Method to Account for Human Intervention in Calculating the Probability of Failure

Although human and organizational factors play a major role in the performance of civil infrastructure, risk assessment does not often explicitly account for them. Although these factors can cause failures, they can also significantly improve a system's reliability, provided that appropriate procedures are in place to be performed by individuals and the organization as a whole. It is therefore important that engineers, operators, and planners incorporate human and organizational factors into the overall risk-management paradigm. This paper builds on previous risk-assessment methods to develop a framework for quantifying the contribution of human intervention to the overall probability of failure of a system. The six steps of the approach are (1)system definition, (2)conceptual model, (3)event tree, (4)task structure map, (5)quality-management assessment system, and, ultimately, (6)the probability-of-failure computation. The Sherman Island flood-protection system in the Sacramento-San Joaquin Delta, California, is used as an illustrative example of how to estimate the influence of human and organizational factors of an infrastructure system.