Converting tanks to Nitrox

[fredk]

Most shops in the Ottawa area do partial pressure blending so in that case 100% o2 is going into your tank so they will also need to be o2 cleaned also make sure your lds is using a hyper pure filteration system or you could end up with hydro carbon traces in your tank.

 

[MikeFerrara]

I have a new compressor so my air meets modified grade E (tested every three months). I prefer to use the hyper filter but confess to not always using it. In theory even the small amount of hydrocarbons you get from a well maintained compressor can build up over time eventually causing a problem while adding the O2. Machines with more hours on them will not be as clean and even with a new one without the hyperfilter there is no gaurantee. Again the potential problem is the build up of contaminants over time. When fires do happen it is almost always while transfilling with O2. And yes I have IANTD blender and LSST certs.

Ron
The DSAT blender course seems more comprehensive than the others. No way to do it a single day that's for certain. The only problem I have with it is the cleaning process they specify. The nice thing is they combine nitrox, trimix and LSST (equipment prep) all in one class.

 

[jonnythan]

Originally posted by WreckWriter


And how long is that oxygen pure in your tank? Is it EVER pure anywhere other than in your tank? Is 40% EANx more corrosive than air? Likely not much.

That negates the corrosive factor. As for it being combustible, not exactly..... Pure O2 in a clean environment will not burn. What it does is make combustible materials burn much better. In a welding class the instructor may take a tiny dab of grease and direct a stream of O2 onto it. The grease will catch fire, the fire will not run up the stream of O2. The O2 isn't burning, the grease is.

Hopefully you are keeping your scuba gear away from oil and other petroleum products anyway, aren't you? (this includes having your tanks filled only from well maintained compressors)

OK, it is definately better to have tanks oxygen cleaned and to use viton o-rings. For standards EANx mixtures I just don't think it's terribly critical. You certainly don't need to be concerned about your BC....

Tom

I think you misunderstood.. I'm not concerned about my BC because I don't put pure O2 in it. I was saying that *if* I put pure O2 through any of my gear, I would be concerned about the long term. Therefore, I am concerned about putting 400 psi of pure O2 in my tank regularly.

I don't trust the filters of all compressors my tanks have used to have 0 hydrocarbon content, and I definitely don't want excess byproducts of combustion (water, CO2, other impurities) in my air when I'm at 80 feet. So, I would certainly go with the O2 cleaning every now and then, and especially before the first Nitrox fill

 

[roakey]

Originally posted by Ron Brandt
How many on this discussion have Blender Credientials ?

I'm an IANTD blender. That and a quarter will get you a cup of coffee.

To answer BEM's question you have to know how the shop dispenses Nitrox. There's two main ways to do this. If the shop banks Nitrox, such that they deliver Nitrox into your cylinder at concentrations no greater than 40% O2, you need do nothing, except probably pay big bucks for a bumper sticker that says “Nitrox” on it. If your shop demands an expensive sticker for pre-blended fills, realize that it’s simply another example of extortion-because-they-can shop behavior and buy the sticker, because you won’t get fills without it.

The way pre-blended works is if you want, say, 32% Nitrox and the shop banks 40%, they’ll dump some 40% in your cylinder and then dilute it by blowing air on top of it to give you 32%. Because no part of the system is ever exposed to anything above 40% O2, there is no need for cleaning. This is why paying big bucks for the sticker (if they require one) is extortion – there’s no need to do ANYTHING to your equipment if your fills are from a pre-mixed bank.

Things change if they do what’s called “partial pressure blending.” In this method pure O2 is introduced into the cylinder and then hydrocarbon-free (usually called “hyper-filtered”) air is blown on top to dilute the pure O2 down to the percentage you require. In this case the cylinder IS exposed to pure O2 [for those of you that have been here for awhile, I’m going to simplify here] so in this case your cylinder needs to be “ready for oxygen service” since it’s exposed to pure O2. Note I didn’t say “O2 clean.” O2 clean is only half the equation, though the phrase is typically misused to mean ready for oxygen service. To make something ready for oxygen service you have to O2 clean it AND make sure that all materials that come in contact with the pure O2 are oxygen compatible.

A typical dive shop will tell you that making stuff O2 clean is rocket science. To quote The Oxygen Hacker’s Companion “It’s not rocket science, it’s kitchen science.” If your cylinder is in relatively good shape it’ll be tumbled with glass beads and a commercial O2 cleaner or most likely “Simple Green” which is a widely-available citric cleaner, the valve will be ultrasonically cleaned and all its O rings and lube replaced with O2 compatible components. Voila’ a cylinder “Ready for oxygen service.”

