Most experts agree that air bags represent a very important advance in automobile safety. These bags, which are stored in the auto´s steering wheel or dash, are designed inflate rapidly (within about 40 ms) in the event of a crash, cushion the front seat occupant vision and movement after the crash .Air bags are activated when a severe deceleration (an impact) causes against impact. The bags then deflate immediately to allow a steel ball to compress a spring and electrically ignite a detonator cap, which, in turn, causes sodium azide NaN3 to decompose explosively, forming sodium and nitrogen gas:
2 NaN3(s) → 2 Na (s) + 3 N2(g)
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This system works very well and requires a relatively small amount of sodium azide (100 g yields 56L N2(g) at 25ºC and 1.0 atm).
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When a vehicle containing air bags reaches the end of its useful life, the sodium azide present in the activators must be given proper disposal. Sodium azide, besides being explosive, has toxicity roughly equal to that of sodium cyanide. It also forms hydrazoic acid (HN3), a toxic and explosive liquid, when treated with acid