Fire-resistant materials are used in multiple applications where protection from fire is needed. Their fire-resistant capacity is often tested under specific conditions that might not represent the situation in an actual fire. Particularly relevant for this work is the application for astronaut spacesuit, since a spacecraft environment may be different than earth atmospheres. There, a material is exposed to low velocity flows, microgravity, reduced pressure, and enriched oxygen concentration. Under these conditions, material flammability can be altered. In addition, flammability tests are based primarily on the exposure of the material to an external radiant flux to simulate an adjacent fire, but not a real flame. In this work, an experimental study was performed to investigate the effect of ambient pressure and oxygen concentration on the concurrent/upward flame spread over a 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 experimental results show that an external heat flux extends the limiting oxygen concentration (24% LOC) of Nomex. This effect is more pronounced when the PMMA flame provides the heat flux (17% LOC). For oxygen concentrations larger than the Nomex LOC, the flame spread rate decreases as the ambient pressure is decreased, indicating that reducing buoyancy reduces the flame spread rate. A simple analysis of concurrent flame spread that incorporates mixed flow heat transfer correlates well with the experimental data. This suggest that flame spread in microgravity can be predicted in terms of a mixed flow velocity that includes the Reynolds and Grashof numbers. The results of this work provide further information about the effect of the type of external heating on material flammability. They may also guide future fire safety design in space exploration.

耐火材料用于需要防火保护的多种应用中。它们的耐火能力通常在可能无法代表实际火灾情况的特定条件下进行测试。与这项工作特别相关的是宇航员太空服的应用，因为航天器的环境可能不同于地球大气层。在那里，材料暴露于低速流动，微重力，减压和富氧浓度中。在这些条件下，可以改变材料的可燃性。另外，可燃性测试主要是基于材料暴露于外部辐射通量下以模拟相邻的火灾，而非真实的火焰。在这项工作中，进行了一项实验研究，以研究环境压力和氧气浓度对暴露于两种不同外部热源的耐火织物（Nomex HT90-40）上同时/向上火焰蔓延的影响。一种是来自红外灯的辐射，另一种是来自放置在织物下方的燃烧的聚甲基丙烯酸甲酯（PMMA）薄板的火焰。实验结果表明，外部热通量扩展了Nomex的极限氧浓度（24％LOC）。当PMMA火焰提供热通量（17％LOC）时，这种效果更加明显。对于大于Nomex LOC的氧气浓度，火焰扩散率会随着环境压力的降低而降低，这表明减小浮力会降低火焰扩散率。结合混合流传热的同时火焰传播的简单分析与实验数据很好地相关。这表明可以通过包括雷诺数和格拉斯霍夫数的混合流速来预测火焰在微重力中的扩散。这项工作的结果提供了有关外部加热类型对材料可燃性影响的更多信息。它们还可以指导未来太空探索中的消防安全设计。