Complacency or Confidence?: Follow Up

[RN]

I have a 13 ft3 bottle filled with air and I calibrate my sensor to this known gas before each usage.

How do you know it's air?

I've wanted to do the same thing. Actually, I want one with air and one with 100% O2 since analyzers should actually be calibrated at the low end and at the high end. Problem is I haven't gone by any shop that doesn't fill anything but air. And I won't trust a calibration tank to be filled at a shop that fills both, especially when they use the same whips and just bleed them down to switch between air and nitrox.

You should own your own analyzer, you can make the Oxychek El-Cheapo for about $100, includes the first 02 sensor.

I just remembered a time when I borrowed a couple of tanks that the last time they went out were filled with trimix. No one had bled them out, so I got topped off mix. Fortunately, since I dive mix, my analyzer also analyzes for helium. Also fortunate was the last person to dive those tanks was a hoover so the helium content wasn't that high (I didn't analyze until I was at the dive site...d'oh). There was no problem adjusted my deco for the mix. That taught me to analyze borrowed tanks before getting them filled, though. And to not rely on an O2 only sensor at shops where you can get trimix. It makes me wonder how many people have done trimix dive inadvertantly...

[Jim Wyatt]

How do you know it's air?

I pump the air from my own compressor -- straight off of the compressor LONG after the 7 minutes dwell time for my filter stack has cleared all other gas from it.

Generally I refill this bottle after I am done filling my drive gas bottles for my Haskel. Usually about 400 cubic feet of volume to fill the drive gas bottles. (I have run my haskel on breathing quality air for years and it never gets dirty)

Do you get pure 100% air at dive shops...?? Doubtful, if they mix anything other than air. Reason being that after they shut off O2 flow from a CF blender the gas has to go somewhere & it takes 5-7 minutes for the gas to clear the filter stack (dwell time) -- so for a period of 5-7 minutes the air bank has nitrox pumped into it. Probably neglible depending upon bank volume, perhaps not if a small volume air bank is involved.

As an aside - I am banking 30-31% at home to keep the PO2's down- I rarely ever mix 32%, if ever anymore.

I ALWAYS analyze ALL my gases just prior to diving it. I encourage everyone else to do so as well.

Buy an analyzer. Build an analyzer. Explain what an analyzer does to your wife, husband, kids and see if they think you need one too.

Jim

[Slüdge]

Our shop ran a trip to the panhandle several years ago and I blended eight AL80s of 32%. The next week the shop owner berated me for mixing high, something like 33.5% consistently.

I asked what they calibrated the analyzer to, and he said, "20.9, of course."

At 90° and 80% relative humidity, the analyzer should be calibrated to 20.1%. That's why they got high readings.

In my trailer I have a digital temperature/humidity meter on the wall. I don't think I've ever calibrated to higher than 20.7% outdoors.

[jmaddox]

Problem is I haven't gone by any shop that doesn't fill anything but air.

Ginnie : )

ah ha, the olde scuba tank, what a novel idea. why didnt I think of that. calibrating your analizer from of all things..a scuba tank. brilliant.

cheers!