I was chatting a little bit with the guy who delivers liquid O2 to the hospital where I work. It's not a fuel that can combust like propane or hydrogen but it creates a condition where almost any type of fuel can combust extremely easily. As an example I noticed the guy put down a piece of cardboard under the valves of his truck as he offloaded to catch the drips of O2 that leaked from the connections. When I asked about it he said that if there was a stain on the asphault from a drop of oil or something and the O2 got on it that it would explode from the pressure if he backed his truck over it on the way out. He said he had done it before and it blew the tire right off the rim.
I'm sure not only the Nitrogen but also the lesser concentration of O2 makes NO2 way way safer than carrying around and plumbing all that O2.
