increased PO2 at depth

[NC Wreck Diver]

Thinking back, I don't recall feeling narced, but I wasn't performing tasks under water either, which is where impairment shows up.

Hi Cruiser:

I'm going to say you just might have been narced. It's insidious. I'm taking this information from listening to my trimix buddies (I have not started a Trimix class yet). They tell me that we are all narced to some degree or another when we dive with air, or even Nitrox. It's almost impossible to tell. They state that when they dive with Helium, they are far more clear headed then when we dive our gas (air or EANx). I have been narced, and it was obvious. But on most dives, I don't feel like I am. They assure me that it's true. And I believe them. I guess I will see when I go through a Trimix course and try Helium as one of my inert gases.

Everything has it's drawbacks too. They warn me often about Helium Bends. You must come up really slow.

Safe diving to you.

 

[PfcAJ]

If you compare ascent times with Helium based gases to Nitrogen based gases, the ascent time is the same (within a minute or two). The slow ascent thing is a myth.

Buhlmann 20/85 gives you 36mins of ascent from a 150' dive for 30mins on air with 50% as the deco gas.

The same dive on trimix 21/35 results in 33mins of deco.

Myth.

There is some evidence to suggest that Helium is actually better to decompress from.

 

[NC Wreck Diver]

If you compare ascent times with Helium based gases to Nitrogen based gases, the ascent time is the same (within a minute or two). The slow ascent thing is a myth.

Buhlmann 20/85 gives you 36mins of ascent from a 150' dive for 30mins on air with 50% as the deco gas.

The same dive on trimix 21/35 results in 33mins of deco.

Myth.

There is some evidence to suggest that Helium is actually better to decompress from.

I assume that I will get very accurate information when I get to this Trimix class.

 

[rjack321]

I assume that I will get very accurate information when I get to this Trimix class.

Depends on the instructor, some will give you yesterday's news, others something more contemporary. Same with suitable ENDs, recommended ppO2s and just about everything else in a scuba class.

There's nothing about deco which is "very accurate" though, its mostly a WAG despite the purported precision of all the various models and computers.

 

[PfcAJ]

Ya man, there are some instructors out there that teach certified goobery. Chose wisely.

 

[Dr Deco]

Hello Readers:

Decompression Schemes and the “WAG”

I have written, for years, “Because decompression tables are written in discrete numbers, they give an appearance of precision that does not exist in reality.”

Why A Difference?

1. Divers are individuals. They differ in their response to medicines, to foods, to coffee and to decompression bubbles.

2. Divers have different heart rates, capillary densities, and tissue perfusions. Perfusion [local circulation rates] affect nitrogen loading and unloading.

3. Divers differ in their ability to produce micronuclei; the nuclei grow into decompression bubbles and lead to possible DCS. No one knows the nuclei concentration.

4. Musculoskeletal activity levels during decompression [offgassing] change the concentration of tissue micronuclei in the tissues of any one diver. This affects the probability of DCS.


Dr Deco :doctor:

 

[tlj3071]

Pretty much, yes.

... It's not the drop in O2 that makes you feel like you need to breathe. It's the buildup of CO2, which you can ignore (or learn to ignore more) for brief periods.

Thinking back several decades to when I took my EMT class, the primary mechanism that causes humans to breath is - in fact - a buildup of CO2, however in some patients - especially those with COPD or emphysema, that mechanism can get "burned out", and a fail-safe backup mechanism takes over. The back up is based on a lack of oxygen, which is why - occasionally - COPD patients that are treated by EMS crews stop breathing altogether and need to be placed on a respirator when given 5L/min O2 via a full non-rebreather. ER docs really hate that .

Tom