Deriving a Mixture of Combustible Materials Burned in American Homes at the Wildland-Urban Interface for Exposure and Toxicity Studies
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Wildfires in the Wildland-Urban Interface (WUI) are an increasing concern, with approximately 39% of homes in the U.S. now located in the WUI and at elevated risk of burning during wildfires. WUI wildfires are unique as they emit a cocktail of chemicals from the combustion of anthropogenic materials in affected homes, including chemicals that may be absent in biomass-only wildland wildfires. There is currently limited knowledge on the mixture of combustible materials in homes in WUI regions. If better defined, such mixtures could be used to characterize exposure chemistries and toxicological impacts of WUI-relevant smoke exposures. To address this rate-limiting step in wildfire research, the current study set out to integrate all combustible materials in an average American WUI home from structural materials, plumbing, wiring, and furnishings to the laundry and chemicals under the sink for use in upcoming exposure and toxicology studies. Relevant data were first gathered across peer-reviewed articles, census data, fire damage inspections, industrial suppliers, retail companies, and gray literature searches. Structural calculations were based on the average American household, a 2,016 sq. ft. single family home of four bedrooms, with structural and siding materials prioritized to model homes burned in WUI wildfires in California, due to the high incidence of wildfire events in that geographic region. The main combustible component amounts for furniture and appliances were determined from fire emissions data and lifecycle inventories. All combustible materials were then sorted and summed by type of material. We found that the total combustible mass of an average American family home was around 36,600 kilograms. Structural combustible materials alone were comprised of 81.75% wood, 3.25% polyurethane foam, 2.07% plastic, and 11.92% petroleum-based products . Furnishing and appliances were composed of 76.73% wood materials, 6.89% polyurethane foam, 7.67% plastics, 5.12% natural textiles, 0.21% assorted liquids, and 0.93% food. Collectively, this list of materials can now serve as a foundational mixture of home materials to address multiple research goals including the characterization of exposures, health effects, and mechanistic toxicology related to wildfires occurring at the growing WUI.