Towards a reference polyurethane foam and bench scale test for assessing smoldering in upholstered furniture

Smoldering poses a severe fire hazard due to the potentially lethal amount of toxic carbon monoxide released, and the possible transition from smoldering to flaming (eventually leading to rapid fire growth and flash-over) with ignition 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 behavior. However, the preparation of a reference foam has proven to be a challenging task, and the bench-scale tests currently in use may underestimate smoldering in actual furniture. The aim of this work is to provide guidance for the selection/development of: (i) a reference flexible polyurethane foam with reproducible and well-characterized smoldering behavior, and; (ii) the development of a bench-scale smoldering test capable of identifying the upholstery materials (e.g., fabric, filling/padding, barrier, welt cord) that most likely prevent smoldering ignition in actual furniture. In the first part of this 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 an adjustable smoldering intensity as a function of their average cell size. In the second part of this paper, a bench-scale smoldering test (currently employed in a number of test procedures and standards) is redesigned in such a way that the buoyant airflow within the foam is enhanced. Up to a three-fold increase in the rate of smoldering propagation and 400 degrees C increase in smoldering temperature is observed in the modified test as compared to the current tests. Transition to flaming was observed, only in the modified test, when an external enclosure was used. The modified test 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. Published by Elsevier Ltd.