Nitrox Blending Rental of Air Cyclinders

[JohnnyC]

Sort of. Nitrox sticks do not filter out anything. They mix the air and O2. That's it. Any filtration comes after the stick.

You are right. I assumed that whoever would read that would understand that using a stick means the gas must go through the compressor, ergo the compressor filter stack before it winds up in the tanks.

CO should be taken out by the compressor filter. For the average filter on the average HP compressor CO2 is taken out for a period of time then it passes through.

Also correct, but we're the issue I'm talking about isn't compressor induced contamination.

If it's like methane or propane, ethane and other VNMH (and I suspect it is) nothing does. That's why all O2 cylinders are vacuumed out.

I'm still not sure this is the case. Do you have proof that all gas suppliers do this for ALL O2 cylinders? If this is the case, it's new to me, as I have personally worked with people whose contaminated oxygen cylinders have ruined some rather expensive parts for aerospace use. They were not pleased, it cost more than just the materials ruined.....

It seems (anecdotally) that several posters gas suppliers do this, but I cannot actually find any documentation that it is standard operating practice throughout all of their locations.

And it doesn't need to be. Outside of methane, H20 and trace CO2 there is nothing in it.

Except when there is. And when there is, you don't want to be breathing it. And since you don't have chain of custody of the tanks, you have no guarantee.

Until there's an industry wide guarantee that all O2 rental cylinders are evacuated before refill, you might as well be on the safe side.

The answer is owning your own cylinder and making sure that when you send it to get O2, they don't swap your cylinder.

 

[nadwidny]

I'm still not sure this is the case. Do you have proof that all gas suppliers do this for ALL O2 cylinders? If this is the case, it's new to me, as I have personally worked with people whose contaminated oxygen cylinders have ruined some rather expensive parts for aerospace use. They were not pleased, it cost more than just the materials ruined.....

You do realize that you are arguing against anecdotal evidence with an anecdote?

 

[walkonmars]

Just to update...
I spoke to a Linde/Airgas representative and their management when they were auditing our facility (we have a large account with them) and they told me that medical grade oxygen is batch tested only.
Airgas is such a large company with so many satellite offices and stores in my city (Los Angeles) that they simply cannot give you back you OWN cylinder in return without very much trouble.
I have tried to request this before when I purchased a brand new 120 cu ft oxygen cylinder from a small shop for my welding needs. Getting it refilled at the shop purchased only gives me the option of industrial grade oxygen. So I turn to Airgas whom could not fully guarantee I would get my own cylinder back, again.
Once more...many of us do not have the option to get our own cylinder re-filled with aviator or breathing oxygen...only swap/exchanges.
-Nadwindy, please update us on any details you learn concerning getting back your own cylinder (I have been down your road but perhaps not as far as you are at).

Back to the point...Since cylinders are batch tested, even for medical grade, you are hoping that everyone in the filling and processing line have done their job correctly and no-one has deliberately (it has to be deliberate or fluke negregence) has backflushed oil, water or other contaminants into your cylinder. Like one contributor said, ANY contaminant with an oxidizer is bad and industrial is no exception. The usual steps (prior to filling) to evacuate the cylinder to fractions of a Torr pressure (not in the milliTorr or lower range) will not remove these liquid or solid contaminants we are worried about. We hope that everything is put together correctly in our lives with accidents waiting to happen, anywhere(your regulator, your car, your airliner, food, your train, your ski-chair lift, etc.). One contributor has posted that the medical and breathing grades are filtered again prior to going into a cylinder? I will not dispute this but only add that numerous conversations with gas supply people (although, not all Quality Engineers) have told me all the oxygen comes from the same source. Medical grade having a batch test of a random cylinder or at the source is the only difference. In a smaller city that allows you to drive up to the filling and pumping facility (not just the distribution facility) may be different but I am only speaking with respect to my experience, only.
I just "Googled" the search terms "medical oxygen contamination" and there is a journal article (Anesthesia & Analgesia:November 1989 - Volume 69 - Issue 5 - ppg 674-676) and it describes mass spectrophotometer (MS) testing of anesthesia oxygen gas during surgery and medical procedures but "uncommon" elsewhere including large deliveries of filled portable/transport cylinders. In the article an incident regarding a contaminated cylinder, the contaminant was water and became a hazard when the cylinder was inverted causing delivery of rusty colored water.
There is another report of trichloroethylene contamination of a bulk supply bank resulting in deaths at a hospital in 1996 that was detectable because of the bad odor from the delivered gas. The trichloethylene was residual cleaning solvent from a recent service change.

