Having worked in the medical area in a past life, this sort of thing would not have happened if they took the lessons learnt from medicine. A long time ago, Doctors discovered that if you fill a patient up with the incorrect gas, the results were not conducive for a long life. Following some investigation they came up with the idea that if you make each gas fitting unique, then the possibility of placing the wrong gas in the wrong area was removed from the equation. As a result, oxygen cylinders can not be connected to CO2 cylinders because the collar is different. It is the same with nitrogen and the other gases found in hospitals. Anaesthetic gases work along a similar line when added to the anaesthetic machine.
The question I ask is "How difficult would it be to have unique fittings for each gas cylinder?" I know of nitrogen and oxygen being used in an aircraft, but are they any other ones? Maybe the gingerbeers out there can help.
Tinkicker