Evaluation of Heat Flux Profiles Through Walls in Support of Fire Model Validation
Fire investigators leverage fire dynamics models to predict fire growth and fire pattern development. These fire models incorporate simplifying assumptions in their representation of heat transfer through compartment walls, but the impact of these assumptions on fire model predictions is not well understood. This study aims to create a novel dataset that will inform if, and when, these models are appropriate tools for fire investigation.
UL’s Fire Safety Research Institute (FSRI) will collaborate with the Bureau of Alcohol, Tobacco, Firearms and Explosives - Fire Research Laboratory (ATF-FRL) in this novel research endeavor. Experiments will be conducted in which freestanding walls are subject to exposure from controlled fire sources, including gas burners, liquid fuels, and furnishings. Experiments will be conducted at both the FSRI laboratory in Philadelphia, PA, as well as the ATF-FRL (Fire Research Laboratory) in Ammendale, MD. These tests will generate a robust dataset for validation of fire dynamics models, including field heat flux exposure to walls, heat transfer through walls, and wall surface temperatures.
The results of this work will directly address fire and arson investigation research issues and support further development of the fire dynamics model's implementation of boundary heat transfer. This work will provide a technical basis for the adoption of this approach by fire investigators. This research is supported by Grant Number 15PNIJ-21-GG-04167-RESS, awarded by the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice.
Fire models are presently employed by fire investigators to make predictions of fire dynamics in enclosed volumes within structures. Predictions include the evolution of gas temperatures and velocities, smoke movement, fire growth and spread, and heat exposures to surrounding objects and surfaces (e.g., walls). These heat flux profiles vary over exposed surfaces based on the complex interactions between walls and the fire environment.
A fire model predicts the temperature and heat transfer through walls based on field predictions, such as radiative and convective heat flux, and is also subject to the boundary condition representation, which is at the discretion of model practitioners. In practice, fire investigators favor simplified representations of this boundary condition, for example, isothermal or insulated walls. Presently, FDS can represent in-depth heat transfer through walls, but transverse heat transfer prediction is still in a preliminary development stage. Furthermore, limited suitable validation data exists for quantification of heat transfer through walls exposed to fires. It is crucial that the representation of transverse heat transfer through walls in fire models be validated to ensure that fire investigators can produce accurate simulations and reconstructions with these tools.
The purpose of this project is to characterize the spatially and temporally varying heat transfer through walls subject to realistic fire exposures. Specific objectives are to:
- Develop a novel dataset that will be of direct utility for the validation of present and future models of fire dynamics incorporating boundary heat transfer. The primary measurements will include field heat flux from diffusion fires and controlled radiative exposures to walls, gas temperatures, and surface temperatures.
- Produce a set of thermophysical properties for a selection of materials that will support not only the proposed work, but also future work involving those materials (e.g., fabrication of custom instruments utilizing those materials).
- Develop an optimization model for deducing the heat flux field to a wall from a fire using a large thin-plate sensor and infrared thermography measurements. The optimization model will be validated using a controlled bench-scale heat transfer experiment.
- Evaluate the present capability of fire dynamics models to make predictions of heat transfer through walls exposed to fires and disseminate guidance to fire model practitioners and the fire investigation community based on the research results.