To summarize this before I ramble on any longer...
The odor of your oxygen should be "odorless". Anything else should be held suspect.
I will not attempt to convince aviator and medical grade users to do anything other than what they are currently doing.
Is there an easy way to test your oxygen? Perhaps a "drive up" testing facility? (Maybe a shop running a used, retired medical oxygen Mass Spectrophotometer?)
Any comment or criticism is welcomed.
-T

---------- Post added September 26th, 2015 at 05:29 PM ----------

I have seen trace hydrocarbons in more than one welding gas supply. I'll see if my friend still has the quality reports. His shop was contracted out for some aerospace stuff. Their oxygen bottles were contaminated. It ended up costing them a bunch of money. If I can get them I'll post them here.

The Praxair and Arigas shops that I used to get welding bottles from had an entirely different O2 supply for med and av gas.

Again, why risk putting contaminated O2 into a tank you're going to be breathing from, whether partial pressure or through a compressor, potentially causing flashing and carbon monoxide build up that can overwhelm a filter stack introducing CO into a tank. There's a reason that there are purity standards when it comes to medical O2 and Aviator O2 for a reason. The fact that some people have gotten by makes no difference. 60 fpm ascents used to be recommended too, and a bunch of people never had a problem....still not a great idea.

Johnny C, I wonder what city you live in? Here in a city of over 15 million (including adjacent counties) the Airgas facilities (all of them) keeps telling me it comes from the same source.

Also, if your aerospace people were so concerned about the gas quality and purity, they should have purchased a cylinder that has been tested with a certificate of conformance (you pay extra for it) and the cylinder comes with a tag stating the results, date tested. The aerospace folks in your example tried to save a little and paid a lot in damages. As an alternate, they should used a specialty gas supplier (Matheson) that deal with research grade gas. They are as careful as it gets. Sometimes you get a new small cylinder that disposed and is not re-fillable. To back up your point, I suppose that is not much different than us. I could get a bad batch of gas that kills me. There is a certain degree of trust we put into all this. Otherwise, I would stop diving, stay in my house and never answer the door.
I don't want to encourage dangerous complacency but I don't exactly trust shops and boats to be 100% safe all the time. I feel I'm as safe as it gets. I would like to see filling facilities CONSTANTLY test compressor outlet gas for carbon monoxide. I feel this is an easy sensor to add inline and procedure to dump suspect gas is very cheap insurance since it is only air. If you get an alarm for high CO, stop filling, capture some of the outlet gas, utilize your "bump" gas and re-test. If you are high in CO dump everyone's gas on the boat and re-fill them.

 

[nadwidny]

-Nadwindy, please update us on any details you learn concerning getting back your own cylinder (I have been down your road but perhaps not as far as you are at).

I'm not sure where this came from but we don't try and get back our own cylinders. For our calibration gases we just buy the cylinder. Even for something as simple as nitrogen for flushing our system we don't even try to get our own cylinder back based on Praxair's recommendation. We rent and then transfill with a Haskel into our own cylinder.

Is there an easy way to test your oxygen? Perhaps a "drive up" testing facility? (Maybe a shop running a used, retired medical oxygen Mass Spectrophotometer?)

There is no way I would trust a non-accredited outfit, especially an LDS, to do such testing.

