Analyzing multiple nitrox tanks

[IBjones]

Recalibrating your analyzer between tanks of nitrox will cause your reading to be lower than actual. The analyzer takes awhile to get the higher O2 air flushed out and if you calibrate it at that point it accepts that high O2 air as 21% lowering subsequent readings.

I don't know how you do yours, but around here we don't just throw the analyzer on and zap the calibration knob to 21%.

You let the air flow thru the meter for a minute or two to flush out whatever is in there.
Old Army adage when it comes to clearing buildings in Afghanistan...."Don't be in a hurry to die."

The same goes for analyzing your tanks. Take your time and let the damned thing flush. Then adjust the knob to 21%. It isn't like if you let the air flow over the sensor for 2 or 3 minutes you're gonna use up all that 3000 PSI in the tank.

 

[BRT]

I don't know how you do yours, but around here we don't just throw the analyzer on and zap the calibration knob to 21%.

You let the air flow thru the meter for a minute or two to flush out whatever is in there.
Old Army adage when it comes to clearing buildings in Afghanistan...."Don't be in a hurry to die."

The same goes for analyzing your tanks. Take your time and let the damned thing flush. Then adjust the knob to 21%. It isn't like if you let the air flow over the sensor for 2 or 3 minutes you're gonna use up all that 3000 PSI in the tank.

And the tank you are using to adjust to 21% might even actually be 21%. None of mine are but hey, it could happen.

 

[RainPilot]

My analox has the little dome with a barb for testing, if I pop that off the cell is open to the atmosphere so no gas retention. I calibrate carefully with ambient air, correcting for temp and humidity as per the little table that came with it then I don't fiddle with it until the next day I'm analysing.

I generally try to go from lean to rich tanks if possible since the readings cant be artificially high from gas retention, if it's a bunch of the same, usually 32, then I will analyse, wait till stable and mark tag. I take it off the tank, wait till it drops down a couple of percent then do the next one so I see a positive climb and stabilise cycle.

Lather rinse repeat.

I NEVER use a tank to calibrate. Never know what's in there.

 

[IBjones]

And the tank you are using to adjust to 21% might even actually be 21%. None of mine are but hey, it could happen.

As they say in court, anything is possible.

My LDS has a medical grade air quality cert hanging on the wall and gets a re-inspection every 90 days. Could their system malfunction one hot summer day and I get a bad mix before anyone caught the problem? Sure.

We could also argue that the Carteret County General Hospital could have a malfunction and they might fill a oxygen patients 02 tank with "bad air" before someone caught the problem.

The only way diving is every going to be 100% safe for you is stop diving.

 

[BRT]

As they say in court, anything is possible.

My LDS has a medical grade air quality cert hanging on the wall and gets a re-inspection every 90 days. Could their system malfunction one hot summer day and I get a bad mix before anyone caught the problem? Sure.

We could also argue that the Carteret County General Hospital could have a malfunction and they might fill a oxygen patients 02 tank with "bad air" before someone caught the problem.

The only way diving is every going to be 100% safe for you is stop diving.

One way to be sure of 20.9% air is to use the air around you.

 

[IBjones]

One way to be sure of 20.9% air is to use the air around you.

Is smoggy San Francisco air the same 20.9% that the air from Grandfather mountain in the Blue Ridge mountains is? Never thought to ask that before. Would using air from Jacksonville Florida VS the "pure" air from the dive shop affect the 02 sensor?

 

[uncfnp]

Is smoggy San Francisco air the same 20.9% that the air from Grandfather mountain in the Blue Ridge mountains is? Never thought to ask that before. Would using air from Jacksonville Florida VS the "pure" air from the dive shop affect the 02 sensor?

There is no air as rarefied as the air from the Blue Ridge Mountains.

 

[tursiops]

Yeah, air may be 20.9% O2, but that doesn't mean you set your analyzer calibration on 20.9. The galvanic cells are sensitive to the temperature and humidity of the gas, so the calibration is usually to a lower number, like 20.6 or 20.7. You are not saying the "air" is 20.6, but rather what the analyzer sees is 20.6. It is not a big difference, but all those little 0.2's and 0.3's add up between calibration, gas flow rate on the sensor, residual gas in the analyzer, sloppy fit between the analyzer and the tank, etc. So, eliminate the errors you can.

 

[BRT]

Is smoggy San Francisco air the same 20.9% that the air from Grandfather mountain in the Blue Ridge mountains is? Never thought to ask that before. Would using air from Jacksonville Florida VS the "pure" air from the dive shop affect the 02 sensor?

A little internet research says that the O2 level from place to place doesn't vary anywhere close to the accuracy of the sensors.

 

[RainPilot]

As they say in court, anything is possible.

My LDS has a medical grade air quality cert hanging on the wall and gets a re-inspection every 90 days. Could their system malfunction one hot summer day and I get a bad mix before anyone caught the problem? Sure.

We could also argue that the Carteret County General Hospital could have a malfunction and they might fill a oxygen patients 02 tank with "bad air" before someone caught the problem.

The only way diving is every going to be 100% safe for you is stop diving.

They might put their super clean air into a tank that had a couple of bar of O2 left in it from being a deco tank etc. If they can guarantee that their tanks are exactly what they said then why are you analysing at all?

No operation is perfect, if it's in a tank someone put it there, therefore there is potential for error.

If the atmosphere is more than a half percent off where you are, I suggest diving is the least of your problems....