Ean 18 ???

[H2Andy]

yeah .. the question is what the other 82% is ... if it's N2, you'll be ok (partial pressure will take care of you)

i don't know if He presents any deco issues above and beyond N2, but i suspect it does .. so anyway, not qualified to comment on that

I have heard of steel tanks that have sit for a while have a lower % of O2 due to oxidation of the steel inside the tank. I have never verified it and it may just be a wives tale, but also a possibility.

it would literally take years ... that's not what's going on here

 

[Charlie99]

How are you calibrating the unit? Is it possible that you are calibrating using a tank that you think is air but which is really a lean nitrox? If this is what's going on, then the tanks that you think are air, are really slightly enriched nitrox.

What does the sensor read just sitting in room air? It should be pretty close to 21%.

 

[yak]

I calibrated it by swinging it in the air for 30 seconds as specified in the manual.

The tank was topped off with air (from a shop that only fills air) after I used the 35% mix.

I'll definitely have the tank drained before using it again.

 

[do it easy]

Only air at the shop huh? My guess is that it's either a conspiracy against you or maybe the compressor gremlins are at work. Does the "air" in the tank smell funny?

 

[yak]

Only air at the shop huh? My guess is that it's either a conspiracy against you or maybe the compressor gremlins are at work. Does the "air" in the tank smell funny?

I breathed this tank for over an hour while lobster hunting at 24 feet. It has been sitting since. And my other two tanks (that I don't use for nitrox) are filled at the same shop, and they're registering 21%.

 

[H2Andy]

ok ... so ... you fill the tank with a 35% mix

did you test it? (i assume yes)

you use it up to about 800 psi

you put air in it from a shop that only pumps air, no nitrox, no O2, no He

you test it and you get about 18% O2

do i have the sequence right?

 

[Rick Murchison]

Well.... it doesn't make any sense.
When somethng doesn't make any sense with my breathing gas, it's time to dump that load and have a look inside the tank.
Rick

 

[yak]

ok ... so ... you fill the tank with a 35% mix

did you test it? (i assume yes) I tested it using the shop's analyzer.
you use it up to about 800 psi

you put air in it from a shop that only pumps air, no nitrox, no O2, no He

Then I dove it and I am now testing the leftover gas that has been sitting for 8 months. I expected it to be somewhere between 21 and 35, more towards the lower end.

you test it and you get about 18% O2 Yes, 18.1%

 

[yak]

Well.... it doesn't make any sense.
When somethng doesn't make any sense with my breathing gas, it's time to dump that load and have a look inside the tank.
Rick

Yep, that's next on my to-do list.

 

[nwbrewer]

I'm not really familiar with how these analyzers work, but could it be that they detect an offset in the oxygen %, and then add that to the calibrated 0 ( In this case 21%) ? If so it could be that the tank contains 24% and not 18%. Try it with a different analyzer and see what yo get.

Also try a tank known to be 36, and see if it winds up being 6%. (21%-15%) If so the logic in your analyzer is reversed?