Nitrous oxide = not flameable. if the tank was punctured, it would vent all the gas, unless it was not firmly enough mounted, in which case it would take off like a rocket. But it would NOT explode. The only reason it would is if the pressure got too high (bottle heater left on or over filled, and the "blow-off" valve did not function), and the tank exploded from too much pressure.
A puncture would not be all that bad. (And don't say "I think it would be cool because the car would fill with laughing gas" because automotive grade N20 would just kill you, not make you high.)
Sean Cathcart