Nitrox: Should I be worried?

[fullytek]

Got a somewhat related question for those using their own analyzer. Since O2 sensors eventually need replacing, what happens to cue you in on that? Is it age, # of tanks analyzed, does the analyzer display an alert, or do you get suspicious when the reading is much different from what the tank is supposed to be, so you check against another analyzer?

Richard.

As an o2 sensor ages it looses capacity or its ability to achieve peak output.

All an analyzer dose is express the sensors milivolt output as a percentage.

Let's say 54 mv is represents 100 percent o2 and 0 mv = 0 percent o2. Plus or minus 10 mv that's why we have to calibrate.

As the sensor ages its ability to read in air is not affected but its ability to reach to max mv or 100 percent will be apparent.

Only way to validate the proper function of an analyzer is 2 point calabration.
This means calabrating in air then checking against a known 100 percent source. You may also have to factor in altitude and some analyzers come with an altitude calibration chart . If the analyzer cant achieve 100 percent or the factored value then the sensor is current limited and needs to be replaced.


Any one diving nitrox should have their own analyzer. Any shop providing nitrox should be asking all coustomers to analyze and sign an fill log prior to the dive.

 

[dhaines429]

For nitric always analyze yourself or watch tank being analyzed, period. I have sold thanks to people with nitrox blends in them and have told them not to take my word for it but go to a shop and have it analyzed.
I even have tanks analyzed when I have asked for air. I have heard stories of mistakes happening where tanks were filled with nitrox instead of air accidentally at busy shops.
All I know is I want to know exactly what I'm breathing so I know my limits.

 

[jstownse]

This is a valuable discussion. I'm very much a beginner compared to many here. The thought of analyzing tanks had never occurred to me (I do not dive EAN). In all of my dives, I don't recall ever seeing a member of the crew or fellow divers analyzing the tanks.

I like to think at least one of the crew is conducting this procedure prior to boarding, but I have no idea. I suppose I always just had peace of mind that if the dive leaders are willing to dive any of the tanks, that's good enough assurance for me.

Will certainly be inquiring in the future.

 

[DandyDon]

like to think at least one of the crew is conducting this procedure prior to boarding, but I have no idea. I suppose I always just had peace of mind that if the dive leaders are willing to dive any of the tanks, that's good enough assurance for me.

No way. The scuba industry developed significantly before affordable testers became available, and it largely operates on many out of date ideas & practices. None of the agencies are going to adopt general testing as a recommendation as that would increase costs & prices so discourage new students from entering. Only with the nitrox course do they bring up testing at all, but that helps support their excessive rates for that course, as well as helps sell O2 testers, but then they are dealing with divers who are more committed than entering students. So they keep doing the same old things they've been doing, which works as long as injuries can be discounted as sea sickness or party flu, and deaths are kept low enough to written off as drownings.

I just had a phone chat with the product manager at Inspector Tools, makers of the Sensoron Inspector. I have mine calibrated every other year with battery change and try to allow for possible drift over time, ignoring the EOL flashing in the screen. The maximum drift is 2% or 2ppm per six months, whichever is greater. So if mine is approaching 24 month, then I need to allow for 8ppm or 8%, whichever is greater. That's close enough for me as no tanks should have any CO, so if I get a reading of 10ppm - I'm not concerned about how accurate that may be as I am going to reject the tank either way.

The Sensorcon is not my primary tester, but I like to carry it for backup. Also doubles as a hotel room alarm since no hotel rooms have any, but all hotels have water heaters, some have room heaters.

 

[Just Anthony]

I recently did the course work and became Nitrox "Certified", but haven't yet used a tank. Now I'm in Cozumel, doing a week's worth of diving and the outfit I'm with said they have nitrox available, if I want it for $10 more. I'm interested in trying it, but I don't think that I will be able to analyze the air in the tank. I just arrive at the marina, jump on the boat, and they setup my gear, attach the tanks, etc.

My PADI Nitrox course made me scared enough about using enriched air if I cannot check the gas myself, and a buddy back home tells me the guy who runs one of the LDS' had his brother die from bad air in Mexico...

am I being unreasonably paranoid?

No. Ultimately, YOU are the guy who may die if the fill station monkey gets it wrong, not the fill station monkey.

