Smoldering Propensity in Upholstered Furniture: Effects of Mockup Configuration and Foam Thickness

Reduced-scale mock-ups had been developed to assess and regulate smoldering ignition resistance of residential upholstered furniture (RUF). However, there are limited data available on the effects of the mock-up test configuration and foam thickness on smoldering propensity and how they affect the degree of correlation with full-scale performance. In this work, the smoldering propensity for standard mock-ups (SMs, where the foam is in contact with a support frame) and modified mock-ups (MMs, where a 12.7 ± 1 mm air gap is introduced between the foam and the frame), were computationally simulated and compared to experimental results. The model results indicated that the buoyant airflow at the bottom of the mock-up was enhanced in the MM, giving rise to a higher foam oxidation rate, a higher peak smoldering temperature and higher mass loss rate as compared to the SM, and; that oxygen supply was dominated by diffusion-driven transport from the boundaries in proximity of the heating source in the SM. Additionally, the effects of foam thickness on smoldering propensity in the SM and MM were studied with foam thicknesses of 51 mm (2 inch) and 76 mm (3 inch). With an increase in the foam thickness, the smoldering propensity is weakened in the MM but enhanced in the SM. The model was able to predict the ranking of smoldering propensity quantified by the mass loss (ML) in experiments: $\text{ML}{\left(\text{t}\right)}_{\text{SM}2}<\text{ML}{\left(\text{t}\right)}_{\text{SM3}}<\text{ML}{\left(\text{t}\right)}_{\text{MM}3}<\text{ML}{\left(\text{t}\right)}_{\text{MM}2}$ , where subscripts of SM2 and SM3 refer to cases with 51 mm and 76 mm-thick foam in the SM, respectively, likewise, MM2 and MM3 refer to cases with 51 mm and 76 mm-thick foam in the MM, respectively. These results indicate that reduced-scale tests based on SM2 tends to underpredict smoldering propensity and that MM2 may offer a near-worst-case scenario, useful to identify the upholstery materials that prevent most smoldering ignitions independent of the construction and geometry of the actual furniture.