Evaluating smoldering behavior of fire-blocking barrier fabrics

This study reports on the smoldering propensity of commercially available barrier fabrics in a small-scale mock-up configuration. Most barrier fabrics are smolder resistant when tested alone over a standard flexible polyurethane foam. However, when covered with a smolder-prone cover fabric, most barrier fabrics failed the smoldering ignition test described in the Consumer Product Safety Commission’s proposed standard 16 CFR Part 1634. The results of this study suggest that the smolder-prone cover fabrics, when placed on top of a number of barrier fabrics, are capable of releasing sufficient heat to initiate the char oxidation smoldering process of some of the barrier fabrics and subsequently transmit the heat to the underlying flexible polyurethane foam. A smoldering index for barrier fabrics was derived from the measured char volume fraction of the flexible polyurethane foam by varying the barrier fabric component in the flexible polyurethane foam/barrier fabric/cover fabric mock-up systems, while holding the other two components constant. The smoldering index for self-extinguishing barrier fabrics was 0. Barrier fabrics with smoldering index of 1 or more resulted in sustained smoldering in the flexible polyurethane foam. The smoldering propensity of barrier fabrics and the amount of heat transmitted to the flexible polyurethane foam varied depending on the barrier fabric structure, fiber content, air permeability, and bulk density. Flame-retardant treatments and use of char-forming fibers showed a greater tendency for barrier fabric smolder in the presence of the smolder-prone cover fabric. Barrier fabrics with char-forming fiber blends had greater smoldering propensity as compared to barrier fabrics with low charring fiber blends. The lower the smoldering propensity of the barrier fabric, the less likely was the development of sustained smoldering in the flexible polyurethane foam.