Humankind plays a major role in the life cycle of structures or equipment, as represented by the overall processes of design, manufacture, operation, inspection, and maintenance. Any failure or damage to a structure or equipment is therefore associated with human actions. The effects of human factors on structural reliability are studied. Classification of the causes of equipment and structural failure falls into three groups in terms of the effects on stress and strength of equipment and structures. To assess the effects of factors in these three groups on structural reliability, mathematical models are reviewed and appropriate models for each group are selected. By applying these models to simple piping, they are found to be appropriate for assessing human factors. In addition, simplified models for assessing the impact of human factors on structural reliability during an earthquake are studied.