nitrox analyzing question

[divnlite]

I have been diving Nitrox all over the carribean (Bonaire, Cozumel, Belize, Caymans, Roatan ~ liveaboard and land based) and have never had a problem analyzing my own tanks. As TSandM says everywhere seams to have their own system for the diver to analyze and record the info.
Learning a bit about the different analyzers available and how they are calibrated, how long the sensors are good etc... is a good thing as well. If you get a questionable reading or different readings on multiple tests you can always analyze an air tank for comparison. I would never dive a Nitrox tank that was given to me that I wasn't allowed to analyze myself and I have never run into this.
I would say if you plan on diving some remote areas etc it would probably behoove you to go ahead and get an analyzer.

 

[TxHockeyGuy]

my first nitrox dive - outside of the class - i was unable to analyze or witness my tanks being analyzed - they just showed up at the dock already labeled.

my dive buddy was fuh-reaking out, after realizing there would be no analyzing our own tanks. I asked for an analyzer and the guy said, 'I marked 'em all, they're right'. He was also the Instructor that coordinated the trip ***not my instructor btw*** so i just didnt know what else to do.

i guess i thought it was acceptable....no one else seemed to mind. But now that i am reading all of these replies...i am looking for an analyzer.

The only time I would even consider doing something like that would be in our local quarry which I typically dive to a max of 35' (got to stay above that thermo). In order to have a MOD of 35' (calculated at 1.4) they'd have to have put in EAN68. I have picked up tanks before when no analyzer was available but I did analyze it before I dove it, just not at the shop.

 

[msmendel]

You DO want to analyze your own tank every time, rather than rely on anyone else's analysis. That said, EVERY dive operation of any size I've dived with that supplied Nitrox has had one or more analyzers available for you to do just that.

Standard procedure for a land based operation on a boat dive is for you to take an already filled tank, analyze it and record the result on a clipboard for the operator (fill station). You then, note the result, and your name, on a strip of masking tape you afix to the tank. They suppply the masking tape, if you wondered. That's all before the tank is placed on the boat, either by you or by them.

One time (in Florida) diving with a less sophisticated operation, I analyzed the tank (after my request to do so) on the boat, and there was one analyzer to share between two boats. That was unusual and a pain. If that occured a lot, I'd buy my own analzyer. But it doesn't.

I have no idea about live-aboard operations, OTOH.

 

[djanni]

I have my own analyzer.

Most operators have analyzers for you to use but not always. In those unusual cases you either trust the % written on the small piece of masking tape or you don't dive.

I've had it less than a year and used it about 20 times so far. So far the readings I get are within a percent or 2 of the number written on the tank.

We had about 160 dives on nitrox before getting the analyzer. We're still alive. I think.

It's mostly a matter of how much risk you percieve and what your risk tolerence is. Since you're a diver I would assume you have a reasonabley high risk tolerence.

My risk tolerence - I have my own analyzer. I guess I heard enough stories like the one UndrWatrDan told for us to fork over the money so we could analyze in those rare occations when we can't anaylze the tank with someone elses analyzer.

Of all the divers we've dived with I can think of only 1 who had their own analyzer. I trusted his judgement and decided to buy one. That happens to be Rick Murchison.

 

[Gene_Hobbs]

Lang, M.A. (ed) 2001. DAN Nitrox Workshop Proceedings. Divers Alert Network, Durham, N.C., 197p.

RECOMMENDATIONS:

1. No evidence was presented that showed an increased risk of DCS from the use of oxygen enriched air (nitrox) versus compressed air.
2. A maximum PO2 of 1.6 atm was accepted based on its history of use and scientific studies.
3. Routine CO2 retention screening is not necessary.
4. Oxygen analyzers should use a controlled-flow sampling device.
5. Oxygen analysis of the breathing gas should be performed by the blender and/or dispenser and verified by the end user.
6. Training agencies recognize the effectiveness of dive computers.
7. For recreational diving, there is no need to track whole body exposure to oxygen (OTU/UPTD).
8. Use of the "CNS Oxygen Clock" concept, based on NOAA oxygen exposure limits, should by taught. However, it should be noted that CNS Oxygen toxicity could occur suddenly and unexpectedly.
9. No evidence was presented, based on history of use, to show an unreasonable risk of fire or ignition when using up to 40% nitrox with standard scuba equipment. The level of risk is related to specific equipment configurations and the user should rely on the manufacturer's recommendations.

