For example United Airline assigns specific seats because the large oxygen cylinder is strapped in the overhead compartment. Whereas Alaska Airlines has no specific seat requirement. Usually bulkhead, aisle and exit seats are unavailable. Some know how to turn the oxygen on and change oxygen cylinders. You must have a clear understanding of your oxygen liter flow and check to see that the attendant has correctly set the flow meter.
Masks can be unsafe for some people to use.
They also interfere with talking and eating. TWA offers mask only. They will allow you to bring your own nasal cannula. The oxygen provided is compressed gas. The cylinders range in size from 3,228 liters to small 300 liters.