Evaluation of Heat Flux Profiles Through Walls in Support of Fire Model Validation

Underwriters Laboratories, Inc. (ULI) proposes to lead a 2-year study to investigate heat transfer through walls exposed to fires, in support of fire model use by fire investigators for the prediction of compartment fire dynamics and fire pattern development. This study will be conducted in collaboration with the Bureau of Alcohol, Tobacco, Firearms and Explosives - Fire Research Laboratory (ATF-FRL). Fire models are presently employed by fire investigators to make predictions of fire dynamics in enclosed volumes within structures. Fire Dynamics Simulator (FDS) is the most prevalent fire model in use by investigators. 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 heat flux to solid surfaces based on radiative and convective exchange with gases that are in contact with the solid surfaces. These predictions are subject to the representation of the heat transfer boundary conditions on walls, which is at the discretion of model practitioners. In practice, fire investigators favor simplified representations of these boundary conditions; for example, isothermal or insulated walls. In addition to the heat flux to walls, a fire model predicts heat transfer through walls (which is directly linked to heat retention and fire dynamics within the compartment). 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. It is the objective of the proposed work to develop a novel dataset to characterize the spatially and temporally varying heat transfer to walls and through walls subjected to fire exposures. This will be achieved by a combined experimental and modelling approach. First, a series of small-scale experiments utilizing a controlled radiative source will be conducted. These data will be suitable for verification of the modelling code developed, and validation of the code relative to a known heat source. Next, a series of full-scale experiments utilizing diffusion fires will be conducted; these will include: a gas burner, liquid fuels, and furnishings. 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 support further development of the fire dynamics model's implementation of boundary heat transfer, and provide a technical basis for the adoption of this approach by fire investigators. ULI proposes to conduct this project with the fire investigation community to inform forensic science practice surrounding the dynamics of compartment fires. Underwriters Laboratories Inc., a 501(c)3 public charity, uses research and standards to continually advance and meet ever-evolving safety needs.