Nitrox tanks

[Bigcape]

since we are talking about O2 clean.

I have yet to understand the true dangers of small amounts of oil in a tank as a danger. I realise that if the oil were to ignite somehow, that fueling it with 100% O2 will make a bigger flame. But how is few tiny drops of oil going to ignite in the first place? Are we talking about possibly static electricity from scuffing accross the carpet??

Is there a chemical reaction I have not read about like there is between Titainium and over 50% O2?


I understand high levels of O2 can eat away at O-rings.

I know that 02 is not flamable but is an excellerant. (makes small flame bigger and burn faster)


My LDS fills with the PP method. He puts 419psig of 100% O2 into my empty tank and then tops off with 2581psig of the SAME air he fills other tanks for Non-Nitrox people to give me my EAN.

I am good with that. That is an approved way of doing it.

However I am having a hard time with understanding why all the hub-bub of having to get my tank RECLEANED if I go in and my fill my tank with 100% "air" with The SAME compressor, the same banks of air that make up my Nitrox mix.

I have yet to understand the logic!

 

[pescador775]

Among the laboratory tests which all compressor oils are subject to is the 'oxygen bomb" test. Briefly, a quantity of oil along with a metal catalyst and pure oxygen are placed in a bomb (container), heated, pressurized and stirred. When a predetermined quantity of oil has been oxidized this is recorded and listed on the MSDS. The actual method for determining this is to measure the oxygen pressure until it drops to a predetermined level. I have never heard of a fire incidental to this test. Relative to a scuba tank, the amounts of oil which accumulate are related to the filter efficiency of the compressor and the amount of gas which has passed through the tank. The CGA list 5 mg/cu meter as the maximum allowable for grade E. No way do i believe that a compressor in good shape puts out this much oil but that is what they say. In that case, after 100 fills, the maximum quantity of oil would be 1 gram, well mixed with water. Any visual inspection would detect this since the quantity of water would be on the order of 20 grams. Time to clean, and maybe, tumble. That would be an extreme case and cause for concern, mainly because water and O2 cause rust or corrosion. Not to discount the potential danger of oxygen but these risk factors are relative. If oxygen is heated in the presence of a flammable the combustible will ignite at relatively low flash point. Hence, as a general and sensible precaution, PP filling with oxygen is conducted relatively slowly in order to reduce heating. If a tank is going to ignite it will probably start with the valve since this is a choke point and well known for being heavily lubed by some folks. The valve must absolutely be "oxygen" clean. Carbon monoxide is a product of incomplete combustion caused by low oxygen. Personally, I am not concerned that CO could accumulate in a Nitrox tank. However, I am concerned about rust which can be dangerous. A tiny quantity of oil on the tank wall would quickly oxidize but this process might be altered in the presence of water. An insignificant amount of acidic residue could be produced. Suppressing humidity and odor will pretty much eliminate the oil mist (actually an emulsion of oil and water) coming from a compressor block and minimize any flammability concerns when PP filling. Specifics of the filter system would depend on the size of the compressor and some other factors peculiar to the requirements of the operator and/or divers. However, in my opinion, most commercially produced compressors are safe to use with PP filling provided the scuba tank is cleaned yearly. It is the responsibility of the owner/operator to maintain the system and to replace filtrants per factory recommendations or sooner under extreme conditions.

 

[oxyhacker]

If he is using plain ol' Grade E air, then it isn't necessarily the approved way. In the early days of nitrox, the feeling was that Grade E air was not clean enough for PP nitrox mixing, and most "experts" and tech agencies called for using something cleaner, variously referred to as Grade E, Modified Grade J, OCA, hydrocarbon-free air, or just "nitrox air", but basically air containing only a tenth to a hundredth of the hydrocarbons allowable in Grade E.

In recent years many have begun to feel that this is unecessarily strict and while most of the agencies still call for hyper-clean air for PP mixing, many mixers use Grade E without incident. However, most shops doing PP mixing stick with the hyperfilter, for liability reasons, and because they'd rather err on the side of safety.

However, while Grade E air may be clean enough that it will not combust in the presence of oxygen, there is another concern, that the contaminants in it might over time and many fills accumulate in the tank to the point where they might become dangerous. Hence the need for regular O2 cleaning in tanks that will see high FO2s.

My LDS fills with the PP method. He puts 419psig of 100% O2 into my empty tank and then tops off with 2581psig of the SAME air he fills other tanks for Non-Nitrox people to give me my EAN.

I am good with that. That is an approved way of doing it.

 

[jpcpat]

Yes I have a NITROX card, I guess I missed the tank part, I'll go back and reread it.
I guess what lead me to believe that there was a difference is there's a price difference between air and Nitrox tanks.

Thanks for ya'lls help.

Rereading when you've forgotten is a great idea!! My memory sucks, so I do it all the time.

As for the extra cost for Nitrox tanks, it's for the cleaning and special o rings, lubricants, etc, to bring it up to Oxygen service standards. Filling it once with air that's not up to O2 specs will probably not get anybody killed. In my book, probably isn't good enough. YMMV.

 

[Bigcape]

When I said "grade e" I forgot to add "modified" besides he has a poster posted with the analysis of his air. So, I ment it was being done correctly for the sake of arguement.


However I am still having a hard time with understanding why all the hub-bub of having to get a tank RECLEANED if I go in and my fill my tank with 100% "air". The SAME compressor, the same banks of "air" that made up my Nitrox fills when I get them.

 

[pescador775]

A note to compressor operators. If you are PP filling or using a Nitrox stik then you may have a natural interest in the oil which is used in the compressor. While I don't wish to present a deep level of knowledge on this subject I have consulted with some manufacturers of compressor oils. Reviewing the results of tests conducted by these entities, it does appear that use of a "food grade" oil is advisable. This is not for avoiding any alleged toxicity of particular types of oil but rather for stability in high O2 environments. The H1 (food grade) oil produced by Ultrachem called Omnilube 455 appears to be highly stable per the oxygen bomb test results. Anti wear, anti corrosion look good. This oil is sold in small quantities suitable for retail customers under the Nuvair brand.

 

[duckster3d]

Yes I have a NITROX card, I guess I missed the tank part, I'll go back and reread it.
I guess what lead me to believe that there was a difference is there's a price difference between air and Nitrox tanks.

Thanks for ya'lls help.

Don't take this wrong, but you may have the C-Card, but either you skipped class, or your instructor was, sub standard.

you need to do more than re-read the book, you need to retake the class, and learn about this subject. I say this due to your first post and follow up answer about tank thickness. You can not proplely learn to dive nitrox, on the internet.

While nitrox is a great thing, gives a longer bottom time at a given depth compared to air. using it incorectly, not properly taking care of your tanks, and getting air from iffy compressors. can cause yours or someones elses injury and/or death.

 

[JAMIE MCG]

forget I asked

 

[duckster3d]

whether or not you like my answer, it is the most correct one.

whether or not you want to admit it you do not know the materail that you hold a card for!

good luck to you, and dive safe.

 

[Damselfish]

Think about it, you gave several people (and probably many more who didn't say it) the impression you weren't certified for Nitrox. There's a reason for that. By all means ask anything, but there's a difference between clarifying things or asking for tips, and not knowing really fundamental info from a class. In the latter case people will wonder what else was missing and don't want to see people get injured. Believe it or not they are actually thinking of your best interests, even if it doesn't come across nicely. Maybe you just had a lousy instructor, but you're saying things that indicate basic stuff was missed someplace. If that's really the case it's better that you realize this.