Nitrox question

[Epinephelus]

spurtill once bubbled...
As for filling your own Nitrox. all you do is oder a cylinder of O2 and buy the whip to connect it to your bottle. Put the O2 required in the bottle and top it up with air from a normal filter.

All you do?
Please don't just run out and buy an oxygen whip and start filling bottles. Do some homework first.
In addition to cleanliness, flow rates are critical.
Just opening the valve too fast can cause combustion where otherwise there would be none.
Y'all may think I am chicken little... I have a vision that won't go away - a young sailor who looks like he was dipped in plastic, no hair, no ears, no nose, no eyelids, gasping, groaning, beyond screams, dying in agony, knowing we could do nothing for him. He'd been at the oxygen farm for years, knew it all, just got a little careless once too often.
You can get away with things like (as a specific example) cleaning and reusing buna o-rings previously lubed with silicone (which penetrates) for years before the combination of residual hydrocarbons and just enough adiabatic heating reach out and touch you, but considering the consequences if you are the one there for that one in a zillion event, why not just use new ones?
Yes, you can do your own cleaning; you can do your own mixing; you can do your own equipment prep and maintenance. You can even build your own whips and manifolds and other stuff. None of it is difficult and none of it is rocket science. But cut corners and you will eventually get burned.
I say again, trifle with oxygen at your own peril.
E.

 

[spurtill]

Just to clarify, I did say to go do a blending course before even thinking about blending your own Nitrox. But follow the rules and its safe and you are in no more danger than when running a compressor.

As for the in-line filter yeah all they do is remove the oil from the air. I assume you can get other types but thats what all the ones i've used to. The explanation i got was that the air is sucked into a compressor and filtered, so you get more or less perfectly clean and suitable air, for anything. then you go and use an oil lubricated compressor to compress it and what do you know? There is now oil mixed back in with your nice clean air. So you wait until the air comes out of the compressor and refilter it to get rid fo the oil, it should be clean other than that.

 

[Epinephelus]

spurtill once bubbled...
Just to clarify, I did say to go do a blending course before even thinking about blending your own Nitrox.

Yes, you did - I saw that "all you do" statement and blasted away without even seeing the "take the course."
Sorry.
E.

 

[sylvester]

No, reason for concern on my part I will take the nitrox class probley this winter just to have something to do. I am just trying to gather info and make my self alittle more informed.

The in line filter has me courious because I never thought about the compressor oil getting back in to the air, but now I can see it (or the mechanics of the seepage). But it must not be enough to worry about for normal compressed air diving. Which would explain why I have never heard anything about it being an issue.

So the oil residue reacts with, O enhanced air, and can create a fire? How? and Why?

Excuse my questions if they seem simple, but I am curious.

Now back to an earlier question I asked in this thread. If the Oil residue is bad when mixed with increased oxygen mixtures, then how can I use the same regulator for nitrox and regular diving.

This makes me think I would need dedicated nitrox equipment. Or skip the nitrox class and do something else.

 

[Rick Murchison]

sylvester once bubbled...
So the oil residue reacts with, O enhanced air, and can create a fire? How? and Why?
Excuse my questions if they seem simple, but I am curious.
Now back to an earlier question I asked in this thread. If the Oil residue is bad when mixed with increased oxygen mixtures, then how can I use the same regulator for nitrox and regular diving.

The 40% rule states, basically, that oxygen percentages below 40% don't require special handling. Since your regulator only comes in contact with the premixed gas, it's no problem until you start using mixes richer than 40%.
100% oxygen, unlike 40% and below, can cause spontaneous combustion and subsequent fire or explosion when in contact with hydrocarbons (greases, oils & fuels) at very modest temperatures. Tanks and tank valves can come in contact with 100% oxygen during partial pressure blending, and so must be oxygen clean (free of hydrocarbons) and oxygen service rated (assembled with oxygen compatible components and lubricants). The air added to the 100% oxygen must also be free of hydrocarbons since initially the mix is right at 100% oxygen.
Rick

 

[spurtill]

So as said above the only peice of equipment you need to changed for Nitrox diving (where the highest mix you'll use is 40%) are you bottles.

Your regs will handle 40% easily so they don't need to be modified in any way.

You bottles will probbaly be filled at some stage using the partial pressure method described earlier, so they need ot be able to handle 100% O2.

