Human reliability analysis as a modeling tool for homeland defense

This paper establishes an initial framework that uses human reliability analysis (HRA) methods as a tool to support mitigation of terrorist actions. Accounting for human performance is key to conceptualizing and implementing the appropriate barriers for defending against terrorist attack. Barriers can either be physical or administrative in nature. The determination of human error probabilities (HEPs) associated with HRA can be used to support a variety of systems planning tools, e.g., fault trees and events trees, event sequence diagrams, and influence diagrams used in conducting a facility risk analysis. Once human actions involved in operating and defending a potential terrorist target are identified, the risk analyst estimates the likelihood of human error using an established HRA modeling method. These estimates in the form of HEPs, are used to populate system event trees and fault trees. The process is generic. In this paper, we use the SPAR-H HRA method developed at the Idaho National Laboratory to calculate initial error probabilities. We present the human factors portion of a preliminary risk analysis and corresponding human error list for personnel involved in operating a generic target facility. The computed human error probabilities are explained in light of mitigating factors such as the facility 's physical system vulnerability, and the quality and availability of defense mechanisms including engineered safety features and availability of intelligence information.