Who DOESN'T analyze their gas?

[kensuf]

Who ever said to calibrate off a tank of who knows what? Calibrate to a tank of air; it'll be dry, and not likely to be at 90 F.

The other day I analyzed a tank that I thought was air. It was supposed to be air. The fill station where it came from only has air. We're not supposed to put anything but air inside of any of the tanks in our dive locker.

It had 26% in it.

Apparently, someone borrowed some of the tanks, filled them with nitrox somewhere else, and dove them. Then returned them without properly marking them.

I think the people that are calibrating on ambient air are probably onto something.

[a64pilot]

I think the people that are calibrating on ambient air are probably onto something.

Nope Spelodiver and Geschaut (sp?) have it right, only way to calibrate anything is with a known standard, one where all the variables are controlled

[FW]

Nope Spelodiver and Geschaut (sp?) have it right, only way to calibrate anything is with a known standard, one where all the variables are controlled

True, but the "known standard" should be marked as such.

[MichaelAngelo]

True, but the "known standard" should be marked as such.

Absolutely but at some point that tank had an analizer put on it. So when and how was that tank analized? Most shops I deal with in the great white north have tanks that are only for calibration purposes and are certified to be 20.8 when their fill station is certified. I know the folks and trust them but I still double check with my O2/He analizer and my Co analizer because mistakes happen and it's my life.

[corvettejoe]

I always analyze my gas at the dive shops so when I get to the dive site, I just pull my tanks out and go.

This way you can fix any mistakes made while there instead of waiting until you get to your dive destination only to realize your gas is the wrong mix or bad gas.

Every shop has an analyzer. If they don't... you really don't want to be doing business with them.

As for calibrating the tester, I always remove the caps, wave it around back and forth in the air and adjust from there.
After a test or two, the gasses get trapped inside the cap and cause it to read incorrectly, so every few tanks, I take the cap back off and let it "air out" so it reads ambient air again.

[gschaut]

Nope Spelodiver and Geschaut (sp?) have it right, only way to calibrate anything is with a known standard, one where all the variables are controlled

http://www.brandtinst.com/Gasco/Gasc..._Cylinder.html

In the fire dept, we use small cylinders of known, certified gas content (bump gas) to test and calibrate our gas meters. Granted, we are metering for different gas values than diving. But the principal is the same.

For diving, I usually just calibrate my O2 meter to both ambient air (with temperature/humidity compensation table), then recheck the meter on a 100% oxygen gas supply at the fill station. If the values I get on the meter are close to 100% on the O2 source, I presume that the O2 meter is properly calibrated. The odds of having BOTH a meter calibration error on my O2 meter AND the shop's Oxygen tanks contaminated with less than 100% oxygen (to the EXACT same level as the meter error) are small enough I can live with it.

[Greenwood_60]

Every shop has an analyzer. If they don't... you really don't want to be doing business with them.

Every cave country shop has an O2 analyzer... Amigos is the only one I've personally seen with a CO2 analyser for customers to use. Which other cave shops have CO2 analysers for customers to use?

[LCF]

I looked at the linked abstract, and I'd really like to know what units they were using. If they were using grams/deciliter, which is the usual in the US, the reduction is enormous and frankly unbelievable. If they were using grams/liter, it was about an 8% reduction, which is honestly still a bit surprising, but more reasonable.

The difference in magnitude of effect between hypoxia and hyperoxia is easy to understand if you understand the dynamics of oxygen in the blood. It isn't dissolved . . . it's carried on hemoglobin. At sea level, breathing air with normal lungs, hemoglobin is between 99 and 100% saturated; raising the inspired ppO2 results in very little additional oxygen content in the blood, as oxygen is very poorly soluble in plasma. On the other hand, lowering the inspired ppO2 results in very little content change at first, but once you hit a threshold, the content falls very fast, as the hemoglobin is desaturated. Poor oxygen content is what stimulates the kidneys to release the hormone that causes red blood cells to be made. The process is not instant, which is why Jax mentioned the waiting period for exercising testing at altitude.

The lack of change in O2 content is why I wouldn't expect to see a big change in red cell count with prolonged hyperoxia. Apparently there is some effect, but if the units are what I suspect, it's pretty small. (In contrast, the hematocrit can go up 25% or more in chronic hypoxia.)

Oh, and I label my tanks to the .1% . . . it makes sure I know I've actually analyzed the tank, and not labeled it for desired content.

[gschaut]

Every cave country shop has an O2 analyzer... Amigos is the only one I've personally seen with a CO2 analyser for customers to use. Which other cave shops have CO2 analysers for customers to use?

Should that read "CO analyser"?

[Greenwood_60]

Ugh, yeah. My mistake.