California Air Resources Board

What was done?

On July 10, 2024, the first Structure Separation Experiment burning full-scale Auxiliary Dwelling Units (ADUs) was conducted at the Insurance Institute for Business & Home Safety (IBHS) Research Center in Richburg, South Carolina. A fully furnished ADU was ignited in this demonstration to test the impacts of heat and ember exposure from an ADU downwind to a “hardened” home built to California’s WUI building code and spaced 30 feet away. IBHS is conducting the Wind-Driven Building-to-Building Fire Spread Research project to determine the proper building-to-building separation. IBHS has partnered with CalFire and UC Berkeley (UCB) to conduct this multi-phase, multi-year test series of structure separation burn experiments. The ultimate goal of IBHS research is to determine critical pathways of building-to-building fire spread and how that can be applied to help home and business owners reduce their wildfire risk.

The UCB team measured emissions using drone sampling platforms during controlled structure burns. IBHS conducted extensive measurements on the ground, which will provide fire physics and behavior data. IBHS videotaped the first structure separation burn, which took about 4 hours. A shortened video with highlights created by IBHS is available here. Please note that about 7 minutes into the video, you will see a drone used to capture emissions from the smoke plume over the burning ADU unit. A PowerPoint file was assembled with screenshots from the IBHS video and UCB team photographs.

Accessory Dwelling Units (ADU) Burn Specification:

• A 625-square-foot home is typical of an accessory dwelling unit and outfitted with all the regular furniture.
• It was built following Chapter 7A of the California Building Code. Under this Code, a structure's exterior must remain ember-resistant and flame-resistant during wildfires.
• It has an open floor plan with a kitchen, laundry room, bedroom, bathroom, and office room.
• An adjacent full-size home was placed as a target 30 feet downwind to measure heat transfer between structures and assess whether ignition could occur to an adjacent building built to CBC Chp 7A.

Additional Testing

In this structure burn experiment, the ADUs were fully loaded with furniture and standard building materials. The UCB Team has already started studying several of these materials in the laboratory. Three more burns are planned in 2024, with the remainder continuing in early 2025. The UCB team will obtain all building materials and concurrently test them in the laboratory to compare each component's full-scale emissions and laboratory emissions (e.g., siding, couch, shingles, etc.).

Related Information:

• Shortened structure separation burn video from IBHS.
• Learn more about structure separation experiments at IBHS here.
• Recent publication from research contract 22RD004: Wang et al., Flaming vs. smoldering emissions of pine needles under limited oxygen and fuel moisture conditions. Proceedings of the Combustion Institute Volume 40, Issues 1–4, 2024, 105616.  
  • This article describes a detailed analysis of laboratory-scale and steady-state emissions of vegetation burned under varied conditions. It focuses on non-ideal, limited oxygen conditions closely mimicking real wildfire situations. Examining a range of oxygen concentrations from zero (pure pyrolysis condition) to 21 % (ambient condition) revealed a significant correlation between emission factors of various species and oxygen concentrations, external heat fluxes, and fuel moisture contents.  This study provides important validation data that are repeatable in the laboratory and can be expanded upon to other fuels and measurement techniques in the future. It also has important implications for efforts to model emissions from wildland fuels, as a broader understanding of the processes driving emissions production considering variations in the fuel moisture content, oxygen supply concentration, and combustion modes is needed to better inform future emission management and wildfire management strategies.

Return to 22RD004 contract page