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malley1717
03-24-2008, 14:34
here is a stupid question for you guys-

If you get a tank, can you use it for air and nitrox, or just for one or the other?

UCFKnightDiver
03-24-2008, 14:42
It depends on how they have/make the nitrox, most I have seen use partaial pressure blending in this case you would need a dedicated nitrox tank because they put pure O2 in and then top it off with air to get the correct mix of nitrox (?also something to take note if you get I think its called ultra or highly clean air you do not need to dedicate a seperate nitrox tank? of course the shop would need to know you had clean air in it) So if you were to use a regular tank filled previously with air you would need to get it O2 cleaned, and also have some of the o-rings changed

Also have seen some shops that use the partial pressure blending system and fill regular non dedicated tanks, doesnt seem to safe to me(i really dont know)but I guess youy could always ask

Then some use premix where they mix it before hand and then keep it on site (bank it) or some use a membrane system which filters some of the Nitrogen (i believe) out of the air Both premix and membrane systems do not require a dedicated nitrox tank

terrillja
03-24-2008, 14:44
here is a stupid question for you guys-

If you get a tank, can you use it for air and nitrox, or just for one or the other?
Depends. If you are getting premixed nitrox, then you can use it for nitrox as well as air from any scuba compressor. If you are getting partial pressure nitrox, where the nitrox is made in the cylinder, by adding pure O2 and then air to top off, you will need the tank and valve to be cleaned for enriched air, after which only oxygen-compatible air can be used. This is still regular air, but it has been filtered more to maintain the oxygen cleanliness of the cylinder.

Some more info about how you can get nitrox locally would be helpful.

navyhmc
03-24-2008, 16:38
As terrillja and rox said, if there is a chance that your nitrox fills will be from parital pressure fills, the tank needs to be oxygen cleaned to get it as hydrocarbon free as possible to prevent the risk of explosion when pure O2 is placed in the tank. This can be an expensive venture, the local LDS charges $50 to O2 clean. If you're not using nitrox, you don't want to just get a "regular" fill. You need to use "Clean" air that has more oil filtered out or the compressor must use nonhyrdocarbon lubricants as the miniscule amounts that go into a tank when filled will build up over time to a possibly disasterous level.

There have been cases of low order explosions in tanks that were partial pressure filled.

terrillja
03-24-2008, 17:21
The way it was explained to me, if the cylinder isn't clean, the oxygen being put in won't go boom, but it will have small fires inside the cylinder, introducing CO and CO2 into the breathing air, both of which can be fatal at high levels, such as those experienced while breathing compressed air at depth.

CompuDude
03-24-2008, 20:43
The way it was explained to me, if the cylinder isn't clean, the oxygen being put in won't go boom, but it will have small fires inside the cylinder, introducing CO and CO2 into the breathing air, both of which can be fatal at high levels, such as those experienced while breathing compressed air at depth.

No, the issue is most assuredly risk of explosion, generally during the filling process when the o2 is being compressed.

cummings66
03-25-2008, 14:50
You do run a risk of small flash fires that won't take out the tank, or so I was told. The most likely result might be a big bang, but it could be a small puff and you're breathing nasty stuff.

That was one of the reasons they said you should analyze tanks, even months after a fill. Just in case.

cummings66
03-26-2008, 18:55
I forgot to add, Chapter 4 of the TDI Advanced Nitrox book talks about the small flash fires, that's where I found the info at. I assume it's possible based on that. I couldn't place exactly where I come across it until I was reviewing it today. Carbon Monoxide is the risk.

The analysis was due to possible rust, no other reason. Rust would use up some O2 so if you had 40% and later had 30% you've probably got some serious rusting going on.

frogman159
04-01-2008, 19:57
This was a great thread!:smiley20:

Black-Gorrilla
04-02-2008, 00:09
I forgot to add, Chapter 4 of the TDI Advanced Nitrox book talks about the small flash fires, that's where I found the info at. I assume it's possible based on that. I couldn't place exactly where I come across it until I was reviewing it today. Carbon Monoxide is the risk.

The analysis was due to possible rust, no other reason. Rust would use up some O2 so if you had 40% and later had 30% you've probably got some serious rusting going on.

would it really make a 10% change? over what period of time are we talking about here? days? weeks? more?

ChrisA
04-02-2008, 00:31
Rust would use up some O2 so if you had 40% and later had 30% you've probably got some serious rusting going on.

10% of the O2 used up to make rust? That could be about 1/4 pound of O2. That mass of O2 would combine with a HUGE abount of iron. That woul d destroy the tank. I'm to lazy to work out the exact mass of Fe but it's
a lot" so much that I doubt the 10% figure is possible. The tank would likely leak out the gas first.