ICD and gas swaps

[PfcAJ]

Which is you plan for a 100 meters / 328 feet dive?

10/85
21/35 at 190’
35/25 at 120’
50% at 70’
100% at 20ft

Two on the chest, two on a leash. Done.

 

[TheSnake]

Which is you plan for a 100 meters / 328 feet dive?
10/85
21/35 at 190’
35/25 at 120’
50% at 70’
100% at 20ft

Two on the chest, two on a leash. Done.

This seems to be a Heliox dive instead of Trimix dive.
You seems extremely conservative, using a END = 20 meters, which forces to make a big jump in END when switching on first deco gas:

when switching on Tx 21/35 your PpN2 jumps from 0,33 to 2,95 instantly ( @ 190 feet ).
( PpN2 on orange line )

Assuming a dive with 18 mins of bottom time, and a use of VPM+2, your dive gives a Runtime of 121 minutes.


Now, using the same decompression algorithm and the same number of deco tanks, with for example, the following gases:
Bottom: 12/60
Deco: 20/50 @ 230f
30/38 @ 135f
50/15 @ 72f
OXY @ 20f

you have no big jump in END and a smooth gas/Pps progression.

The final RunTime is now equal to 115 minutes.

 

[PfcAJ]

This seems to be a Heliox dive instead of Trimix dive.
You seems extremely conservative, using a END = 20 meters, which forces to make a big jump in END when switching on first deco gas:

View attachment 439676
when switching on Tx 21/35 your PpN2 jumps from 0,33 to 2,95 instantly ( @ 190 feet ).
( PpN2 on orange line )

Assuming a dive with 18 mins of bottom time, and a use of VPM+2, your dive gives a Runtime of 121 minutes.


Now, using the same decompression algorithm and the same number of deco tanks, with for example, the following gases:
Bottom: 12/60
Deco: 20/50 @ 230f
30/38 @ 135f
50/15 @ 72f
OXY @ 20f

View attachment 439677
you have no big jump in END and a smooth gas/Pps progression.

The final RunTime is now equal to 115 minutes.

View attachment 439679

1.6@ 230ft?
Vpm?
100ft end below 300ft?
Dat gas density?


No thx.

 

[TheSnake]

1.6@ 230ft?
Vpm?
100ft end below 300ft?
Dat gas density?
No thx.

You have not specified if you use Buhlmann or VPM.
Gas density ( EADD ) is 43m / 142f. What's the problem?
pp = 1.6? This is normally used ... but in every deco planner you can adjust deco PpO2 as you want ..... ( however in deep stops you have a PpO2 = 1.6 for a very short time when switching, and it decreases while ascending, so this is not really a problem ).

If you calculate a RunTime with a max deco PpO2 of 1.4 you got 127 mins. ( + 6 mins on your Runtime, so not significantly longer ), but evitating
a brutal jump on PpN2 @ 190f and consequent ICD risks, with same number of gas swaps.

 

[JohnnyC]

Standard gases make so many things much easier. And if there was such a huge ICD risk, guys using standard gasses would be getting torched all the time, and it's just not happening.

I'm with AJ on this one. I mean, aside from his use of imperial witchcraft when it comes to diving, I just don't see a problem with what he would do, and a great many other divers who are successfully doing these dives do not see any problem with it either.

 

[TheSnake]

Everyone make it's own choices based on it's own experience and it's formation. And I agree that.

I replied to a supposed additional risks taking care about ICD on gas switches because this require more tanks. This is not true and I explained with a rapid example.

However I see that it has different approach to similar problems.
Yes, ICD is a problem that satistically rarely occurs, exactly as Narcosis at 30m/98f. ( Never seen that ).
( I have 2500+ dives, a lot of air dives at 60m/196f and deeper, I have never faced to a buddy narcosis problem. Much more rarely ( NEVER ) on trimix dives using PpN2 = 3.5.
Despite my personal experience i dont think that narcosis do not exists )
It's choice is to ignore ICD problem and taking extremely care of Narcosis, using a END = 65 feet. ( Narcosis at 20m/60f is statistically = 0 )

 

[PfcAJ]

Everyone make it's own choices based on it's own experience and it's formation. And agree that.

I replied to a supposed additional risks taking care about ICD on gas switches because this require more tanks. This is not true and I explained with a rapid example.

However I see that it has different approach to similar problems.
Yes, ICD is a problem that satistically rarely occurs, exactly as Narcosis at 30m/98f. ( Never seen that ).
( I have 2500+ dives, a lot of air dives at 60m/196f and deeper, I have never faced to a buddy narcosis problem. Much more rarely ( NEVER ) on trimix dives using PpN2 = 3.5.
Despite my personal experience i dont think that narcosis do not exists )
It's choice is to ignore ICD problem and taking extremely care of Narcosis, using a END = 65 feet. ( Narcosis at 20m/60f is statistically = 0 )

You’ve never seen narcosis present itself at 98ft?

I might suggest trying a dive on nitrox then doing it again on 30/30. The different is marked.

 

[PfcAJ]

Regarding gas density:
Carbon Dioxide, Narcosis, and Diving | Global Underwater Explorers

 

[TheSnake]

You’ve never seen narcosis present itself at 98ft?
I might suggest trying a dive on nitrox then doing it again on 30/30. The different is marked.

Never

 

[TheSnake]

Regarding gas density: Carbon Dioxide, Narcosis, and Diving | Global Underwater Explorers

Yes I kwow that .... by the way I put in my software a EADD ( Equivalent Air Depth Density ) indication when choosing bottom gasses and deco gasses ( I think it's the only software with this option ).
As conservatism ( Buhlmann w/GF's or VPM +xx factor ) everyone chooses what is best for him ( within certain limits ).