This report provides the results of the study conducted by NRC on developing a tool and testing procedure for rating resilience of critical infrastructures to extreme fire. Resilience of critical infrastructures to extreme fire is also referred in this report as extreme fire resistance or fire endurance. The current available test procedures for testing structures in extreme fires or hydrocarbon fires were reviewed. The available guidelines and standards were developed mainly for application in oil refinery and chemical industry facilities. The only available standard in North America that addresses the transportation infrastructure is the NFPA 502 standard. However, even this standard has only a procedure for testing of tunnel linings in extreme fire to some extent. No standard, guidelines or document was found for assessing bridges or important buildings to extreme fire. Through this project and based on the review of information available, a draft of a new testing procedure was prepared for resilience assessment of critical infrastructures to extreme fire. An Advisory Board with members from the regulatory bodies and related experts was formed to review the draft document and provide recommendations toward developing a practical testing procedure. The testing procedure was reviewed by the Advisory Board membersand discussed through two meetings. The outcome was presented in this report and recommendedas guidelines for extreme fire resistance of critical infrastructures. Finally, to demonstrate the applicability of the guidelines, a commissioning test was carried out successfully using the NRC column furnace test facility based on the developed guidelines. This report presents the outcomes of the review study, the developed testing procedure, and the results of the demonstrated test.