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View Full Version : can you go from air to nitrox and back



bigman241
06-11-2010, 14:04
Been thinking about doing the peak performance buoyancy to help with air consumption and doing nitrox for safety reasons. FIgure if I stay with normal padi tables and use nitrox it will reduce increased risk I have to decompression sickness.

Plan is to pick up two steel 130s within the next few weeks. If I do the nitrox and have them set up for nitrox can I fill them with air then go back to nitrox without the cost of an O2 cleaning a second time?

Noob
06-11-2010, 14:05
Legality answer. NO.

Also, A Nitrox tank will always be Nitrox unless completely emptied.

ScubaToys Larry
06-11-2010, 14:10
Actually... yes.. sure... no problem.

As long as you are getting your nitrox from someone who is continuous blending, banking, etc... just can't partial pressure fill unless the tanks are clean.

So it's a question for where you are getting your gas, not here....

bigman241
06-11-2010, 14:15
I will ask next time I go over there. If I could only have you fill them I would have no need for another shop :smiley20:
Actually... yes.. sure... no problem.

As long as you are getting your nitrox from someone who is continuous blending, banking, etc... just can't partial pressure fill unless the tanks are clean.

So it's a question for where you are getting your gas, not here....

Noob
06-11-2010, 14:15
Actually... yes.. sure... no problem.

As long as you are getting your nitrox from someone who is continuous blending, banking, etc... just can't partial pressure fill unless the tanks are clean.

So it's a question for where you are getting your gas, not here....

Ok, Ok, I guess it is ok to post that answer. LOL

ScubaStevo
06-11-2010, 15:03
Yeah, I get my Nitrox from a LDS that does that. No O2 cleaning required, it usually pre-mixed ~ 35%.

navyhmc
06-13-2010, 16:59
Not to mention that if your air fill source is "Clean Air" i.e. okay for partial pressure blending, you're still good to go.

KWS
07-02-2010, 14:58
Been thinking about doing the peak performance buoyancy to help with air consumption and doing nitrox for safety reasons. FIgure if I stay with normal padi tables and use nitrox it will reduce increased risk I have to decompression sickness.

Plan is to pick up two steel 130s within the next few weeks. If I do the nitrox and have them set up for nitrox can I fill them with air then go back to nitrox without the cost of an O2 cleaning a second time?

air is nitrox.... the tank is good so long as you dont fill air of less than grade e, or remove the valve. or get a cotaminated fill somewhere. the idea of the nitrox sticker is that you have a clean tank and use clean air sutabile with higher o2 gas and maintain that condition.

KWS
07-02-2010, 15:08
there is a lot of bad info around about filling nitros. most of it is going overboard to prevent suits. example. agencies now claim that it is a requirement that any nitrox tank with greater than 23.5 requires an o2 clean tank. look deaper and you will find that that standard????? is because that if you use it above 23.5 thatn some one might mix you a 23.5 gas using pp filling. the precaution is not the 23.5 it is the interm 100% till deluted with air to get the 23.5%. banked nitrox is not a problem. but as usual it is the insurance carier of the filler that rules.

you will see a lot of paranoia about words like <40% is treated like air

do some digging and you will find all sorts of entertaining stuff on nitrox. mostly fear based.

some references to start with is the o2 hacker book to get you started in making a list of questions..

in_cavediver
07-02-2010, 19:52
KWS,

Few corrections - in the dive world, O2 clean air meets the Modified grade E standard, not the grade E standard. Most consider Grade E standard air not clean enough for PP blending of nitrox.

Next - the 23.5% as pure O2. This is fact and comes directly from the CGA (Compressed Gas Association). If you think dive labeling/handling is an issue, according the CGA regs, a tank that has 23.5% or more 02 in a air mix must be cleaned to o2 service standard for each fill and properly labeled for contents. If you go from 24% o2/N2 mix to 21%, you have to drain, clean and relabel the contents for air service. Air tanks do not require the cleaning with each fill by standard.

So, the CGA covers commercial rules, how about the government. Well, NOAA, the Navy and NASA all have slightly different rules regarding its handling as well. For the most part - these agencies are on the same page though and thats where the 40% rules come from that most dive industry folks use.

The reality is that most dive shops really fall under the CGA rules and also under the DOT Hazmat rules as well. Fortuneately, its such a small subset of HP gas users compared to the commerical compressed gas industry as a whole, in both volume and risk exposure, it is left to self police. That self policing has brought the industry norms such as the VIP program (annual visual inspection is dive industry standard not DOT or CGA).

