In a real fire scenario, the distribution of fire loads may not be continuous. In this paper, PMMA blocks (8 cm × 10 cm × 1 cm) are used as experimental materials to carry out upward flame spread experiments with different air gaps (0–18 cm) to analyze changes in burning rate, flame shape, flame height and pyrolysis front position. It is found that as the air gap increases, the burning rate and flame height both increase first and then decrease, and the turning point of this trend is predicted to be between 6 and 8 cm. In addition, it is founded that the pyrolysis reaction is accelerated due to the additional air entertainment provided by the air gap when the pyrolysis front passes through the air gap. However, this effect becomes insignificant for a larger air gap.

在真实的火灾场景中，火灾荷载的分布可能不是连续的。本文以PMMA块（8 cm × 10 cm × 1 cm）为实验材料，在不同气隙（0-18 cm）下进行向上火焰蔓延实验，分析燃烧速率、火焰形状、火焰高度的变化和热解前沿位置。发现随着气隙的增大，燃烧速度和火焰高度均先增大后减小，预计这一趋势的转折点在6~8 cm之间。此外，发现当热解前沿通过气隙时，由于气隙提供的额外空气娱乐，热解反应被加速。然而，对于较大的气隙，这种影响变得微不足道。