Experimental Study of Bulk Storage Ignition by Hot Points

An experimental study of ignition risk due to hot points in the storage of bulk materials is required to ensure fire safety. Many parameters are involved in this phenomenon: nature of the material, storage volume and temperature, type and size of hot point, etc. The aim of this study is to determine critical ignition temperatures of hot spots embedded in powder materials for different conditions and with several types of hot points. Materials selected for this study are pulverized coal, wood dust, cocoa powder, alfalfa, rice husks and coffee husks. Ignition tests were carried out in 1,000 and 2,700 cm cubic baskets containing the combustible sample and using an inert sphere at a given initial temperature as well as a glowing cigarette butt and charcoal as ignition sources. The critical ignition temperature is defined in terms of the hot point temperature that is able to ignite the sample. Differences between the results obtained under these test conditions have been explained by the oxy-reactivity of materials tested, different basket sizes and specific heat or heat production of hot points. Data obtained need now to be compared to available theoretical modeling. These results will then allow the prediction of material behavior under other storage conditions.