NOS is flamable, in liquid state it isnt once it is in a gas state it is highly flamable. also those tanks DO NOT SMOKE NEAR THEM(amd run your ass off if someone is) they are full of 100% oxygen under pressure...the presence of a spark in that or to much heat will cause an explosion, oxygen by itslef isnt flamable but under pressure its another story.
O2= oxegen gas
N= nitrogen
nitrogen is not flammable
o2 isn't flammable alone
oxygen is a catalyst not a fuel