In certain types of side collision, the head-protection airbag is triggered on the impact side of the Audi A4 Fig. 1. Further airbag systems 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. In this way the system is able to protect both the front and the rear occupants on the side of the Audi A4 where the impact occurs. The head-protection airbag inflates to soften the impact if an occupant strikes parts of the interior or objects outside the Audi A4 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.

In order to provide the desired extra protection in an accident, the airbags have to inflate extremely rapidly (within fractions of a second). The airbag releases a fine dust when it inflates. This is quite normal and does not mean there is a fire in the Audi A4.