What they don't teach you in Nitrox class...

[The Kraken]

Some LDS's absolutely mystify me with their Nitrox filling protocols and procedures, or should I say "lack thereof".

Was doing a dive with an LDS in Panama City, Florida. Wanted to dive nitrox because of the dive site.

I prudently took my tanks in the day before the dive and asked to have them filled. I was told at that point that the only mixture offered by the LDS was EAN32.

No problem.

I go back to the LDS the morning of the dive. My tanks (119's) had not been filled. Thank God I got to the dive shop 1-1/2 hours early!

I come back later to check my tanks. The fellow that filled my tanks didn't offer me an O2 meter to test the gas, so I asked for one.

(Now, when I dropped the tanks off for filling, they were partially filled.)

I test my gas and find it running in the mid 20's O2 percentage wise.

The doofus just topped off the tanks without draining them first.

MAN, was I ticked off !!!!

I made him drain the tanks, refill them and hold up the dive boat while he did so.

Needless to say I threatened the LDS manager with exposure on the web if he didn't abide by my wishes.

the K

 

[Soggy]

Soggy, when using the air around you to calibrate, do you compensate for the fact that the flow rate on the sensor is not the same as it will be when connected to a tank or do you calibrate it fo 20.9 regardless.
I know that with my meter this factor needs to be compensated for or else your reading will be off by close to 3%.

I remove the sensor cap and shake the thing around a bit and calibrate to 20.9%. If I later analyze dry tank air, I usually end up around 20.6%. I think you need a new sensor if you are off by 3%.

The other thing you can do (depending on the analyzer design) is stick the hose in your mouth and inhale thru it. This will give you a reasonably accurate flow rate.

 

[pickens_46929]

There might be something to the heat affecting the final mix and reading the mix issue for sure, also with the mixing procedure and the material of the tanks.

When I get my Faber LP98's filled the fill is usually bang on (+/- 1%) and it takes a good hour or so do it, but when my buddy takes his PST HP120's to the same place, same blender, same time.....his always come out funky. The tanks heat up a lot quicker and cool down slower making the fill that much more difficult to get right, not just that the mix doesn't settle for at least 6-8 hours and changes and the gases cool inside the tank. When asking for a 32 mix, he often gets a 35.8% at the initial testing (despite using the predetermined charts) and later on that same mix will trickle down to a 33.6% a few hours later.......again the shop does the fills at the same rate yet the PST's behave and handle the gas differently.

One thing I've noticed a difference with is shops that use a water trough to hold the tanks while filling versus those that don't. The ones that put your tanks in water *and* have a good tech filling them tend to be spot on.

 

[do it easy]

I turn the sensor on and check that it's somewhere near 20.9. This gives me some confidence that the calibration isn't way off. Depending on temp/humidity/sensor age it might read 20.3 or something like that.

Then I analyze a tank that is supposed to be air to make sure that the meter reads 20.9/21, whatever it takes. If it reads 32, the tank probably isn't air. If it reads 21.1, it's probably air, so I'll calibrate the meter.

Now I feel comfortable that the tank and the air are "close enough" to accurately measure my gasses.

Lastly, after measuring my gasses, I will re-measure the air tank to make sure the calibration didn't get out of whack or drift while I was doing all this.

It's probably overkill, but 1) I sometimes blow (grade e modified) air into partially filled nitrox tanks, and 2) he usually does a good job, but I just don't trust the guy that used my tanks last to keep the stickers up to date.

 

[Soggy]

Do it easy, I use a similar methodology upon picking up my tanks, or when I get them home. Subsequent analysis (I always reanalyze the night before the dive and immediately before getting on the boat) is just done by calibrating to ambient. At this point, if my analysis is way off from what the sticker says, I know there is a problem.

 

[Kevfin]

Jim,

Thank you for bringing this up.

What a hassle to have to deal with all the LDS Bozos. If we didn't have the ability to share experiences and ideas here on Scuba Board, I think a lot more people would be getting ripped.

I know people have different ideas on how to analyze (notice the word "anal" in there?), but the bottom line is you have to be an informed diver/consumer and are ultimately responsible for your safety. Buyer Beware!

If you need your own O2 meter, I've read that this one is pretty good DIY:

http://www.oxycheq.com/el_cheapo_II.html

It's on my list of things to buy.

 

[do it easy]

I forgot to mention that part- I didn't want to seem too paranoid.

I also re-analyze if the reg comes off the tank and I want to use it again, such as after I pack up for the night and do another dive in the morning.

And when the other teammates are analyzing, I personally look at the reading on the meter to confirm- I might have to breathe that gas!

And when I'm in the water, I'm constantly looking over my shoulder too!

Do it easy, I use a similar methodology upon picking up my tanks, or when I get them home. Subsequent analysis (I always reanalyze the night before the dive and immediately before getting on the boat) is just done by calibrating to ambient. At this point, if my analysis is way off from what the sticker says, I know there is a problem.

 

[Jason B]

I remove the sensor cap and shake the thing around a bit and calibrate to 20.9%. If I later analyze dry tank air, I usually end up around 20.6%. I think you need a new sensor if you are off by 3%.

The other thing you can do (depending on the analyzer design) is stick the hose in your mouth and inhale thru it. This will give you a reasonably accurate flow rate.

It is a new sensor.

If I connect it to a tank of air, and adjust to 20.9% then read O2, I read 100%. If I then expose the sensor to ambient air with no flow, it will read 17.7%.

If I calibrate it to 17.7% on ambient air, then connect it to a bottle of O2, I read 100% so I'd say the sensor is fine. It's all about the flow rate.

The hose that connects to the sensor, if you put it into your mouth you could not blow through the restriction, it takes more pressure to allow the correct flow than a humans lungs can create, hence the need for a first stage connected to the tank.

 

[Soggy]

New or not, it sounds like you have a lousy sensor. I've never seen or heard of that type of behavior except at high altitude. Are you up in the mountains? With my oxycheq, I pretty much get the same readings regardless of the flow rate.

It is a new sensor.

If I connect it to a tank of air, and adjust to 20.9% then read O2, I read 100%. If I then expose the sensor to ambient air with no flow, it will read 17.7%.

If I calibrate it to 17.7% on ambient air, then connect it to a bottle of O2, I read 100% so I'd say the sensor is fine. It's all about the flow rate.

The hose that connects to the sensor, if you put it into your mouth you could not blow through the restriction, it takes more pressure to allow the correct flow than a humans lungs can create, hence the need for a first stage connected to the tank.

 

[Scuba_Steve]

It is a new sensor.

If I connect it to a tank of air, and adjust to 20.9% then read O2, I read 100%. If I then expose the sensor to ambient air with no flow, it will read 17.7%.

If I calibrate it to 17.7% on ambient air, then connect it to a bottle of O2, I read 100% so I'd say the sensor is fine. It's all about the flow rate.

The hose that connects to the sensor, if you put it into your mouth you could not blow through the restriction, it takes more pressure to allow the correct flow than a humans lungs can create, hence the need for a first stage connected to the tank.

Soggy, your suspicions were close, but I guess it's not the sensor, it's the user. LOL

I can't believe it either.