The cylinder will then be marked with a special sticker. These ready for oxygen service stickers come in a variety of flavors from the mondo wrap-around “Nitrox” stickers down to a simple PSI stickers that look just like your normal VCI sticker but they’re green (the latter being the kind of sticker I support).

Because the PP mixing is done in the cylinder, by the time you use the gas its concentration less than 40% O2 (I’m assuming recreational Nitrox here) so there’s no need to make your regulator ready for oxygen service (read: no need to buy a “Nitrox” regulator). Your normal regulator will work just fine.

Important safety tip: Once ready for oxygen service, you have to be careful where you get air or pre-blended Nitrox from that point forward to assure that they only deliver hyper-filtered air into your cylinder. If a bad compressor delivers hydrocarbons into your cylinder they’ll condense on the cylinder walls and the next time pure O2 is introduced into your cylinder for partial pressure blending, you could have “complete and rapid disassembly of the cylinder.”

I mentioned The Oxygen Hackers Companion. This is an excellent book, and that’s putting it mildly. It’ll teach you everything that a mixing course will teach you and much, much more. If you’re the least bit interested in the nuts and bolts of Nitrox, I HIGHLY recommend you buy it, it’s worth far more than the $35 you’ll pay for it.

To order, see: http://www.airspeedpress.com/

So to recap: If the shop only introduces pre-mix into your cylinder, you need do nothing to it. They may demand you get an unnecessary sticker, but that’s their way of saying they love you(r money). An unethical shop will demand making your cylinder ready for oxygen service for pre-mix, so watch out for this. If your shop does partial pressure mixing, you’ll have to have your cylinder and valve made ready for oxygen service. Cost of this is anywhere from $30 to $100 dollars in the states, a fair price is probably about $35-$50 when you include the labor, given the parts probably run less than $10.

In all cases for recreational Nitrox you need do nothing to your regulators.

Roak

Ps. 10 years ago who would have thought that we’d be saying “recreational Nitrox!!”

 

[BEM]

Thanks to everyone for their input and information.

I did get the tanks “ready for oxygen service” and as soon as the weather warms up, and the water, we’ll get wet.

My LDS uses partial pressure blending and has made the cylinder and valve ready and filled them with 36%.

Once again, thanks – I learned a lot, hopefully more posts will follow.

 

[Ron Brandt]

"Ron
The DSAT blender course seems more comprehensive than the others. No way to do it a single day that's for certain. The only problem I have with it is the cleaning process they specify. The nice thing is they combine nitrox, trimix and LSST (equipment prep) all in one class"

Thanks but I had Member Forum at my house. Seen the material.
Can sign myself off as a DSAT blender.Equipment prep was part of the course as I did it with other dive shop managers.

I had to become nitrox certified, become a scuba instructor , work for a store , befor I even qualified to take a blender course.

I do mix my own trimix and dive it.

Seems like the value has gone out the window. I will probably make more money selling "fill kits" to go along with the course.

BTW : My course was 8 hours. One day. Could have been shortened to a morning.

Ron

 

[Ron Brandt]

"Can sign myself off as a DSAT blender"

Did'nt proof it. Should have read. " I qualify for Blender Instructor status"

Blended for two years. Blended over 50 tanks. Am an MSDT.

This was once an elete certification. I was only one of Three certified techs in the province

Ron

 

[MikeFerrara]

Ron,
Why the need for blending to be an elite cert? While recreational nitrox is a commodity that is typically purchased from a dive center it is very hard in most areas to get mixtures over 40%. Trimix is extremely hard to get from a shop even if you can afford it. The term “technical diver” means different things to different people but having to rely on someone else to build you mix doesn’t seem appropriate. My students who dive doubles are required to assemble their own set. Yes I could do it and make a few bucks. But…when their off somewhere diving and have to do a repair or make an adjustment should they be reliant on someone in a recreational lds who has never had their hands on a set of 104’s. I don’t know about you, but I will not do a deep dive with mix I purchased over a counter. I don’t think you need to worry about DSAT blenders causing you to loose money. The average rec nitrox diver isn’t going to blend their own and the serious divers are, with or without DSAT.

Mike

 

[Ron Brandt]

Mike , just thought I would see what kind of reaction I would get.

Quite frankly , I pretty much agree with you.

Ron

 

[roakey]

There's a good, existing discussion on gas blending as well as the PADI gas blender course and gas blending courses in general in:

http://www.scubaboard.com/t4727/s.html

Roak