 

[walkonmars]

One last personal example to add. I purchased new cylinder valved for inert gas mixes as I mentioned earlier. It was filled with Argon/CO2, 90%/10% (used for MiG and wire fed welding).
I wanted it re-filled at a small shop with 100% Argon and wrongfully assumed they would drain the remaining 500psi tank before re-filling. They did not... so when I was TIG welding with the gas I got all sorts of contamination in my welds. I drained it and filled it again and all the contamination went away.
Getting to the point...I now trust the larger, more established firms for my gas because they use a standard procedure and protocol when treating their cylinders. The periodic inspection and hydro test is automated (I have seen facility video), vacuum out before filling is standard(for some), and there is no person allowed to deviate from standard company procedure. Let us say you can be promised your personal tank back from a large firm. They have deviated from their standard protocol to fill your tank...Do you still want that tank and use that gas? Unless you have full visual control during the process, I don't recommend giving up a tank to have it filled and insist on getting that tank back.
One thing I noticed in both the gas service and welding shops is that there is a very wide range of knowledge base out there. Some that know a lot and understand your requirements and others that have just worked around gasses a lot and understand little. My story concerning the tank here was a guy whom worked around gases a lot but understood only what he thought was relevant. In our case, the shops rarely deal with divers so we should always ask the right questions and be cautious.
I went through a couple purchases of aviator grade oxygen myself but realized it is a pointless exercise. If I were diving in icy cold water (Arctic) or I was an pilot, then I need extra dry gas so I don't get a mechanism freeze up. I dive in S. California so aviator is not relevant for scuba here.
Lastly, if you folks getting your oxygen re-filled at a small shop, make certain they bleed the lines to your tank prior to opening your personal tank valve. Typically, they will hook everything tight, open the fill source valves, then the valve to your tank. Ask them to open all source valves, then purge the lines by a special bleed valve at the fill whip end at your tank. Better yet, crack the CGA nipple fitting 1/8 turn at your personal tank end to bleed out the gas for a several seconds and tighten it back snug and begin filling. Your local gas guy will think you are a pain but that will be your problem (LOL).

What has happened to my nice new cylinder? It has been delegated as a "travel" tank since it is a 1/3 the size of big full size tanks and I can take it to a welding job away from my garage easily. I only re-fill it myself from full size tanks using whips and purge the lines as I described.

(I'm not making recomendations. I'm only describing what I do.)

 

[walkonmars]

OK, I have an update related to keeping and re-using your own cylinders:
There are a few folks at work that use a tremendous amount of gas but cannot tolerate even a little impurity above the normal specified amount.
They keep their own cylinders and never swap out other cylinders when a new batch of gas is ordered. They will arrange with a local site/facility representative from the gas supplier for refill of cylinders, clearly mark/tag our company ownership of the cylinders, then have the cylinders re-filled, analyzed/tested and returned to us. This process takes a couple months or more! This is a very special application worth hundreds of thousand dollars in order to warrant this arrangement. I also do not know how much more it will cost. Lots of trouble to do but you folks that want your cylinders back can go through the process of getting your cylinders back. You will need to make special arrangements with a local area manager and explain to a local manager what you are trying to do.

On the other hand, it was suggested that if you want your cylinders back, a much easier way is to fill them at a local small shop that fills cylinders on site, as you wait. Bring your cylinder in your own vehicle to the shop and fill them. If you want breathing grade, you will need to call the shop and ask if their gas is certified to that standard (keep in mind that industrial grade, by specification requirement, is a higher purity than breathing grade anyway.
If anyone finds out new info, please keep us posted.

