Critical Infrastructure as Complex Emergent Systems

The United States Department of Homeland Security (DHS) charge is to, “Build a safer, more secure, and more resilient America by preventing, deterring, neutralizing, or mitigating the effects of deliberate efforts by terrorists to destroy, incapacitate, or exploit elements of our Nation’s CIKR …” using an all-hazards approach. The effective implementation of this strategy hinges on understanding catastrophes and their potential effect on the functioning of infrastructure. Unfortunately, there has been no unifying theory of catastrophe to guide decision-making, preparedness, or response. In this paper, the authors present a framework based on network science and normal accident theory that can be used to guide policy decisions for homeland security. They show that exceedance probability encompasses operational definitions of risk and resilience and provides a unifying policy framework for homeland security investments. Such an approach allows one to classify hazards as ‘high’ or ‘low’ risk, according to the resiliency exponent, and guide investments toward prevention or response. This framework is applied to cyber exploits and electric power grid systems to illustrate its generality.