Normal air does have oil in it, which is why you get the cylinders O2 cleaned every year.

The oil does not mean your bottle WILL explode or anything, it just increases the risk of it happening.

In anything less than 40% O2 this risk is generally presumed to be low enough to be discounted. Hence even though your regs will aso have a small amount of oil stuck to the hoses and lubricating parts it is not seem as a high enough risk to advise against it.

In summary the only thing that get 100% O2 and hence needs to be O2 clean are the bottles (and pillar valves). The reast of the gear only comes in contact with mixes of less than 40% O2 and are deemed safe to have oil in.

 

[pipedope]

Oil is not safe for divers in any significant quantity.

The amount of oil that is OK in breathing air (a very small amount) is also OK with 40% nitrox. For high pressure O2 you need to get and keep things VERY clean and be careful of fill rates.

A very good practical resource on this stuff is, "Oxygen Hacker's Companion" by Vance Harlow. He is "oxyhacker" on scuba board and his web site is;
http://www.airspeedpress.com/index.html

 

[buttermanr]

sylvester once bubbled...
If I take the Nitrox course will it require me having a 2d set of regulators for nitrox, or can I use my normal gear and just rent nitrox filled tanks.
My current gear is a mk25/s600 with g250 octo and nitrox compatable ai computer.

Watch out. There is a lot of misunderstanding about nitrox compatibility and lots of people on this board vent their opinion on this subject without really understanding it.

There are really 2 questions you should ask:
-1- is my equipment suited for use with Nitrox?
-2- can I use Nitrox and standard air interchangeably?

Is my equipment suited for use with Nitrox?
Most regulators are nitrox compatible up to 40%. This means that they do not use certain type of materials (e.g. titanium, magnesium), which are incompatible with nitrox. Check your user manual (or call ScubaPro) to find out whether your set is.

Can I use Nitrox and standard air interchangeably?
This is where misunderstandings come in. Virtually every gear manufacturer will tell you no. The reason is that standard air contains hydrocarbon contaminants (or "oil" as some in this thread called it). These contaminants react with the pressurized oxygen and the resulting combustion causes a short but very high temperature increase of many hundreds of degrees. This can cause damage to parts in your regulator, SPG and/or HP hose. Gear manufacturers recommend to oxygen clean any regulator/hose/SPG that has been used with standard air, before using it with Nitrox. This is a cleaning process that removes any hydrocarbons that have built up in your system. Many dive centers that offer nitrox also offer this service, but it will get a little expensive if you switch frequently.

An alternative solution is to use so-called oxygen compatible air. This air contains less than 0.1mg/m3 of hydrocarbons (standard or Grad E air contains up to 5mg/m3). Oxygen compatible air can be safely alternated with nitrox.
ScubaRon

 

[buttermanr]

sylvester once bubbled...
So the oil residue reacts with, O enhanced air, and can create a fire? How? and Why?

OK, you asked for it. Now I have to get technical.
When gas flows from high to low pressure it reaches velocities in excess of the speed of sound. If gas hits an obstacle (e.g. a hydrocarbon particle or a piece of rust) at these speeds it instantly recompresses (this is called adiabatic compression), and creates a momentary temperature increase (combustion). In pure oxygen systems this increase can be well in excess of 1000 degrees F and this in turn will ignite almost any material. Even a teflon coated hose will burn like it is a fourth of July sparkler.
In 40% nitrox the temperature rise will be much lower and is unlikely to ignite anything, but the rise is high enough that it will damage parts inside your regulator or your hose and thus increase the risk of failure.

Many divers unfortunatly mistake combustion for explosion and draw the conclusion that, since their regulators haven't exploded in the last 3 years, there is no risk. This conclusion is wrong: combustion damage in regulators is real and there are also some reports of "flashes" in regulators. The question is how big this risk is and I wish an organization (e.g. DAN) would study this.
ScubaRon

 

[paulwlee]

buttermanr once bubbled...
Most regulators are nitrox compatible up to 40%. This means that they do not use certain type of materials (e.g. titanium, magnesium), which are incompatible with nitrox.

Well, the Atomic Aquatics manual states that the T1, that is solid titanium and in which most components are titanium is compatible with Nitrox up to 40%.