; and example deco profiles for bottom times at 30m and 33m, for Ean 32 and Helitrox w/ & w/o O2
http://www.scubaboard.com/forums/te...358026-recreational-trimix-7.html#post5564996

The greater diffusivity of Helium from a free phase bubble model perspective (i.e. RGBM) means possibly loading idiopathic bubble seeds/bubble nuclei and having a Boyle expansion pathology resulting in DCS upon ascent --even if you were diving trimix within air or nitrox NDL's. . .

 

[bap]

No . . . Not quite:
From Bruce Wienke, Technical Diving in Depth, Reduced Gradient Bubble Model (RGBM) In Depth:


Translating BRW's conceptual take on why shallow Helium has shorter NDL's than Air or Eanx 32 into practical and proper decompression profiles is not difficult: the NAUI RGBM Deco Tables have been out since 2003. Below (linked) are the comparative NDL's for Ean 32 and Helitrox; and example deco profiles for bottom times at 30m and 33m, for Ean 32 and Helitrox w/ & w/o O2
http://www.scubaboard.com/forums/te...358026-recreational-trimix-7.html#post5564996

The greater diffusivity of Helium from a free phase bubble model perspective (i.e. RGBM) means possibly loading idiopathic bubble seeds/bubble nuclei and having a Boyle expansion pathology resulting in DCS upon ascent --even if you were diving trimix within air or nitrox NDL's. . .

got it, that's good stuff. Should have stopped and thought about the diffusion rates for He and N a bit more.

I went back and read on Mass Transport limits and that makes sense on the effect of the NDL

http://www.scubaboard.com/forums/as...es-quality-inert-gas-saturation-he-vs-n2.html

Mass transport of inert gases into biomass
depends on the product of gas solubility times
diffusivity. Helium has faster diffusivity,
and N2 has higher solubility relative to each
other (like 1/2.8 and 4.2 roughly). For short,
shallow exposures, the slower diffusivity
of N2 results in less total gas buildup in bulk
tissue, and hence shorter NDLs than He. For
longer and deeper exposures, He wins because
of its lower solubility. The point where
He and N2 NDLs meet, or cross over, is called
the "mass transport boundary".

 

[ianr33]

and 2 the addition of Helium will extend my NDL since Helium is not an absorbed gas like Nitrogen.

And this is why you should not learn to dive on the internet.

 

[chrpai]

And this is why you should not learn to dive on the internet.

But he's a dive master!

 

[dumpsterDiver]

But he's a dive master!

Helium is NOT absorbed during the dive. The DM just blows it out his a##

 

[mathauck0814]

So we have a rebreather diver who is asking about appropriate nitrox mixes and extending NDLs and we have a trimix certified diver claiming that helium does not impact dive profile. Anyone else concerned?'

OP - Assuming your CCR cert is a MOD1 (based on the question), I'd just dive your KISS Sport. This is exactly the type of dive where that unit will shine. The constant PPO2 will give you greater bottom times as the mix adjusts to accommodate changes in depth and will keep your offgassing more efficient as you ascend.

Don't park the unit because your dive buddies have insufficient gear - get dive buddies who have rebreathers

 

[chrpai]

So we have a rebreather diver who is asking about appropriate nitrox mixes and extending NDLs and we have a trimix certified diver claiming that helium does not impact dive profile. Anyone else concerned?

I'm staying out of it less I be accused of being uncivil yet again.