Flammability, smoke and toxic gas response of novel treated end-grain balsa core materials: Fid-Bau Portal

Flammability, smoke and toxic gas response of novel treated end-grain balsa core materials

Feichtinger, Kurt / Gätzi, Roman / Ma, Wenguang

End-grain balsa is the only natural, renewable core material used for structural sandwiches, and has enjoyed abundant applications due to its low density, attractive properties and pricing. Durability toward the effects of water absorption had been demonstrated recently, with quite modest reductions in physical properties, and that could quite easily be accommodated by typical design safety factors (1). One might assume that end-grain balsa would vigorously support combustion upon exposure to an incendiary source. Serendipitously, during a characterization of a new, chemically treated, fungus resistant end-grain balsa core product in support of a door manufacturer, this new product was found to exhibit a much higher self-ignition temperature, suggesting improved flammability/smoke/toxic gas (FST) responses in general (2). The object of this study was to characterize the FST performance of untreated end-grain balsa as well as panels thus chemically treated at two different levels. Testing was performed on the cores, alone, to be most critical of their FST response. For US building construction, the ASTM E 84 ''Steiner Tunnel'' was employed. Automotive flammability testing used the FMVSS 302 method. For US Federal Transit requirements, ASTM E 162, ASTM E 662 and BSS 7239 were enlisted. For the commercial aircraft industry, the Federal Aviation Administration FAR 25.853, Appendix. F, Parts I, IV and IV, were performed. Lastly, the French Norm. NF 16-101 was selected as representative of a possible future light rail standard for all EU Nations. In general, all end-grain balsa core material variants exhibited quite low optical smoke densities, in those tests for which it was measured. The chemical treatment reduced time to ignition, rate of burning and rate of heat release in direct proportion to the level of treatment. While most of these industry FST standards require evaluation of the finished laminate or assembly, remarkably ''core-alone'' characterization of all variants, treated or otherwise, met the automotive interior material flammability requirements of FMVSS 302, the US Federal Rail toxic gas concentration requirements of BSS 7239, and the ASTM E 662 smoke density requirements for interior materials for both the US Rail standard as well as FAA 25.853 Appendix F Part V commercial aircraft standard. The chemically treated variant may prove valuable in providing an added margin of safety where borderline FST results are obtained for end-grain balsa-cored sandwiches.