The chest of occupant who does not wear the seatbelt is not only restrained by the driver side airbag but also receives the reaction force applied by the steering wheel. This reaction force takes the form of more concentrated load than from the airbag. On the other hand, the larger chest deflection has some potential to cause the higher risk of the chest injury. Because the human rib cage is relatively compliant under a concentrated load, a concentrated load may have a tendency to cause a higher risk of the chest injury. It is estimated that the reaction force applied by the steering wheel to the test dummy has some increased potential to cause the chest deflection.

However, it is impossible to measure the reaction force that is applied by the steering wheel to the occupant’s chest. For this reason, a driver side airbag simulation that uses a finite element model(FEM) to attempt to measure the reaction force applied by the steering wheel was developed.

The results of the developed simulation reveal that the Contact force caused by interacting with the steering wheel and the occupant's chest is reduced and the risk ofthe chest injury is somewhat lower with deploying the airbag comparing to the case without deploying the airbag in certain circumstances.