Gaithersburg, Maryland -- Researchers at the US National Institute of Standards and Technology (NIST) have devised a new method to evaluate the flammability of soft furnishing using a smouldering model after the key California regulation removed an open-flame test.
The Cal-117 flammability standard is the de facto US National regulation and Chemtura has filed a legal challenge to the change.
NIST said its researchers found the current test inhibits smouldering.
Under current standards, two fabric-covered foam pieces are positioned like seat and back cushions on a small solid wood support structure. A NIST-certified and consistently-burning cigarette is placed in the crevice formed by the two pieces.
To pass, the fabric covering must prevent the burning cigarette from igniting the underlying foam so that it does not smoulder on its own even after the cigarette goes out.
The study found that directly placing the test samples on top of the wooden support impedes air flow and inhibits smouldering.
According to the study, ‘Towards a reference polyurethane foam and bench scale test for assessing smouldering in upholstered furniture - Polymer Degradation and Stability’ by Zammarano, Matko, Pitts, Fox and Davis, the current test fails to represent furniture with cushions that rest on air-permeable substrates such as springs or cloth where air is allowed to circulate. These scenarios, said the team, which promotes smouldering.
By introducing gaps between the foam samples and the underlying wood allows air flow and the rate at which smouldering spread in the foam increased up to threefold. It also generated higher smouldering temperatures in the foam which were up to 400oC higher than the Californian test.
The report included guidelines for making a reproducible reference foam with a network-like, open-cell structure controlled sufficiently to minimize differences in cell size. The researchers claim average cell size can be "easily tuned" so that the sample mimics the smouldering intensity observed in foams used in actual upholstered furniture.