Airbag Chemistry

Folded (undeployed) airbags—in the steering-wheel assembly and passenger-side dashboard of all new vehicles—contain sodium azide (NaN₃), a potent metabolic poison. Although the precise formulations used are guarded as trade secrets, a well-known one includes potassium nitrate (KNO₃) and silicon dioxide (SiO₂) as secondary reactants. In the gas generator, a mixture of sodium azide, potassium nitrate, and silicon dioxide is ignited by an electrical impulse. This liberates a volume of nitrogen gas (N₂), which rapidly fills the airbag:

2NaN₃ 2Na + 3N₂ .

Sodium metal (Na), the other byproduct of this reaction, is an unstable substance that can undergo an explosive reaction with water at room temperature (a common demonstration in college chemistry classes). This sodium reacts with the potassium nitrate to generate additional nitrogen for the airbag in a second reaction:

10Na + 2KNO₃ K₂0 + 5Na₂0 + N₂ .

The other products of the reaction—potassium oxide (K₂0) and sodium oxide (Na₂0)—react with the third compound of the original airbag mixture, silicon dioxide (Si0₂), to form alkaline silicate, or glass, a stable (unreactive) substance that is harmlessly discarded in a deployed airbag.

The use of BTATz, which produces only water, carbon dioxide, and a large amount of cool, inert nitrogen gas upon ignition, would eliminate the need for the supplementary chemicals and secondary reactions, and more important, would eliminate the need to dispose of the toxic sodium azide from undeployed airbags.

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