Homebrew Nitrox?

[Teamcasa]

OK, I keep reading about how dangerous Oxygen is in pure form. So be it, pure Oxygen can be very dangerous if exposed to a source of ignition. As a welder, (certified in ’68, now just for fun) I can tell you the Scuba industry is by far way more cautious and concerned about handling O2 than anyone else. Go by any auto or muffler shop, metal fabricator or junk yard and see how clean the environment and tools used around the O2. A close friend of mine also fills the O2 systems on small general aviation aircraft from a portable bank of 8 AV200 (200CF). His shop and whips are clean and there is no smoking but other than that, no big deal.

I’m not going to officially recommend that a home user, not experienced handling O2 fill his tanks but with a little training and the appropriate equipment I would think partially filling a tank should be no problem. Frankly the danger of dealing with extremely high pressure poses significantly more risk.

 

[dogblues64]

I say, buy an air compressor and start mixing your own and supply it locally, since no one else is... I see a vacuum there! You really could start a trend there!

 

[cool_hardware52]

OK, I keep reading about how dangerous Oxygen is in pure form. So be it, pure Oxygen can be very dangerous if exposed to a source of ignition. As a welder, (certified in ’68, now just for fun) I can tell you the Scuba industry is by far way more cautious and concerned about handling O2 than anyone else. Go by any auto or muffler shop, metal fabricator or junk yard and see how clean the environment and tools used around the O2.

I too do a bit of welding, and have been handling O2 for a very long time. Nobody will confuse a welding shop with a clean room. I have also used the welding shop as an example of less than ideal conditions for handling O2. Welding shops do occasionally blowup, usually from some gross negligence, or stupidity.

OTOH, the welding tanks and the associated supply bottle valves, and the welding regs are all designed for O2. A welder does not typically transfill HP O2, boost O2 or decant it into scuba bottles via valves not designed for such purposes.

Welding and cutting torch hoses are at very low pressures, typically ~40 psi, not the 400-500 psi required to PP blend and empty scuba cylinder, or the ~3000 psi necessary to fill a RB tank.

Almost all welding operations will simply use O2 from a supply bottle. They don't mix it with other gas in a high pressure cylinder.

A close friend of mine also fills the O2 systems on small general aviation aircraft from a portable bank of 8 AV200 (200CF). His shop and whips are clean and there is no smoking but other than that, no big deal.

I've filled my share of O2 bottles in Light aircraft too, usually from a 4 cylinder cascade.

Transfill / boosting O2 for general aviation is much more analogous to PP blending, and the risks are almost the same, except the bottle in the aircraft is for pure O2, not O2 + some (maybe) O2 clean air.

I’m not going to officially recommend that a home user, not experienced handling O2 fill his tanks but with a little training and the appropriate equipment I would think partially filling a tank should be no problem. Frankly the danger of dealing with extremely high pressure poses significantly more risk.

What are the real risks of decanting O2 up to ~500 psi at home and then getting an "air Top" from a friendly (or blissfully ignorant) fill station operator?

Probably pretty low.

Here's my real concern. Take a newly O2 cleaned cylinder and decant ~500 PSI of O2 into it using good procedures. The tank is still pretty clean, not perfect, but pretty clean.

Now top it with some Grade "E" air. Now the tank and valve are a little less clean, but nobody makes the evening news.

Do it again, and again, and again, and eventually you can develop enough "fuel" in the valve for bad things to happen.

When is the most likely time for this "bad thing" to occur? The next time the home PP blender is introducing the HP pure O2.

IMO, topping with Grade E is a numbers game. Frequent O2 cleaning and reasonably good clean air tops, probably low risk.

Infrequent cleaning and marginal gas quality could be "eventful"

Tobin

 

[pescador775]

Before topping off at a shop for first time it would be prudent to inquire in a congenial manner. Perhaps, the shop owner would have time to show off his expensive equipment and certificates. Other divers might share their opinions about the operation. Buy something or offer to help with something. Bring in the tank later.

