Non Nitrox certified using 21%

[Mscdex]

I am planning on buying 2 tanks and wanted to make them nitrox. My question is, if my non-nitrox certified friend wants to use them at 21% oxygen, is that frowned upon?

 

[boulderjohn]

This is an oft-repeated problem compounded by misinformation in typical nitrox classes.

If a tank is going to be used for partial pressure blending of nitrox, it has to be oxygen clean because pure oxygen is put in the tank first, and then the tank is topped off with air from the compressor.

Many nitrox courses teach that if you then use a tank for air diving, then it must by oxygen cleaned again to be used for nitrox, because the plain air might contain contaminants that will make the tank unsafe for introducing pure oxygen again.

Now, read those last two paragraphs one at a time, go back and forth, and see if you can spot the problem. In paragraph 3, we learn that putting air from the compressor into a tank makes it unsuitable for making nitrox through the partial pressure system. In paragraph 2 we learn that making nitrox through partial pressure blending requires putting air from the compressor in the tank.

If the air from the compressor is clean enough to use in making nitrox through partial pressure blending, it is clean enough to use in an air fill without contaminating the tank.

 

[tbone1004]

that's fine, but if they are filled with nitrox they have to be drained completely to get them back to a true 21%. Better to get your buddy nitrox certified or buy his on tanks....
There is nothing special about nitrox tanks if they are banked nitrox, they have to be O2 cleaned if they are filled via partial pressure and that can get expensive. Make sure to check craigslist before buying, and don't be afraid of tanks that are doubled up for cave diving, very simple to break down and you can often get better deals on them.

 

[Mscdex]

I was looking at 2 80cf Catalinas on Amazon for $180. They come with a fresh vis

 

[g1138]

As long as the air from the compressor is modified Grade E you can pump your Nitrox tanks with it and still put it through partial pressure blending on the next fill without having to O2 clean it again.

Modified Grade E has extra filters to limit Carbon sources into your tank.

The only exception is if you only fill at shops that bank Nitrox only and you never expose your tank to partial pressure blending. In that case, it doesn't matter that your tank be O2 clean and it doesn't matter if you use normal Grade E or modified (O2 clean air).

 

[Dr. Lecter]

that's fine, but if they are filled with nitrox they have to be drained completely to get them back to a true 21%.

Whether they're 23% or not is irrelevant unless his buddy is a pedantic fool, in which case I'd tell him to find his own damn tanks.

 

[tbone1004]

If you're diving locally, I'd really consider buying steel tanks. Take weight off the belt, lighter on land for the same capacity, last longer etc etc. Check craigslist out, not much you can do to ruin a scuba tank, and they don't depreciate with age.

Doc, I'm CMOA on that one, if his buddy isn't nitrox certified I'm not going to condone him diving enriched air. I agree his buddy should get his own damn tanks, or better yet get nitrox certified because if one is on nitrox and the other is hitting ndl's on air, it's going to be a royal PITA. for recreational depths if he was diving 32% it doesn't actually matter either as long as he's diving air tables, but I'm still not going to say it's ok on here

 

[NAM001]

I have had one problem with what the op asked. I have a dive location that,, if it has a sticker on it They treat anything that goes in to it as nitrox. If it had 21 in it and you ask for a fill they fill with 21, charge for nitrox perhaps 15 per tank instead of 7 and require a nitrox card to get the fill. This is a shop by shop thing I know , however problems can and do arrise. Another aspect is that if you have the nitrox band around the tank and the shop does not have hyper air they may refuse to fill it or even scrape the vis sticker and charge for a vis prior to filling with air. Its retatded but it is happening in places. The first place i mentioned required me to do a nitrox fill when i wanted to be topped off with air. so i said if i have to pay for nitrox in your 25 ft lake i want nitrox. He had banked 32 and he TOPPED off the tank with 32%. Then wouldnt acept a trimix card cause its not a nitrox card. Boy do i like having my own compressor and lots of tanks.

 

[DaleC]

Just to keep it real, I would like to know the profile that a rec diver could do and get into trouble with using a tank filled with air that originally held a small amount of nitrox.

Some Mods at 1.4 ppO2:

187'
177'
168'
160'
152'
145'
138'
132'

[TD="class: o2perc"]21%[/TD]

[TD="class: o2perc"]22%[/TD]

[TD="class: o2perc"]23%[/TD]

[TD="class: o2perc"]24%[/TD]

[TD="class: o2perc"]25%[/TD]

[TD="class: o2perc"]26%[/TD]

[TD="class: o2perc"]27%[/TD]

[TD="class: o2perc"]28%[/TD]

 

[Dr. Lecter]

I have had one problem with that the op asked. I have a dive location that if it has a sticker on it They treat anything that goes in to it as nitrox. If it had 21 in it and you ask for a fill they fill with 21, charge for nitrox perhaps 15 per tank instead of 7 and require a nitrox card to get teh fill. This is a shop by shop thing I know , however problems can arrise. Another aspect is that if you have teh nitrox band around the tank and the shop soes not have hyper air they may refule to fill it or even scrape teh vis sticker and sharge for a vis prior to filling with air. Its retatded but it is happening in places. The first place i mentioned required me to do a nitrox fill when i wanted to be topped off with air. so i saiid if i have to pay for nitrox in your 25 ft lake i want nitrox. He had banked 32 and he TOPPED off the tank with 32%. Then wouldnt acept a trimix card cause its not a nitrox card. Boy do i like having my own compressor and lots of tanks.

It's not happening anywhere I would spend money. I did have a local tank guy recently do a double-take when I asked for air in an AL80 that had a green and yellow sticker on it:

Tank monkey: 'But it has a Nitrox sticker!'
Me: "No, read the sticker."
Tank monkey: <reading aloud> THIS IS NOT YOUR TANK! DO NOT USE, EVEN IF SOME IDIOT TELLS YOU TO! May contain mixes other than air! 'Oh, well I guess that's alright then.'