-Where you want the safety part of a gas that would not entertain a flame (planes, heavy things operating on burning coals, blast furnaces, etc)
This might be a valid use of nitrogen as a filling gas if the tires weren't surrounded by an oxidizing atmosphere. Since the air that the tires are operated in is 20% oxygen, any nonflammable benefit of nitrogen
in the tires is far outweighed by the air surrounding it. If a tire is going to start to burn, it will burn from the outside...where the oxygen is...to the inside...where the nitrogen is. If a nitrogen filled tire were to start to burn, it would have to almost completely destroyed by the fire before the nitrogen would become part of the equation.
Why? another myth is that N2 molecules are bigger than air.. that's just a myth.
N2 is less heavy than air, has a triple joint in the molecule (which common sense says it's smaller than a double joint found in oxygen), and on the contrary N2 molecules would be smaller than air, so it can creek out more easily.
Um...air, the stuff we breathe, is 78%
nitrogen. So nitrogen molecules can't really be larger or smaller than
air because 'air' is largely nitrogen. The density of nitrogen at STP is only
slightly less than the nitrogen/oxygen mixture we call air.