An experimental setup for observation of smoldering‐to‐flaming transition on flexible foam/fabric assemblies

Abstract

SummaryFires that involve upholstered furniture frequently begin as a smoldering combustion and, with time, transition to a flaming combustion, which sharply increases the level of hazard. Therefore, understanding how the compositions of the primary flammable components of the furniture, ie, flexible foam and upholstery fabric, affect this transition is important for fire safety considerations. In the current study, an experiment was designed to observe this transition using a sample consisting of 30 × 15 × 6 cm 3 rectangular foam block covered with 30 × 15 cm 2 piece of fabric. For a representative system of 1.8 lb/ft 3 (29 kg/m 3 ) flexible polyurethane foam and 11 oz (0.37 kg/m 2 ) cotton fabric, 0.69 transition probability was measured. This probability decreased by a factor of 4 when a small amount of phosphorusbased flame retardant, Fyrol® HF-9, was added to the foam. The transition to flaming was speculated to be associated with the formation of adjacent pyrolysis and smoldering regions within the foam. The pyrolysis region, dominated by anaerobic decomposition, provided gaseous fuel, the ignition of which resulted in the transition. The smoldering region, dominated by oxidation reactions at the solid-gas interface, generated the heat necessary to maintain the pyrolysis process and ignite the gaseous fuel.

Review of the Transition From Smouldering to Flaming Combustion in Wildfires

“…† Computationally predicted by Dodd et al (2012). result is in agreement with recent findings by Stoliarov et al (2017), who performed a series of experiments of smouldering PU foam under natural convection with an adjustable vertical channel gap between the front face of the PU foam and a thermal insulation plate ( Figure 6A). With a large gap, the oxygen supply was adequate, and smouldering was the dominant reaction ( Figure 6B).…”

“…The external supply of heat flux minimises heat loss and assists the fuel heating required for self-sustained smouldering progress and pyrolyzate production. Assistive fuel heating can be in the form of external heat flux such as embers in the case of WUI fires or from pertinent features of the fuel configuration such as when heat loss is minimised by the possible presence of radiation exchange between smouldering surfaces, i.e., smouldering at the fuel crevice or smouldering in U-shaped fuels (Alexopoulos and Drysdale, 1988;Ohlemiller, 1991;Ogle and Schumacher, 1998;Manzello et al, 2008Manzello et al, , 2009Manzello et al, , 2012Stoliarov et al, 2017;Hakes et al, 2018).…”

“…Vertical channel formation in smouldering at a crevice leads to radiation exchange between smouldering char surfaces and the chimney effect, increasing airflow from the buoyant flow (Ogle and Schumacher, 1998;Manzello et al, 2008;Stoliarov et al, 2017). The radiation exchange between smouldering surfaces leads to more effective heating, while buoyant flow increases the oxygen supply to smouldering fronts.…”

“…In all investigated consolidated WUI fuels (Table 2), the StF transition occurred only if the smouldering sample was assisted with heat insulation, heated boundaries, and increased ambient oxygen concentration (Ortiz-Molina et al, 1979;Tse et al, 1996;Bar-Ilan et al, 2005;Putzeys et al, 2006Putzeys et al, , 2007Putzeys et al, , 2008Chang et al, 2011). However, this finding is not the case when there is a radiation exchange between smouldering char surfaces (Alexopoulos and Drysdale, 1988;Ohlemiller, 1991;Stoliarov et al, 2017). In this case, the critical airflow velocity of the StF transition can be lower than 1 m/s, even without assistive external heating and elevated ambient oxygen concentration.…”

Effect of particle granularity on smoldering fire in wood chips made from wood waste: An experimental study

“…For instance, increased levels of oxygen or airflow can strongly induce the transition to flaming, caused by a spontaneous gas‐phase ignition or induced by glowing embers . Transition from smoldering to flaming fire has previously been only sporadically reported, but has more recently been investigated more systematically …”