Concurrent Upward Flame Spread over a Fire Resistant Fabric (Nomex) under External Heating

Abstract

Fire resistant materials are used in multiple applications (clothing, curtains, tents, etc.) were protection from a potential fire is needed. Particularly relevant for this work is the application for astronaut space suits since a spacecraft environment may be different than atmospheric ones. Furthermore, their fire resistant capacity are often tested under very specific conditions that might not represent the real fire situations. For example, when a material is exposed to a near fire or different environmental conditions like reduced pressure, enriched oxygen concentration and micro-gravity, its flammability and fire behaviors can be altered. In this work, an experimental study was performed to investigate the effect of ambient pressure and oxygen concentration on the upward flame spread over a typical fire resistant fabric (Nomex HT90-40) exposed to two different external heat sources. One is the radiation from infrared lamps and the other is the flame from a burning polymethyl methacrylate (PMMA) sheet placed below the fabric. The limiting oxygen concentration (LOC) was first quantified under different external heating, and then the upward flame-spread rate above LOC was measured. Experiments show that the flame from nearby burning object not only can ignite the fire resistant fabric, but also extend the LOC of the material to lower oxygen concentrations. Moreover, the heating from the attached flame is different from an external radiant flux. The results of this work also provide important information about the fire interactions of different materials, and guide the future fire safety design in space exploration.