For critical facilities, survivability and reconstitution in stressful environments generated by electromagnetic transients, sabotage, terrorist activity, military conflict, or Murphy’s laws are issues of concern. Critical fixed facilities are likely to be functionally complex and their system-wide failure probabilities, modes, and consequences are often not obvious. To analyze and quantify survivability, existing probabilistic risk assessment tools usually provide a “snapshot” of failure modes at a single point of time for certain initiating conditions. Likewise, elaborate physics models developed to treat weapons effects on structures and individual functional components compute effects at a single time point.

We have developed a tool that improves upon existing computational models by adding the time dimension to the evaluation of functional mission susceptibility to failure of interdependent subsystems of complex facilities. The tool computes the evolution of overall mission failure probability in time by evaluating initial failure probabilities, effects onset times and system repair times for single or combinations of critical facility subsystems. The tool allows the aggregation of scenario and facility functional tree/diagram inputs into an overall system effects evaluation. The model breaks new ground in quantifying and predicting not only initial probability of effect on facility mission execution, but mission outage longevity. Computations invoke a component-up functional fault tree/diagram system analysis to synthesize and quantify overall facility mission survivability. The model is unique in that time evolution of the probability of effects on mission is built-in effectively as a stochastic finite difference equation with initial conditions, deterministic and stochastic, and uses as coded inputs 1) the adverse scenario environmental stresses, 2) the system fault analysis, 3) the individual functional components' damage threshold probability distributions, and 4) the time constants of effects and repairs. The code provides output to users by plotting system mission PE and conditional PE vs. time.

The code is useful for determining the most critical failure points and the most cost-effective protection upgrades. It is a tool well suited for predicting functional impairment due to overstress effects in critical infrastructure systems.