Is a Nitrox test at the dive site necessary?

[Skulmoski]

Depends on your propensity for risk; I check the mix on the boat before I dive. One less thing to leave to chance or error.

GJS

 

[DiveNav]

Any word on how the CooTwo performs in the field? I'm in the market for an analyzer, and like the idea of having O2 and CO in one box.

Doing good if you ask me ..... but I am biased as I have designed it

Seriously, there is a thread on cootwo here on SB --> see link

 

[gr8jab]

I never dive at home. I always fly somewhere to dive. Considering the amount of equipment I have to pack, I don't want another fragile expensive device to be lost or damage in my checked luggage or spend 15 minutes explaining to a TSA agent after searching my carry-on. I analyze once - sometimes in the shop, but I always label my tank; sometimes on the boat, but always just before attaching my regulator. Sometimes they don't want to get the analyzer out again, and ask me to analyze both my tanks. Labeling is then necessary, since tanks get moved.

TSA in Houston, Orlando, and Cozumel can ID scuba gear from x-ray. Here in the pacific northwest, the agents are experts at dealing with body piercings, but most have never heard of scuba.

"That's a SCUBA regulator, you breath from it."
"No, it is not like a gas-mask."
"That's a flashlight. No, it's not broken, it's UV."
"UltraViolet - invisible..."
"Yes, here is the TSA policy on traveling with Lithium batteries."
"That analyzes gas... G A S..."
"Yes, I'm sure that other thing is not a gas-mask."
"Yes, I'll wait while you call a supervisor."
"This room over here, behind this steel door?"
"Wanna share a cigarette when we are all done?"

 

[BoltSnap]

Yes. And they are probably also afraid that if they accidentally dip below the MOD for 10 seconds they will suffer immediate oxygen toxicity. Things are not that precise, and the standard protocols allow a lot of room for error. We instructors teach those protocols, and we tell people not to violate them at all, but the reality is that you have to more than a little out of line to have a problem on a recreational dive. The dangers are much more pronounced on a technical dive.

Rules are rules and they can go either way. You can chose to follow the rules all the time or not and take the consequences especially when you are diving/living in the third world country.

 

[NAM001]

For all those who think that when you partial pressure fill and dont mix the gas before testing, the difference is minimal, I did an 80 mix a week ago with interesting results.

Finished topping with air, did the first test 35%, rolled it on the grass for a few minutes 57%. Now I am thinking I didn't get this blend that far bad surely, rolled again and swung it up over my shoulder a few times and rolled again, 80.5%. Left it over night and it was stable.

On another occasion recently had a PP fill from a shop, tested after 24 hrs after the fill on pickup, 75%, rolled it around, 80%.

I usually fill, mix and test. Wait 24 hrs and test again. Test prior to loading in my car for use.

I also check all tank pressures prior to loading. Got a suprise the other day after blending a borrowed tank. tested pressure after 5 days and found only 170 BAR instead of the original 210 BAR. Quick check revealed a neck O ring leak.

Rule 1; Never assume anything ever. Murphy is far smarter than you and just waiting for the chance.

I keep hearing stories like this but have never been able to make it happen at home. I put in O2 and then pump them up with the compuressor. I check them when done and the next day maybe .1 difference. I roll them on the grass and no change. Are people filling so slow there is no mixing ?, if that is possible. my system has nothing but a compressor and a filter system. I fill with the tank valve shut till the filter has 3k+ in it ans then open the tank valve a little and run the filter down to about 2k and shut it again till I get above 3k again. It is so hard for me to imagine filling from an air bank and having such a jet of air going into a tank hitting the bottom and circulating that there is reduced or no mixing. If this is soch a problem how do you get 32 from a 32 bank with out rolling the bank? Although by shere numbers of those reporting this I can not denie it is happening but some would have to show me to make me a believer.

 

[Peter69_56]

Come over any time and see. I would say 90% of my blends need mixing. I fill from an O2 cylinder then connect my compressor and top up. The back pressure on my filter stack/compressor is about 140 BAR. I also have 2 filters in series and 2 back pressure valves, one built in to my bauer, and the second after my second filter stack.

I didnt believe it when first told either, but from experience it happens. I can't get my head around why the mix doesnt mix well because as you say the air squirts in and one would think the blend would be a total mix. Clearly this is not so. Perhaps someone much wiser than us can explain how the gases seem to stratify, or at least not mix well.

If you saw the show I think Deep dive detectives or one like that with a father and son doing deep dives. They show it happening when they do a blend one day with helium. Had to roll the cylinder to mix it.

 

[NAM001]

Come over any time and see. I would say 90% of my blends need mixing. I fill from an O2 cylinder then connect my compressor and top up. The back pressure on my filter stack/compressor is about 140 BAR. I also have 2 filters in series and 2 back pressure valves, one built in to my bauer, and the second after my second filter stack.

I didnt believe it when first told either, but from experience it happens. I can't get my head around why the mix doesnt mix well because as you say the air squirts in and one would think the blend would be a total mix. Clearly this is not so. Perhaps someone much wiser than us can explain how the gases seem to stratify, or at least not mix well.

If you saw the show I think Deep dive detectives or one like that with a father and son doing deep dives. They show it happening when they do a blend one day with helium. Had to roll the cylinder to mix it.

I cant speek for blends with helium only standard nitrox

 

[lerpy]

I treat it like my luggage going to the airport. If I was there when it was packed, and I know exactly what is in it, and I put my label on it making the mix and MOD and it stayed in my possession from the fill to the water then I would not have concern, unless I had one of those, did I mark that right moments. In that case I never say, I'm sure I did, I re-check.

 

[Stoo]

This one shows up a lot, is it a good one?

Analox O2EII Nitrox Analyzer

That's what I use... It's quick to use and simple. I used to use an OMS one, but it meant mounting the reg, and connecting it to a BC hose.

Analox makes a nice little CO detector too and they're often available as a matching set. I have the CO as well, but only tend to use it when we're at some tiny little place on some tiny little island.

 

[The Chairman]

Ok. I admit physics is not my thing but how does a change in temperature within a closed system (tank) change the percentage of the mix? Pressure, yes. But percentage?

It doesn't. However, the cell used to perform the test is affected by both heat and moisture. The relation is seldom linear or predictable. Why add variables? I've seen a 3% variance between hot and ambient testing. Ergo, I try to test all tanks at ambient temperatures.