gzt: As I understand it Christchurch has many in roof water cylinder installations. Does that apply to gas?

Noppees. That would be more likely to asphyxiate someone in their sleep as it made its way to ground (heavier than air - is why the people likely were burnt waist down)

Reticulated comes from pipe to the house via a meter. Bottled is strapped to an outer wall

No internal storage generally. Even under sink bottles are now banned I believe