There was a very interesting supplement in Autocar about the Corsa D development just before it was launched... it was subjected to simulated animal impacts, basically driving it into a barrel sized horizontal tight bundle of sticks about 30" off the ground... completely trashed the headlights, radiator, slam panel, bonnet and windscreen. All absorbing the impact beautifully. But the engineer was really narked because it also fired the airbags.
The reasoning being that in a worst case 'ohshitweregoingtodie' moment, the timing is critical as the airbags can only be fired once. The scenario he described was as follows.
Driving along a fast country road in the damp.
1. Driver loses control on a bend and clips the kerb.
2. Car launches from the road edge.
3. Car flies through a post and rail fence about a foot off the ground.
4. Car lands violently on a scrubby slope.
5. Car finally stopped by a hundred year old tree.
At which point do you need the airbag? Answer is 5. any other time is a wasted opportunity with fatal consequences... certainly 1. and 4. have scope for the driver to regain control... almost impossible if the airbag has fired. 2. and 3. simply don't warrant the airbag firing.
Have done 1. through 4. in a Vectra C without the airbags firing.