Several injuries to operators of underground coal mining equipment have led to an investigation of safe vertical velocities of a roof bolter boom arm at the National Institute for Occupational Safety and Health (NIOSH)'s Pittsburgh Research Laboratory. There are currently no regulations or method of determining the safe speed of roof bolter boom arms. Accident investigation reports from the Mine Safety and Health Administration (MSHA) do not usually contain enough information to aid in studying interactions between a machine and its operator. Lab experiments with human subjects also are not feasible because of safety and ethical issues. With this in mind, NIOSH researchers successfully developed a computer model that uses simulation software. This report documents the development of special features of the computer model, random virtual human motions and behaviors, which made it possible for researchers to study hazardous interactions between the operator and machine