Heat Transfer from Structure Fires

Heat transfer from structure fires to other targets such as nearby structures, vehicles or responding firefighters has critical implications for establishing proper control measures, protecting firefighters, and supporting code development in urban and wildland urban interface (WUI) environments. This project promotes improved fire safety using collaborative research and, ultimately, data sharing for homeowners, home builders, community planners, code and standard organizations, and firefighting personal protective equipment (PPE) manufacturers. The resulting data will allow for quantification of building-to-building fire spread mechanisms, which in turn may inform control measures to reduce this risk. This data may also help guide WUI firefighter PPE standards, selection, and maintenance.

The first set of experiments related to this project, conducted at UL's Northbrook, IL facility in 2021, was divided into three phases:

• Phase I focused on radiant heat transfer to exterior building materials. These experiments examined the ignition potential and behavior of various building material samples (roofing, decking, siding, windows) over a range of heat flux exposures. A heptane spray burner oriented under an oxygen consumption calorimeter was utilized as the fire source for these experiments.
• Phase II incorporated findings generated in Phase I to inform the construction of an 8 ft x 12 ft x 8 ft compartment with a false façade attached. The façade was equipped with three different cladding assemblies: fiber cement lap siding, T1-11 plywood siding, and vinyl siding over expanded polystyrene insulation. These experiments examined the contribution of different siding types to the overall exposure from the compartment fire. The compartment contained two sofas on top of carpet and padding and two layers of plywood along the walls and ceiling. Each experiment began with the ignition of one of the sofas. The fire was allowed to spread throughout the compartment and to the exterior façade and then transition through flashover to simulate fire spread from the interior to the exterior of a structure. The heat release rate profile of each fire was obtained via oxygen consumption calorimetry, and heat flux gauges were positioned at various distances from the structure to characterize the heat flux exposure from each fire.
• Phase III examined the potential for fire spread from a post-flashover compartment fire to a nearby target structure. The compartment and façade configuration characterized in Phase II was utilized as the source fire during these experiments. The target structure consisted of a false façade wall assembly with two windows. Based on the results from Phases I and II, a 16 ft separation distance between the source and target was implemented. Experiments were conducted to examine the impact of different cladding assemblies installed on the target wall as well as the impact of different intermediate fuels between the structures (shed, car, deck) on the potential for fire spread to the target structure. Additionally, the heat transfer through and failure of the windows was quantified during these experiments.

Context

The work included in this scope will inform future full-scale field experiments in acquired structures and, ultimately, will help improve fire safety for communities at risk of fires at the WUI. The largest stakeholder impact will be for urban fire departments that also protect WUI regions. Results will be useful for standards organizations, fire modelers, fire behavior analysts, firefighting PPE manufactures and training organizations.

Objectives

This project will further the understanding of risk generated from residential structure fire related to igniting nearby structures and generating thermal injuries in responding firefighters. Specific objectives of this project are to:

• Characterize ignition potential of various construction materials at different exposure intensities from a well-characterized fire source
• Characterize radiative exposure from various siding configurations of mock-up structures consisting of a single room and false façade
• Characterize potential for structure-to-structure fire spread due to radiative exposure from a post-flashover compartment fire
• Evaluate the effect of various “intermediate” fuels at aiding structure-to-structure flame spread
• Examine the failure mechanisms of various types of window glazings and frame constructions due to radiative heating from post-flashover compartment fires