You can download the proceedings here: http://www.si.edu/dive/library_nitrox.htm

 

[spectrum]

Just to add another spin...

Assuming you dive locally and rent cylinders it can be wise to check those to make sure that what you think is plain air is plain air. It's not unheard of to have a cylinder go out with EAN and just get topped off with air and be returned to the rental cue. Depending how hot the prior mix was and how much remained trouble is possible.

Always analyze and it's always good to be in a position to recheck at will. We made the investment and will be using it for the first time soon.

Pete

 

[Web Monkey]

ok, hubby and i are starting our nitrox course tonight. (yippee!) and so we've been reading the book like we're supposed to beforehand (haven't finished yet, about 2/3 through though) and i have a question.........on the part about analyzing your tank. i'm guessing that most people don't actually buy an analyzer, but rather

If I'm local, I analyze my own tanks at the shop. If I'm anyplace where I didn't bring my gas with me, I always check it with mine, regardless of who said what was in the tank. Here's what sent me down the road of minor paranoia or exceptional care (depending on your point of view).

I was in Tobermory and dropped off my tanks for a fill. Came back the next day and asked them to analyze them.

The girl behind the counter attaches the analyzer hose then cranks the zero-adjust until it says "32", then looks at me and says "32 percent". I tried explaining that the knob she was turning was for calibrating the analyzer against air or O2, and that she wasn't supposed to crank it while analyzing a tank.

She looked at me the same way my dog does when I make funny noises.

Anyway, to make a long story shorter, I didn't dive the tanks (weather was getting bad anyway) and then bought my own analyzer.

They're not cheap, but also not hugely expensive, and if it only saves me from passing out underwater once, it's a bargain.

The really short answer is that if you always use tanks from someplace that you trust to analyze your tanks properly or where you can analyze them, you don't need one. If you might not trust the shop or the analyzer (human or hardware), you need your own.

Edit: The paragraph above refers to you watching them analyze the tank, not just assuming they did it or did it correctly.

Terry

 

[bubba105]

Bought my own and when I went to Cozumel right after that we tested tanks that said 32 and got readings of 25 and 36's that read 27. I dive without changing my computer, for that extra safety margin but my friends who like to push the limits were fuh-reaking (great word, mynamehere). Funny thing was the next day we tested and 32's were 32 and 36's were 36. The dive op didn't fill the EAN, just ordered the tanks.

 

[TASea]

I personally observed the following in Cozumel a couple weeks ago.

Everyone gets on the boat, the boat heads out, the DM says we have to stop at another pier to pick up tanks of nitrox for two of our divers. We stop at the pier, and someone hands down a couple tanks of nitrox - at least I assume it was nitrox. The only indication was a strip of green paint around the top of the tanks. No contents label. The divers hook up their gear to the tanks and make the dive.

Those divers had no idea what O2 percentage they were breathing, they just blindly trusted the op to provide what they asked for. Evidently it was ok, since they didn't die, but I would have tested those tanks before using them. Perfect case for having (and carrying) your own analyzer.

 

[Charlie99]

.........on the part about analyzing your tank. i'm guessing that most people don't actually buy an analyzer, but rather they observe the guy at the dive shop analyze the tank? or let's say you're on vacation in the caribbean on an island for example.........maybe they've already loaded the tanks on the boat when you arrive at the dock or whatever.........then you would need your own analyzer on hand? right? let me know what most of you do ok? thanks,donna

Only in a couple of cases has an analyzer not been available. I either use the shop's/dive op's analyzer, or watch while they do it. If you just observe the analysis, be sure to also observe a calibration check.

Often the analyzer will have already been calibrated using a tank of air. In that case, I'll just do a coarse check by waving the analzyer back and forth in the air to see if it comes back down to around 21%. It won't go to exactly 20.9% because of humidity in the air, and because it doesn't have the same flow rate/pressure at the sensor as the nitrox being tested, but the real danger isn't in being off a percent or two, but in having some sort of gross error.

Charlie Allen