Stan Wilder wrote:

> Just as general information, many aircraft wheels are made of magnesium
> and sand is about the only way to remove the supply of oxygen if they
> catch fire.
> Also aircraft tires that fly at high altitudes are filled with nitrogen.
> Won't freeze, Won't hold moisture, Won't expand at altitude but with a
> nice magnesium fire it provides additional fuel.
>

Freezing (or more likely liquefaction), holding moisture, and expanding
at lower pressures are properties that are about the same for pure
nitrogen as for air ( 80% nitrogen and 20% oxygen, roughly).
  I don't have much experience with aircraft tires, but I suspect the
advantage of nitrogen is that it is nearly inert and would reduce the
aging (oxidation) of the rubber.
  At the extremely high temperature of a magnesium fire, nitrogen does
react, forming magnesium nitride.

Larry A.