Wildland-Urban Interface (WUI) Fire Spread and Modeling

Summary

This project combines experimental research with advanced computer modeling to improve understanding of how fires spread in the Wildland-Urban Interface (WUI) and to drive the development of the next generation of physics-based models for predicting WUI fire behavior. In recent years, fires in WUI communities have become the most devastating type of fire disaster in the United States, causing significant loss of life, property damage, and overall financial cost. Despite this growing issue, science-based engineering tools that allow rigorous evaluation of potential fire spread in WUI fuels, where both vegetation and building materials play a role, remain elusive. To address this gap, this project focuses on providing carefully controlled and well-instrumented experiments to analyze how WUI fuels burn. These experiments will generate crucial data to improve and validate physics-based fire models, helping engineers and policymakers develop better risk assessment strategies and fire-resistant designs for WUI communities.

Description

An experiment on the burning dynamics of a surrogate vegetative fuel alongside a numerical prediction.

Credit: E. Mueller / NIST

Objective - To provide data on fire dynamics and fire spread in WUI fuels, particularly to drive the development of physics-based Computational Fluid Dynamics (CFD) models – introducing new model capabilities and building model confidence.

What is the new technical idea?

A significant gap exists in capabilities for supporting risk assessment and engineering design around fire safety in the Wildland-Urban Interface (WUI). This is particularly true in the context of numerical modeling tools. While there are still significant research challenges to address, numerical models for the built environment are comparatively more mature. These have been developed over decades of complementary research with experiments which are often designed specifically to meet the needs of model development, addressing deficiencies in submodels or filling in critical gaps in data.

The NIST WUI group is in a unique position to apply this same approach for WUI model development. We are leveraging expertise and facilities in the National Fire Research Laboratory (NRFL) to perform well-controlled and well-characterized experiments on burning dynamics and fire spread in WUI fuels. At the same time, we are leveraging world-leading fire modeling expertise which exist within the Fire Research Division, particularly in collaboration with the development team of the Fire Dynamics Simulator (FDS).

This cooperative and iterative effort will lead to the generation of unique model benchmarking and development data. Undertaking both the experimental measurements and the modeling efforts will allow us to produce datasets with the necessary parameterization for physics-based models and which are designed to exercise relevant parameter spaces and target known model deficiencies. For example, we know that fluid-vegetation interactions, such as drag and convective heat transfer, are not well quantified and are crudely represented in modeling approaches, and we will focus on experiments which characterize these phenomena. As an added benefit, these data will contribute to the NIST Fire Calorimetry Database (FCD).

What is the research plan?

To fill the knowledge and data gaps around fire spread in WUI fuels, we are focused first on vegetative fuel structures. We are conducting experiments on both burning dynamics of individual specimens and on flame spread in fuel beds. We will not only capture global combustion properties but provide measurements of exposure conditions, such as heat fluxes, which are relevant to WUI fire scenarios. We will also conduct such tests in both quiescent and wind-driven conditions, recognizing the significant role that wind plays in exacerbating the consequences of WUI fire spread.

At the same time, we are running numerical simulations of these scenarios using FDS. This goes beyond simply providing comparisons between observations and numerical predictions, as we are focused primarily on identifying model shortcomings and directly implementing algorithmic improvements. This covers all parts of the model, from improving input capabilities for vegetative fuel structures, to submodels for describing physical processes, to enhancing output capabilities relevant to vegetation and WUI fire spread. We are also driving these efforts by evaluating model needs beyond the laboratory scale. Making use of existing datasets for large-scale fire spread in vegetative fuel, we are able to identify physical processes or scenarios that are poorly represented by current modeling approaches and further inform our experimental design in the laboratory.

Major Accomplishments

• NIST researchers have begun collecting data on the burning dynamics of vegetative WUI fuels, including calorimetry, products of combustion, and radiant emissions.
• A new wind tunnel has been constructed and commissioned in the National Fire Research Laboratory which will begin enabling measurement of WUI fuel burning dynamics under highly controlled conditions.
• Project efforts have been supplemented by external funding  for the evaluation of modeling approaches for wildland/WUI fuels in the context of prescribed fires.