CITROËN DS 4 Handbook page 180

Lateral airbags
System which protects the driver and front
passenger in the event of a serious side impact
in order to limit the risk of injury to the chest,
between the hip and the shoulder.
Each lateral airbag is fitted in the seat backrest
frame, door side.
deployment
A lateral airbag is deployed unilaterally in the
event of a serious side impact applied to all or
part of the side impact zone B, perpendicular
to the longitudinal centreline of the vehicle on a
horizontal plane and directed from the outside
towards the inside of the vehicle.
The lateral airbag inflates between the hip and
shoulder of the front occupant of the vehicle
and the corresponding door trim panel.
Impact detection zones
A. Front impact zone.
B. Side impact zone.