If dive shops did get truly policed for OSHA/DOT/CGA rules, you would see a lot of changes. Not the least of which is a new requirement for OWSI/DM's who transport equipment to have a hazmat CDL to drive to the dive sites and has the '24 hr available dispatch' available for tracking the hazmat materials/bill of lading/placards etc. Remember, this is a commercial for profit entity and pretty much every state has adopted the DOT rules for intra-state commerce as well as the inter-state commerce (requirement for some federal road dollars - similar to the speed limit rules)

Now that I have completely moved off topic, below is a good synopsis of what a nitrox diver (with tanks) needs to know.

1) If you dive nitrox, you have to know how its made. Banked, membrane or DNAx nitrox fill stations can put nitrox in any tanks suitable for scuba diving. If you get Partial Pressure blened nitrox (PP), the tank must be O2 clean since during the PP blending process, 100% HP o2 will be introduced to the tank/valve.

2) Labeling is a mixed bag. Many in the rec context teach bumper stickers. many in the tec world simply use contents lables. Ultimately, its up to the diver to know what is in the tank they intend to use. Analyze it or dump it and start clean if you are not sure.

3) If you have o2 clean tanks, be careful with thier use. Each fill cycle, whether o2 compatable air or not, will introduce contaminents to your tank. When possible, you should use only Mod Grade E, hyperfiltered or O2 clean air to preserve the clean status as long as possible. Also, one grade E fill will not immediately void the O2 clean status - though it will shorten the expected 'clean lifespan'.

The determination of whether something is o2 clean is really about the level of accumulated contaminants. An O2 clean tank with 1 grade E (not 02 clean air) fill will be cleaner than a tank with 100 hyperfiltered air fills. The rules of when to clean are fuzzy but come down to usage and fills and VIP. Its generally considered needed every year but may be sooner.

4) The last one again is for O2 clean tanks. If you think its contaminated, get it cleaned. To steal a quote from Vance Harlow (Oxy Hacker), "O2 cleaning is kitchen science, not rocket science". When in doubt, do it or get it done. If you maintain a lot of tanks, consider doing a PSI inspectors class and then O2 clean you own tanks. If you do it, you know its clean.


there is a lot of bad info around about filling nitros. most of it is going overboard to prevent suits. example. agencies now claim that it is a requirement that any nitrox tank with greater than 23.5 requires an o2 clean tank. look deaper and you will find that that standard????? is because that if you use it above 23.5 thatn some one might mix you a 23.5 gas using pp filling. the precaution is not the 23.5 it is the interm 100% till deluted with air to get the 23.5%. banked nitrox is not a problem. but as usual it is the insurance carier of the filler that rules.

you will see a lot of paranoia about words like <40% is treated like air

do some digging and you will find all sorts of entertaining stuff on nitrox. mostly fear based.

some references to start with is the o2 hacker book to get you started in making a list of questions..

KWS
07-02-2010, 21:48
THE MAIN problem with the rules is that the federal laws were written to say that handling will be done in compliance with recommendations set by ie cga and others. that put the ownership of all accidents on the cga ect. the 50% line of treat as pure o2 or air was given a safety margin and hence the 40% rule. commercial divers were told to use 40% so as not to push the 50% line. they were cut back from the danger line of o2 acting as pure o2, not given a higher limit. since the cga and others have been put to fault in an accident they have lowered the linmit to now 23.5. with other requirements attached so an not to be liable for any accident.

Transportation of tanks have been exempt for sport diving as opposed to bulk comercial shipping of tanks.

I saw on a board somewhere talking about 16 yo's handling and filling tanks. the inference that they are transporting and filling tanks. From that you can see that the thought of some is if you touch or move a tank you are transporting. this is the paronoia i speek of. once again like i said on the psi site they say o2 cleaning is required on all tanks filled with 23.5 or greater because SOME ONE MIGHT BE MIXING USING PP fill process. This is all legal CYA and so far from the regs except for the catch of "according to recommendations" which are driven by fear.

How long do you suppose it will be before you cant carry a 150# tank of air to fill your tire with out it being o2 cleaned? or is that why the low end os 23.5 and not lower.

in_cavediver
07-03-2010, 06:13
KWS,

I would like to see the exemption 'in law/regulation' you mention for sport diving tanks. It exists for noncommercial use but I have never seen it for commercial use.

Also - be careful mixing info. The CGA has nothing to due with the 50%/40% rules. That came from NOAA and the US Navy.

KWS
07-03-2010, 12:23
KWS,

I would like to see the exemption 'in law/regulation' you mention for sport diving tanks. It exists for noncommercial use but I have never seen it for commercial use.

