How does an airbag inflate?

A number of different methods are used see wikipedia article "Airbag" for a pretty full account. The most intersting from a chemistry point of view is the original method which used sodium azide, Na3N which was detonated to produce sodium and nitrogen gas:

2 NaN3 → 2Na + 3 N2

The sodium metal was mopped up by silica, SiO2, to produce silcates.