Experimental investigation of smouldering fire behaviour of agricultural food grains

Abstract In agricultural storage, transport, and processing facilities, food grains are available in large quantities and can be involved in severe fires. This study considers the propensity of self-sustained smouldering propagation and transition to flaming of food grains in natural airflow. The experimental setup consists of a 40-W electric heating coil, embedded in grains contained in an insulated stainless steel tube 100 mm in diameter and 315 mm high. This simulates an internal heat source leading to upward and downward smouldering propagation. The temperature at various locations and mass evolutions were obtained and analysed. Oven-dried cowpea, lentils, millet, soybean, flax, unshelled peanuts, sunflower, shelled peanuts, and sesame which have different oil content, bulk densities, and porosities, were tested. Apart from unshelled and shelled peanuts, the other grains ceased to smoulder when the power supply was cut off, which is positive from a fire safety perspective and indicates a low probability of smouldering fires occurring in such facilities. The results show that peak temperatures and mass loss rates varied from 640 to 10 °C at the heater location and 5.0–22.0 g min −1 , respectively. Bulk porosity, which influences airflow, was noted as a major factor for unshelled peanuts to transition to flaming, completely burnt. The results highlight which materials present greater smouldering fire risks for bulk storage facilities, thereby impacting fire safety system design. Also, smouldering combustion mechanisms are analysed and quantified.