Towards a Reference Polyurethane Foam and Bench Scale Test for Assessing Smoldering in Upholstered Furniture
Mauro Zammarano, Szabolcs Matko, William M. Pitts, Douglas M. Fox, Rick D. Davis
Smoldering poses a severe fire hazard due to the potentially lethal amount of toxic carbon monoxide released, and the possibility to reach flashover (through transition from smoldering to flaming) with heat sources otherwise too weak to directly induce flaming. Smoldering in residential-furniture upholstery materials can be assessed at a bench-scale by using reference materials with consistent smoldering. However, the preparation of a reference foam has proven to be a challenging task and the bench-scale tests, currently in use, might underestimate smoldering in the real furniture. The aim of this work is to provide guidelines for the selection/development of: (i) a reference flexible polyurethane foam with a reproducible and well-characterized smoldering; and (ii) the development of a bench-scale smoldering test able to identify the upholstery materials (e.g., fabric, filling/padding, barrier, welt cord) that may prevent severe smoldering in real furniture. In the first part of the paper, the impact of foam morphology on smoldering is discussed. It is shown how reticulated flexible polyurethane foams, possibly filled with carbon black, can be exploited as reference foam materials. Their fully open cell structure ensures consistent air permeability with a tunable smoldering intensity as a function of their cell size. In the second part of the paper, a standard bench-scale smoldering test is redesigned in such a way that the buoyant air flow within the foam is enhanced. Up to a 3-fold increase in the rate of smoldering propagation and 400 C in smoldering temperature have been observed in the modified test as compared to the standard test; these increases are sufficient to induce transition to flaming in two out of three types of flexible polyurethane foams tested in this study. The modified test may offer a close to worst case scenario, useful to identify the upholstery materials that prevent smoldering ignition, independently of the furniture construction.