In a method of operating a passive safety system, such as an airbag supplemental restraint system in a motor vehicle, the trigger threshold value for triggering the deployment of the airbag or the like is updated or changed over time as the vehicle deteriorates with age or operation. As a result of material fatigue, rust and the like, the vehicle chassis becomes less stiff with increased age and/or increased operation. Consequently, the crash behavior of a deteriorated vehicle differs from that of a new vehicle of the same type. Namely, the deceleration during a crash will be less abrupt. To achieve reliable, consistent and timely triggering of the airbag regardless of advancing deterioration of the vehicle, the trigger threshold value is reduced by pre-determined correction values responsive to an increase of one or more degradation-related parameters, such as the age of the vehicle as indicated by a clock, the cumulative operating time of the vehicle as indicated by an operating hour meter, and/or the cumulative distance traveled by the vehicle as indicated by an odometer.