Also - be careful mixing info. The CGA has nothing to due with the 50%/40% rules. That came from NOAA and the US Navy.

sport diving is non commercial use. that is why you can haul your own tanks.

the difference between noaa and cga is moot now the gov has placed all responsibility on the agencies. they have what would have been known decades ago as a gas war.... in this case it is the conservitive recommendations war. cga will not have a higher limit than anyone else. so long as they are the most stringent they are lowest on the lawsuit totum pole.

i strongly suspect that the 23.5 is set because of having to make car tires o2 clean.

by doing this dot regs have been allowed to be used by the insurance cos to control the lds's with the loose interpretation of ie what is transporting. now some some think that shop employee's carrying a tank to the fill room is transporting.

Most of this may all be moot anyway when bodies of water of <10 acres will be subject to fed control and make diving in those lakes a polluting activity and thus prohibited by law.

enough rant.

vegas911diver
07-03-2010, 12:42
The reality is that most dive shops really fall under the CGA rules and also under the DOT Hazmat rules as well. Fortuneately, its such a small subset of HP gas users compared to the commerical compressed gas industry as a whole, in both volume and risk exposure, it is left to self police. That self policing has brought the industry norms such as the VIP program (annual visual inspection is dive industry standard not DOT or CGA).

If dive shops did get truly policed for OSHA/DOT/CGA rules, you would see a lot of changes. Not the least of which is a new requirement for OWSI/DM's who transport equipment to have a hazmat CDL to drive to the dive sites and has the '24 hr available dispatch' available for tracking the hazmat materials/bill of lading/placards etc. Remember, this is a commercial for profit entity and pretty much every state has adopted the DOT rules for intra-state commerce as well as the inter-state commerce (requirement for some federal road dollars - similar to the speed limit rules)
[/quote]

Without taking up too much space, I am going to put a link on here to the PSI Inspectors page, that refers to what you are implying.

Cylinders & Manifests (http://www.psicylinders.com/library/Current/Hazmat.htm)

vegas911diver
07-03-2010, 12:44
The readers digest version is...

A cylinder must be valved, have 40 psia (49 CFR 173.115(b) (1)) or more of gas, and be used for commercial purposes. That’s it! So a dive instructor transporting his own tanks to a dive site is hauling HAZMAT, but if his students take their tanks, those are not. However, when the students take the tanks to the fill station and the operator approaches the tanks (becomes “affected”), the cylinder becomes HAZMAT because a dive store’s fill station is a commercial activity. Now, for those employees “affected” by HAZMAT, we already know they must receive function specific training to the HAZMAT, cylinders must be hydro’d, inspected, etc, but many shops mistakenly believe the owner is not an employee. While this may be the IRS or OSHA’s viewpoint, it is not the DOT’s. Under DOT, the owner is also an employee and must received training and abide by the HAZMAT regulations as well. So, a dive store owner filling his personal cylinders out of hydro is illegal. Having defined what a HAZMAT is and who is affected, lets look at the heart of the subject, transportation.

Transporting our type of HAZMAT, breathing cylinders with a combined weight of more than1000 pounds, (cylinders, valves, and contents are weighted) which is around 28 tanks gets very complicated. Commercial transportation of 1000+ pounds requires the operation to become a fully registered, licensed, and insured commercial HAZMAT transportation company.

in_cavediver
07-03-2010, 15:44
Mostly correct but one minor deviation and that's the 1000lb rule. HP gas cylinders can fall outside of the rule - especially if the CGA standards are used. IE - a tank with more than 23.5% O2. This would be classified as oxidizing gas as per the regs and may require placards for less than 1000lbs.

The worst part - there is no easy way to get the actual limits for what a diver would use. Again - for the most part, the DOT leaves divers alone about these rules. The volume of use/transport is just to small in comparison to the compressed gas industry as a whole.


The readers digest version is...

A cylinder must be valved, have 40 psia (49 CFR 173.115(b) (1)) or more of gas, and be used for commercial purposes. That’s it! So a dive instructor transporting his own tanks to a dive site is hauling HAZMAT, but if his students take their tanks, those are not. However, when the students take the tanks to the fill station and the operator approaches the tanks (becomes “affected”), the cylinder becomes HAZMAT because a dive store’s fill station is a commercial activity. Now, for those employees “affected” by HAZMAT, we already know they must receive function specific training to the HAZMAT, cylinders must be hydro’d, inspected, etc, but many shops mistakenly believe the owner is not an employee. While this may be the IRS or OSHA’s viewpoint, it is not the DOT’s. Under DOT, the owner is also an employee and must received training and abide by the HAZMAT regulations as well. So, a dive store owner filling his personal cylinders out of hydro is illegal. Having defined what a HAZMAT is and who is affected, lets look at the heart of the subject, transportation.

Transporting our type of HAZMAT, breathing cylinders with a combined weight of more than1000 pounds, (cylinders, valves, and contents are weighted) which is around 28 tanks gets very complicated. Commercial transportation of 1000+ pounds requires the operation to become a fully registered, licensed, and insured commercial HAZMAT transportation company.