Medical gases are piped through copper pipes. There are special precautions taken to ensure cleanliness to avoid explosions when exposed to high pressure oxidants.
The only indication as to the composition of the gas is provided by the labels stuck to the pipes. It is possible for these labels to be applied incorrectly.
Given that the pipes are similar, and it is difficult to see which outlet they are attached to, you should expect that there will be errors in new gas installations, or after repair work.
The current Australian Standard requires the installing engineer to check the composition of gas at every outlet. If non respirable gases are involved, the outlets must also be checked by an anaesthetist.