My AN/DP/Helitrox course

[ChuckP]

I would strongly advise you to back off the "best mix". People have toxed at that depth on similar mixes. Pushing ppO2 1.4 on the bottom saves you at most a couple minutes of deco. Check out this tox incident from July 14, 2007 in FL at a cave called "the crack". You will have to scroll down and find it by date.
Incident List - IUCRR

She toxed at minute 31 or 32 on 24/26 ascending from a 160ft dive. She died. (coincidentally she had planned on using 80% as well but didnt survive to use that). She was well within CNS limits, but there is some speculation that trimix exacerbates (or doesnt ameliorate O2 toxicity to the same extent N2 does). Pushing trimix ppO2s working/swimming on the bottom is bad news.

Best mix thinking (for me) comes from that recreational thinking to get most bottom time within NDL limits, then you get the tech training and (exaggerating this) you could care less about NDL's. Also, in the Great Lakes area where there's more custom mixing verses banking, I'm sure best mix is still pushed - regional thing.

The Heliox class goes to 180', so 21/35 has a po2 of 1.4 at 187'........ Get's you thinking

Really strange accident report there - seems nothing odd at all which is scary spooky. You got any reading on that higher PO2 and Helium line of thinking? That's just really weird as don't the CCR guys try and stay at a constant PO2 of 1.2 which would expose you more than a brief stint above 1.4........

 

[rjack321]

Best mix thinking (for me) comes from that recreational thinking to get most bottom time within NDL limits, then you get the tech training and (exaggerating this) you could care less about NDL's. Also, in the Great Lakes area where there's more custom mixing verses banking, I'm sure best mix is still pushed - regional thing.

The Heliox class goes to 180', so 21/35 has a po2 of 1.4 at 187'........ Get's you thinking

Really strange accident report there - seems nothing odd at all which is scary spooky. You got any reading on that higher PO2 and Helium line of thinking? That's just really weird as don't the CCR guys try and stay at a constant PO2 of 1.2 which would expose you more than a brief stint above 1.4........

Well you are always rolling the dice with O2 and doing any kind of work. And yes sometimes O2 does crazy things which is a good reason to just roll with the extra 5mins of deco by being conservative during the working phase.

As a working bottom gas, I wouldn't dive 21/35 deeper than about 160-165ft. ppO2 ~1.2 is my target knowing I can dip a little deeper if I had to in a pinch/emergency.

 

[Scuba Cobra]

I definitely concur with going to helitrox from the get go. 150' on air in current has made me feel pretty gasped for breath and narced. I have never used helium but with as much as everybody else talks about how much better it is I have wanted to have the ability to just add a little bit of helium for some of the harder dives I'm doing where I know ill be task loaded or in current.

Unfortunately everybody wants trimix course cost to do my helitrox (even though it's literally deco procedures on a different mix and theory work), and I don't have anything deep enough to justify full trimix.

 

[rjack321]

Unfortunately everybody wants trimix course cost to do my helitrox (even though it's literally deco procedures on a different mix and theory work), and I don't have anything deep enough to justify full trimix.

Have you tried some of the FL instructors? Not that far of a drive for you and you could do it in the "off" season for NC

 

[Marie13]

Best mix thinking (for me) comes from that recreational thinking to get most bottom time within NDL limits, then you get the tech training and (exaggerating this) you could care less about NDL's. Also, in the Great Lakes area where there's more custom mixing verses banking, I'm sure best mix is still pushed - regional thing.

The Heliox class goes to 180', so 21/35 has a po2 of 1.4 at 187'........ Get's you thinking

Really strange accident report there - seems nothing odd at all which is scary spooky. You got any reading on that higher PO2 and Helium line of thinking? That's just really weird as don't the CCR guys try and stay at a constant PO2 of 1.2 which would expose you more than a brief stint above 1.4........

Helitrox class goes to 150ft.

@rjack321

So you are advocating for mixes not containing over 21% O2 (such as 21/20, for example) or only standard mixes (21/35)? Your post wasn’t clear on that point.

Regardless of the O2%, there is no reason for me to pay a great deal extra for helium just to get a standard mix. Maybe it’s banked in your area. It’s not banked here.

 

[kensuf]

There are a number of people here who would likely love nothing more than to see me fail. They’d probably be even happier if I was to just totally give up diving. So this whole thread is a big middle finger in their direction. I’m very stubborn and very determined.

Tell me I can’t do something and I’m going to prove you wrong.

I'm made of that same material so understand your motivation. But you really don't have to prove anything to them, if they delight in watching others fail then they themselves are incredibly sorry and pathetic individuals.

 

[Manatee Diver]

So you are advocating for mixes not containing over 21% O2 (such as 21/20, for example) or only standard mixes (21/35)? Your post wasn’t clear on that point.

I read @rjack321 post more as advocating using a PPO2 max of 1.2.

 

[rjack321]

Helitrox class goes to 150ft.

@rjack321

So you are advocating for mixes not containing over 21% O2 (such as 21/20, for example) or only standard mixes (21/35)? Your post wasn’t clear on that point.

Regardless of the O2%, there is no reason for me to pay a great deal extra for helium just to get a standard mix. Maybe it’s banked in your area. It’s not banked here.

I didn't say standard mix anywhere in my post. I don't care about the 17% helium (which was or might still be a NAUI standard mix btw...) My post was about oxygen toxicity and the entire concept of "best mix". Which is why I cited someone who toxed and died - diving your chosen fO2 at a very similar depth.

Your fO2 is too high and thus your ppO2 during the working portion of your dive is too high.

 

[Marie13]

I didn't say standard mix anywhere in my post. I don't care about the 17% helium (which was or might still be a NAUI standard mix btw...) My post was about oxygen toxicity and the entire concept of "best mix". Which is why I cited someone who toxed and died - diving your chosen fO2 at a very similar depth.

Your fO2 is too high and thus your ppO2 during the working portion of your dive is too high.

What is your reference for this?

 

[rjack321]

What is your reference for this?

A reference for oxygen being toxic and high ppO2s, especially when doing any kind of work, are inherently more risky? Sorry no, not going to play your internet tech instructor.

If you want to run a ppO2 of 1.4 for bottom gas knock yourself out. I gave you a dramatic case of how that can bite you in the butt. I was taught 1.2 for the working phase over 15 years ago (and multiple times since then). 1.6 for deco/at rest.

21/17 @ 150ft (ppO2 1.16) for 20mins has 41 mins runtime (GF 50/80 on EAN50)
25/17 @ 150ft (ppO2 1.38) for 20mins has 39 mins runtime

Your choice saves 2 minutes on the ascent but comes with more risk.