Abstract Drying of grain is a crucial process for long-term preservation, while having a significant fire risk. This work investigated the ignition risk and fire behavior of paddy rice (~1 kg) with the drying airflow velocity up to 0.9 m/s. Results showed that there was a minimum internal flow velocity for a given spotting ignition protocol, so that a stronger drying flow has a greater ignition risk. Once ignited, three stages of fire spread processes hidden below the surface were revealed, (I) smoldering spread, (II) flame spread, and (III) smoldering spread. The smoldering rice was glowing hot (800–900 °C). With a forced airflow, the downward smoldering spread (about 2 mm/min) was comparable to or faster than the horizontal spread, different from the natural smoldering fire. The regression of rice bed in Stage-I smoldering increased the drying airflow, which created a cavity and further accelerated the downward smoldering spread. Moreover, the smoldering-to-flaming transition is triggered to sustain the flame spread on and below the free surface. By increasing the drying flow velocity, the fire-spread rate, and the fire hazards in all stages increased. This work reveals the complex fire dynamics of rice storage and supports fire protection during the grain drying process.

中文翻译：

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大米对流干燥过程中的火灾风险与行为

摘要 谷物的干燥是长期保存的关键过程，同时具有显着的火灾风险。这项工作研究了干燥气流速度高达 0.9 m/s 的水稻（~1 kg）的着火风险和火灾行为。结果表明，对于给定的点状点火协议，存在最小内部流速，因此更强的干燥流具有更大的点火风险。一旦点燃，隐藏在地表以下的三个阶段的火势蔓延过程就显露出来，（I）阴燃蔓延，（II）火焰蔓延，以及（III）阴燃蔓延。闷烧的大米炽热（800-900°C）。在强制气流下，向下阴燃蔓延（约 2 毫米/分钟）与水平蔓延相当或更快，这与自然阴燃火不同。第一阶段阴燃中稻床的回归增加了干燥气流，从而产生了空腔并进一步加速了向下阴燃蔓延。此外，触发阴燃到燃烧的过渡以维持自由表面上和下的火焰蔓延。通过增加干燥流速，火势蔓延速度和各阶段的火灾危险性增加。这项工作揭示了大米储存的复杂火灾动态，并支持谷物干燥过程中的防火。