The effect of pressure and external heating on the nomex flame spread limits (LOC)

Nomex is used in multiple applications (clothing, curtains, tents, etc.) were protection from a potential fire is needed. Furthermore, its fire-resistant capacity is 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, its flammability and fire behavior 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.