The vehicle seat suspension system of the present invention utilizes an extensible linkage supporting a seat frame. Height adjustment of the seat frame on the extensible linkage is done through an adjustable air spring. Movement of the seat frame due to jostling of the vehicle is normally dampened using a variable damping rate, extensible shock absorber. The damping rate is essentially pushed in infinity, fully locking the shock absorber positionally in response to detection of an accident condition. In one embodiment of the invention, a bleed valve between the compression and rebound chambers of the shock absorber is closed to effect lock up. In an alternative embodiment, the electrorheological or magnetorheological working fluid of a shock absorber may be solidified to lock positionally the shock absorber. Condition detection sensors include accelerometers and roll over detectors. To allow for the possible loss of vehicle power, the lock up signal is supplied by an independent power source.