Applying importance measures in resource-constrained operation schedule risk analysis

Emergency operations are fast response operations for preventing adverse events from harming a system, for responding to and mitigating their consequences, and for recovering from them. This report concerns schedule risks associated with them. The topic is examined in a resource-constrained setting, where replacements for broken or otherwise failed resources are not necessarily available within the operation's time frame. In probabilistic risk analysis and reliability engineering, reliability importance measures give the sensitivity of risk to component failures or other events. Schedule risks can be defined as the delay of the completion of the operation or some specified part of it. The probability of this may be regarded as the failure probability of the operation, which enables the application of importance measures in this context. We show how to interpret importance measure concepts in this context, define various kinds of events that may cause delay in operation completion, and show how to estimate importance measures from simulated, experimental or observational data. The importance measures are applied to an operation of clearing roads leading to a nuclear power plant from fallen trees after a storm. A stochastic activity network model developed earlier is used and improved, estimation of the most important PRA importance measures from simulation data is implemented, and estimation results are presented. Importance measures have many applications in the risk management of emergency operations, such as resource allocation.