What makes that an airbag inflates itself so quickly? A gas is injected in the airbag with a very big speed. How? By a chemical reaction....

When a shock occur, the airbag spreads out to a speed of 150-200Km/h.

This spreading speed is only possible thanks to an exploding chemical reaction that propels gas produces with a very big speed. The chemical reactions put in play in the system of airbag are complex enough.
The reagents are:

- the sadium azoture NaN3

- The potassium nitrate KNO3

- The silice SiO2

2 NaN3             2Na + 3N2

The inflammation of the NaN3 results in a combustion that expulse a pre-calculated volume of N2 gas that inflates the airbag. 

The problem of this reaction is that it forms solid sodium Na, that ignites hardly in presence of water. It is necessary to neutralize it therefore by a second reaction :

10 Na + 2 KNO3             K2O + 5 Na2O + N2

The sodium Na is going to react with the potassium nitrate KNO3 to give du Na2O.
You will notice that the only product of this reaction is azote N2.

The K2O and the Na2O react on the SiO2 silica to form a sodium salt and potassium K2Na2SiO4 that is an alkali silicate, in other words a powder of glass (innocuous, inert, and non flammable product).

K2O + Na2O + SiO2           K2Na2SiO4

Attention :

 NaN3 is an extremely toxic compound (30 times more that arsenic)