NITROX CERTIFICATION PROTOCOLS - REAL WORLD

[Wibble]

Ok...Can someone please help me with this. WHY is it necessary to calibrate at all? Won't holding it to my EANx tank provide me with an accurate reading, of the percentage of O2, in that particular tank? Provided of course, the analyzer is functioning properly and its batteries are fine. Isn't my Analox O2Ell specifically designed to analyze the percentage of oxygen, present in any device I analyze? Do I have to "teach" my analyzer, what oxygen is, each time I use it?

The sensor will slightly drift over time. The OE2 has a potentiometer (knob!) on it which can be turned.

It's really simple. Turn it on (it being the OE2), pull out the restrictor dome and wave it around in the air for a couple or three seconds. Then adjust the knob to 20.9, subject to the humidity pointed out earlier.

The actual reality is that for recreational non-deco-limit nitrox, it doesn't need to be that accurate; a couple of percent either way probably won't matter.

If you're diving deep on a single cylinder, you will be way more gas constrained than CNS loading (for oxygen toxicity). It does affect your NDL, but again, the deeper you go, the more gas you'll be consuming, so will need to shorten your dive for that.

Being accurate is fine, but a bit of leeway is fine.

The most important thing is always analyse your gas. You're looking for the 1 in 1000 error where your cylinder was filled with 100% oxygen by mistake. That would ruin your day.

 

[360GUY]

Yikes! A tank loaded with 100% O2.

Just for shi** and giggles, play that scenario out for me. I’m ready for the dive. I enter the water. I place the regulator in my mouth and with my compadres, I begin my descent, unknown to me, that my tank contains 100% oxygen.

What happens next…

 

[BRT]

Depends on the analyzer.

Which analyzer will calibrate correctly when reading an O2 level higher than 20.9% unless you are calibrating to 100%?

 

[tursiops]

Yikes! A tank loaded with 100% O2.

Just for shi** and giggles, play that scenario out for me. I’m ready for the dive. I enter the water. I place the regulator in my mouth and with my compadres, I begin my descent, unknown to me, that my tank contains 100% oxygen.

What happens next…

As you descend, the partial pressure of oxygen increases. It reaches 1.6 atmospheres at 20 ft. Below that, after a few minutes, you risk oxygen toxicity, which causes convulsions. The convulsions don't kill you, but the drowning does. This is not theoretical; many of us know someone who died from this.
Analyze your damn gas.

 

[Efka76]

In all my Nitrox dives o2 analyser was available, everything was done by the book. Never follow crowd as this is your life. You have to know exactly what you are breathing, have correct data for your computer. Also, always make sure that you are diving within your MOD limits. People get into serious accidents if they do not follow simple rules.

 

[tursiops]

Which analyzer will calibrate correctly when reading an O2 level higher than 20.9% unless you are calibrating to 100%?

NO analyzer will calibrate correctly unless you know the percentage O2 in the gas you are using for calibration. Using air -- even ambient air -- and pure O2 are the usual calibration gases.
But SOME analyzers assume your calibration gas is air so default to assuming 20.9% O2 and there is no way to change that. If you use one of those analyzers with a bottle of pure O2, it will call the O2 "air" and if you then try and analyze your Nitrox, you'll get some ridiculously low number.

Now, what is the problem with recalibrating -- correctly -- in-between bottles of Nitrox?

 

[Wibble]

Now, what is the problem with recalibrating -- correctly -- in-between bottles of Nitrox?

Of course not if it's in your possession! The point is if you've picked it up a day/week/month later then just resetting it to 20.9 is plain prudent (with the OEii). Same with any analyser TBH; it should be reading 20.9 (adjusting for humidity...) when you start puffing your gas into the sensor.

 

[360GUY]

Excellent feedback. Very helpful. So then it seems like the three basic rules for diving nitrox is:
1. Trust no one but yourself
2. Trust no one but yourself
3. Trust no one but yourself
Oh…Analyze your gas

 

[tursiops]

Of course not if it's in your possession! The point is if you've picked it up a day/week/month later then just resetting it to 20.9 is plain prudent (with the OEii). Same with any analyser TBH; it should be reading 20.9 (adjusting for humidity...) when you start puffing your gas into the sensor.

I agree completely. What do you think was meant here?

One thing you don't want to do is calibrate the O2 sensor between tanks of nitrox. You will get bad readings because the sensor will reset to accepting a high O2 level as 20.9%

 

[BoltSnap]

1. Trust no one but yourself
2. Trust no one but yourself
3. Trust no one but yourself

1. Always doubt yourself and those around you.
2 Trust no one but yourself
3. Trust no one but yourself
4. Trust no one but yourself