How Does an Airbag Deploy?

Airbag deployment is one of the fastest mechanical processes in everyday life. Accelerometers (crash sensors) in the car body detect rapid deceleration exceeding a threshold (typically equivalent to hitting a brick wall at about 16-24 km/h). The airbag control unit sends an electrical signal to the inflator module in about 15-20 milliseconds. The inflator contains a small pyrotechnic charge that ignites sodium azide (NaN3), which rapidly decomposes into sodium metal and nitrogen gas (N2). The nitrogen inflates the nylon airbag within about 20-30 milliseconds — faster than a human blink (300-400 ms). The bag inflates to full size just as the occupant body moves forward from inertia, cushioning the impact across a large area rather than concentrating force on the steering wheel or dashboard. Small vent holes in the back of the bag allow it to deflate as the occupant presses into it, absorbing energy gradually. Modern cars have 6-10 airbags (front, side, curtain, knee), each with independent sensors.