NSW is a dangerous and savage land. HW systems should be outside the house, not in it.

If we can use a high pressure flammable gas safely, then we can use a high pressure non-flammable gas safely.

Agreed on all counts :-)

Welding cylinders run 2000 psi+ and are trucked around regularly with safety.

Actually, they are exceedingly dangerous in a vehicle fire, especially acetylene which is not stored at very high pressure because it will spontaneouly explode.

In the UK nobody will go anywhere near a fire with welding cyliders involved - that includes the fire brigade.

Several times this year alone major motorway routes have been closed for twenty four hours after a vehicle has been left to burn itself out before anybody will go within several hundred metres of it.