Polymers and Composites- An Examination of Fire Spread and Generation of Heat and Fire Products

Abstract

Fiber reinforced composite (FRC) materials are used extensively because of their favorable physico-chemical properties and high strength- to-weight ratio. The use of composites in Army vehicles as a means of decreas ing weight and enhancing survivability, without reducing personnel safety, has been under study for some time. Although FRC materials are very attractive in terms of their physico-chemical properties, concern for possible fire hazard is understandable as organic polymers are one of the major constituents of the materials. A joint study thus was undertaken by the U.S. Army Materials Tech nology Laboratory (MTL) and the Factory Mutual Research Corporation (FMRC) to quantify flammability behavior of selected composite materials for the assessment of fire hazard. In the study, eight FRC materials, identified as MTL #1 to #8, were used. The FRC materials were 3 to 45 mm in thickness. The flammability behavior was examined by using the FMRC Flammability Apparatus (50 kW-Scale) and Ox ygen Index (OI) apparatus, Thermogravimetric Analysis (TGA) instrument, NBS smoke chamber (ASTM E 662), and Gas Chromatograph-Mass Spec trometer (GC-MS) instrument at MTL. This article presents results for ignition, flame spread, heat release rate, gen eration rates of products, light obscuration by smoke and flame extinction by Halon. In comparison to ordinary combustibles, such as cellulosics and most non fire retarded plastics, the eight FRC materials have higher resistance to ig nition (as indicated by the Thermal Response Parameter, TRP) and flame spread (as indicated by higher values of the Fire Propagation Index, FPI). The FPI values for the FRC materials, examined in this study, ranged from 3 to 13, indicating that for Group 1 FRC materials (FPI < 10), self-sustained flame spread beyond the ignition zone would be difficult, whereas for other Group 2 materials ( FPI ≥ 10), flame spread beyond the ignition zone would be ex pected, although at a slower rate. For Group 2 materials fire protection is re quired, which could be provided by techniques such as surface coating, surface lamination using highly fire resistant FRC materials, and others. Generation of heat, smoke, toxic and corrosive products is closely related to FPI. Within the FRC materials, examined in this study, differences were found between the generation rates of heat, smoke, and other products. Results for flame extinction by Halon 1301 are also discussed. The flame ex tinction data are consistent with the design of the current suppression system for the crew compartment of Army combat vehicles. The study suggests that the FPI concept and associated parameters related to generation of heat, smoke, toxic, and corrosive products, is a useful concept for realistic flammability quantification and screening of FRC materials and for use in the hazard assessment. This, however, needs to be validated by perform ing large-scale fire tests.