The Chemistry of Fires at the Wildland-Urban Interface (2022) / Chapter Skim
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3 Materials, Combustion, and Emissions in WUI Fires
3 Materials, Combustion, and Emissions in WUI Fires
Pages 31-68
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From page 31... ...
Combustible materials in the WUI have different chemical compositions and densities, and are present in different quantities, than the vegetative biomass combusted in wildland fires. The urban materials and their characteristics present in the WUI impact the combustion conditions, the chemical reaction pathways that dominate during combustion, and the emissions and residue released into the environment.
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From page 32... ...
: Species emitted into the air, water, soil, or other media, from a process; these are sometimes called releases Enclosure fire: A fire contained within a room or compartment inside a building in which oxygen supply is typically constrained, contrary to open fires; these are sometimes called compartment fires Energy content: The amount of energy contained within a mass of fuel; it can be quantified as the higher heat ing value (or gross calorific value) , defined as the amount of heat released from complete combustion of a dry material when the products are returned to 25°C, or the lower heating value (or net calorific value)
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From page 33... ...
: A complex mixture of solid particles and liquid droplets found in the air Pollutant: A chemical or biological substance that harms water, air, or land quality Plume injection parameters: The initial characteristics of a fire plume, including its injection altitude and multi-phase chemical composition Pyrolysis: The thermal decomposition of a combustible material in the absence of molecular oxygen; the term "pyrolysis" sometimes appears in wildland fire literature to represent oxidative pyrolysis Secondary organic aerosol: Organic particulate matter that is formed in the atmosphere from precursor gases Semi-volatile organic compounds (SVOCs) : Organic compounds that, based on their vapor pressure, tend to evaporate from the particle phase within near-field dilution of plumes; SVOCs are of concern because of their abundance in the indoor environment and their ability to accumulate and persist in the human body, the infrastructure of buildings, and environmental dust Smoldering combustion: Combined processes of thermal decomposition and slow, low-temperature, flameless burning of porous solid biomass fuels; sometimes called glowing combustion Toxic product yield: The maximum possible mass of a combustion product generated during combustion, per unit mass of test specimen consumed (typically expressed in units of grams per gram or kilograms per kilogram)
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From page 34... ...
The unique elemental composition of the materials in the urban environment has a direct impact on the combustion chemistry and emissions described in the other sections of this chapter. Table 3-1 summarizes some of the most common building materials and their fire emissions (Blomqvist et al., 2013; Stec, 2017; Stec and Hull, 2010, 2011; FIGURE 3-1 Examples of the types and quantities of materials that can be found in the home.
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From page 35... ...
. Table 3-1 relates the materials in the urban environment to the WUI fire emissions that impact the atmosphere, water and soil, and human health as described in Chapters 4–6.
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From page 36... ...
In addition, the differing energy density in urban areas compared with wildlands may impact combustion conditions, modifying the timing of emissions and the physical nature of the WUI plume in comparison to the plume of a surrounding wildland fire (Trelles and Pagni, 1997)
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From page 37... ...
Flame retardants are increasingly used in exterior and interior structural materials (Lowden and Hull, 2013) , with the types of compounds evolving over time (Popescu and Pfriem, 2019)
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From page 38... ...
. The long lifetimes of houses limit the impact of building codes introduced in the last three decades that mandate the use of ignition-/fire-resistant materials to reduce the risk from wildland fires, leading to regulatory initiatives to promote retrofits for existing homes (State of California, 2019)
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From page 39... ...
. Batteries may be a potent source of compounds of concern that could be liberated during a WUI fire or become a source of toxic combustion products.
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From page 40... ...
Table 3-5 presents examples of fire emissions from car components (Larsson et al., 2017; Lönnermark and Blomqvist, 2006; Willstrand et al., 2020)
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From page 41... ...
examined major trends in consumer products and building materials since 1950 and noted that usage of chemicals of concern varied considerably over time, and that historical usage was difficult to quantify. Many factors may impact material choices in the home, but the identification of health, environmental, or fire hazards were important drivers of usage trends (Weschler, 2009; Cooper et al., 2016)
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From page 42... ...
