Nitrox - O2 Clean/Refilling
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NV
There is a lot of opinions about what you are asking. There is the 60% study by nasa. the 40% rule derived from the 60% rule to define scuba use. If i am correct the current requirements are 23+/-% or greater under psi of 50 or greater requires O2 cleaning. I personally do not agree with this but your question is about requirements. I would strongly suggest you take a course on o2 tech and gas filling. This is why: There are many factors involved such as fill station piping and right angles gas flow speeds, heat generation at bends and obsticles, hydrocarbons in piping conpressors, tank valves and cylendar internals. Although it is not rocket science, there is a wealth of information to pur together that most do nt realize inregards to O2 handling. I took my course from NAUII and was amazed at the amount of info. My course included cleaning component rebuilding valves ect, by the time you are done you will not need a LDS for any tank related issues. You learn O2 cleaning and ultrasonic cleaners tank tumbling cleaning drying assembly and trimix gas mixing with booster pumps ect.
There is a lot of opinions about what you are asking. There is the 60% study by nasa. the 40% rule derived from the 60% rule to define scuba use. If i am correct the current requirements are 23+/-% or greater under psi of 50 or greater requires O2 cleaning. I personally do not agree with this but your question is about requirements. I would strongly suggest you take a course on o2 tech and gas filling. This is why: There are many factors involved such as fill station piping and right angles gas flow speeds, heat generation at bends and obsticles, hydrocarbons in piping conpressors, tank valves and cylendar internals. Although it is not rocket science, there is a wealth of information to pur together that most do nt realize inregards to O2 handling. I took my course from NAUII and was amazed at the amount of info. My course included cleaning component rebuilding valves ect, by the time you are done you will not need a LDS for any tank related issues. You learn O2 cleaning and ultrasonic cleaners tank tumbling cleaning drying assembly and trimix gas mixing with booster pumps ect.
See this is something I run into, I want to learn all of the info once I start to scratch the surface haha!!
At the end of the day I am a bit more hesitant to how LDS maintain their fill stations and the more I learn about it, the nitrox side.
So I have come to the conclusion that if it is banked sub 40% I am good without o2 clean. If it's partial pressure blended then I need o2 clean. Need modified grade e air on all fills to main the o2 clean tank. I can dive pure modified grade e air and then go to higher mix without compromising the o2 clean tank. It is no longer an o2 clean tank once none modified grade e gas is used to fill. Correct?
Can it be assumed that by asking for nitrox all the requirements have been met and that if I only want air in a o2 clean cylinder that they will use o2 compatible air?
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Ricky B
Contributor
My understanding, based on what is in the PADI Enriched Air Diver Manual, is that that 02-compatible air is Nitrox that is 21% oxygen. The manual says (in bold face):
The problem with conventional fill stations is that they don't filter out the hydrocarbons, which present a risk. I suppose that there are fill stations that are not "conventional" that do filter out the hydrocarbons, but you'd have to make sure that the compressed air is free of hydrocarbons.
This manual has a 2005 copyright date, and maybe things have changed (and maybe PADI is wrong), but this info is consistent with presentations on Nitrox that I have see on the web.
The problem with conventional fill stations is that they don't filter out the hydrocarbons, which present a risk. I suppose that there are fill stations that are not "conventional" that do filter out the hydrocarbons, but you'd have to make sure that the compressed air is free of hydrocarbons.
You hit all the tough questions. If a tank has a sticker on it for nitrox the shop is not supposed tofill with anything less than O2 compatable air or hyperfiltered air.
Supposed to will do shoulda coulda woulda. Most cases shops as long as teh compressor is good teh quality of air exceeds teh hyperfiltered standard even if it has only a grade E system. You will dfind system filters that say good for 40k cu ft of grade e. Guess what the air is better than hyperfiltered at the start. It is my opinion, and i say opinion because no one will agree with it,that the standards were written for the worst case scenereo. cup of oil in the tank shaken and not stirred to a vapor mist brought to full presur in 1 min from empty heating tank to 300 degrees adn 3000 degrees at the pipe jointing from air flow explosion free. There are plenty of cases of accidents that do not fit this catagory of thought. Primarily if you keep you system reasonable clean adn oil free and fill slow in a good tank that is not pitted through you should ever have any problems. Here is a story. Nasa apollo capsule fire resulted in a study that was to figure out how to not have another fire again. they found that in O2 consentrations > 60% the atmosphere acted like pure O2. Less than 60 acted like air. At that time nitrox for scuba was being introduced with the 32 and 36 stqndards. People being people and causing greater thatn 36% mixes the Limit of 40 was established. along wih that the rule of 60% was shifted to 40% to make the rules simple for ascuba. recerational <40 was same as air technical > 40 was to be treated like pure O2. That provided a 20% safety buffer for those sivers with less than pristeen clean tanks. This became simple recreational did not need to be O2 clean and Tech did. Then came PP blending into the picture and since concentrations of >40/60% was used the necessity of o2 clean tanks were necessary when o2 was used adn then diluted with air. Different situation when air is being diluted with O2 using a booster. But oe rule fits all with scuba. Then the feds no longer regulated that air systems adn legislated that standards will be in accordance with agency recommendation's / sandards of teh CGA DOT ect. With that those agencies were hung out to dry for and accident. Sooooo they stiffened up thier requirements adn standards to insure no acident would e thier fault. Hence >23.5% requires O2 cleaning. As said before this is a controversal topic and there are many INTERPRETATIONS out there including mine. For some the world will end if you ahve a regular tank with 24% in it. for others it is no biggy. Remember there are differences in teh risk taken depending if ou are a shop or a home filler. Everyone puts thier safety factor into the mix including the insurance co's. I think a good reference for you to taunt your intrest would be to read Airspeed Press's "Oxygen Hacker." I am not sugesting you learn to cheat the system. I am saying be knoledgable in what you are doing, combine that knowledge wiith some formal training and go through life filling without fear of a mushroom cloud eminating from your use to be enclosed/ roofed garage. You wil find out with a little exposure tank filling is not much different than airing you your car tires. Qua;ity knowledge training adn process will produce quality breathing gas for lots of dives.
