CSA Z767 stipulates that human factors must be considered in risk identification and quantification. In doing so, the design of operator process/equipment interfaces with written guidelines and procedures, staffing levels, and the working environment (noise, vibration, lighting, temperature) should all be considered from the perspective of their effect on both the levels of protection (line of defense) against hazard occurrence provided by operators and the possibility that their actions might initiate hazard occurrence. Errors of both commission and omission need to be considered. The operator will contribute to one or more lines of defense (one or more layers of protection).