Residential Structure-Resolved Fuel Loading for Emissions Estimation in a Wildland–Urban Interface Fire

Hanyang Li , Ehsan Goftari, Kamden Conley, David Goldstein, Andreas Lundberg, Luca Carmignani, Neil E. Klepeis

Fuels in the Wildland-Urban Interface (WUI) include a variety of anthropogenic materials connected to historical and socio-economic backgrounds in addition to biomass. Yet current emission inventories rely on uniform fuel loading factors (FLFs) that treat all structures as compositionally identical. In this study, we develop a structure-resolved combustible fuel inventory for ~5,400 single-family homes destroyed in the January 2025 Eaton Fire (Los Angeles, California) by linking CAL FIRE Damage Inspection records and county assessor data with era-specific material quantities derived from six architectural plans and two published residential fuel inventories. A component-based model assigns era-specific rates for structural lumber, sheathing, insulation, and minor combustibles, adjusted for foundation type, story count, roof covering, and cladding. The aggregate structural combustible mass is approximately 79,000 tons, with a mean FLF of 92 kg/m². This estimate is 65% lower than the 151.6 kg/m² uniform FLF applied in prior work, with overestimation ranging from 48% for post-2000 homes to 80% for the 1960 to 1979 cohort. This bias has two reinforcing sources. First, the material inventory used to derive the uniform FLF reports approximately twice the wood mass obtained from independent building plan analyses, including both the architectural plans evaluated here and prior published estimates for similar homes. Second, this elevated rate is applied uniformly to all structures without differentiation by construction era or regional building practice. In the Eaton Fire, 88% of the destroyed homes were built before 1960, when Southern California construction practices typically incorporated less sheathing and insulation than are required under modern building standards. Sensitivity analyses indicate that reconstruction with modern construction practices would increase total structural combustible mass by approximately 5.5%, as the greater material intensity of modern wood-frame construction outweighs reductions from non-combustible roof coverings and slab-on-grade foundations. Because fuel load estimates propagate directly into pollutant-specific emission factors and air quality models, the structure-resolved inventory presented here provides a more accurate foundation for exposure assessment and public health analysis of WUI fire events.