Just been looking on another (non car) forum and found a thread about an 04 Astra which was involved a head on collision with a bus. According to the thread the car was doing 20-25 MPH.
The OP asked why the airbags didn't go off but it was soon hijacked into why the car was parked on the pavement
Anyway I'm puzzled as to why the airbags didn't go off too.
The accident was last week and nobody was hurt. Here's a picture he posted up.