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Bounding the Structure Separation Distance: A Modeling Study in Support of the Structure Separation Experiments Project



Kuldeep Prasad, Alexander Maranghides


The primary objective of the Structure Separation Experiment project is to assess structure-to-structure fire spread for structures located in the Wildland Urban Interface (WUI). As part of this project, full scale fire experiments will be conducted in which various types of structures (sources of fire) will be used to generate typical radiative and convective heat exposures on target structures (residential dwellings). The spacing between the source and target structures will be varied to identify safe structure separation distance (SSD). Most experiments will be conducted with construction materials currently listed in State of California building codes and using code compliant structural assemblies. A limited number of experiments will be conducted with enhanced, ignition resistant, materials that may not currently be listed by the State of California. The project is divided into three phases. Phase 1 will test sheds as fire sources, Phase 2 will test "in-law" buildings and Phase 3 will test single-family homes. Source terms from 1.39 m² to 24.8 m² (15 ft2 to 267 ft2) will be tested in Phase 1. Phase 2 will examine exposures from a 40.87 m² (440 ft2) "in law" building and Phase 3 will characterize exposures from approximately 92.90 m² (1000 ft2) residences. The goal of this report is to present a preliminary modeling approach for estimating an upper bound for the safe structure separation distance (SSD). This work is part of the larger modeling effort for the Structure Separation Experiments project and is intended to compliment the vast number of full-scale experiments that are being performed as part of this project.
NIST Interagency/Internal Report (NISTIR) - 8436
Report Number


Modeling, Structure separation distance, wind, heat release rate, wildland-urban interface.


Prasad, K. and Maranghides, A. (2022), Bounding the Structure Separation Distance: A Modeling Study in Support of the Structure Separation Experiments Project, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online],, (Accessed April 17, 2024)
Created October 20, 2022, Updated November 29, 2022