We open with a Takata airbag sitting on the desk in front of us: a unit manufactured at the Monclova, Mexico plant at the center of the recall disaster, purchased on eBay and arrived by UPS ground. We couldn't determine whether it's one of the recalled units.

The Takata airbag recall is the largest and costliest in automotive history, spanning just about every major automaker and now approaching 30 US deaths. We reconstruct the engineering story: how ammonium nitrate became the propellant of choice over cheaper and less stable alternatives, how its crystalline structure degrades through heat cycles and humidity over time, and how that degradation turns a supplementary restraint system into shrapnel. We also CT scanned the airbag, and we walk through what the scan reveals about how these assemblies are constructed.

The organizational s ...