using "hand-held" type O2 analyzers for deco mixes

[Narcoz]

DGX does not recommend using hand-held O2 analyzers for technical diving applications, and instead recommend using "technical-grade" analyzers have built in compensation for humidity, barometric pressure etc.

I have never seen anyone using a $1000+ trimix analyzer to get a reading on anything else but actual trimix so wondering what everybody's thoughts are about using standard recreational nitrox such as Palm D on nitrox deco mixtures.

 

[michael-fisch]

Properly calibrated before use, they work fine.
"Properly calibrated" means using a 2 point calibration.

Michael

 

[barth]

In the past analyzing a couple of tanks took me 8 hours.

I started searching for the right tanks. These were tanks filled with mixtures. Those were also compared with tanks and analysis from labs in other countries. The tanks were cleaned before filling and vacuum before filling. There were studies done on the stability of those mixtures in those tanks.

I took 5 till 10 of these tanks with different percentages of gas. Lower and higher percentages then the tanks I wanted to measure. Program everything in a computer. Everything was in a room with stable temperature and humidity and thing like that.

Then I went home. While I was sleeping all the tanks were measured three times. Next day when I came back I checked the data. Decide if I want a temperature and/or barometric correction.

Now I use oxygen sensors in my rebreather with high humidity. Pressure is also changing because depth is changing.

My handheld analyser is using the same sensor as my rebreather. Conditions for my handheld analyser are much better then I my rebreather.

Handheld analysers are accurate enough for analyzing decogas.

And if dxg is telling you that they are not accurate enough that doesn’t make sense. I think every diver could improve his measurements. But how much time and money do you want to spent? How accurate should your measurement be? A handheld analyser is accurate enough for decogas.

Maybe if you want to verry deep dive with low amount of oxygen In a bottom mix then it should be good to use an more accurate method. But not for deco gas.

 

[JahJahwarrior]

It's funny, because a few paragraphs above that, they say "Given that digital depth gauges are typically only accurate within 3 to 5 feet, and analog depth gauges can be even less accurate, obsessing over obtaining an exact analysis of the breathing gas is unnecessary."

As was said, my rebreather uses 3 of the same sensor in a humid environment with changing temperature and pressure and I trust that with my life, so I'm personally fine with using something like a Cootwo or the El Cheapo to check o2 on a deco mix or backgas mix.

What's shocking to me is how that we don't see any commercial units that do o2, he and CO in same unit.

 

[Graeme Fraser]

I won't loose any sleep using my Analox OE2EII handheld for any /all my deco gases. As @michael-fisch rightly points out, 2 point calibration, and not abusing the oxygen cell, will provide readings within acceptable tolerances.

For hypoxic gas, I'm using a helium analyser anyway, so using that for the oxygen content at the same time.

 

[PfcAJ]

The impact from humidity is pretty darn minor.

 

[tbone1004]

measure with a micrometer, mark with chalk, cut with an axe. No ones analyzer is that accurate and you'd have to be calibrating with reference gas that was within a couple of points of your target gas, i.e. a 30% mix to analyze 28-32% in order for it to matter that much. Even then, the practical difference in MOD and EAD between 30 and 32% is almost non existent. If you measure 32, and your buddy measure 31, it's close enough.
Now, if you're doing hypoxic mixes and doing 100m+ dives, that is a VERY different discussion because you're working at 10atas instead of 4, so everything compounds, but not at nitrox depths.

 

[Johnoly]

I insist my 5mm neoprene suit be within a thousandths tolerance +/- so my weight belt is correct.

 

[ScubaWithTurk]

measure with a micrometer, mark with chalk, cut with an axe. No ones analyzer is that accurate and you'd have to be calibrating with reference gas that was within a couple of points of your target gas, i.e. a 30% mix to analyze 28-32% in order for it to matter that much. Even then, the practical difference in MOD and EAD between 30 and 32% is almost non existent. If you measure 32, and your buddy measure 31, it's close enough.
Now, if you're doing hypoxic mixes and doing 100m+ dives, that is a VERY different discussion because you're working at 10atas instead of 4, so everything compounds, but not at nitrox depths.

This ^^^^

 

[rjack321]

good grief.

If you are attempting doc deco kinds of nuttery then yes a handheld analyzer is not the right tool

For the rest of us diving in the 0-100m range the plain galvanic sensors are fine. If 1% precision is too big then you need to rethink why you're so close to the edge.