Nitrox Only

[DevonDiver]

Tanks could still be filled with regular (not nitrox compatible) air. Unless, of course, you specifically marked/designated your tanks to ensure blenders knew that your tanks should be kept nitrox clean.

Normally, the presence of nitrox markings (green band etc) and O2 clean sticker (added after cleaning/valid 1 year unless contaminated) fulfill that role. There's no harm in the additional marking however, if your intention is to preserve those cylinders for nitrox use (at any vendor, via any blending method).

 

[Wookie]

Is the reason that oxygen is added first because O2 tanks are only filled to 2000 psi?

That's part of it. The most difficult gasses are added first. Helium would be most difficult of the breathing gasses because of the small molecule size. It escapes from everything. Then oxygen because oft he handling requirements. Gaseous oxygen acts weird above 3000 psi. You add oxygen first to a nitrox blend so you don't wear out your booster, and so the short amount in the hose isn't at high pressure, and last so you don't get stratification of the gas.

 

[dfx]

Now what if the Nitrox fill doesn't come from a partial pressure fill? If a membrane system was used for example, couldn't the air used still be "un-clean"?

 

[Wookie]

Now what if the Nitrox fill doesn't come from a partial pressure fill? If a membrane system was used for example, couldn't the air used still be "un-clean"?

Those who can afford a membrane system can afford a compressor that produces oxygen compatible air. So, you could use regular grade e air, but you wouldn't use grade e air.

 

[eponym]

Those who can afford a membrane system can afford a compressor that produces oxygen compatible air. So, you could use regular grade e air, but you wouldn't use grade e air.

Membrane systems aside, here's a question I'd like to ask:

Assume that the compressor air is grade E, which goes into a blending stick fed by a dedicated pure oxygen tank. The appropriate electronic controls are in place to create and bank 40% nitrox in the bank of nitrox tanks.

I believe that when my cylinder is filled partially with this premix and then topped off with grade E air to produce my desired mix (let's say 34%), this procedure invalidates the O2-clean rating of my cylinder.

In other words, I would not later want to do in-tank blending using that cylinder.

Comments?

-Bryan

 

[101recon]

The danger comes from the fact that many substances will ignite when they come into contact with a high enough percentage of oxygen. Most petroleum products like oil, grease, Vaseline, and even some hand lotions will ignite when exposed to a high enough percentage. Things like these coming into contact with pure oxygen is where the risk of fire or explosion comes from.

 

[boulderjohn]

Is the reason that oxygen is added first because O2 tanks are only filled to 2000 psi?

That's part of it. The most difficult gasses are added first. Helium would be most difficult of the breathing gasses because of the small molecule size. It escapes from everything. Then oxygen because oft he handling requirements. Gaseous oxygen acts weird above 3000 psi. You add oxygen first to a nitrox blend so you don't wear out your booster, and so the short amount in the hose isn't at high pressure, and last so you don't get stratification of the gas.

And for those of us who do not have a booster, we have to go in that order to be able to make best use of our supply tanks. They are only filled to 2,400 PSI to begin with, and when you transfill to your tanks, you can only fill your tanks to the PSI in the supply tank. That's why people without boosters often need to bleed tanks down before filling them. You end up needing a lot of supply tanks, first putting gas from the least full one and then working your way up to the most full one. What a PITA! Doing helium first saves a few bucks because you can get the one you do first lower before you reach the point that you can't get any more out, and helium is much more expensive than oxygen.

 

[RJP]

The danger comes from the fact that many substances will ignite when they come into contact with a high enough percentage of oxygen. Most petroleum products like oil, grease, Vaseline, and even some hand lotions will ignite when exposed to a high enough percentage. Things like these coming into contact with pure oxygen is where the risk of fire or explosion comes from.

You'll need more than merely "coming into contact with a high enough percentage of oxygen" in order for the substances you cite to ignite. (A source of ignition, for one thing...)

 

[Tigerman]

To summary all the (relevant) posts in one post..

1. o2 cleaning is ONLY required for partial pressure blending
2. Filling air does NOT automatically mean its contaminated, you need to know how clean the air is to say its NOT contaminated - If you dont know its not contaminated, it is.
3. Air IS nitrox, just not pp blended

As to the more interesting off topic posts..
If the tank is contaminated and exposed to high ppo2 you still need a source of ignition (heat) for it to go off. Unfortunately tanks get heated by increased pressure, which causes potential fire hazard with o2, but also cause a much more annoying issue - the tanks lose pressure as they cool down and if theire not topped off I might lose a few minutes of precious dive time!

 

[101recon]

You'll need more than merely "coming into contact with a high enough percentage of oxygen" in order for the substances you cite to ignite. (A source of ignition, for one thing...)

No source of ignition is necessary. These substances can self-ignite. This may be even more likely under pressure.
https://www.google.com/search?as_q=&as_epq=Petroleum+based+products%2C+oils%2C+grease+and+lotions+can+self-ignite+in+the+presence+of+&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=&cr=&as_qdr=all&as_sitesearch=&as_occt=any&safe=images&tbs=&as_filetype=&as_rights=#as_qdr=all&lr=&q=can+petroleum+and+pure+oxygen+self-ignite+