The airbag didn't go off because Chevy/Pontiac put the airbag sensors low in front of the radiators, generally in level or even below the front metal crossmember/bumper in some vehicles.
Case in point: 2001 Grand Am GT, all options. My girlfriend didn't pay attention to a line of stopped cars because she was too busy waving to a friend on the side of the ride. She ended up hitting a car and it STACKED ontop of her Grand Am, as in the trunk of their car was located over the cabin of our car. Midway on their car was over our windshield. Speed of impact: 30 MPH. Tore the hood up and over our windshield, ripped the radiator off, BUT missed the impact sensor on the front because it is located below the top of the radiator. Not the safest desing IMO, but I guess they do it to prevent the airbags going off on every fender bender and costing alot of money (Airbag units cost ALOT, roughly 1k-2k per unit, and some cars have 6 units)