 

[frogman62]

I live in Wichita Ks and own my own cylinders (5). I take them to the local (large supplier) who has their own filling facility. They fill all cylinders for hospitals , welders, avaitors, from a Liquid tank (Huge) and fill 40 cylinders at a time. They fill my cylinders and give them back to me the next day (two trips). Most customers just exchange tanks but several hospitals have bulk liquid Oxygen tanks and get them filled from a large transport truck tank that also supplies the welding facility.
Why is this a big deal, I have been doing this for 20 years.
Jim Shelden

 

[Jax]

I live in Wichita Ks and own my own cylinders (5). I take them to the local (large supplier) who has their own filling facility. They fill all cylinders for hospitals , welders, avaitors, from a Liquid tank (Huge) and fill 40 cylinders at a time. They fill my cylinders and give them back to me the next day (two trips). Most customers just exchange tanks but several hospitals have bulk liquid Oxygen tanks and get them filled from a large transport truck tank that also supplies the welding facility.
Why is this a big deal, I have been doing this for 20 years.
Jim Shelden

Again, anecdotal.

Have you asked what grade O2 is in the "huge" tank? If they have aviation grade O2, it can certainly be used for the other two uses.

What is the difference between aviation, medical and industrial grade oxygen?

There is a ongoing controversy about whether there is any difference between the grades of oxygen. Oxygen gas is produced from the boiling off of liquid oxygen. Therefore, it appears that the oxygen grades are the same because the oxygen comes from the same source. However, the standards are different for each oxygen grade. There are four different grades of oxygen that are merchandised or sold to users.

Aviation grade oxygen; 99.5% minimum oxygen content.

Tested for moisture content because of the risk of freezing at high altitudes. Maximum moisture content is guaranteed.

Higher cost when compared to the medical and welding grades.

Medical grade oxygen; 99% minimum oxygen content.

Regulated the same as prescription drugs.

Maximum level of CO and CO2 gas is guaranteed.

Welding (Industrial) grade oxygen; 99.5% minimum oxygen content.

Research grade oxygen; Highest grade of oxygen.

---------- Post added December 6th, 2015 at 10:22 AM ----------

OK, I have an update related to keeping and re-using your own cylinders:
There are a few folks at work that use a tremendous amount of gas but cannot tolerate even a little impurity above the normal specified amount.
They keep their own cylinders and never swap out other cylinders when a new batch of gas is ordered. They will arrange with a local site/facility representative from the gas supplier for refill of cylinders, clearly mark/tag our company ownership of the cylinders, then have the cylinders re-filled, analyzed/tested and returned to us. This process takes a couple months or more! This is a very special application worth hundreds of thousand dollars in order to warrant this arrangement. I also do not know how much more it will cost. Lots of trouble to do but you folks that want your cylinders back can go through the process of getting your cylinders back. You will need to make special arrangements with a local area manager and explain to a local manager what you are trying to do.

On the other hand, it was suggested that if you want your cylinders back, a much easier way is to fill them at a local small shop that fills cylinders on site, as you wait. Bring your cylinder in your own vehicle to the shop and fill them. If you want breathing grade, you will need to call the shop and ask if their gas is certified to that standard (keep in mind that industrial grade, by specification requirement, is a higher purity than breathing grade anyway.
If anyone finds out new info, please keep us posted.

This is totally wrong.

Oxygen Use in Aviation - AOPA

---------- Post added December 6th, 2015 at 10:25 AM ----------

A quick summary from the above link.

All oxygen supplies come from a very small number of vendors and is normally delivered in 25,000 gallon refrigerated tanks. The manufacturing process is so thorough and clean that the finished product meets all usage specifications right from the tank. However, just to be sure, any lot of oxygen destined to be medical oxygen is batch tested for aromatics (oils, Benzene, and other impurities that appear in the manufacturing equipment). ABO (aviation breathing oxygen) is also tested for moisture content, while welding oxygen comes straight from the vendor with no additional additives or testing.

 

[walkonmars]

Hi Jax,

Can you please specify with numbers rather than making us read a large document from your link?
I also could not find any hits from searching "purity" in that document, anyway. Just get to the point, please.

