Biodynamics and injury potential of operators in stand-up rider lift truck accidents have been investigated with a special focus on head injury. An anthropomorphic test device (ATD) model was used as an operator surrogate in computer simulations of off-the-dock (OTD) and tip-over (TO) accidents. The biomechanical model representing the ATD was developed based on rigid body segments, and then combined with a rigid body truck model in the accident simulations. The operator compartment of the truck model was enclosed with a rear door. The computed kinematics are in agreement with the results of previous experimental testing. A 2D finite element model of the head was created to compute head impact decelerations in the sagittal plane. Values of the head injury criterion for the TO cases were computed from the model and shown to compare favourably with experimental values. The results advance the state of knowledge concerning injury potential in TO and OTD accidents and simulation models for such accidents.