Do you analyze?

[OutlawCaver]

I mix my own gases, although I use the LDS for air, 32, 36 or 100 top offs. All of my tanks are numbered and tracked in a gas analysis chart that I keep in my van. Trimix & 50/50 gets analyzed at least 5 times prior to a dive over a five day period. At least twice during this process, I use two seperate oxygen sensors with a flow meter and a high resolution voltmeter. I calibrate the sensors with 100% O2, 100% He and dry filtered air. I input these 3 calibration points into a linear regression program using one of my TI 83, 84 or 89 calculators. I then sample the unknown gas and enter it's oxygen sensor output into the linear regression formula to achieve my FO2.

Although, this may seem excessive, my life, and that of my buddies, is well worth the effort. It is a far superior way of getting accurate analysis over a broad range of oxygen fractions using 3 calibration points versus the typical single calibration point offered by commercial oxygen sensors.

Since I am rarely starting with empty cyclinders, I run calculations for what FO2 & FHe I plan to finish with and then mix by partial pressure (pp) method using a bench digital pressure gauge. Experience has shown me that van der Waal forces can effect my final gas outcome fractions. In essence, oxygen and helium do not act like ideal gases. Oxygen is slightly more compressable than air and helium slightly less compressable than air. Therefore, I knock off about 2% of the calculated oxygen pressure and then add about 2% more helium pressure than calculated.

I analyze FHe, although this is much less critical than FO2, since +/- 5% helium has very little impact on deco schedules for the duration/depth dives I conduct.

I have found that gas homogeneity of heliox or trimix mixtures, is not achieved, for at least a day after my final top offs.

I also confirm manifold crossovers are open each time I analyze.

The day before a dive I label all tanks with appropriate MODs on the sides and bottom of the cylinders.

In case you are wondering, I neither iron or fold my underwear and socks. I am only anal about breathing gases.

I would be glad to show &/or demonstrate, to anyone interested, my mobile calibration system that fits into a oversized briefcase.

[MORGAN]

This is the type of thread I really enjoy. The opportunity to see what other people are doing and why they're doing it is extremely valuable.

I analyze my gas all the time except when I don't.

I'm not mix certified, so the only gases I use are air, nitrox, and 100% O2 in my deco bottle.

I don't analyze air or 100% 02.

I analyze partial pressure blended nitrox every time.

When I get a one-time fill, or any fill from a shop that I'm not very familiar with, I analyze every time.

IF I'm changing my fO2, such as adding air to nitrox to increase my MOD, I analyze every time.

When I'm diving in cave country, and getting repeated fills of banked nitrox from a shop I'm very familiar with, I tend to analyze the first fill of the day, and then slack off, lapsing into indolence and sloth, and not analyze subsequent fills the same day from the same banks. I know that this is not the thing to do, but I sometimes do it anyway.

Reading this thread has gotten me thinking that I need to throw off my laziness and complacency and go back to analyzing every gas I breathe, every time.

Mike

[Sludge]

Vince, I thought I was going to get razzed for analyzing nitrox three times!

[icestac]

In case you are wondering, I neither iron or fold my underwear and socks. I am only anal about breathing gases.

I would be glad to show &/or demonstrate, to anyone interested, my mobile calibration system that fits into a oversized briefcase.

Good job! I'd like to see a picture of your setup if you have one. I'll have to go scrounge up one of my old TI calculators. They may even still have some games on them

BTW - Nothing wrong with ironed and folded underwear... just go easy on the starch.

~Jeff

[flyczek]

I'll admit to slacking off on analyzing banked 32 from a trusted shop. I might analyze the first fill, but not the second.

Interesting thread, it does make you rethink your procedures.

[flyczek]

Here's an experience I've had that raised questions in my mind:

As per manufacturers instructions, I keep my sensor in the fridge when it isn't going to be used for awhile. So the other day, when I needed to do some analysis, I got the sensor out and allowed it to sit about an hour before use. I calibrated, then analyzed, the percentages lined up with my target mix.

Later that day I analyzed what should have been the same mix, another tank I filled with the same mix on a different fill whip, and I noticed a significant variation in readings (>2%). I wasn't sure if this was from the sensor still warming or if it was from changes in air temp or humidity, or something else. I decided to recalibrate and try again.

I grabbed an air tank and recalibrated, but the reading was so far off, it made me question if I really had air in that tank. I didn't want to use a "known mix" to calibrate off of, because even though I mixed, analyzed and labeled it myself, I could have made an error. I thought about calibrating using my O2 bottle, but then I wasn't sure if that would be an accurate way to calibrate and whether it should read 98, 99 or 100. Finally, I grabbed a air mattress pump and used that to push air through the sensor, as I knew that would really be air.

So what do you guys use to calibrate with? Anyone else keep their sensor in the fridge when not in use?

[RN]

Before I moved to N. Florida and was travelling here from the desert every few months, I noticed a significant difference in readings from my analyzer depending on where I was. The analyzer I had at the time was self calibrating to air by waving it back and forth for about 30 seconds. I quickly realized the humidity in N. Florida threw the readings off a lot! Refridgerated air will cut down the humidity and do the same thing. The longer your analyzer is exposed to humid air, the more "off" it will be. My analyzer stays in a storm case now (actually it was built into a storm case).

[BabyDuck]

yay! just found my analyzer - it had been mia after the move.

love my little pink box...

[Lamar English]

I analyze every time, without exception. What you don't know can kill you!
People screw up sometimes; like the young F-Tard who accidently filled my 120' nitrox deco bottle with pure O2... Had I not analized my gas, I would be dead and Diepolder's would surely be closed.

Wake up!

[cavediver256]

I analyze every time, without exception. What you don't know can kill you!
People screw up sometimes; like the young F-Tard who accidently filled my 120' nitrox deco bottle with pure O2... Had I not analized my gas, I would be dead and Diepolder's would surely be closed.

Wake up!

Well put Lamar.....I don't know of anyone I would trust that much with my life. Accidents do happen, and the only dumb accident is one that could have been prevented !!!! Analyze your gas people !!!!