Nitrox Certification?

[Canadian_Diver]

You guys must have the most amazing lung capacity ;0)

(In the voice of Arnold Schwarzenegger)
"Only girlie-men need to dive with air!"

 

[DiveGolfSki]

Well.... that's why stuff like rescue breathing/CPR work. Ambient air has roughly 21%O2, we metabolize about 4%O2 and breath out roughly 16%O2. This is pretty common knowledge for anyone who has ever taken basic CPR or high school human physiology....

-- Matt

They're teaching human physciology in HIGH SCHOOL??? Sheesh in my day, we simply dissected frogs.... s

 

[DiveGolfSki]

Well.... that's why stuff like rescue breathing/CPR work. Ambient air has roughly 21%O2, we metabolize about 4%O2 and breath out roughly 16%O2. This is pretty common knowledge for anyone who has ever taken basic CPR or high school human physiology....

-- Matt

Been reading up on this (I know I was asleep at HS human physiology or looking at a different part of human physiology ... usually blondes). What's the effect of pressure or higher PP02 on this consumption rate? At 4 ATA, do we still only metabolize 4% even though we're now breathing in 4x that?

 

[BarryNL]

I think a lot of people would disagree with that. It depends on *how* you go about things as much as the tools you use.

The reason agencies refuse to publicly acknowledge the safety benifits may have more to do with liability than you think. The PADI public line and the things they write to their members, for example, are completely opposite on this point.

Moreover, all of these "safe enough" arguments are a load of b.s. if you're the one getting the hit. DCS incidents are still very common and I see nothing wrong with tilting the odds in your favor.

R..

Considering the number of "undeserved-hits" that seem to be related to dehydration I'd say you're better off having a couple of glasses of water an hour before the dive than trying to reduce the risk with Nitrox.

But then, as a dry-suit diver I can also see the downside to this...

 

[BarryNL]

Been reading up on this (I know I was asleep at HS human physiology or looking at a different part of human physiology ... usually blondes). What's the effect of pressure or higher PP02 on this consumption rate? At 4 ATA, do we still only metabolize 4% even though we're now breathing in 4x that?

Theorising a bit here, but I'd say no. You only extract oxygen from the air to replace that your body is burning and you're not burning any more at 30m (unless you're swimming hard, which is bad). Therefore you probably only use about 1% O2 at 30m and breathe out air containing 20%.

In fact, if you think about it, theoretically at 90m you could breathe a hypoxic 2% O2 mix - and you'd have trouble metabolising 4% then

 

[serambin]

Theorising a bit here, but I'd say no. You only extract oxygen from the air to replace that your body is burning and you're not burning any more at 30m (unless you're swimming hard, which is bad). Therefore you probably only use about 1% O2 at 30m and breathe out air containing 20%.

In fact, if you think about it, theoretically at 90m you could breathe a hypoxic 2% O2 mix - and you'd have trouble metabolising 4% then

Are you saying that at 66 feet, we absorb 3 * 4% = 12 % O2?

Stan

 

[ScubaSixString]

Are you saying that at 66 feet, we absorb 3 * 4% = 12 % O2?

Stan

That is correct. That's why at 100ft a mix that is unbreathable shallower can be used

5% 02 times approx 4 gives you a 20% po2 (almost normoxic)

 

[mstudley]

Been reading up on this (I know I was asleep at HS human physiology or looking at a different part of human physiology ... usually blondes). What's the effect of pressure or higher PP02 on this consumption rate? At 4 ATA, do we still only metabolize 4% even though we're now breathing in 4x that?

I'm not sure. Regardless of depth the FO2 stays the same while the PO2 changes but I don't know whether or not what you metabolize stays the same or changes. If I had to guess I'd say yes, you metabolize more O2 at greater depth hence the need for things like hypoxic trimix and such....

 

[Atticus]

I'm not sure. Regardless of depth the FO2 stays the same while the PO2 changes but I don't know whether or not what you metabolize stays the same or changes. If I had to guess I'd say yes, you metabolize more O2 at greater depth hence the need for things like hypoxic trimix and such....

The amount of oxygen that you metabolize is based on your work load and physiology. The ppO2 that you expose your body to does not affect how much oxygen you metabolize (well, unless you are at a hypoxic ppO2).

Oxygen toxicity is caused by having excess oxygen pressure well beyond what you can metabolize.

The reason for hypoxic trimix is to limit the ppO2 that you will be exposed to. At 300 fsw you're at 10 ata. A reasonable fraction of oxygen for this depth would be 12%, for a bottom ppO2 of 1.2. If you breathed air on this dive you would be at a ppO2 of 2.1, which puts you at moderate risk for an oxtox episode.

Instead of thinking about 4% fO2 metabolism, think about how much mass or how many molecules of oxygen your body metabolizes in each time period. That's going to remain directly proportional to your exercise rate.

A good trimix and/or rebreather course should cover this in depth.

 

[DiveGolfSki]

The amount of oxygen that you metabolize is based on your work load and physiology. The ppO2 that you expose your body to does not affect how much oxygen you metabolize (well, unless you are at a hypoxic ppO2).

Oxygen toxicity is caused by having excess oxygen pressure well beyond what you can metabolize.

The reason for hypoxic trimix is to limit the ppO2 that you will be exposed to. At 300 fsw you're at 10 ata. A reasonable fraction of oxygen for this depth would be 12%, for a bottom ppO2 of 1.2. If you breathed air on this dive you would be at a ppO2 of 2.1, which puts you at moderate risk for an oxtox episode.

Instead of thinking about 4% fO2 metabolism, think about how much mass or how many molecules of oxygen your body metabolizes in each time period. That's going to remain directly proportional to your exercise rate.

A good trimix and/or rebreather course should cover this in depth.

Thanks Atticus. The issue on O2 metabolism arose regarding the narcotic effect of oxygen. String, made a point that we only metabolize 4% of oxygen. Mstudley pointed out that it was basic human physiology (of the 21% of oxygen in air, we exhale 16% ergo consume 4%).

It's not part of the original thread but do you have any info on this?