Keywords: expert opinion, fuzzy pair-wise comparison, fuzzy logic, fuzzy set theory, counter-terrorism, public utilities, construction, design.

This paper describes a method for assessing subjective vulnerability of components of an infrastructure system to Premeditated Destructive Events (PDEs) and presents its application to a large municipal water treatment system. Increasingly, citizens throughout the world are beginning to realize the potential impact of a PDE that could disrupt the working infrastructure of their country. This paper draws most heavily upon the authors' experiences and knowledge of the United States, but it also seeks to capture some aspects of other nations too. Moreover, there appear to be good lessons that nations, states, agencies and organizations can learn from one another about combating PDEs.

The method captures expert opinion from professionals as well as those responsible for maintaining the day-to-day functioning and maintenance of the infrastructure system. It uses fuzzy logic and fuzzy set theory as the basis for fuzzy pair-wise comparison to relative vulnerabilities of infrastructure system components. By identifying critical components of the system and vulnerability of these components to PDEs, it provides a basis for allocation of resources to secure these critical components.

The civil infrastructure in the United States, as in many other countries, is constructed and maintained both publicly and privately by many organizations and governing bodies. In some ways, this is one of its strengths. Because of decentralization of control over infrastructure, in general terms there is some level of built in redundancy and distribution in its organization, both of which are key elements of a strategy for reliability.

Each organization, (i.e. companies, municipalities, state governments) responsible for elements of infrastructure is faced with protecting a particular part of the infrastructure from PDEs. This paper addresses how such agencies and organizations can capture the knowledge required to conceive, design, implement and maintain an infrastructure protection system.

The method is also based on the supposition that within each agency and organization there are experts, not limited to professional personnel, with intimate knowledge of the inter-workings of the respective infrastructure systems. These experts might include laborers with years of experience with various processes and procedure, management at all levels, highly trained technical experts, and design and engineering personnel.

The expert advisor software developed using this method contains knowledge generic to the industry and permits the individual groups to capture knowledge specific to their system configuration, location and any other unique features specific to their infrastructure system. The expert advisor assesses infrastructure component vulnerability and proposes solutions based on the funds available.

Expert advisor software has many potential advantages as a counter-terrorism tool by circumventing some traditional risks. Many of the traditional methods used by agencies and organizations to assess how to determine priorities and allocate funds, such as public debate of issues, simply do not provide the security required when terrorism is involved. Exposing existing and known vulnerabilities to the wider public not only may provide those individuals and organizations planning to enact PDEs with just the information needed to do the job, it could also assist the terrorist's greatest weapon: fear.

A comprehensive defence of a municipal water treatment system from terrorist attacks is prohibitive from the standpoint of cost. So assessment of vulnerabilities and assignment of funding priorities is required. Furthermore, no one single person has all the expertise necessary to make an assessment of vulnerabilities or assign funding priorities. However, using fuzzy logic and fuzzy set theory, the expertise of a diverse group of individuals can be captured and operated on to draw conclusions as if that knowledge could be accessed by a single expert.

With the help of an expert advisor, these agencies and organizations might increasingly capture the expert knowledge already existing within an organization's human and physical capital. Knowledge that could be captured and controlled locally further adds to the reliability of the infrastructure because no single attack on a centralized knowledge base could fatally damage the entire infrastructure protection plan.

The prototype expert advisor described in this paper has many obvious extensions, one being application of the method developed for physical PDEs to chemical, nuclear, biological and cyber PDEs. This method is not only applicable to water treatment systems but to any infrastructure system that can be represented in terms of components that can be defined independently of each other. It is especially applicable to utilities, because this group of infrastructure systems shares a common structure of source, processing and distribution.

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