Bleed old air from tank?
- Thread starter Airfree
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Absolutely correct.
The problem is that you don't know if you had a dry fill or a wet fill unless you drain the cylinder and look inside. So you've always got to assume that somewhere along the line you recevied a wet fill, and inspect the cylinder according to the recommended inspection frequency. You've also got to analyze the gas if you store the cylinder for more than 2-3 months, assuming a wet fill.
So much bad info on this board sometimes. You can store a steel cylinder for more than a year without issue.
If the tank had the worst case scenario for rust, it still would not eat more than 1 percent of the oxygen in the tank. It takes 16 percent O2 to support life on the surface. 20 percent will easily do it.
LOL, how many people drain their steel tanks every 3 months when they can't dive? I have about 14 tanks, half steel half aluminum. You think I'm using all 7 steel tanks? Not even close. I have a single LP95 that gets used about once a year. It's labled with nitrox sticker, when it was filled and what percent. When I go dive it, I analyze it again. It's within 1/2 a percent from original analyzing. I've been doing this for more than a decade. It's simply not an issue.
If the tank had the worst case scenario for rust, it still would not eat more than 1 percent of the oxygen in the tank. It takes 16 percent O2 to support life on the surface. 20 percent will easily do it.
LOL, how many people drain their steel tanks every 3 months when they can't dive? I have about 14 tanks, half steel half aluminum. You think I'm using all 7 steel tanks? Not even close. I have a single LP95 that gets used about once a year. It's labled with nitrox sticker, when it was filled and what percent. When I go dive it, I analyze it again. It's within 1/2 a percent from original analyzing. I've been doing this for more than a decade. It's simply not an issue.
You can store a cylinder indefinitely only if the air is dry. But you'll never know if the air is dry unless you drain the cylinder periodically and look inside. Therefore, you really can't store a cylinder indefintely unless you inspect the interior of the cylinder. A stable pO2 suggests that you have a dry fill, but says nothing about corrosion that might weaken or even condemn the cylinder. Periodical visual inspections are also necessary.
Seems you didn't read the thread. There is one fatal case (documented and researched by NOAA) where the rust reduced oxygen content to 2%-3% in only 3-months of storage. That's not enough to sustain life. Other research performed by the University of Rhode Island found significant decreases in oxygen content in rusting steel cylinders. These cases all involved significant amounts of moisture inside of the cylinders.
If you can keep your fills dry, then you shouldn't have any problems. Everyone thinks their cylinders are dry and free from corrosion, and everyone with a corroded cylinder is surprized when they see the corrosion when the valve is removed for inspection.
I don't care how wet the air is... the tank will last a year. The most oxygen it could take would be 1 or 2 percent at the most extreme circumstance, and that still leaves more than enough oxygen to support life.
And you're right, I didn't read the thread because quite frankly, I don't trust the data. It's simply not possible to reduce oxygen content by 1 percent in a month. I'm going to go fill my LP95 with a cup full of water, top it off with air and analyze it. I'll post pictures every step of the way. Then I'm going to re-analyze it at the end of the month. It's going to read 20.9% at the end of the month. We could do this 100 times, 1000 times, and every time, it's going to come back the same. IS there a chance in 10,000 times that we could get a critical loss of oxgyen? Sure, but there's a 1 in 10000 chance that you'll be hit by a bus on the way to a dive site too.
*edit
Then your next argument will be that all the rust and depletion of oxygen happens at the 3rd month. Fine, I'll leave it for 3 months.
It's not only possible, it's also been documented by research facilities and it's also resulted in at least one death. And from a thermodynamic perspective, the reduction in oxygen content correlated well with the amount of rust produced.
Which research facility?
LOL< your thread says the air in the tank had reduced oxygen content by 3 percent. That's 18 percent left in the tank? At the surface, our bodies only require 16 percent to support life. Underwater, we require even less. I'm starting to question your knowledge on the human life. 
Angry Turtle
Contributor
I believe this post from Doc Harry responds to the question, and quotes the source.
http://www.scubaboard.com/forums/3966349-post3.html
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