Diving nitrox when you don't own an analyzer

[Pullmyfinger]

I agree.....every shop I have ever been to that offers Nitrox, also had analyzers available.
They all had logbooks that you had to sign after analyzing and labeling the tank(s) you were getting filled.

With that in mind; you would do just fine without your personally owned analyzer.

I also analyze my tanks prior to diving them, so I chose to have my own analyzers.

They are kind of expensive, so keep an eye out for used ones if you decide to buy your own.
I bought my second one here for $100. It came with a brand new sensor, so I jumped on that deal.

Keep in mind that if you aren't going to use it much...then it will just be an item that requires a new sensor every year or so. Those cost $75.
Use the shops analyzer, and then you won't have to worry about that.

Cheers,
Mitch

 

[Dirty-Dog]

I'm a noob compared to others who have contributed in this thread, but... what's wrong with using the shop analyzer? Part of using an analyzer is calibrating it each time, right? I used the shop analyzer for most of this year until I bought my own.

There is really nothing wrong with using the shop analyzer. There's also nothing wrong with buying your own, of course.

 

[Searcaigh]

So you assume the label is correct for the MOD? I don't think this is such a genius idea. You analyze gas to make sure it is what you think it is. If you can't analyze it and the 28% turns out to be, say 50%, and you dive the MOD for 28%, you're likely to find the experience unenjoyable.

I've personally never seen anyplace that provided nitrox that didn't also have one or more analyzers available, if you don't have one of your own.

Fair point Dirty Dog, I did not think that through about a higher percentage being in the tank.

I have been offered Nitrox with no analyser available once in Jeddah (and I did dive air), as well as some other dive ops that don't normally supply EAN but have rented EAN from another dive op. Now I always carry my own and label the tanks with my name, percentage and MOD when renting Nitrox tanks.

All analysers I have used have a calibration mode, which I use before making the analysis.

 

[Dive-aholic]

Worse case scenario, treat as air but do not go beyond the MOD for the labeled mix (i.e. EAN 32 stay above 32M)

This is really bad advice. Never dive a gas you have not analyzed! How do you know it's 32% if you haven't analyzed it yourself. Someone died a few months ago because he thought he had air in a tank but actually had 100% O2 in it. If the shop you are getting fills from also provides Nitrox fills then you should even analyze air tanks. How do you know the tank monkey didn't open the wrong bank or use the wrong fill whip? Never dive a gas you haven't analyzed! That's how people die. You should also be analyzing for carbon monoxide. Yes, even in the US.

---------- Post added November 17th, 2013 at 07:30 AM ----------

I'm a noob compared to others who have contributed in this thread, but... what's wrong with using the shop analyzer? Part of using an analyzer is calibrating it each time, right? I used the shop analyzer for most of this year until I bought my own.

I had an analyzer that was acting wonky on me. I could calibrate it to 21% but it was only giving me 27-28% readings. I have my own shop/fill station and blend my own Nitrox so I knew that was wrong. I got out another analyzer and got the correct 31% I was expecting. The sensor was about a year old so I knew it was time to replace it. Lesson - just because you can calibrate an analyzer doesn't mean you will get a proper reading. If you aren't familiar with the analyzer you are using and know how old the sensor is, how it usually works, etc, then you could be getting bad readings. How do you know the shop hasn't been blending gas based on an old and going bad sensor and that 32% isn't actually 36% and you're diving to 115 with an MOD of 95?

I trust my life to no one else. For under $300 you can have a brand new O2 analyzer. Isn't your life worth that?

 

[Searcaigh]

This is really bad advice.

I agree, and have commented elsewhere on that

Never dive a gas you have not analyzed! How do you know it's 32% if you haven't analyzed it yourself. Someone died a few months ago because he thought he had air in a tank but actually had 100% O2 in it. If the shop you are getting fills from also provides Nitrox fills then you should even analyze air tanks. How do you know the tank monkey didn't open the wrong bank or use the wrong fill whip? Never dive a gas you haven't analyzed! That's how people die. You should also be analyzing for carbon monoxide. Yes, even in the US.

