Nitrox Blending Rental of Air Cyclinders

[tomfcrist]

Questions: So Tom and sealark I guess you keep an O2 clean tank that you get filled with oxygen (aviator grade) for blending your enriched air? Do they evacuate your O2 cylinder before each fill?

I own bottles yes. They get filled with O2 at the supplier. No they don't evacuate the tank.

 

[v101]

Tom -
did you buy your bottles from the LGS? or did you already own them and were able to get them refilled easy enough at the LGS ? I am asking as I called a few gas suppliers in my local area and they all seemed to indicate that they preferred customers rent/lease the bottles for a daily rental fee. I asked if I had my own bottles If I could just get them refilled, and he said he would have to get back to me.. argg.. not sure if I need to talk to someone else, or if I should just drive down and talk to someone face to face.
I can't imagine it being that hard to get some bottles filled with oxygen if you own them and they are oxygen cleaned...

 

[tomfcrist]

I bought from the LGS many years ago

 

[nadwidny]

If there are any hydrocarbons in an oxygen tank at 2200psi I'm pretty confident they will become CO2 in a flash, so to speak.

In Canada the allowable limit for hydrocarbons, in the form of methane, is actually a lot higher for medical O2 than for air. Go figure.

I analyze breathing gas for a living. Medical O2 pretty much always has methane levels anywhere from 25-100ppm. The standard we most often test for has a limit of 100ppm.Breathing air is normally around 2ppm. Breathing air has a max of 10ppm.

Add me to those who use welding O2 for mixing. I talked to guys at Praxair and Air Liquide. it all comes from the same place, all filled from the same whips and they are all vacuumed out prior to filling. Welders can't afford contamination in O2 any more than people who breathe it.

 

[walkonmars]

I am currently using the industrial/welding oxygen as well. The standards for medical, breathing grades are a joke. You are paying more for the breathing and medical grades because it requires regulation as "drug". The breathing grades are typically 99.5% as a minimum requirement (but dispensing gas exceeding the grade is OK). Industrial grades are at the very worst 99.8% but in reality, they come from the same bank and are usually 99.9 or better (likely 99.95%---wow!). The differences in prices are very dramatic. If you own your personal cylinder industrial can be $20 and aviator can be $60 for a size 300 cylinder on an exchange basis. It is too expensive to pump a typical gas from multiple supply banks so large suppliers will pump all the gas from the same good banks. A special grade such as research, ultra high pure and reference gas grades will be individually tested with a certificate of test and conformance. I admit, there are some variations from large shops to small shops. Some evacuate a cylinder before pumping (as a exchange use tank) and some just pump it into your tank you bring them on site. You may want to call the shop you go to and ask them what their exact process is. Typically, the first person you speak to will have NO CLUE what you are asking them. You will need to talk to the pumping plant and not the distributor. In a large city (Los Angeles where we are) the cylinders from Airgas, Co. are processed at a pumping, purification and filling facility and batch tested. Typically the cylinders are evacuated prior to filling (not baked out like they used to) and NOT individually tested. I toured a WestAir facility in Anaheim, CA and they evacuate all cylinders prior to filling and they are a local, small filling facility (not a pumping and purifying facility). The breathing grades MAY be individually tested this way but I highly doubt that (please confirm if you know!). Think about how many small bottles of oxygen going to hospitals, patient homes and treatment offices and you will likely see analysis of each cylinder is overwhelming. What are you testing for? Aviator needs low water and hydrocarbon content and are you testing through a mass spectrometer? You are more likely prone to introduce impurity by your own filling station by not purging the gas lines and whips after attaching them to the cylinders (purging the farthest point from source and closest to the cylinder filled). In our case, it is not a major issue if you are blending, anyway. Aviators are dispensing pure oxygen at very cold temps so moisture can freeze lock parts and clog passages. My suggestion is a find out how your cylinders are filled. I believe large oxygen banks are liquified storage tanks. The only gas I am fearful of the carbon monoxide and pumping and filling stations won't be able to contaminate their gas with it because the oxygen is produced from a batch tested bank and filling plants typically do not have a source of carbon monoxide present (internal combustion engine or gas furnace nearby). Also, the oxygen is dispensed at a high pressure and even exposed to a hazardous gas won't allow any to sneak into your lines or tank. Any leak in your trans-filling station is a escaping gas. Hope this helps. Any gas industry people willing to comment is requested.
Lastly, I also weld using TIG/GTAW process. I have welded titanium and it is VERY sensitive to impurities. Industry calls for 99.98 and Ultra High Purity (UHP) grades are 99.999% but titanium so sensitive, you can see impurities dis-color adjacent metal of the weld zone even with UHP grade gas. Considering the gases are dispensed at the same facilities and quality protocol is the same, you can likely say with confidence industrial oxygen is very, very pure. I still would not argue with someone wanting to test and let us know if anyone has tested and confirmed a "bad" batch of gas.
Thanks,
-T

