why a 32 mix standard?

[texdiveguy]

Why wouldn't it be?

We normally within the scuba community consider a blend of 17/He to be hypoxic. I understand there is no actual defined % break....I just have never heard of a 'slightly' hypoxic mix.

 

[Soggy]

?? Since when did 18/45 TMx become hypoxic?

It's a semantic issue. Some people call < 21% O2 hypoxic, others call < 16% (minimum FO2 to maintain consciousness at 1 ATA) hypoxic.

 

[texdiveguy]

It's a semantic issue. Some people call < 21% O2 hypoxic, others call < 16% (minimum FO2 to maintain consciousness at 1 ATA) hypoxic.

"(minimum FO2 to maintain consciousness at 1 ATA)"

Which is normally considered to be in the area of 16%.

I have yet to meet a diver who considers 21-18% to be hypoxic.

 

[LG Diver]

We normally within the scuba community consider a blend of 17/He to be hypoxic. I understand there is no actual defined % break....I just have never heard of a 'slightly' hypoxic mix.

I'm just curious as to why you would take issue with the use of the term "slightly hypoxic" in reference to 18/45 if, by your own admission, there's no actual defined % break.

 

[nadwidny]

"(minimum FO2 to maintain consciousness at 1 ATA)"

Which is normally considered to be in the area of 16%.

I have yet to meet a diver who considers 21-18% to be hypoxic.

Apparently you just did but didn't notice.

 

[texdiveguy]

I'm just curious as to why you would take issue with the use of the term "slightly hypoxic" in reference to 18/45 if, by your own admission, there's no actual defined % break.

LOL, no 'issue' taken.... but I questioned the term 'slightly hypoxic'....thats a new one.

In my circle of mix divers we consider hypoxic TMx blends as 17% and less....with 18% being normixic.

 

[do it easy]

slightly hypoxic, slightly normoxic... what's the difference?

 

[SDAnderson]

I have yet to meet a diver who considers 21-18% to be hypoxic.

Admittedly, we haven't met but let me offer this:

Hypo-: Prefix meaning "low, under, beneath, down, below normal" ... The opposite of hypo- is hyper-.​

Ever wonder why so many flatlanders spend their first few days in Denver (.83 ata) complaining about headaches and gasping for air? They're adjusting to a ppO2 of ~.175. I like something less aggressive than "Wow, man, I thought I was going to pass out!" as the definition for hypoxic. I understand what you're saying though - you probably won't be breathing 18% mixes on the surface long enough to need to worry about time of useful consciousness problems. Still...when it comes to breathing gas, using a conservative definition seems the prudent thing to do.

 

[lamont]

32% is a good choice because 100-110 fsw makes a good floor to keep you above concerns about narcosis, lower ppO2 would restrict NDL time more in 100-110 range, while higher ppO2 decreases the MOD without usually increasing actual dive time.

i've also had accidentally hot mix (36%) in my tanks sit for weeks before i could burn them off in a shallow 30 fsw dive just to get rid of it and get something useful that I could go to 100 fsw with...

it also works well from a dive planning perspective... everyone just shows up with 32% and everyone stays above 100-110 fsw, everyone turns the dive after 30-35 mins deep and it works every single time...

 

[DeepSeaExplorer]

"(minimum FO2 to maintain consciousness at 1 ATA)"

Which is normally considered to be in the area of 16%.

I have yet to meet a diver who considers 21-18% to be hypoxic.

I hear ya...

Normoxic trimix divers like to consider 18/45 normoxic so they can extend their diving to greater depths and boat operators allow it because it helps fill the boat. I've done it myself and don't really see an issue with extending the limits in a controlled way. However, I think you'll find that most agency standards (and divers for that matter) consider anything less than 21% hypoxic.