When Is It Safe to Return to My Home After Contamination from Wildland-Urban Interface (WUI) Fire Smoke?

MICHAEL LINK, Nathan Lima, Aika Davis, Thomas Cleary, Rileigh Robertson, Ryan Falkenstein-Smith, Rodney Bryant, Steven Emmerich, Dustin Poppendieck, National Institute of Standards and Technology

     Abstract Number: 466
     Working Group: Burning Questions of Aerosol Emissions, Chemistry, and Impacts from Wildland-Urban Interface (WUI) Fires

Abstract
At the wildland-urban interface (WUI) structural fires can generate smoke enriched with toxic chemicals from the burning of mixed fuels such as lumber, polyvinyl chloride pipe, carpet, electrical wire, etc. These chemicals, emitted as gases and adsorbed to particulate matter, can infiltrate nearby buildings exposing occupants to undesirable contaminants. Smoke chemicals can affect indoor air quality in the short-term or in the long-term, through deposition on surfaces and subsequent development of surface-gas equilibria. Thus, the different chemical properties (e.g., volatility, polarity) associated with the suite of chemicals emitted from structural fires will persist indoors, after infiltration from the outdoors, on different timescales. Non-methane organic gases (NMOGs) are an important class of emissions that are likely to impact indoor air quality from WUI fires quantified extensively from biomass burning, but few measurements of these chemicals exist from structural fires.

We investigated the effects on indoor air quality from a simulated WUI fire by burning surrogates for residential building structures outside of a test house on NIST campus and measuring the smoke infiltrated into the house. We first performed a detailed chemical characterization of NMOG emitted from the burning of surrogates under the National Fire Research Laboratory's 0.5 MW calorimeter and quantified over 200 NMOG emission factors (in grams of gas per kg of fuel burned). Informed by these measured chemical profiles from the burning of the surrogates under the calorimeter, we tracked how much of the NMOGs infiltrated the test house after burning the surrogates outside. We then quantified the timescales that it took for different NMOGs to evacuate the house over a month and a half of subsequent burn experiments. We find that NMOGs that are either semi-volatile and/or have a propensity for partitioning into from the air into organic films (e.g., naphthalene) persisted indoors after burn experiments and created elevated gas-phase concentrations by up to and order of magnitude above background concentrations. Additionally, we find that the timescales of NMOG evacuation we measured from the test house were comparable to those measured by another study from a residential building affected by the Marshall Fire in Colorado in 2021. After two months nearly all NMOGs originating from the surrogate burns were at concentrations typical of the test house background. However, non-volatile chemicals deposited within the carpet and on surfaces likely continue to be sources affecting indoor air quality.