The flammability limits of flat materials with different moderate thickness in opposed flow were investigated to clarify the effect of sample thickness on flammability limit. Thin poly-methyl methacrylate (PMMA) sheets and polycarbonate (PC) sheets were used as samples. The thickness was varied as 0.2 mm, 0.5 mm and 1.0 mm for PMMA, and 0.1 mm, 0.2 mm, 0.5 mm and 1.0 mm for PC. The limiting oxygen concentration (LOC) of each sample was obtained by 20 s parabolic flight experiments in mild and low flow velocity condition, and by blow-off tests on ground in high flow velocity condition. The flight experiments showed that there existed significant difference in LOC according to the sample thickness especially in mild flow condition; the thicker the sample was, the larger the LOC became. We applied a hypothesis of heat penetration zone shape into the heat balance equation around the preheat zone to account the effect of sample thickness on quenching phenomena. Although the hypothesis was not confirmed by experimentally, the obtained empirical model based on the hypothesis well represented the trend of the change of LOC when the sample thickness varied not only for the PMMA and PC samples, but also for low-density polyethylene (LDPE) and high-density polyethylene (HDPE) samples with relatively thick thickness. The modified model states that increase in the sample thickness has equivalent effect to increase in the radiative heat loss and such thickness effect is amplified when the pyrolysis temperature of the material is high.

研究了在相反流动下具有不同中等厚度的扁平材料的可燃极限，以阐明样品厚度对可燃极限的影响。薄的聚甲基丙烯酸甲酯（PMMA）片和聚碳酸酯（PC）片用作样品。对于PMMA，厚度变化为0.2mm，0.5mm和1.0mm，对于PC，厚度变化为0.1mm，0.2mm，0.5mm和1.0mm。每个样品的极限氧浓度（LOC）是通过在低流速和低流速条件下进行20 s抛物线飞行实验以及在高流速条件下通过地面吹气试验获得的。飞行实验表明，根据样品厚度，LOC存在显着差异，特别是在轻度流动条件下。样品越厚，LOC越大。我们将热渗透区形状的假设应用于预热区周围的热平衡方程中，以说明样品厚度对淬火现象的影响。尽管该假设尚未通过实验得到证实，但基于该假设的经验模型很好地体现了当样品厚度不仅对于PMMA和PC样品而且对于低密度聚乙烯（LDPE）发生变化时LOC的变化趋势。以及厚度相对较厚的高密度聚乙烯（HDPE）样品。修改后的模型指出，样品厚度的增加与辐射热损失的增加具有同等作用，并且当材料的热解温度较高时，这种厚度作用会放大。