The airbag is the more common name for the Supplemental Restraint System (SRS)—supplemental because it’s intended to support seatbelts in keeping passengers safe. In the event of a crash, they need to slow down a passenger’s forward motion as evenly and as quickly as possible. If the car’s computer senses sudden deceleration (usually the equivalent of hitting a brick wall at 10 to 15 mph), it activates a chain of events in the blink of an eye.
The vinyl panel on the front of the airbag unit is designed to break apart instantly when the airbag expands, without creating stray debris that could injure the driver. There’s an indented break line running across this airbag’s front cover.
The airbag itself is folded into two neat coils, tightly packed above and below this line. It’s coated with cornstarch or talcum powder to keep it pliable and ready to unfurl at all times.
In this view, we’ve adjusted the opacity to show only metal components. There’s a big metal cylinder in the center of the airbag assembly. Now we'll see what's inside...
When the car’s computer detects a crash, it sends current through an igniter that heats up this inflator cylinder filled with pellets of sodium azide, a solid chemical propellant similar to rocket fuel. The sodium azide burns rapidly and releases harmless nitrogen gas to inflate the airbag in less than one-twentieth of a second. The bag is fully inflated for only one-tenth of a second and almost completely deflated by three-tenths of a second after the initial impact.
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