I'm writing this as someone wearing a couple of hats right now. I am a CH sufferer and a member of the medical community for 30+ years. I served as a Combat Medic in the US Army and when I finished my tour and returned home I went onto the streets as a Paramedic where I still work to this day as a Critical Care Paramedic. I'm in Texas and know the Texas Laws and each state is different, but the oxygen law is pretty much the same. Because of my job I transport a considerable amount of patients that are on ventilators and are sedated and require oxygen. This is one of the apps I use to help me with oxygen calculations that is free on Google Apps: https://play.google.com/store/apps/details?id=com.ccn8.gasdurationcalculator Just enter the values of your device to get the amount of minutes left on your personal bottle.
Because Medical Oxygen is listed under the USP (United States Pharmacopoeia) it is a drug and requires a prescription. However, welding oxygen isn't. The only difference is, from what I'm told is that welding oxygen isn't filtered as medical oxygen is and it may have some impurities in it that may cause a certain pneumonia. That is what I've been told, but I've never seen it ever happen nor has anyone ever produced any citations to back this up. It's just taken at face value. Anyways, the Medical Oxygen Supply folks that I have met that run the desk that I have met have not exhibited with much medical training. They know some things, but it usually involves billing issues. A concentrater has an upper limit of 10Lpm. What we do for patients at home that require a higher output is "daisy-chain" two concentraters. Take two 10Lpm concentraters and use an adapter to connect both hoses together into one to the delivery device. It's called a "T" device or a "Pigtail." Plug it in and let it run. It does work. That is what the military is using in field hospitals in combat zones today. The difference is the concentrater pumps out about 94% on average versus 100%. They'll both work. 100% is more effective, but I can make the concentrater work just fine it just takes just a little longer and more patience. I use a 10Lpm concentrater at home, but it takes a little training. One should not use anything other than a non-rebreather for it to work properly. I hope this helps.
-Willie