Question about filling a tank with enriched air

[mer]

For non-cleaned tanks, pre-mix, continuous mixing and membrane fills are all okay. As is topping with air.

If you, or the shop, does not have an analyzer, you should bleed the tank and refill with air. Any nitrox mix needs to be analyzed.

 

[peterbj7]

To the OP - yes, it's quite OK to add non-clean air to a tank that doesn't purport to be O2 clean anyway.

And on the question of the resulting mix - the calculation is quite simple and by the end of your course you should be able to calculate the final %age, so long as you know the initial %age and the start and finish pressures. If at that point you don't feel you can do it then go back to your instructor and keep on at him until you can. It is made more complicated by the US system of measuring tank volume, but it's still perfectly possible. You should still analyse it, though.

 

[dannobee]

Now just for fun,

I have dive shop top off my tank containing 1000 psi at 32% topped off with regular air. New mixture is unknown but somewhere between 21-32%. Assume dive shop doesn't have an analyzer or won't let me use it for whatever reason. Is it considered acceptable to use my own analyzer to check the mixture myself or does the diving community frown upon this?

The shop that fills it with air might assume that it was simply filled with air to start with and/or not have an analyzer.

You should have some sort of idea what your ending mix will be, then verify with an analyzer. It's easy if you use the partial pressure method.

The math goes something like this:

You have 1000 psi of 32%, that's (1000 x 0.32) 320 psi of oxygen.

You want to fill to 3000 psi, so you're adding 2000 psi of air (21%). That will contain (2000 x 0.21), or 410 psi of oxygen.

Add the 320 psi and the 410 psi to get 730 psi. This is the amount of total oxygen in the tank. Divide that by your final pressure (3000 psi). 730 / 3000 = 24.3% oxygen.

Verify with an analyzer before you dive.

 

[pescador775]

Fox, here is a recent thread on your subject.
http://www.scubaboard.com/forums/co...tems/236471-how-do-i-get-28-1000psi-32-a.html

Also, since you seem so enthusiastic about this subject suggest you purchase OXYGEN HACKERS COMPANION

 

[pescador775]

Fox, I don't want you to leave your class with the impression that dive shops are pumping "unclean" air. The majority of shops offer air that is very clean indeed and will not cause contamination of your oxygen certified tank regardless of what is or is not guaranteed in writing. In fact, most commercially made compressors and quite a few home made units pump air which exceeds Grade E standards, the generally applied criterion for diver air. The dive community has accepted the notion that oxygen certed tanks should only be charged with air which has an extreme level of cleanliness. To this end, there is a lively after-market in extremely expensive "hyper filters" to meet this modified standard. However, in many, if not most, cases additional filtration on a good, well maintained, oil lubed compressor is unnecessary to provide air which is safe for use in O2 clean tanks. I would only stipulate that the tank which has been filled from various sources be cleaned somewhat more frequently. As time goes on, you may realize that some of the stuff in the books is bogus or misleading at best and as confidence builds your approach to teachings of some of the pedagogues may be more pragmatic and contain a whiff of skepticism.

 

[Standingbear56]

Fox, I don't want you to leave your class with the impression that dive shops are pumping "unclean" air. The majority of shops offer air that is very clean indeed and will not cause contamination of your oxygen certified tank regardless of what is or is not guaranteed in writing. In fact, most commercially made compressors and quite a few home made units pump air which exceeds Grade E standards, the generally applied criterion for diver air. The dive community has accepted the notion that oxygen certed tanks should only be charged with air which has an extreme level of cleanliness. To this end, there is a lively after-market in extremely expensive "hyper filters" to meet this modified standard. However, in many, if not most, cases additional filtration on a good, well maintained, oil lubed compressor is unnecessary to provide air which is safe for use in O2 clean tanks. I would only stipulate that the tank which has been filled from various sources be cleaned somewhat more frequently. As time goes on, you may realize that some of the stuff in the books is bogus or misleading at best and as confidence builds your approach to teachings of some of the pedagogues may be more pragmatic and contain a whiff of skepticism.

