Explosive Safety

Automobile safety is an explosive issue. Literally. New cars have several features that, if employed in a different manner, would earn you a visit by agents of the Bureau of Alcohol, Tobacco, Firearms and Explosives, and, perhaps, a forced, multi-year vacation at taxpayer expense. If you modified these safety features or employed their components for ulterior motives, the ATF would call them "destructive devices," a category that includes things like machine guns, sawed-off shotguns, and rocket-propelled grenades.

Airbags
One of these concealed weapon-like devices is the ubiquitous airbag. Next is the seatbelt pretensioner, just one item on the long list of features automakers and car writers throw around as if they expect everyone to understand. A safety device soon to be fitted to new cars surely will raise a few eyebrows at the ATF: exploding hood hinges.


Airbags are inflated by burning sodium azide, the stuff used in detonators and other applications the ATF would just as soon you not know about, and potassium nitrate, which is commonly called saltpeter and a key component in "blackpowder" gunpowder. But don't be afraid, the result of this reaction is non-toxic nitrogen gas. The "smoke" reported by accident victims is largely the corn starch or talcum powder used to lubricate the folded nylon bag and facilitate its opening.


Many airbags use crash sensors based on high-powered magnets. These magnets are forced apart if the crash is big enough (definition of a "small crash": one you're not in.) and in a direction the airbags can help. For front airbags, the threshold is equal to hitting a solid wall head-on about 12 to 15 mph. When the magnets are flung apart, a signal is sent to a computer. After its digital brain confirms that, yes, indeed this is a crash and not a spurious signal, it sends an electrical charge into the solid propellant. From the instant the magnets move to the moment when the airbag is fully deployed is about 30 milliseconds.


The inflated airbag prevents occupants from slamming into the interior of the car. In a severe crash without an airbag, the driver's head might hit the steering wheel even if he's wearing a seatbelt. Airbags also avert a forward neck-snap that might produce a basal skull fracture of the type that killed Dale Earnhardt.