Researchers have used models and WUI fire observations to better understand how a high structure density in interface WUI areas impacts the rate of spread and the heat release rate of a fire in an urban area in comparison to the surrounding wildland fire. For example, the high density of combustible materials in a structure in comparison to surrounding wildlands increases the duration of the fire and may influence the spread of the fire (Maranghides et al., 2013, 2015)
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From page 43... ...
For example, California building codes such as Chapter 7A of the California State Building Code (State of California, 2016b) or the National Fire Protection Association Standard for Reducing Structure Ignition from Wildland Fire (NFPA, 2018)
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From page 44... ...
The design, maintenance, and use of defensible space for fire protection is improved when neighborhoods are developed more densely and are built with stringent fire-resistant building codes; however, clustering may contribute to high fuel loadings. Wildland fire–resistant construction techniques to harden all the homes in a community can be used to minimize risk and protect homes from wildland fires with minimal additional cost (Quarles and Pohl, 2018)
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From page 45... ...
For solid combustibles, all progress through slow and fast decomposition stages to emit volatile, semi-volatile, and particulate combustibles; wildland, urban, and WUI fires can all experience a variety of different types of combustion conditions, and leave residual char and noncombustible materials. Once in the gas phase, combustible materials can further react in flaming combustion and/or in hot regions without flames that support chemical oxidation reactions producing soot precursors, PAHs, and carbon-containing particulates.
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From page 46... ...
Typically, the characteristic reaction times at temperatures below ~500 K are too long to be relevant to the gas phase of the flame and near-field plume but may be important in terms of condensed phase processes (for example, spontaneous heating to ignition; Jones et al., 2015)
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From page 47... ...
. This holds for all homogeneous, gas-phase oxidations of mixtures of RiH species found in wildland and WUI fires.
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From page 48... ...
. In general, in wildland and WUI fires and their hot plumes, where intermediate and high temperatures are present, the gas-phase oxidation of CO to CO2 will be negligibly slow in mixtures of larger-carbon-number hydrocarbons, oxygenated hydrocarbons, and CO, as long as the following is true: ([CO]
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From page 49... ...
The unknown extent of halogen chemistry in WUI fire plumes limits the applicability to WUI fire plumes of empirical results relating emissions to CO concentrations that are based on wildland fire plumes. The Effect of Nitrogen Species Nitrogen species in flames can be produced at relatively low temperatures from the oxidation of organically bound nitrogen species such as nylon, and from the oxidation of plastics (Chaos et al., 2009)
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From page 50... ...
The unknown extent of nitrogen chemistry limits the applicability to WUI fire plumes of empirical results relating emissions to CO concentrations that are based on wildland fire plumes. Finally, both halogenated and nitrogen-containing WUI plume species that evolve from the combustion of synthetic materials are important to initializing subsequent secondary aerosols and emissions generated in plume dispersion and transport (Cai and Griffin, 2006; Choi et al., 2020; Wang and Ruiz, 2017)
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From page 51... ...
. Different approaches are employed for wildland fires and enclosure fires, but most approaches use empirical relationships between EFs or ERs and some measure of combustion efficiency.
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From page 52... ...
Data from Recent Measurement Campaigns Several intense field campaigns and emerging analyses of the resulting data show an improved ability to define the composition of wildland fire and WUI fire plumes. For example, the National Science Foundation and National Center for Atmospheric Research used a C-130 research aircraft during the 2018 Western Wildfire Experiment for
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From page 53... ...
. These types of field programs undertaken for wildland fires demonstrate the types of advances that can be made in developing emissions estimates; however, data for WUI fires similar to the wildland fire data from WE-CAN and FIREX-AQ are
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From page 54... ...
, consisting of species contained in a liquid or solid atmospheric aerosol, is one of the most important pollutants associated with fires. While PM accounts for only about 2 percent of the carbon emissions from wildland fires (Urbanski, 2014)
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From page 55... ...
Nonetheless these data show important distinctions in urban fire emissions from wildland fire emissions that should be evaluated for WUI fires. Ventilation conditions and the chemical composition of the fuel likely play an important role in the formation of some pollutants like HCl, HF, SOx, and metals, as these species are emitted only if their precursors are present in the original material consumed in the fire.