Never seen a CO analyser at any dive op

---------- Post added November 17th, 2013 at 07:30 AM ----------

I had an analyzer that was acting wonky on me. I could calibrate it to 21% but it was only giving me 27-28% readings. I have my own shop/fill station and blend my own Nitrox so I knew that was wrong. I got out another analyzer and got the correct 31% I was expecting. The sensor was about a year old so I knew it was time to replace it. Lesson - just because you can calibrate an analyzer doesn't mean you will get a proper reading. If you aren't familiar with the analyzer you are using and know how old the sensor is, how it usually works, etc, then you could be getting bad readings. How do you know the shop hasn't been blending gas based on an old and going bad sensor and that 32% isn't actually 36% and you're diving to 115 with an MOD of 95?

I trust my life to no one else. For under $300 you can have a brand new O2 analyzer. Isn't your life worth that?

Ideally you really need two reference gases for calibration, air is easy, its all around, but how do trust a reference gas if it is just another tank labeled from the same dive op?

 

[Dive-aholic]

Never seen a CO analyser at any dive op

Which is unfortunate. I have one and analyze all gas that leaves my fill station and also analyze all gas my students bring from elsewhere.

---------- Post added November 17th, 2013 at 07:30 AM ----------




Ideally you really need two reference gases for calibration, air is easy, its all around, but how do trust a reference gas if it is just another tank labeled from the same dive op?

Good point. While not ideal, you can just calibrate to ambient air before calibrating using the reference gas. That will at least alert you to any possible issues you may not otherwise be aware of.

 

[mala]

The shops I've dealt with all had analyzers and a bottle of 21%. With the analyzer mounted on the bottle of 21% check the reading if it's close 20.? - 21.?% the analyzer can be adjusted to 21.0%. Known standards is the way to make sure any analyzer is accurate.

also nice to check against a 100% 02 bottle.

when the cell starts to die it fails to read up at the high end.
so you could get a reading of 21% even tho the bottle you are testing is richer.

 

[Dive-aholic]

also nice to check against a 100% 02 bottle.

when the cell starts to die it fails to read up at the high end.
so you could get a reading of 21% even tho the bottle you are testing is richer.

Be careful with that. Calibration works for a range. If you calibrate at 100% and then analyze 32% you will not get an accurate reading in that range. Better to just calibrate with 21% to get a closer to accurate reading at 32%. This usually will mean your 100% reading will be over 100%.

 

[M-diver]

I've been diving recreationally on nitrox for years using standard banked mixes of 32 and 36 and was comfortable to use shop analyzer to verify the mix. As I progressed into more advanced diving, requesting more specific mixes that require shop to blend gas to my requests, I found that testing gas immediately after the fill and on the next day will give somewhat different results. This is due to the fact that air and O2 are used to top the tank in order to get the desired mix and gas diffusion takes some time.

This was the time where I found myself in a need for my own analyzer as I do need to know the actual gas and testing in the shop after the fill turned out to be inaccurate. I would not dive any tank I don't have confidence that I know what gas is in it, regardless what the sticker says.

 

[NAM001]

I bought my own because the LDS had 2 analyzers and they read differently. 10-15% different. One needed a new sensor the other was ok.
The shop determined which one was correct because they PP blended and knew from the Pure o2 added what the mix was. However when i picked up my tank the wrong tesster was used when i verified the conents, and it read 24% vice 32. Only after getting the other tester did i get a 31.9 reading. The next day i bought an elcheapo from oxycheq. Another occasion was going to coz and getting nitrox 32 tank. thier tester said 32 mine read 28. A third party also read 28. So the shop cut corners with a low mix knowing the customer would use thier faulty tester and be happy. Given the dive planned. the error was of no effect. But it could have been if teh error was off the other way and the best mix process was used. Could have ended up with 40+ thinking i had 32. The shop i used sampled the o2 content as it was pumped at the hp end of the compressor. Once again a faulty low reading testor would have resulted in a higher than desired tank content. I always test prior to using the tank. If there is any question in the contents then i use anothers tester. anyones but the shops if available. of course a decision on how to proceed has to be made. A one dive day to 60 ft or less is totally different than a 3 dive day to 100 ft. The shallower the dive the more forgiving an innaccurate air mix will be.

As for someones post about cal gas i have a 6 cuft bottle of gas from another system to cal with. after cal I then read the atmosphere it is alwasys a point or so from the 20.9. It will always be off a bit given it is not dry air.