Best Mix VS Standard Gasses (split from a GUE fundies course report)

[Billy Northrup]

Helping with your efficiency problem, most standard gases can be blended by mixing helium with 32% nitrox. It’s super easy and convenient.

Exceptions are 100% (duh) 50% (duh) 30/30, and 35/25. The rest are just helium and nitrox.

Yeah I know, we make banks of standard gasses with a Trihunter (BTW I have and almost new trihunter for sale). It's a speed thing for us, turn 6-10 sets of doubles and deco gasses in an hour really can't be done custom mixing everyone. Makes tiny RB bottles a no brainer. It wouldn't be a stretch to push 6-10K cf of trimix in a weekend

 

[Storker]

if all that the shops pump is 30% then I'll dive 30%, but I'm not diving it below 100ft.

Huh. I'd dive 32% to 30m, and even I believe I'm rather conservative.

 

[Storker]

heading out for a 90' dive off Key Largo and diverting to a 40-ish foot dive. Like I said in the preceding paragraph, EAN32 will work. But, EAN36 would work better....

How long time are you planning to spend underwater? And how big is (are) your tank(s)?

With my gear setup (and my bladder capacity) I see very few advantages with 36% over 32%. It's not just about the NDL, it's also about min gas and getting cold (or bored).

 

[PfcAJ]

Huh. I'd dive 32% to 30m, and even I believe I'm rather conservative.

Because of narcosis, not po2

 

[rjack321]

The practical difference between 32% and 36% at 40’ is nonexistent. The NDL time is absurd, longer than you’ll be diving a single tank for anyways. 310mins according to the NAUI table for 32%....

This is really what it comes down to.
If you limit yourself to 30m/100ft on nitrox there's not much value in worrying about best mix.
36% gets you a tiny bit more bottom time at 80-90ft.
By the time you get up to 60/70ft the NDL is plenty long on 32% anyway.

Once you get >110ft the 50-60ft operational windows of the other standard gasses work marvelously.

 

[Storker]

Because of narcosis, not po2

Ah. Of course. Thanks.

 

[rjack321]

Yeah I know, we make banks of standard gasses with a Trihunter (BTW I have and almost new trihunter for sale). It's a speed thing for us, turn 6-10 sets of doubles and deco gasses in an hour really can't be done custom mixing everyone. Makes tiny RB bottles a no brainer. It wouldn't be a stretch to push 6-10K cf of trimix in a weekend

The local GUE shop here wont fill 2-3L CCR bottles because "they are too small to do accurately". I find that hilarious but if they are that dumb what can you do.

 

[CAPTAIN SINBAD]

Because of narcosis, not po2

How do you use 30/30 for 120 ft dive without violating GUE guidelines for keeping PPO2 under 1.2? At a 120 ft dive you are at a PPO2 of 1.4 which is accepted by mainstream but not by GUE as I understand.

 

[rjack321]

How do you use 30/30 for 120 ft dive without violating GUE guidelines for keeping PPO2 under 1.2? At a 120 ft dive you are at a PPO2 of 1.4 which is accepted by mainstream but not by GUE as I understand.

30/30 is a 30m/100ft gas nowadays. For Ginnie and Little River and high flow caves like that. Kicking into Little River is arduous. And its easy to make navigational errors when you have a CO2 narc going.

Those of us who have been around awhile remember when the MOD was 120ft and we still use it that deep - if at all. Its a bit of an evolutionary dead end with rising helium costs and the proliferation of scooters. I'd rather scooter Little River or Manatee on 32% than kick on 30/30.

In open water 30/30 is pretty much not used by any of my GUE friends. its 32% or 21/35. The operational window is too narrow unless you're diving a very specific site (like the known caves above). My UTD friends have 25/25 in their toolbox for 100-130ft dives as a little bit of a gap gas.

ps a few people have toxed at <1.4, its a bit unclear if helium makes increases susceptibility to O2 (or lack of N2 increases susceptibility). One young woman cave diver died on 24/26 at 140ft (ppO2 = 1.25 at the time but they had been to 160ft before turning around) the IUCRR has the recovery report for July 14, 2007.

 

[ChuckP]

30/30 is a 30m/100ft gas nowadays. For Ginnie and Little River and high flow caves like that. Kicking into Little River is arduous. And its easy to make navigational errors when you have a CO2 narc going.

Those of us who have been around awhile remember when the MOD was 120ft and we still use it that deep - if at all. Its a bit of an evolutionary dead end with rising helium costs and the proliferation of scooters. I'd rather scooter Little River or Manatee on 32% than kick on 30/30.

In open water 30/30 is pretty much not used by any of my GUE friends. its 32% or 21/35. The operational window is too narrow unless you're diving a very specific site (like the known caves above). My UTD friends have 25/25 in their toolbox for 100-130ft dives as a little bit of a gap gas.

ps a few people have toxed at <1.4, its a bit unclear if helium makes increases susceptibility to O2 (or lack of N2 increases susceptibility). One young woman cave diver died on 24/26 at 140ft (ppO2 = 1.25 at the time but they had been to 160ft before turning around) the IUCRR has the recovery report for July 14, 2007.

The narcosis from CO2 has affected me way more then N2 - How is He offsetting any amount of pure CO2 narcosis? My understanding is CO2 comes from work and eventually overbreathing while working...

Very little dives over 120' but I notice almost nothing in the 100' 120' range, I dive almost daily and 32% at those depths on first dives..

In my AN/DP and Trimix class, I've been to the Hydro twice - first time worked way too much, and definetly was narced, second dive was with 20/5 due to class requirements but felt no different than any other dive - was very relaxed.

I so much wish that those classes offered a way to really tell the difference at the moment - breath air at 170 and switch to some safe He blend to show the difference - even if that's possible.