Air bags are now widely used in automobiles in North America to protect the occupants in the event of a collision. It is essential that the bag inflate very quickly: that is, within a few one-hundredths of a second. Thus, the gas used must be produced by some very rapid reaction. Moreover, that gas should be nontoxic and non-inflammable.
Most current designs of air bag use sodium azide as the source of the inflating gas. Sodium azide contains 65% nitrogen by mass. It is used because it decomposes cleanly and rapidly, but without any flame or explosion, at temperatures of 350oC or higher. The decomposition is initiated by a device which produces red-hot sparks.
Because sodium azide is poisonous, all the reactants are kept in a sealed container and only the nitrogen gas is allowed to enter the air bag. Typically the sodium azide mixture is triggered to react at about 10 milliseconds into the crash. The bag is completely filled within 30 milliseconds and porous sections in the bag allow it to deflate in 100-200 milliseconds.