Analyzing your own nitrox tanks

[drrich2]

I wish quality control was such in nitrox tank supply that we could just take and use it. I don't test my air tanks for contaminants. I don't test the diet soda I drink or the gas I put in my car. But as you can see, reliably great quality control is not there. Even the 'test it in my presence' thing indicated people don't consider the quality control in dive op. staffing to be sufficient.

Now, if I'm getting a nitrox tank and the analyzer breaks or some such, will I still dive it (especially if not doing so means thumbing the dive)? As a matter of personal risk acceptance, I would consider:

1.) Was is partial blended in the tank? If so, did someone test it & give a %? If not, do not dive; a mistake could kill. If it was tested, I'd make a judgment call as to whether to trust them. The politically correct (& lowest risk) answer is 'do not dive any tank you did not personally analyze or witness analyzed.' I'm not always politically correct.

2.) Was it banked? A large scale operation (let's say I'm at Buddy Dive in Bonaire) using banked nitrox, where all the tanks should be very nearly the same, and I know a number of other people have been using the tanks and analyzing them, so it is extremely unlikely the one I grab is some how, some way, dangerously off. I would probably dive it. Politically incorrect.

Factors that might impact my decision:

1.) Depth plan. Other threads have made the point that the PPO2 limit of 1.4 is a serious one; exceeding it can put you in jeopardy. Were I planning to dive to 105 - 110 feet on EAN 32, or otherwise skirt the MOD, I'd want to know the % mix more precisely. Because if memory serves, EAN MOD is 110 feet, EAN 36 MOD 90 feet?

2.) Time plan. We use nitrox mainly to extend NDLs by reducing nitrogen uptake rate at depth. If I plan depth, time and repetitive dives that will put me near NDLs, then the mix % needs to be known more precisely. For a couple of fairly shallow dives with a surface interval that will put me nowhere near NDL's, that's different.

Other people have told you the industry ideal standard 'politically correct' most risk conservative answer; never dive a nitrox tank you did not personally analyze, or witness analyzed, and be mindful of whether the analyzer appears correctly calibrated (reads 21% with air).

You've seen that in the real world, some people and businesses do it differently. I told you my view. I'm not endorsing it as something others should do. Imitating me is probably statistically more likely to get you killed. How much risk you're willing to take on to add convenience and perhaps avoid thumbing dives is up to you.

Richard.

 

[NAM001]

I check the tank at the shop and just befor diving. At the shop i ask for a different analyzer than they used to make sure thiers was not on the fritz when they checked. I use mine to insure more than one analyzer arrived at the same reading. I once in coz got 2 tanks f 32 and when i checked tham i got 28 on my tester and 32 on thiers. when i got home i checked it at a shop and mine was correct. I think they depend on trusting divers. At santa rosa wall you have a lot of forgiveness for a 70 ft dive with 32% but what if you were doing 100 and had a 5% error, or was doing repeditive dives. My elcheapo has never let me down. I always have someone else check my tank also to insure my testor is still close and not suddenly victom to a failing cell. Perticularly if i am diving close to MOD.

 

[Andyoak]

KWS: I assume you mean ensure not insure?

If I was diving with you, I would be happy to test your tanks to ensure they are the right mix, but I would not insure you

 

[Redshift]

They just handed you tanks like that? Not only I've always analyzed the gas I'm getting, usually there's a log to be filled before taking the cylinders.
And a reading cannot be drifting off! Was it even going back to 21% after analyzing the mix?
Don't accept to dive with gas you haven't analyzed or when you don't trust the analysis.

 

[TSandM]

Every Nitrox tank I have ever dived has been analyzed -- even in Quintana Roo, where sometimes the max expected depth is 15 feet. If the mix is way off, what else could be wrong?

But I think the OP has asked a question which has direct implications for a lot more than Nitrox. What we are taught to do for safety is often jettisoned as soon as the class is over. I can remember diving with my OW instructor and being somewhat baffled that we did not do a buddy check, since he was the one who taught me that you are always supposed to do that. I've been on boats in various places where my husband and I were the ONLY people doing any kind of dive plan or pre-dive check. There is an enormous amount of casualness in many people's approach to diving, and the scary part is that we all get away with it, until we don't.

The list of people from whom I would accept a Nitrox tank and trust the analysis they put on it is very short, and doesn't include anyone from a shop or a dive op.

 

[Searcaigh]

I analyse my tanks at the dive shop and later when I get home I use one of my own analysers.

I have several tanks and if I lend one to one of my buddies I insist that they also analyse it before using it. Up until recently my tanks that are air only were filled by a dive op that only supplies air so no issues regarding what the contents are, but now I check and in fact use one of my air only tanks as a reference for 21%

For just over $100 you can buy this model

DiveNav - Products - Nitroxbuddy

I have been using one of these for 6+ months and it compares well to my other O2 analyser an OxySpy DYNATRON AG - OxySpy

that I have been using since 2004 or thereabouts

 

[kwinter]

The guy who blended it is not going to breathe it. The guy who tested it at the shop is not going to breathe it. I am the only one whose life depends on that gas. Certain things are within our control, and others are not. Whether I choose to test it myself (for O2 content as well as CO) or rely on someone else is just another part of the risk acceptance level we each determine for ourselves.

 

[Splitlip]

This is reminiscent of my first nitrox dives.
My training was very thorough. Instructor was great. He kept hammering home the importance of analyzing your own mix/tanks. He accompanied the training with horror stories.
The class included two boat dives. We got to the boat and I dutifully analyzed. Once on the boat we started assembling gear. While we were moving, the other student was still fumbling with his rig. Turns out his yoke wouldn't go over the valves of his tanks. Our instructor tells us to switch tanks. I say "sure". "Now give me the analyzer".
By now we are out the inlet, and the instructor didn't want to break out the analyzer. It was kind of a complicated affair. Big old box that had to be connected to a lp inflator hose. Susceptible to water damage. Instructor tells me he analyzed the tanks himself. "Tim, trust me."
Of course I was adamant. Finally instructor acquiesced and said "Ok. By the numbers."

i analyze every very fill personally. Even my daughters air tanks.

 

[chillyinCanada]

Deleted

 

[Damselfish]

It's true there are rules you are taught at first to keep things simple and straightforward, that can be modified - once you have the understanding and experience to do so. Always analyzing a Nitrox tank isn't one of the rules you should break. I know I've had a few surprise tanks over the years. Perhaps the odds are low, but if one of those times I happened to be lazy and not analyze, then I happened to do a dive incompatible with the gas I didn't know I was diving...

Even though it's not one of the "rules", some will argue that all tanks should be analyzed in case someone screws up completely rather than the mix being off for some reason. I recently saw this happen even on a liveaboard, where the setup and routine make it seem hard to mess up - someone slapped a Nitrox whip on an air tank. Even though the whole row was air tanks and the Nitrox whip had a neon green hose cover, go figure. (Fortunately someone else caught the mistake quickly.)

I don't have my own analyzer, and usually have no problems with a shop having a reliable analyzer to use. I think this is actually true for most divers. But your first problem, which you ran into relatively soon, will certainly get you to consider it. I've had only one experience like that - a Pacific liveaboard where all the sensors were going with replacements apparently on the slow boat. Followed by some time with a land based op that didn't see why people should worry about it, and only arranged things so we could do so after a near mutiny.