On the other hand, here is a link that states "industrial grade" should be 99.5%...and medical grade should be 99.0% . (OK, I mis-quoted. It should have been "medical grade".)
Industrial and Medical Gas Specifications (U.S.)
Did I prove my point?

I do agree that aviator has a tighter requirement for water.
I don't dive in the arctic so I (water) don't see it as an issue over the (normal amount allowed). You seem to be an aviator so the trace water is significant for a pilot using it at high altitudes, at potentially cryogenic temperatures that risk freeze up or orifice/gas line blockages with ice (Please correct me if I'm wrong.).
Matter of fact, I'm certain that the filling process on a dive boat blows initial tiny droplets of sea water into some of our tanks (that was in the valve orifice, adhering to the o-ring), anyway. I see it rather frequently on my yearly vis inspections (cylinders used on boats).
In the rush to fill tanks, boat operators do not take the absolute care to make sure no water is entering the tank.
(Proper process would be: Hook up fill yoke to cylinder with cylinder valve closed. Pressurize yoke from compressor, purge a small amount of gas from the compressor at the yoke without opening the cylinder valve. Then open the cylinder valve and fill as needed.). That is OK as is since it does not cause me to fail annual vis inspections the way it is done now.

Frogman62, Jim---
I live in Los Angeles and all of the Airgas stores swap out cylinders without exception (survey of half dozen shops). They are the biggest retail gas dealer in our area.
Furthermore, I was told "do not go to the filling plant" because every customer will be turned away and it is neither a retail nor wholesale capable location.
The Airgas retail shops do not have bulk gas for oxygen. Processing is done at a controlled plant in order to save money and maintain quality of product entering customer hands.
The gases delivered are constantly monitored of batch tested. (Can your local shop match that?).
This is why getting your cylinder back is a big deal (depending upon whom you deal with).
I have seen some smaller shops evacuate every cylinder before it is filled (West Air Gases, for example). I like this policy. The testing equipment is expensive and not possible at most retail outlets. (Accredited facility required?)
I have been to some local shops and they simply hook up your cylinder to the bulk line and fill it. No mind to what residual was in the tank prior. I have suffered salt and pepper contamination in welds due to this oversight. It is my guess that some small shops get gas bulk from Linde, Airgas, Praxair, Air Liquide with a testing report and that is your guarantee you get good gas.
As the quote from Jax stated: the "medical grade" is batch test (like the Airgas rep told me) but the industrial comes (likely) from the same bulk tank.

I'm not trying to start an argument but I'm telling you my experiences and what I have learned. If enough people tell me I'm going to get someone killed or hurt, I will stop posting any more info. I just believe that enough practical people want to pay $20 for an oxygen cylinder instead of $75 and in reality the gases are from the same bulk source(breathing grade is batch tested, right?).
Why not tell the filler to fill a bunch of breathing cylinders for other customers and include your industrial cylinder in that fill batch. He tests one cylinder out of the batch(not your cylinder) and it analyzes, OK (so the batch is considered OK).
So instead of charging you $20, he charges you $75 because your cylinder was part of that batch test. Let me know if you wouldn't get upset in that situation.

Any comments welcomed.
(P.S. Airgas was recently purchased by Air Liquide.)

CYA remark...My posts describe what I do but I don't recommend anyone else to do any of it. Use only gas certified safe and suitable for your application as directed by an expert and not myself or other forum contributor.

 

[frogman62]

I guess hard heads are difficult to counter. Lampton Welding is the largest supplier of welding supplies in this area. Sells to hospitals, fills medical oxygen cylinders for many suppliers, supplies aircraft plants, etc. They only purchase medical grade Oxygen and purchase from one of a very few extractors in the US which supplies LOX to most all large pumping stations. The Primary difference is for medical Oxygen they evacuate system/cylinders and certify the contents. Medical and welding grade tanks are never filled on the same trunk system -- but the oxygen supply (LOX) is medical grade. Airgas process is just the same.
Jim Shelden