As a qualified chemist, I am astonished that sodium azide is being used in this circumstance. Apart from the toxicity of the substance, it takes very little chemical knowledge to make a high explosive from sodium azide (and people wonder how terrorists can get bomb materials so easily). The substance is an explosive in its own right, which is why it has been chosen - when exploded, it releases nitrogen. On the other hand, why can't the manufacturers use a compressed gas system?

I might also add that when I was at the University of Middlesex, which is the British authority on road safety, I met a man in the bar one night who told me that air bags are nowhere near as good as seat belts as an injury prevention device, but they were more popular in the US than in the UK because more people in the US refuse to wear seatbelts.