Is a Nitrox test at the dive site necessary?

[Stoo]

In another case of memory trumping proper practice, a diver arrived at Ginnie Springs in Florida planning to dive to about 100 feet using a tank that clearly said "oxygen" on it.. His friends asked him about it, and he said that even though it said "oxygen," it was actually air--he had filled it himself. His friends said he should analyze it, but he refused. He knew damn well what he had put in his own tank. After his death, the analysis showed that the tank did indeed contain pure oxygen.

This was the friend I mentioned in my initial post... There's a number of REALLY long threads about this situation that address many things beyond just the need to test gas prior to diving. Regardless of all of that, had he tested at the site, he'd be alive today, his wife wouldn't be a widow and his little girl would have her Dad.

I don't look at testing much differently than I do checking my SPG before I roll off the boat. Intellectually, I "know" the tank is full, because I watched the dude at the shop fill it. I maybe even did it myself. I don't think many people here would suggest that not bothering to check that your tank is full before diving is an "unnecessary" step, so why would checking what you're breathing be any different? For that matter, might as well skip confirming that your computer is set properly. And that your air is on. Really, they're all just unnecessary steps... ;-)

I've been at this a long time, and part of the reason for that is that I don't take shortcuts.

 

[boulderjohn]

I do most of the filling of my own tanks myself. When I have used a tank, I put on new tape describing the remaining contents before storing them. When I am ready to fill the tank again, which might not be for a while, that tape that I myself put on there is still only a guide to what I will expect to find when I analyze it just before the fill. Even though I labeled it and even though it has been sitting in my garage ever since I did that, I simply don't trust myself and my memory that much. I might have done something with that tank after that labeling, forgotten to change the label, and then forgotten that I did that. I am not a particularly stupid person, but I am definitely not perfect.

 

[Chugwhump]

That sounds a bit impractical to me. I tear off the part with the pressure, date and initials to indicate that it's not full anymore. Also, the tape around the valve is gone, so I have two independent indicators that the tank has been used.

Since I usually finish my dive with some 40-100 bar left in my tank, I prefer to have the spent tank marked with the percentage mix. If I fill only 32%, it really doesn't matter, but if I'm switching mixes it does matter as to what mix I should fill to get the mix I want.

We don't mark pressure.
They are full or empty.
If we got caught driving around with our tanks when they were full,
It would be a felony or something.
Not that I think the DOT is looking for us especially hard.
Our system is this:
Tape on means full.
Tape off means empty.
That is all.

I would certainly say that if we put tape on the valve itself, it would have saved me from a slightly abbreviated second dive the last time I was out.
So it might be a good idea for me to implement putting the around the valve cover itself to act as a "Visual Seal" capacity.
I would be able to see better at a glance if the tank is a dud.

On my trip a few weeks ago I could also have just grabbed the two 100's the dive boat captain said were tucked below deck and used them,
But then I would need to make a 25 mile trip one way the following Monday and get the refilled tanks back aboard.
I do hate on many aspects of caves diving....
But on not all aspects of cave diving do I hate.


Chug
Not dead yet....
But getting closer to death by the day.

 

[uncfnp]

As I said in another thread. I analyze when I pick up my tanks. I don't reanalyze unless something happens to make me question myself or my mix. Or if a significant amount of time has past, such as filled tanks stored from last dive trip.

 

[Freewillow]

NO. Provided that immediately after the analysis you label the tank with your name, date, mix and MOD

 

[tbone1004]

I'm sure it's been covered but too many long answers to read, so I'm sure I'm agreeing with someone and disagreeing with others.

The answer is yes, unless.

The unless reason is as follows
If you personally analyzed the tanks *which you should have anyway*, and they haven't been sitting around for any length of time, and no one else has handled them, or you are diving in a location that doesn't warrant a check *that statement will raise some flags, but that's fine*.
So, what do I do?
I analyze when they get filled and mark. FO2, date, initials.
If the time between fill and dive is less than 24 hours, I don't reanalyze. If it is longer than 24 hours, I do, unless...

Unless I am diving a site like a pool, or a shallow confined area like a quarry, in which case I set computer to air, and know that there is something above that in the tanks, but couldn't be bothered to care because I'm not going deep enough or long enough for it to matter. How do I know? The only tanks that are O2 clean are the 50/50 bottle and the 100% bottle, the rest can only have bank filled nitrox of some variety in them and at less than 40%, so I don't care if it is air, or 40% in the bottles because the MOD at 40% is 100ft which is deeper than the areas that I'd be diving at that point and the dives are shorter than the CNS clock

 

[RJP]

I am one of those guys that thinks an analyzer should be included in the cost of any nitrox course, so yes, I think it's a great idea.

So what you actually mean is "I am one of those guys that thinks a nitrox course should cost $400 or so... in order to cover the cost of charging each student for a nitrox analyzer that they don't really need to own."

 

[davetowz]

In my opinion,Knowing, without a doubt, what gas is in what cylinder is crucial. How you personally implement that is up to the individual diver. I analyze my gas again before diving. That may be the day we are loading out or on the boat as I set up. If I might be pushing limits ( personal or close to mod ) I analyze just before the dive. The consequences of analyzing are a cancelled dive or a delay while it gets sorted out. The consequences of not analyzing could land me on the A&I forum.

 

[g1138]

Well assuming you Analyze then label the tank properly:
If you partial pressure blend: Fill with O2 then top off with Air, the Analyze you get right after fill will be off from what you analyze hours later. The air has to mix before it is uniform.
It's not a very big change, but it is a change.

Temp can affect the mix, so straight from blend to water doesn't help you with knowing the correct final mix.
If you don't push your MOD and round up to the whole number on your first Analyze then yes you're probably very safe to just Analyze at the Shop, label, then dive.

For Banked Gas you're pretty safe to just Analyze at the shop and that's it.

If you have an Analyzer at the Dive Site, it never hurts. It takes me longer to pee than it does to analyze.

 

[DevonDiver]

The standardized protocol is that the nitrox diver must personally analyze and label the cylinders they will dive.

That is sufficient.

However, I think it is prudent that if the nitrox diver has any subsequent cause to question the contents of their cylinder, then they should re-confirm their analysis.