Nitrox cylinder bands

[Storker]

There we go. Another 'trained' Nitrox user who is unaware that 02 cells degrade over time

I'd be careful with making assumptions about what other posters know or don't know if I were you. I've done my fair share of instrumental analyses in my time, and calibration and instrument reliability is something I believe I know a little bit about.

As you may - or may not - know, most handheld rec nitrox analyzers have only one user-operable calibration knob. Thus, two-point calibration isn't possible. In an ideal world, two-point calibration would be better, but with those instruments we can't calibrate, only check at two points since there's only one adjustment dial..

Apparently, the analyzer manufacturers have reasons for offering only single-point calibration, and I can offer three probable reasons:

1. Two-point calibration (both offset and slope correction) increases the risk that the average user adjusts their instrument way out of calibration. Not good. At all. Particularly given the level of knowledge most people have about calibrating instruments.
2. Offset may be more affected by cell age than slope is, so adjusting offset may be good enough unless high accuracy is needed
3. If the measured value is fairly close to the calibration value - as it usually is for rec nitrox mixes - a simple offset adjustment is good enough. In rec nitrox diving, you're taught to keep within certain margins, and a slight error in measurement will usually be of no importance.

Now, if you calibrate against air and want to measure your tank of 80%, it's obvious that a single point calibration isn't good enough anymore. Particularly for deco at high pPO2s where the margins may be smaller than for rec nitrox diving. In that case it's of course prudent to either calibrate close to your measurement, or preferably check that both offset and slope are correctly adjusted.

and need to be checked regurlarly against 2 known mixes, eg air and pure o2

So, are you saying that rec nitrox divers should start buying pure O2 to properly calibrate their hand-held analyzer? Good luck on implementing that.

to confirm the cells are still producing a linear voltage change..

You can't check linearity with a two-point calibration. One point checks offset, two points checks offset and slope, but for checking linearity you need a three-point calibration. IJS.

Examples of entry level dive courses include the PADI open water course SSI open water or BSAC ocean diver. Sorry if you do not understand that terminology. I did not say entry level eanx courses.

It didn't occur to me that you were setting up that strawman, since I thought we were discussing nitrox diving. Well played, sir. Score one.

What about avoiding the gotchas and strawmen now and discussing as adults?

 

[DJEdB]

Sigh, I have had it with the feeling: those techies allways know better, we rec divers are different and don't need to do what they do. There are no tech or rec divers, we're all just divers! We dive for fun, right? The only question is: what's the risk profile? The higher the risk profile, the more certain you want to be about what you breathe. Exactly what you mention. We have the same way of thinking.

One more time on topic: I'am not saying you have to analyse! But, if you want to know what's in the tank: do it yourself, analyse it yourself. There's no other way, stickers and procedures mean nothing. If you trust the operator, go dive. That's what I do on vacation. I certainly don't analyse every fill knowing it can only be air or EAN32. I just go diving because it does not matter what it is for this kind of diving.

I rest my case.

Obviously just my opinion, personally I like a strong

I'd be careful with making assumptions about what other posters know or don't know if I were you. I've done my fair share of instrumental analyses in my time, and calibration and instrument reliability is something I believe I know a little bit about.

As you may - or may not - know, most handheld rec nitrox analyzers have only one user-operable calibration knob. Thus, two-point calibration isn't possible. In an ideal world, two-point calibration would be better, but with those instruments we can't calibrate, only check at two points since there's only one adjustment dial..

Apparently, the analyzer manufacturers have reasons for offering only single-point calibration, and I can offer three probable reasons:

1. Two-point calibration (both offset and slope correction) increases the risk that the average user adjusts their instrument way out of calibration. Not good. At all. Particularly given the level of knowledge most people have about calibrating instruments.
2. Offset may be more affected by cell age than slope is, so adjusting offset may be good enough unless high accuracy is needed
3. If the measured value is fairly close to the calibration value - as it usually is for rec nitrox mixes - a simple offset adjustment is good enough. In rec nitrox diving, you're taught to keep within certain margins, and a slight error in measurement will usually be of no importance.

Now, if you calibrate against air and want to measure your tank of 80%, it's obvious that a single point calibration isn't good enough anymore. Particularly for deco at high pPO2s where the margins may be smaller than for rec nitrox diving. In that case it's of course prudent to either calibrate close to your measurement, or preferably check that both offset and slope are correctly adjusted.


So, are you saying that rec nitrox divers should start buying pure O2 to properly calibrate their hand-held analyzer? Good luck on implementing that.


You can't check linearity with a two-point calibration. One point checks offset, two points checks offset and slope, but for checking linearity you need a three-point calibration. IJS.


It didn't occur to me that you were setting up that strawman, since I thought we were discussing nitrox diving. Well played, sir. Score one.

What about avoiding the gotchas and strawmen now and discussing as adults?

Hi Storker.
Sorry, my 'trained nitrox diver' comment was off hand and flippant. I appologise.
No offence intended.

The orginal post was asking if there was a reason for nitrox bands on tanks for safety reasons. I think is is a good idea to have nitrox clearly labled, because a novice diver might take the wrong tank by mistake. Somone posted that everyone should analyse thier gas, my point was that novice divers, and holiday maker open water divers aren't trained to do that, and it is unreasonable to think they will do, so I think large clear nitrox bands are a good idea.

Thank you for your correction to my wording regarding calibrating and checking of the analyser. Yes you are correct. There is no option for two point calibration on most analysers. My point is o2 cells degrade over time. They should be checked (ok not calibrated) regularly.
People who own thier own analysers could take it with them when the take thier tanks for filling and check the cells at the filling station, which would most likely have a supply of o2.
Many people who dive recreational nitrox don't own thier own analysers, and would use one supplied by the dive resort.
My point was that cells need to be checked. There is a tank of pure oxygen on pretty much every dive boat anyway. (The medical unit!)
Anyway I hope we are having a discussion, and i didn't intend to start a row. Thanks also for the info about calibration procedures, I feel like I have learnt something.



Ed

 

[NAM001]

As usual I am having trouble relating many comments to the original posting. Well we all do it. It seems to be several things n the fan based on the comments. Are the NITROX bands a safety issue? Two fold answer. Yes for the physical aspects of the tank. (Underlining rusting). That is why they are removed and reapplied. I would sy they present the same problems as repainting your tank. The band is a warning label that says the contents are to be nothing other than nitrox. Nitrogen O2 blends. No trimix allowed in the tank with a Nitrox band on it. It is a notification to the filler to use nothing less than OCA in the tank . That is all the band is for. It is large enough for the blind to see and not mistake for any other gas tank.

 

[Diving Dubai]

Going back to Nitrox bands. I did have some on my tanks, they came off when I re-painted, and we have no need of them on our own tanks. we all use the same LDS for filling and we all have O2 cleaned tanks.

On resort dayboats I've seen removable Nitrox bands (an elastic material) which are just used to designate air and Nitrox - if you dive Nitrox you analyse if not don't pick one up.

Generally the standard mix is 32% so if on was picked up by mistake and dived on the computers air setting it's unlikely the user would exceed the MOD anyhow (most resort divers keep above 30m on these types of trips