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From page 56... ...
Blomqvist, 2005 Scrap tire 114 2.2 0.47 Lemieux and material Ryan, 1993 Vehicle 63 1.6 13 64 3.0 1.1 820 2.1 56 Lönnermark and (medium-class Blomqvist, 2006 1998 car) Electrical wiring 2.3–22.5 48–53 0.06–1.47 0.1–0.6 0.02–2.28 0.19–60.94 Andersson et al., 2004, 2005; Simonson et al., 2001 Simulated room 32–48 1.3–2.2 0.5–1.3 0.17–1.09 0.04–0.20 0.36–1.37 Blomqvist contents et al., 2004 Sofa with flame 24–41 0.9–4.5 0.9–1.4 0.10–1.34 0.5 2.6–25 0.003–1.02 0.2–13.3 Andersson retardant in et al., 2003 room Simulated room 14–51 3.5–15 6–18 45–282 Gann et al., 2010 with sofa Chemicals in 8–293 0.1–36.3 0.8–44.7 77.8–141 7–76 0.04–7.1 Månsson et al., storage room 1996
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From page 57... ...
Despite this variability, these test methods allow the collection of data that examine the dependence of EFs for commonly used materials, and mixtures of commonly used materials, on combustion conditions. These data can serve as a starting point for more extensive examination of WUI fire emissions under realistic combustion conditions.
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From page 58... ...
Y Y Post-flashover N N ? Y Y Advantages Widely available; Modification to widely Simple and low cost Designed for smoke Able to replicate high CO currently used for toxicity used standard test; toxicity assessment; ideal yields for under-ventilated assessment in mass measures flammability as for linear or homogeneous flaming transport industries well as toxicity products; correlates with large-scale tests for all conditions Disadvantages Poor interlaboratory No standard equipment Conditions not related Interlaboratory Expensive; not widely used; reproducibility; unable exists; unable to go above to fire stages; does not reproducibility not proven capabilities insufficiently to force under-ventilated 50 kW/m2; toxic product distinguish between for layered materials; demonstrated flaming; fire stage yields do not correlate flaming and non-flaming; separate assessment of unknown; sample probe to large-scale fire tests; limited volume of effluent flammability required can miss toxic plume equivalence ratio only for analysis known after test SOURCE: Stec and Hull, 2010.
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From page 59... ...
Finding: Limited data exist on emission factors and the sources of uncertainty for WUI fires; no studies of single- or multiple-dwelling, full-scale structures, with realistic contents and realistic WUI fire conditions (e.g., strong winds) , have reported emission factors or yields.
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From page 60... ...
and other wildland fire fuels as they generate fire plumes need to be modeled mechanistically and explored experimentally at bench, laboratory, and larger scales. Research need: Experimental and modeling investigations of WUI fire plume compositions should be used to develop emission factors and chemical fingerprints for WUI fire emissions.
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From page 61... ...
2014. "Wildland Fire Ash: Production, Composition and Eco-hydro-geomorphic Effects." Earth-Science Reviews 130: 103–127.
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From page 62... ...
2015. "Winter Grazing Can Reduce Wildfire Size, Intensity and Behaviour in a Shrub-Grassland." International Journal of Wildland Fire 25: 191–199.
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From page 63... ...
2019. "Speciated and Total Emission Factors of Particulate Organics from Burning Western US Wildland Fuels and Their Dependence on Combustion Efficiency." Atmospheric Chemistry and Physics 19 (2)
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From page 64... ...
2014. "Wildland Fire Emissions, Carbon, and Climate: Modeling Fuel Consumption." Forest Ecology and Management 317.
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From page 65... ...
2020. "Wildland Fire Emission Factors in North America: Synthesis of Existing Data, Measurement Needs and Management Applications." International Journal of Wildland Fire 29 (2)
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From page 66... ...
2014. "Wildland Fire Emissions, Carbon, and Climate: Emission Factors." Forest Ecology and Management 317.
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From page 67... ...
2021. "Boreal Forest Fire CO and CH4 Emission Factors Derived from Tower Observations in Alaska during the Extreme Fire Season of 2015." Atmospheric Chemistry and Physics 21 (11)
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