Case in point. We went diving in Key West in January of this year. usually, we dive 36% around here.
So we had several cylinders that were about 1/2 full or 1/4 full that the Key West dive shop filled for us. They only banked 32%, so we were fine with that. Wasn't a big deal. They didn't empty the cylinders, just "topped them off".

Now the SNAFU comes in that this particular dive shop doesn't analyze the fill for you after they fill them (as you should have learned in the class, that's YOUR job). So the fill station guy fills them, slaps a "32% Nitrox" tape on them and off we go. Werealize later that particular shop's practice is to label the cylinder with WHAT THEY PUT IN IT rather than to analyze it and label what is in it.

So we get to the dive site and throw an analyzer on one of the cylinders just to be safe. Guess what's in the cylinder labeled 32% EAN??

Hint....if you mix 40 cubit feet of 36% EAN with 40 cubic feet of 32% EAN, you don't get 32% EAN.

It wasn't a huge difference, not enough to make it a "dangerous" dive with your computer set to 32%.
But if the problem had different parameters, then it could have possibly been an issue. We were diving shallow reefs, so it didn't matter, but if we had been diving the Speigel Grove it may have made a difference had we decided to go to push the limits.

 

[Alan Browne]

I recently did the course work and became Nitrox "Certified", but haven't yet used a tank. Now I'm in Cozumel, doing a week's worth of diving and the outfit I'm with said they have nitrox available, if I want it for $10 more. I'm interested in trying it, but I don't think that I will be able to analyze the air in the tank. I just arrive at the marina, jump on the boat, and they setup my gear, attach the tanks, etc.

My PADI Nitrox course made me scared enough about using enriched air if I cannot check the gas myself, and a buddy back home tells me the guy who runs one of the LDS' had his brother die from bad air in Mexico...

am I being unreasonably paranoid?

I just got certified and I've yet to actually dive Nitrox.

The course made it plain in all the presentation materials, the quizzes, the "simulations" and the exam that thou shalt not dive w/o analyzing the tank yourself. Period. As others point out it may indeed be enriched - but not the mix you're planning or entered into your computer.

Our plan is to return to Roatan this March and to the same resort. On the "certified divers" boat the captain has an analyzer and I've seen divers using it to check their tanks.

That said, there is _nothing_ about the analyzer that we used on our course that would tell you if you have a tank with, for example, CO in it.

This happened to my instructor on a dive in (IIRC Mexico). It appears the fill station's "intake" pipe was on an alley - the fill had been done with idling trucks outside...

 

[JackD342]

This happened to my instructor on a dive in (IIRC Mexico). It appears the fill station's "intake" pipe was on an alley - the fill had been done with idling trucks outside...

And that is why we teach divers to smell the air in the tank. Not very many divers have a CO analyzer, but the vast majority do have a nose...

Yes, CO is odorless. But you have described one of the most likely scenarios where a compressor is drawing it in, and you would expect to smell the other combustion odors from the exhaust, whether from a vehicle or from a generator.

I know a local shop on a busy street that specifically avoids running the compressor during rush hour, even though the intake is a comfortable distance from the road.

 

[DandyDon]

And that is why we teach divers to smell the air in the tank. Not very many divers have a CO analyzer, but the vast majority do have a nose...

Yes, CO is odorless. But you have described one of the most likely scenarios where a compressor is drawing it in, and you would expect to smell the other combustion odors from the exhaust, whether from a vehicle or from a generator.

I know a local shop on a busy street that specifically avoids running the compressor during rush hour, even though the intake is a comfortable distance from the road.

I am continuously amazed at how many experienced divers and professionals do not understand that overheated compressors burning their on lubrication oil are a bigger risk than air intake. You're not going to suck in 50 ppm CO from the street, but your compressor can create it. Smell all you want. You still die.

 

[uncfnp]

Can anyone give me hard numbers? How many recreational diver deaths/injuries have been attributed to CO poisoning? How many recreational diver deaths/injury from diving wrong nitrox mixes?

 

[Alan Browne]

And that is why we teach divers to smell the air in the tank.

I can't for the life of me ever recall an instructor telling me that. I'm pretty sure it's not in the PADI OW manual - but I'll be reading that on the flight down to Roatan and I'll keep my eyes out for it.