Old air

[Doc Harry]

I'd like to read about the case you mentioned if you have a link.

Ask, and you shall receive.
http://www.scubaboard.com/forums/ta...-cylinder-long-term-storage-fact-fiction.html
Posts #4 and #5 should be of most interest to you.

 

[BRT]

IN the absence of any kind of chemical reaction, how would you suppose air could "go bad". It's not like chicken that you can only keep in the fridge for a couple of days..... Maybe it's the term "go bad" that sets me off. Air in a tank isn't going to turn into something else unless there is something else in the tank and it would take a HELL of a lot of oxidation before the O2 content got so low that it was dangerous.....

I'm not aware of any deaths from air going bad over time but I know of a few from bad fills. I'd like to read about the case you mentioned if you have a link. My knee-jerk reaction would be to say that it must have been a tainted fill that would have been just as "bad" the day it was filled as it was a year or whatever later.

R..

In the absence of any chemical reaction is the key. Rust might be that reaction. I'm not going to worry about it unless my tank sloshes or I am in Mexico. If it rusts the rust closing off the air flow when you go inverted may get you before the lack of O2.

 

[emoreira]

It depends on the tank. If it's an alu tank, there should be no problem.
If it's a steel tank, It's advisable to empty the tank up to 20 ~ 40 Bar just to avoid humid air to enter. With this, the oxygen partial pressure will be low enough to avoid excessive corrosion in the interior.
Of course, keep with anual visual and 5 year hidro tests, as required. Visual should drain the water, if any, inside the tank. So, no air should have more than a year.

---------- Post added April 2nd, 2015 at 08:56 PM ----------

In the absence of any chemical reaction is the key. Rust might be that reaction. I'm not going to worry about it unless my tank sloshes or I am in Mexico. If it rusts the rust closing off the air flow when you go inverted may get you before the lack of O2.

That's why the tank valve should have the little tube that projects inside the tank. This to avoid water and/or dust to enter the valve when it's inverted. The picture posted by Diver0001, the valve is disassembled, without the tube.

 

[ScubaInChicago]

With this, the oxygen partial pressure will be low enough to avoid excessive corrosion in the interior.

Do you store your tanks below sea level? How do you expect the partial pressure of air to increase?

 

[Ozensha]

I have honestly never heard of air going bad. However, I do notice a difference between air that has sat around for months vs. a fresh fill. Back in October I dove on one of my old tanks that had a fill from 3 years ago and noticed that it tasted a little funny and felt excessively dry. At the end of the dive I had a bit of a headache. Not sure if I was just being a hypochondriac or something since I was aware of how old the air was. But aside from that, the fact is I dove on air that was 3 years old without any issues.

 

[tridacna]

Ask, and you shall receive.
http://www.scubaboard.com/forums/ta...-cylinder-long-term-storage-fact-fiction.html
Posts #4 and #5 should be of most interest to you.

Thank you for the link to that thread. That is easily the most useful thread I've found since I joined SB. Very useful info.

 

[Doc Harry]

How do you expect the partial pressure of air to increase?

Partial pressure of gas A = (Fraction of gas A) x (Total pressure)

Therefore the partial pressure of oxygen is directly proportional to the total pressure in the cylinder.

Decrease the pressure in the cylinder and you decrease the partial pressure of oxygen.

Decrease the partial pressure of oxygen and you decrease the rate of corrosion (if water is present).

I have honestly never heard of air going bad. However, I do notice a difference between air that has sat around for months vs. a fresh fill. Back in October I dove on one of my old tanks that had a fill from 3 years ago and noticed that it tasted a little funny and felt excessively dry. At the end of the dive I had a bit of a headache. Not sure if I was just being a hypochondriac or something since I was aware of how old the air was. But aside from that, the fact is I dove on air that was 3 years old without any issues.

If your cylinder is dry and properly maintained, then there will be no corrosion and the air should remain stable indefinitely.

 

[emoreira]

Do you store your tanks below sea level? How do you expect the partial pressure of air to increase?

Partial pressure of the oxygen inside the tank will be the actual pressure X 0.21.
If the tank has 3000 psi inside, the partial pressure of oxygen will be 630 psi. With this, as there is a lot more oxygen inside the tank than outside, the effect of corrosion inside the steel tank is many times superior.
Dalton's Law.

 

[diver 85]

use it---------

 

[emoreira]

I have honestly never heard of air going bad. However, I do notice a difference between air that has sat around for months vs. a fresh fill. Back in October I dove on one of my old tanks that had a fill from 3 years ago and noticed that it tasted a little funny and felt excessively dry. At the end of the dive I had a bit of a headache. Not sure if I was just being a hypochondriac or something since I was aware of how old the air was. But aside from that, the fact is I dove on air that was 3 years old without any issues.

3 years old charge ? Several visual inspections are missing.

---------- Post added April 2nd, 2015 at 11:12 PM ----------

use it---------

Far, the best answer !!!