nitrox, o2 service-rated, o2 clean?

[cra2]

Now, if I recall correctly, I read the other night in my nitrox training manual that anything coming in contact with the gas (tank/hoses/regs) has to be compatible with the gas you're using.

It said if you wanna use a gas with higher o2 content (ie. nitrox) you need to have all of that gear o2-cleaned and o2-service rated.

Right?

So, they said, people often maintain TWO sets of such gear - one for the nitrox and one for air.

It basically told us that if you went on a trip, use your Nitrox first, and THEN use air (if necessary), but don't do it the other way around.

And once you DO put air through the gear, you'll need to go and have your gear o2-cleaned and stuff again.

So... a) am I reading that right?
b) is that really practical? Do people really do that?
and c) how come my LDS rents out regs knowing full well you're using Nitrox, and then checks 'em in, shelves 'em, and lets anyone using Air check 'em out next time?

(of course.. the manual ALSO says don't use any hand-held "sniffer" devices for testing the gas mixture, but my LDS does THAT too. lol. So I dunno WHAT to believe anymore.. the manual or my shop.)

 

[miketsp]

See these recent threads:
http://www.scubaboard.com/t45866.html
http://www.scubaboard.com/t65573.html

and in a similar vein
http://www.scubaboard.com/t66255.html
http://www.scubaboard.com/t66733.html

 

[HammerNoMore]

So... a) am I reading that right?
b) is that really practical? Do people really do that?
and c) how come my LDS rents out regs knowing full well you're using Nitrox, and then checks 'em in, shelves 'em, and lets anyone using Air check 'em out next time?

(of course.. the manual ALSO says don't use any hand-held "sniffer" devices for testing the gas mixture, but my LDS does THAT too. lol. So I dunno WHAT to believe anymore.. the manual or my shop.)

a) not quite
b) nope, nope
c) see a and b.

Assuming for a second we are talking basic nitrox as opposed to advanced. Your regulator will never come in contact with any more than 40% O2. Most in the industry (there are a few who disagree but there alway are) believe that < 40% O2 is generally safe in standard equipment.

What you do need cleaned is your tank and valve. This is because most people fill nitrox by blending air with 100% O2. If you get your tank filled with "dirty" air then, yes it will need to be re-cleaned after. As long as you ensure the shop is using modified grade E air then the tank will remain clean.

James

 

[MechDiver]

(of course.. the manual ALSO says don't use any hand-held "sniffer" devices for testing the gas mixture, but my LDS does THAT too. lol. So I dunno WHAT to believe anymore.. the manual or my shop.)

Does your "manual" indicate what it considers a hand-held sniffer?

IF that would be a hand-held O2 analyzer, then that part of the manual is a good as the rest of what you wrote.
I would strongly suggest finding a door that won't stay open, and sitting the manual on the floor in front of it. At least it will then be useful.

MD

 

[gjmmotors]

What Class was this?
What agency?
Did they offer to give you a discount on a nitrox equipment set?
-g mount

 

[cra2]

Does your "manual" indicate what it considers a hand-held sniffer?

IF that would be a hand-held O2 analyzer, then that part of the manual is a good as the rest of what you wrote.
I would strongly suggest finding a door that won't stay open, and sitting the manual on the floor in front of it. At least it will then be useful.

MD

I shouldn't speak without having it here in front of me, but...
it said that the mix should be checked in a closed system, controlling other variables.
That the hand-held sniffers held in front of the tank valve weren't too reliable.

 

[cra2]

Ok,.. now I have my manual in front of me.
Yes, Goddard, I see what you were talking about (the 40% rule).
Yes, I had forgotten about that stuff since the class.
Thanks.

However, Mech, in regards to the last point about "sniffers", this is exactly what the SSI EAN manual says,

"Occasionally, you may see divers trying to analyze gas by holding the O2 sensor in the general vicinity of the valve orifice. This is called a "sniff" test, and it is NOT an accurate way to analyze cylinder content. It is important you calibrate your analyzer each time you use it - and to do so in a sealed system with the calibration gas at the same flow rate and moisture content as the gas you will analyzing."

 

[wedivebc]

However, Mech, in regards to the last point about "sniffers", this is exactly what the SSI EAN manual says,

"Occasionally, you may see divers trying to analyze gas by holding the O2 sensor in the general vicinity of the valve orifice. This is called a "sniff" test, and it is NOT an accurate way to analyze cylinder content. It is important you calibrate your analyzer each time you use it - and to do so in a sealed system with the calibration gas at the same flow rate and moisture content as the gas you will analyzing."

I agree with that point to the extent that O2 sensors held up to the tank valve have the potential to draw in air with the nitrox thereby affecting the reading and causing innacurate measurement. Some of us have learned to properly use these "sniffers" and for a quick measuement I still use it but if I want to be really accurate I connect a 1st stage to the nitrox tank and let the gas flow through a controlled orifice to the sensor which gives me a more consistant reading (probably)

 

[MSilvia]

"the general vicinity of the valve" isn't good enough. You need to have a pretty direct flow. Folks I know who use a hand held analyzer hold it right against the valve.

 

[jbisjim]

"the general vicinity of the valve" isn't good enough. You need to have a pretty direct flow. Folks I know who use a hand held analyzer hold it right against the valve.

Yup thats right

"the general vicinity of the valve" does nothing but read room air mixed with a little o2.
might as well guess at the mix then...