Fire risk and behavior of rice during the convective drying process

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.