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A Qualitative Description of Enclosure Fires
Published in Björn Karlsson, James G. Quintiere, Nils Johansson, Björn Karlsson, Enclosure Fire Dynamics, 2022
Björn Karlsson, James G. Quintiere
Combustion: In the context of enclosure fires, there are basically two different types of combustion; smoldering and flaming. Smoldering combustion is a combustion process without flames that produces a certain amount of unburned combustible gases, soot, and other combustion products but very little heat. A small ignition source can lead to smoldering combustion of fuels where a larger ignition source instead would result in flaming combustion. The likelihood of smoldering combustion increases if ventilation is limited. Depending on the scenario, smoldering combustion can lead to flaming combustion if the flow rate of combustible gases from the fuel surface is increased or if ventilation is increased. A gas, liquid, or solid that produces flammable gases can undergo flaming combustion. External heating is required to evaporate or pyrolyze enough combustibles in a solid or liquid in order to ignite it. The flame generally heats the liquid or solid to such a degree that a sufficient amount of combustible gas to sustain the flame is produced.
Flammability
Published in Asim Kumar Roy Choudhury, Flame Retardants for Textile Materials, 2020
As discussed in Chapter 1, Smoldering is the slow, low-temperature, flameless form of combustion, sustained by the heat evolved when oxygen directly attacks the surface of a condensed-phase fuel. Many solid materials can sustain a smoldering reaction, including coal, cellulose, wood, tobacco, synthetic foams, charring polymers including polyurethane foam, and some types of dust. Common examples of smoldering phenomena are the initiation of residential fires on upholstered furniture by weak heat sources and the persistent combustion of biomass behind the flaming front of wildfires. To understand the hazards posed by the upholstered fabrics, the development of the small-scale composite test BS 5852 represented a remarkable development of realistic model tests that accurately indicate the ignition behavior of full-scale products of complex structure. This is also known as Smolder Ignition Testing of Upholstery Fabrics. The test is simple to use, cost-effective, and reproducible; it may be conducted in the manufacturing environment, as well as in formal test laboratory environments.
Fire Testing for the Development of Flame Retardant Polymeric Materials
Published in Yuan Hu, Xin Wang, Flame Retardant Polymeric Materials, 2019
Bernhard Schartel, Katharina Kebelmann
Another important fire hazard is smoldering (Ohlemiller 1985; Babrauskas 2003; Rein 2016), characterized by heterogeneous, exothermic, flameless combustion on the surface of a solid porous fuel. It propagates by conduction, convection, and radiation of the heat released during the reaction. The typical propagation rates of smoldering are lower than flame spread rates. Several materials can sustain smoldering, such as cellulose, wood, cotton, but also synthetic foams. Weaker ignition sources, such as cigarettes, hot materials, or glowing wires, typically lead to smoldering. Furthermore, smoldering can be the first stage of a fire, acting as kind of ignition source for flaming combustion. Thus, it provides a pathway to flaming for heat sources too weak to produce a flame directly. Smoldering fires are believed to be one of the leading causes of fires in residential areas. Smoldering typically produces much higher yields of toxic gases and smoke. Since smoldering is based on exothermic thermo-oxidative decomposition rather than endothermic pyrolysis, different materials and different flame retardant approaches are needed as well as specific smoldering fire tests.
Smoldering of Storage Rice: Effect of Moldy Degree and Moisture Content
Published in Combustion Science and Technology, 2022
Jingwen Wang, Weiyi Xing, Xinyan Huang, Xin Jin, Heng Yu, Junling Wang, Lei Song, Wenru Zeng, Yuan Hu
Smoldering is a slow, flameless, low-temperature form of combustion which generates when the oxygen attacks the surface of the condensed phase fuel (Rein 2014). Generally, the energy required for initiating a smoldering fire is lower (Lin, Sun, Huang 2019), and most of the smoldering fires start by self-ignition. The dynamics of smoldering combustion has been studied for a wide range of fuels, such as piled dusts (Palmer 1957; Wu et al. 2015), polyurethane foam (Torero and Fernandezpello 1996), cotton (Hagen et al. 2011; Xie et al. 2020b), and peat (Huang and Rein 2016b, 2019). Smoldering includes three main physicochemical processes, drying, degradation, and char oxidation. The drying process is a robust endothermic course (Yang et al. 2019). The degradation process not only includes the endothermic pyrolysis process but also contains an exothermic oxidation process, depending on the oxygen supply (Huang and Rein 2016b). The smoldering-to-flame (StF) transition is a widely observed phenomenon (Huang and Gao 2020; Santoso et al. 2019), which was also observed in rice (Xie, Gao, Huang 2020a). The moisture content (MC) plays a vital role in the smoldering behaviors, such as the ignition and extinction limit (Huang and Rein 2016a) and the propensity of StF transition (Santoso et al. 2019).
Smouldering combustion in cellulose and hemicellulose mixtures: Examining the roles of density, fuel composition, oxygen concentration, and moisture content
Published in Combustion Theory and Modelling, 2022
W. Jayani Jayasuriya, Tejas Chandrashekhar Mulky, Kyle E. Niemeyer
Compared with flaming combustion, smouldering can persist longer and under conditions that would extinguish flames. This characteristic of smouldering combustion allows it to penetrate deeper into the soil compared with flaming combustion, which generally causes shallower burns [4,5]. Thus, smouldering can actually cause greater destruction in affected ecosystems. Smouldering also emits a large number of pollutants such as carbon monoxide (CO), volatile organic compounds, polycyclic aromatic hydrocarbons, and particulate matter, since it operates at lower temperatures than flaming combustion. Smouldering occurs most commonly in porous fuels like peat, woody fuels, muck, and forest duff [2]. Such fuels are abundant in forests, making it important to understand smouldering combustion in these types of fuels. Woody fuels and biomass generally consist of cellulose, hemicellulose, and lignin in varying proportions, which pyrolyse at different temperatures as shown by Ranzi et al. [6,7]. Yang et al. [8] found that, among the three, hemicellulose pyrolyses earliest, at temperatures of 220 C– 315C, cellulose undergoes pyrolysis at temperatures of 315 C– 400C, and finally lignin pyrolyses at temperatures of 150 C– 900C. Anca-Couce et al. [9] showed similar trends in pyrolysis of these three constituents in their thermogravimetric analysis of pine wood. In addition, these fuel constituents produce different amounts of char [10–12]. Smouldering combustion is generally modelled using a set of global reactions, which include fuel pyrolysis and char oxidation [9,13]. Differences in fuel composition thus may lead to significant differences in smouldering characteristics. This motivates our detailed study looking into how varying fuel composition affects smouldering characteristics.