Nitrox PPO2 blending waiting period for homogenisation of mix

[kawaboy]

Hello all

I'm new to Nitrox, having just completed my course.

I went for a 32 mix fill at my LDS (PPO2 blending) and was told that I had to wait for a few hours before they would analyze the mix and sign it off. Something about letting the mix homogenise. This kinda makes sense to me but this was not mentioned in the TDI/SSI course and I was wondering if anyone has heard of this.

Another question regarding this: Does the temperature of the cylinder (warmish after a fill) affect the PPO2 reading on the analyser? I'm thinking No because the fraction remains the same, right? Comments please.

Regards

Joe

 

[fdog]

Hello all

I'm new to Nitrox, having just completed my course. Congratulations!

I went for a 32 mix fill at my LDS (PPO2 blending) and was told that I had to wait for a few hours before they would analyze the mix and sign it off. Really? They said this?Something about letting the mix homogenise. You don't need to do this with Nitrox. Trimix, ok, but not Nitrox. This kinda makes sense to me but this was not mentioned in the TDI/SSI course and I was wondering if anyone has heard of this.

Another question regarding this: Does the temperature of the cylinder (warmish after a fill) affect the PPO2 reading on the analyser? Nope. I'm thinking No because the fraction remains the same, right? Correct. Comments please.

Regards

Joe

Pick the most likely for your LDS from the following list of possibilities:

• Didn't want to fill it right then, so they had you come back later
• Didn't know how to fill it right then, so they had you come back later
• Misinformed
• Low experience level
• You now have a mix of 21/35

All the best, James

 

[Arizona_SVO]

fdog is right - you need to pick the one you are most comfortable with in the list of BS reasons they gave you.

All they had to do was shake the cylinder after all. Like those paint cans at the hardware store when you get paint done.

If your shop does not have a cylinder shaker, find another shop pronto! They obviously do not know what they are doing.

 

[Rick Murchison]

...If your shop does not have a cylinder shaker, find another shop pronto! They obviously do not know what they are doing.

Cylinder shaker? (for mixing Nitrox?)
Never heard of one...
Got any pictures?
Rick

 

[Rick Inman]

I'm guessing he's joking.

FYI, I've tested PP blends of nitrox in singles and doubles and never seen a reading change when analysed 5 mins after topping and the next day. And no rolling of tanks or other such stuff.

Trimix, yes.

 

[Arizona_SVO]

Cylinder shaker? (for mixing Nitrox?)
Never heard of one...
Got any pictures?
Rick

Rick, I do not have a picture of one - I simply forgot to put the <sarcasm> tags around my post. I'll try to make it a bit more obvious next time as my lame attempt at humor must have missed the mark here.

My point was that he needs to find a new shop - this one can't be bothered with giving him the truth as to why he needs to wait for his nitrox fill.

He needs to wait because they don't have it ready for some reason... most likely they have not done it yet. But to simply tell him that he needs to wait for it to properly mix? c'mon now - we are not talking about an oil and water mix where after time they will separate.... we are talking about 2 gasses (of similiar weight, not like helium) under pressure which mix instantaneously in the cylinder. With seconds, each gas will occupy all space available to it in given it's partial pressure. It's not like the oxygen is going to hang out at the top of the cylinder (because it is not significantly lighter) and the nitrogen will lag at the bottom.

Anyway, I'll get off my rant now... anybody please feel free to correct me if I am in the wrong here, but again, this shop is simply giving him a BS line for some reason... I suspect they either do not know better, or they have just not done the work.

Okay, this time I am really done with the rant.

 

[Rick Murchison]

I'm guessing he's joking...

Ye reckon?
Never can tell... we may have been operating without essential life support equipment for decades!
I want pictures!

Rick

 

[Arizona_SVO]

Ye reckon?
Never can tell... we may have been operating without essential life support equipment for decades!
I want pictures!

Rick

See, now I missed your better attempt at humor! This humor thing is hard to conveigh in an internet forum.

 

[Rick Murchison]

... My point was that he needs to find a new shop - this one can't be bothered with giving him the truth as to why he needs to wait for his nitrox fill...

The need to wait for an accurate analysis is common knowledge, even though bogus, so I wouldn't accuse the shop of deception based on it, nor would I jettison a shop over it.
What I would do is tell 'em "That's ok, I'll sign your log with whatever analysis comes up and reanalyse before I dive it."
If they then change excuses I might consider a new shop - or at least say "ok, let's establish a 'no bs' business relationship now."

Rick

 

[SkimFisher]

I only know this bc I'm fixing to take the course - but the PADI Nitrox book does say that there is a "mix period" before using the cylinder. Something like a few hours. I don't have the book in front of me - but it's there. Just read it yesterday.

The book specifically makes mention of "rolling the cylinder around" to assist in mixing the two gasses.

Whether or not it's just BS to cover their rear ends - you guys can decide.