The head-protection airbag is triggered in certain types of side collisions Fig. 1. Further airbags may also be triggered, depending on the circumstances.

When the system is triggered, the airbag fills with a propellant gas and covers the entire area in front of the side windows, including the door pillars. The head-protection airbag inflates to soften the impact if an occupant strikes parts of the interior or objects outside the vehicle with their head. By reducing the head impact and restraining uncontrolled movement of the head, the airbag also reduces the forces acting on the neck.

The front airbags, side airbags and head-protection airbags may be triggered together in certain types of accident.

In order to provide the desired extra protection in an accident, the airbags have to inflate extremely rapidly (within fractions of a second).