Who DOESN'T analyze their gas?

[Sludge]

I analyze for PO2 three times: after it's filled, when I load it into the car for the trip, and when I put the reg on it. I only analyze once for CO, and that's when I get it home from the fill.

[JahJahwarrior]

I never really thought about how bad gas could result in noxiousness, but now that you mention it...

I won't say that I've never dove an un analyzed tank, but I will say that it is stupid to dive one.

On a recent out of country dive trip, I was surprised that the shop employee wanted me to calibrate with an unmarked tank supposedly full of air next to the analyzer, not with ambient air. I was also amused to watch nitrox divers hook the analyzer reg up backwards to the tank, and also to write down to the .1...while I am sure they were horrified to watch me round up or down after calibrating to nasty old ambient air. To each their own--that's why I write my name on the tanks I intend to breathe.

[IowaCaveDiver]

I analyze for PO2 three times: after it's filled, when I load it into the car for the trip, and when I put the reg on it. I only analyze once for CO, and that's when I get it home from the fill.

why analyze 3 times? the P02 will change after a fill as the old gas homogenizes with the new gas, but I had always been under the belief that as long as I analyze close to the actual dive or at least 24hrs after the fill, I would have the most accurate results. Of course I could understand analyzing at the dive shop to ensure you got the mix you intended.

[a64pilot]

I've only seen someone get sick from bad air once, long ago. The air had oil in it, or at least the tank had about a tablespoon of oil in it when we pulled the valve and looked. You could smell the oil, but of course you don't smell with your mouth so it wasn't noticed pre-dive. Don't think the oil would have been found with an analyzer.
Shops un-familar to me, I always analyze the gas.

[Jax]

Think again. There have been several reports of serious injury from bad gas at USA dive shops.

I got bad gas from a dive shop here in CENTRAL FLORIDA. It was reported and the problem was being worked on that day.

Thanks for the correction, guys. I analyze for CO as a matter of procedure, but hadn't seen any stories.

[Sludge]

under the belief that as long as I analyze close to the actual dive or at least 24hrs after the fill, I would have the most accurate results.

After it's filled to make sure I got what I wanted. Before loading it into the car in case something has changed (after the mix has sat around awhile), so I have time to either run back up to the shop, or plan a stop at a local shop when I get to Florida. And then I analyze when I assemble the rig, just because. It only takes a minute.

[tursiops]

On a recent out of country dive trip, I was surprised that the shop employee wanted me to calibrate with an unmarked tank supposedly full of air next to the analyzer, not with ambient air.

Calibrating to ambient air will usually give a reading that is at least 0.2% lower than calibrating to dry, room-temp air (as in an air tank); on a good "90-90" day you might be almost 1% off. That means the O2 percentage you are breathing is actually lower than what you think, if you calibrated to ambient air. that is conservative for MOD, not so for nitrogen uptake.

If you don't believe this, calibrate to the gas in an air tank, and then read the O2 percentage for ambient air.

I'm sure most of you folks already knew this, but I'm concerned when anyone says ambient air is the way to calibrate.

As to rounding, I round up to figure out MOD, and down to set my computer to add a touch of conservatism. And then I subtract 10 feet from my MOD for the actual dive. I like cushions.

[PfcAJ]

With ambient air at least you know the o2 within a percentage point. +/-1% is good enough for anything scuba.

Calibrating off a tank of who knows what, you're shooting in the dark.

[tursiops]

With ambient air at least you know the o2 within a percentage point. +/-1% is good enough for anything scuba.

Calibrating off a tank of who knows what, you're shooting in the dark.

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.

[bpcfire1]

I've only seen someone get sick from bad air once, long ago. The air had oil in it, or at least the tank had about a tablespoon of oil in it when we pulled the valve and looked. You could smell the oil, but of course you don't smell with your mouth so it wasn't noticed pre-dive. Don't think the oil would have been found with an analyzer.
Shops un-familar to me, I always analyze the gas.

That is exactly what happened to me from renting a tank on a dive. There was so much oil that it left a film on the water when I free flowed my reg. I made it about 20ft and literally could taste this nasty taste. After calling the dive, and going to the shop where I got the tank, it was found that there were several tanks with oil including some others that were in use also.

I have had a situation from my job, where a bottle had some oil in it and after use for a bit I became very ill and had to be taken to the ER.