 

[walkonmars]

I am currently using the industrial/welding oxygen as well. The standards for medical, breathing grades are a joke. You are paying more for the breathing and medical grades because it requires regulation as "drug". The breathing grades are typically 99.5% as a minimum requirement (but dispensing gas exceeding the grade is OK). Industrial grades are at the very worst 99.8% but in reality, they come from the same bank and are usually 99.9 or better (likely 99.95%---wow!). The differences in prices are very dramatic. If you own your personal cylinder industrial can be $20 and aviator can be $60 for a size 300 cylinder on an exchange basis. It is too expensive to pump a typical gas from multiple supply banks so large suppliers will pump all the gas from the same good banks. A special grade such as research, ultra high pure and reference gas grades will be individually tested with a certificate of test and conformance. I admit, there are some variations from large shops to small shops. Some evacuate a cylinder before pumping (as a exchange use tank) and some just pump it into your tank you bring them on site. You may want to call the shop you go to and ask them what their exact process is. Typically, the first person you speak to will have NO CLUE what you are asking them. You will need to talk to the pumping plant and not the distributor. In a large city (Los Angeles where we are) the cylinders from Airgas, Co. are processed at a pumping, purification and filling facility and batch tested. Typically the cylinders are evacuated prior to filling (not baked out like they used to) and NOT individually tested. I toured a WestAir facility in Anaheim, CA and they evacuate all cylinders prior to filling and they are a local, small filling facility (not a pumping and purifying facility). The breathing grades MAY be individually tested this way but I highly doubt that (please confirm if you know!). Think about how many small bottles of oxygen going to hospitals, patient homes and treatment offices and you will likely see analysis of each cylinder is overwhelming. What are you testing for? Aviator needs low water and hydrocarbon content and are you testing through a mass spectrometer? You are more likely prone to introduce impurity by your own filling station by not purging the gas lines and whips after attaching them to the cylinders (purging the farthest point from source and closest to the cylinder filled). In our case, it is not a major issue if you are blending, anyway. Aviators are dispensing pure oxygen at very cold temps so moisture can freeze lock parts and clog passages. My suggestion is a find out how your cylinders are filled. I believe large oxygen banks are liquified storage tanks. The only gas I am fearful of the carbon monoxide and pumping and filling stations won't be able to contaminate their gas with it because the oxygen is produced from a batch tested bank and filling plants typically do not have a source of carbon monoxide present (internal combustion engine or gas furnace nearby). Also, the oxygen is dispensed at a high pressure and even exposed to a hazardous gas won't allow any to sneak into your lines or tank. Any leak in your trans-filling station is a escaping gas. Hope this helps. Any gas industry people willing to comment is requested. Lastly, I also weld using TIG/GTAW process. I have welded titanium and it is VERY sensitive to impurities. Industry calls for 99.98 and Ultra High Purity (UHP) grades are 99.999% but titanium so sensitive, you can see impurities dis-color adjacent metal of the weld zone even with UHP grade gas. Considering the gases are dispensed at the same facilities and quality protocol is the same, you can likely say with confidence industrial oxygen is very, very pure. I still would not argue with someone wanting to test and let us know if anyone has tested and confirmed a "bad" batch of gas. Thanks, -T

Lastly, I need to say I use Industrial oxygen for my usage and not recommending anything. Everyone else should use good judgment as to how and when to use pure and mixed gases.

 

[OkByMe]

NO NO NO NO NO EFF NO!!!!

Welding gas is NOT clean like med grade or Aviator grade. Breathing welding O2 under pressure is extremely dangerous. It is NOT clean breathing gas, and blending with it is an accident waiting to happen.

The material safety data sheet on both industrial, medical and aviation Oxygen are almost identical. If you are feeding a stick, all the gas goes through filtration before it goes into the SCUBA cylinder anyway.

There is another way to go that will cost about $450.00 and you can get all the 95-97% Oxygen you want for blending. Salvaged Oxygen concentrators and oil less pumps that drive them. 4 concentrators with 3 pumps will put out 75% Oxygen wide open at 2.5CFM. Most small compressors output in the 3-4CFM range. I can blend 40% with this rig. Pictures to follow.