 

[Rhone Man]

I think Tobin hits the real problem on the head - the air top up will slightly contaminate each time. So either I do a fresh 02 clean every time. Or there is some risk taking. And I would hate to have something happen to some unsuspecting staff member at the LDS on my account.

*Sigh* I guess I'll just have to wait and see if someone starts offering Nitrox next diving season.

 

[dannobee]

*Sigh* I guess I'll just have to wait and see if someone starts offering Nitrox next diving season.

Why not become proactive and ask the owner of the shop if he's interested in banking some 32%, using a homemade nitrox stick and a couple of his bank cylinders. If you're asking about nitrox on the island, chances are pretty good that others are as well. The owner could become the *only* source for nitrox for a while and make some money in the process.

 

[oxyhacker]

One solution that some mixers use, is put the O2 tank, then take another tank and a "equalizing whip" and put enough air in the tank to bring the F02 down below 50%. Then take it down to the shop and get it filled. A <50% mix is unlikely to cause trouble no matter how dirty the air is, so this transfers all the risk to the mixer, and away from the filler, at only a modest increase in cost (for the extra air fills).

We'd rather see people come clean with their LDS, and get their fills that way, especially because rate-of-fill is probably a greater danger than dirty air, but it is an alternative for the compressor-less.

Oh hey Pesky, what do you mean by "books like Oxygen Hacker's Companion"? There are no books "like" the Oxygen Hacker's Companion - just the Oxygen Hacker's Companion itself, and a bunch of me too, CYA, agency manuals.

I've thought of going this route also since access to O2 is easy. I'm a little leary of taking a tank to my LDS to get it topped off. If you tell them there is pure O2 in it, are they not likely to top it off for you? If you don't tell them and something happens, are you liable? And lastly what is the likelyhood of anything actually occuring (read:BOOM!) when topping a tank to scuba pressures that starts off with pure O2 in it.

 

[pescador775]

Oh hey Pesky, what do you mean by "books like Oxygen Hacker's Companion"? There are no books "like" the Oxygen Hacker's Companion - just the Oxygen Hacker's Companion itself, and a bunch of me too, CYA, agency manuals.

LOL, touche.

 

[oxyhacker]

Tobin is correct, but it is not really a problem. One batch of Grade E air in an 02 cleaned tank is not going to cause it to combust in PP mixing! Nor will 10, or 100, and it is highly unlikely that even 1000 would. So unless you get a fill of really, really, bad air (and this could happen with a hyperfilter system almost as easily as a grade E system) any contamination will accumulate with microscopic slowness, so regular cleaning should be enough to keep it from every reaching the danger point.

There are a lot of people mixing nitrox, who don't have their own compressors.

I think Tobin hits the real problem on the head - the air top up will slightly contaminate each time. So either I do a fresh 02 clean every time. Or there is some risk taking. And I would hate to have something happen to some unsuspecting staff member at the LDS on my account.

*Sigh* I guess I'll just have to wait and see if someone starts offering Nitrox next diving season.

 

[CraigAClark]

There is nothing wrong with using Grade "E" for blending. I think too many people have a misconception of what a "Hyper-Pure" filtration system is all about. Realistically it is a "fail safe", installed to hopefully protect from a catastrophic failure in the primary filtration system. This could be caused from a compressor that is poorly maintained or one that is in need of repair, or any number of other reasons that the primary filtration system is no longer producing Grade "E" air.

I guess the way I look at it is as insurance, just in case. Do you absolutely need one, no.

I am learning that most DIY'ers are much more safety oriented than the majority of stores. A little saying I had back when I used to service dive store equipment. They basically knew three things about the system. How to turn it on, Hopefully check the oil level and change the filter (hopefully before it expires). As far as maintenance, run it till it breaks. I even had folks tell me they knew when to change filters or media by taste. These folks definitely needed Hyper-Pure. Glad air was the only choice back then.


Craig