Supposed to will do shoulda coulda woulda. Most cases shops as long as teh compressor is good teh quality of air exceeds teh hyperfiltered standard even if it has only a grade E system. You will dfind system filters that say good for 40k cu ft of grade e. Guess what the air is better than hyperfiltered at the start. It is my opinion, and i say opinion because no one will agree with it,that the standards were written for the worst case scenereo. cup of oil in the tank shaken and not stirred to a vapor mist brought to full presur in 1 min from empty heating tank to 300 degrees adn 3000 degrees at the pipe jointing from air flow explosion free. There are plenty of cases of accidents that do not fit this catagory of thought. Primarily if you keep you system reasonable clean adn oil free and fill slow in a good tank that is not pitted through you should ever have any problems. Here is a story. Nasa apollo capsule fire resulted in a study that was to figure out how to not have another fire again. they found that in O2 consentrations > 60% the atmosphere acted like pure O2. Less than 60 acted like air. At that time nitrox for scuba was being introduced with the 32 and 36 stqndards. People being people and causing greater thatn 36% mixes the Limit of 40 was established. along wih that the rule of 60% was shifted to 40% to make the rules simple for ascuba. recerational <40 was same as air technical > 40 was to be treated like pure O2. That provided a 20% safety buffer for those sivers with less than pristeen clean tanks. This became simple recreational did not need to be O2 clean and Tech did. Then came PP blending into the picture and since concentrations of >40/60% was used the necessity of o2 clean tanks were necessary when o2 was used adn then diluted with air. Different situation when air is being diluted with O2 using a booster. But oe rule fits all with scuba. Then the feds no longer regulated that air systems adn legislated that standards will be in accordance with agency recommendation's / sandards of teh CGA DOT ect. With that those agencies were hung out to dry for and accident. Sooooo they stiffened up thier requirements adn standards to insure no acident would e thier fault. Hence >23.5% requires O2 cleaning. As said before this is a controversal topic and there are many INTERPRETATIONS out there including mine. For some the world will end if you ahve a regular tank with 24% in it. for others it is no biggy. Remember there are differences in teh risk taken depending if ou are a shop or a home filler. Everyone puts thier safety factor into the mix including the insurance co's. I think a good reference for you to taunt your intrest would be to read Airspeed Press's "Oxygen Hacker." I am not sugesting you learn to cheat the system. I am saying be knoledgable in what you are doing, combine that knowledge wiith some formal training and go through life filling without fear of a mushroom cloud eminating from your use to be enclosed/ roofed garage. You wil find out with a little exposure tank filling is not much different than airing you your car tires. Qua;ity knowledge training adn process will produce quality breathing gas for lots of dives.
@Ricky B
Leading to my question of how to verify that with the shop? Do I ask if you have o2 compatible air?
---------- Post added March 20th, 2014 at 08:59 AM ----------
Refreshing my memory:
Grade E Air is 20% O2, while Modified Grade E is 21% - Is that correct? I assume that Modified Grade E air has a higher O2 content than standard air fill.
Leading to my question of how to verify that with the shop? Do I ask if you have o2 compatible air?
---------- Post added March 20th, 2014 at 08:59 AM ----------
Refreshing my memory:
Grade E Air is 20% O2, while Modified Grade E is 21% - Is that correct? I assume that Modified Grade E air has a higher O2 content than standard air fill.
Scared Silly
Contributor
Modified Grade E air has been hyper filtered to remove almost all traces of hydrocarbons.
Grade E air may have slight traces of hydrocarbons.
Look at this chart ANDI requires Mod Grade E for Nitrox.
http://www.airsystems.com/Reference/CGA Air Grade Specifications.pdf
You also asked about what happens if you get a fill with Grade E air - you risk the chance of introducing hydrocarbons into your cylinder. Thus the cylinder may not be O2 clean anymore.
I am going to skip this O2 clean debate, fascinating as it is, and discuss the question of cost.
The cost of nitrox varies by area. In some places, a nitrox fill is much more expensive than an air fill. In other areas, not so much. In even other areas, not at all.
You happen to live in a pretty good area. Nitrox fills tend to be pretty cheap in South Florida. Here is the price list for a shop a bit north of you: Fill Express at Go Dive Florida - Go Dive Florida. It charges the same price for 32%, 36%, and 40%, and that cost amounts to a TOTAL fill price that is significantly less than the ADDITIONAL price many places charge for nitrox. I assume you will find competitive prices nearer to you. With the prices in your area, I can't see why people aren't diving nitrox all the time.
The cost of nitrox varies by area. In some places, a nitrox fill is much more expensive than an air fill. In other areas, not so much. In even other areas, not at all.
You happen to live in a pretty good area. Nitrox fills tend to be pretty cheap in South Florida. Here is the price list for a shop a bit north of you: Fill Express at Go Dive Florida - Go Dive Florida. It charges the same price for 32%, 36%, and 40%, and that cost amounts to a TOTAL fill price that is significantly less than the ADDITIONAL price many places charge for nitrox. I assume you will find competitive prices nearer to you. With the prices in your area, I can't see why people aren't diving nitrox all the time.
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