Wow, this is new to me, and I am nitrox certified. I always thought that if you have an O2 clean tank and add standard air (grade E) that it is no longer considered O2 clean. May I ask where you got your information as I would like to check it out. This isn't a bash, for me it's new info I want to check into.
Thanks,
George
PADI MSDT 33859
Prime Scuba

 

[sheck33]

Fox, I don't want you to leave your class with the impression that dive shops are pumping "unclean" air. The majority of shops offer air that is very clean indeed and will not cause contamination of your oxygen certified tank regardless of what is or is not guaranteed in writing. In fact, most commercially made compressors and quite a few home made units pump air which exceeds Grade E standards, the generally applied criterion for diver air. The dive community has accepted the notion that oxygen certed tanks should only be charged with air which has an extreme level of cleanliness. To this end, there is a lively after-market in extremely expensive "hyper filters" to meet this modified standard. However, in many, if not most, cases additional filtration on a good, well maintained, oil lubed compressor is unnecessary to provide air which is safe for use in O2 clean tanks. I would only stipulate that the tank which has been filled from various sources be cleaned somewhat more frequently. As time goes on, you may realize that some of the stuff in the books is bogus or misleading at best and as confidence builds your approach to teachings of some of the pedagogues may be more pragmatic and contain a whiff of skepticism.

Indeed. I randomly fill my tanks with air, nitrox, trimix depending on what the dive requires. It is nonsense that an O2 clean tank would have to be re-cleaned after filling it with clean air.

 

[pescador775]

Hi Bear, "Grade E" is a minimum requirement only and does not imply that dive shops are delivering air fills which barely meet the listed criteria. I am convinced that they do much better. The so called "hyper filter" is supposed to be insurance against the day when a shop's installed filter is nearing its service interval. Ho humm, maybe so but I'll bet that is very rare. When PP filling was more popular than today there were many divers topping off tanks with personal compressors or travelling to dive shops (any shop) for a top off. I've not heard of any accidents due to this and surely thousands of tanks have been NITROXed in this manner. (Perhaps someone has some stats on that and can elucidate). Recently, the CGA reduced the "E" number for water content from about 67 ppm to 24 ppm. However, the corresponding number listed under "E" air for hydrocarbons was not reduced in kind. Yet, the same technology which is being used to reduce water content also filter out hydrocarbons and it seems a good bet that the actual hydrocarbon content produced by modern compressors is correspondingly reduced in fact and is far below 5mg. Personally, I feel that the hydrocarbon level of 5mg/m3 requirement under "E" is misleading and slightly ridiculous. If oils or gaseous vapors of that quantity were introduced into a diving tank the users would complain about it. The diving community (ANDI, etc) tend to follow the US govt. Agencies like NASA and the military bureaucacy have unlimited budgets but that is not enough. Building one's own section or branch requires that the managers lobby constantly for more money. A sure fire way to keep the organization funded is to cry wolf. This means they must be constantly finding and solving problems of various kinds depending on their mission statement. It is only natural that it was suddenly decided that NITROX could only be PP mixed if the tank and air were absolutely clean. Once this requirement is published then they must move on to something else because there is nothing left to do in that regard. One must remember that the requirement for modified Grade E or whatever is not necessarily a pressing need for safety reasons. It is however a demonstration of agency vigilance and rectitude. Moreover, they can make sure leftover funds (that's bad) are expended by buying more expensive compressors for their own people. There are many vested, commercial interests who sell stuff and can profit from the more stringent requirements. Also, there is the matter of insurance. Once the insurance companies are aware that there may be a new definition of "best practice" they will be watching. Of course, they don't know anything about the science or technology. It's all one happy family out there.

 

[pescador775]

This is off topic but germane to understanding the powers that be. After New Orleans, the dramatic demonstrations of govt incompetence were lacking. What a boor. Not to disappoint, after effectively ruining an entire seasons production of tomato crop and devastating hundreds of small businesses and families involved in tomato production, the govt inspectors have moved on to Jalapena peppers as the "real" culprit. Off to Mexico, fa la la la.

This gross stupidity did not always exist in so wide spread a fashion. However, nowadays, social conscienceness extends mostly to govt hiring practices not to the welfare of the general public.

 

[Standingbear56]

Hi Pescador 775,
OK, I definitely learned a few things. What, our Government makes rules just because they can?? Say it isn't so!!! (please note biting sarcasm) It makes sense what you said about the oil PPM - if it was too high problems would probably have been noted. Is there any comparison of Grade E vs Grade J? I'd like to compare them to what our samples say.
Thanks,
George
PADI MSDT 33859
Prime Scuba