Heat Transfer and Fire Damage Patterns on Walls for Fire Model Validation

Fire investigators and researchers leverage fire models to predict fire growth and fire pattern development. These fire models incorporate simplifying assumptions in their representation of heat transfer through walls, but the impact of these assumptions on model predictions of fire exposures and fire damage patterns is not well understood. This study aims to create a novel dataset that will support the development and validation of these models, and by extension, their adoption as tools for fire investigation.

UL’s Fire Safety Research Institute (FSRI), in collaboration with the Bureau of Alcohol, Tobacco, Firearms and Explosives - Fire Research Laboratory (ATF-FRL), led this novel research endeavor. Experiments were conducted in which freestanding walls were subjected to exposure from controlled fire sources, including gas burners, liquid fuels, and furnishings. Experiments were conducted at the ATF-FRL in Ammendale, MD. The experiments addressed three validation spaces: field heat flux from a fire to a wall, heat transfer through fire-exposed walls, and fire damage patterns arising on fire-exposed walls. The data acquired from these experiments is available in a public repository, which may be accessed at the following link: https://doi.org/10.5281/zenodo.10543089. The results of this work directly address fire and arson investigation research issues and support further development of the use of fire models by investigators.  The technical report for this study is in review, and the project page will be updated upon release.

Context 

Fire models are presently employed by fire investigators to make predictions of fire dynamics 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, and are the driving factor for thermally induced fire damage.

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. Presently, Fire Dynamics Simulator (FDS) can represent in-depth heat transfer through walls, but transverse heat transfer prediction is still in a preliminary development stage. Furthermore, limited suitable data exists for validation of heat transfer through walls exposed to fires. Mass loss and discoloration fire effects are directly related to the heat transfer and thermal decomposition of walls, therefore it is crucial that the representation of transverse heat transfer in walls in fire models be validated to ensure that fire investigators can produce accurate simulations and reconstructions with these tools.

In the present study, experiments were performed on three types of walls to address the current needs in this validation space:

1. Steel sheet (304 stainless steel, 0.793 mm thick, coated in high-emissivity high-temperature paint on both sides). This wall type was used to support the heat flux validation objective. By combining measurements of gas temperature near the wall with surface temperatures obtained using infrared thermography, estimates of the incident heat flux to the wall were produced.
2. Calcium silicate board (BNZ Marinite I, 12.7 mm thick). This wall type was used to support the heat transfer validation objective. Since calcium silicate board is a noncombustible material with well-characterized thermophysical properties at elevated temperatures, measurements of surface temperature may be used to validate transverse heat transfer in a fire model without the need to account for reaction energetics.
3. Gypsum wallboard (USG Sheetrock Ultralight, 12.7 mm thick, coated in white latex paint on the exposed side). This wall type was used to support the fire damage patterns validation objective. Two types of fire effects were considered: 1) discoloration and charring of the painted paper facing of the gypsum wallboard; and 2) mass loss of the gypsum wallboard (which is related to the calcination of the core material). In addition to temperature and heat flux measurements, high resolution photographs of fire patterns were recorded, and the mass of the wall was measured by cutting the wall into smaller samples and measuring the mass of each individual sample, thereby generating a field measurement.

Objectives 

The purpose of this study is to conduct a series of experiments to obtain data that addresses three validation spaces: 1) thermal exposure to walls from fires; 2) heat transfer within walls exposed to fires; and 3) fire damage patterns arising on walls exposed to fires. Specific objectives are to:

• Develop a novel dataset that may be used to validate predictions of thermal exposures and heat transfer in present and future fire models. The primary measurements to support this objective include: surface temperature of walls, gas temperature near walls, and heat flux to walls subjected to fire exposures.
• Develop a novel dataset that may be used to validate predictions of fire damage patterns, specifically pertaining to discoloration and mass loss fire effects arising on gypsum wallboard from non-impinging fires. The primary measurements to support this objective include: photographs of walls, mass loss of walls, surface temperature of walls, and heat flux to walls subjected to fire exposures. 
• Produce a set of thermophysical properties for the materials that were used in this study (lightweight gypsum wallboard, calcium silicate board, and stainless steel). This property data will be directly used in future exercises in model validation.

Research Output

This public dataset includes raw measurement data, processed data , and video recordings that may be used for future analysis and validation studies.

Access the data repository

Technical Panel

• Michael Browne, City of Philadelphia Fire Department
• Donald A. Brucker, Allegheny County Fire Marshal's Office
• Barry Burnside, Mississippi State Fire Academy
• Kevin Connelly, Bureau of Alcohol, Tobacco, Firearms and Explosives
• Andrew Cox, Bureau of Alcohol, Tobacco, Firearms and Explosives
• Jason Fedoriw, City of Winnipeg Fire Paramedic Service
• Jason Floyd, Underwriters Laboratories Inc., Fire Safety Research Institute
• Timothy Gammage, II, City of Phoenix Fire Department
• Shijin Kozhumal, Eastern Kentucky University
• Robert Mcloud, City of Los Angeles Fire Department
• Randy Watson, S-E-A Limited
• Marcos Vanella, National Institute of Standards and Technology

This research was supported by Award No. 15PNIJ-21-GG-04167-RESS, from the National Institute of Justice, Office of Justice Programs, U.S. Department of Justice. The opinions, findings, and conclusions or recommendations expressed in this publication / program / exhibition are those of the author(s) and do not necessarily reflect those of the Department of Justice.