These are Sequal medical Oxygen concentrators (15LPM modules) that became saturated and did not meet specs. I de-saturate them (there a method for this) and they are back to 95%or better when fed with the spec air flow rates and throttled to the spec output flow rate. When you push them to higher pressures and flow rates, the production falls to 75-80%, which is enough to feed the compressor. I have to throttle the output to control the rate going into the SCUBA air compressor to keep it below 40%.

In case anyone is confused... the rest of the gas is still Nitrogen. The plus to this, is that the air going into the supply compressors is filtered. And after going through the supply compressors, the air is heated and goes through a water separator - removing moisture. The air goes down a cooling manifold and into the molecular sieve of the concentrator where moisture is again removed, so by the time it hits the compressor intake, almost all the moisture is removed. I can run the compressor for 3 hours to fill the cascade NITOX cylinder and only get a couple tablespoons of water from the auto drains.

 

[JohnnyC]

The material safety data sheet on both industrial, medical and aviation Oxygen are almost identical. If you are feeding a stick, all the gas goes through filtration before it goes into the SCUBA cylinder anyway.

The problem is the chain of custody of the rental cylinders, not the gas they put in it. It doesn't matter what they put it in if they don't evacuate the cylinder prior and the cylinder has already been contaminated. It appears (anecotally) that most Praxair and Air Liquide evacuate all O2 cylinders, in which case the point is moot. However, if they don't evacuate ALL O2 cylinders, it's prudent to order medical or aviator grade simply as a precautionary measure

tomfcrist owns his own cylinders, he knows what's in them, and knows that in his case it's impossible for them to be contaminated. You don't have that same guarantee with rental industrial supply cylinders unless the filler evacuates them prior.

You are correct, if it goes through a stick it gets filtered for CO2 and CO. I don't know what filters out acetylene, but I don't think hopcalite does. Also, not everyone blends that way. If you're partial pressure blending straight out of the O2 bottle, nothing gets filtered.

 

[OkByMe]

The problem is the chain of custody of the rental cylinders, not the gas they put in it. It doesn't matter what they put it in if they don't evacuate the cylinder prior and the cylinder has already been contaminated. It appears (anecotally) that most Praxair and Air Liquide evacuate all O2 cylinders, in which case the point is moot. However, if they don't evacuate ALL O2 cylinders, it's prudent to order medical or aviator grade simply as a precautionary measure

tomfcrist owns his own cylinders, he knows what's in them, and knows that in his case it's impossible for them to be contaminated. You don't have that same guarantee with rental industrial supply cylinders unless the filler evacuates them prior.

You are correct, if it goes through a stick it gets filtered for CO2 and CO. I don't know what filters out acetylene, but I don't think hopcalite does. Also, not everyone blends that way. If you're partial pressure blending straight out of the O2 bottle, nothing gets filtered.

I don't where you came up with the possible Acetylene contamination of the Oxygen cylinder...Presumed to be used in conjunction with a welding/cutting rig. First anyone who does not have check valves on the hoses is setting themselves up for gas mixing in the hose, which "could" be a little dangerous depending on hose length.

But in any case, that "aint" how the regulators work. If the Acetylene cylinder valve is opened to the regulator, and the gas is allowed through the first stage into the second stage and the diaphram is compressed, it will allow the gas down the hose to the control valve handle. And that valve is open - then it will exit the tip. If the tip has a lot of flow resistance it may back up into the Oxygen hose if the Oxygen control valve is also open - Well that is just stupid operation, but lets assume the worst. The pressure would build up in the oxygen hose equal to the Acetylene second stage pressure setting less the pressure drop across the tip - presumably less than 15PSI. This pressure would be against the second stage diaphragm of the Oxygen cylinder regulator, but would not pass to the first stage whether the Oxygen cylinder valve is open or closed. If the Oxygen cylinder valve is opened, that pressure will move to the first stage and if the second stage "T" handle has the diaphragm compressed, Oxygen will flow down the hose - pushing out the Acetylene. This where gas mixing in the hose could be a problem.

Now I will admit that industrial Oxygen cylinders are not as pristine as Aviator and Medical cylinders - but they are all held to cylinder contamination oversight since any fuel mixed with an Oxidizer is bad news. Owning you own cylinder has an initial cost and can be difficult to fill because most will want you to leave it. And if you leave it, you can lose it to someone who will want to swap it out for one of theirs.

 

[nadwidny]

You are correct, if it goes through a stick it gets filtered for CO2 and CO.

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

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.

I don't know what filters out acetylene, but I don't think hopcalite does.

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.

If you're partial pressure blending straight out of the O2 bottle, nothing gets filtered.

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