IGNITION EFFICIENCY OF GLOWING NESTS AND EMBEDDED HOT BODIES IN DUST DEPOSITS

Glowing nests appearing in deposits of bulk materials have rather freq uently been identified as probable ignition sources for dust fires and explosions. Therefore the investigation of the conditions for the gen eration and propagation of smouldering fires by glowing nests is of sp ecial interest in process safety. The present paper describes experime nts on the initiation and propagation with time of smouldering fires i n dust deposits, where glowing nests of different sizes have been intr oduced. Volumes of the deposits of 6, 12 and 50 litres were used. It c ould be shown, that for the onset of smouldering a minimum size of the glowing nest is required, which depends on the properties of the subs tance used. However, after once being initiated the smouldering fire p ropagated with a velocity independent of the ignition source used. On the other hand it could be observed, that that the propagation velocit y of the smouldering fire depends on the volume of the deposit. For ho t bodies embedded in the deposit a certain minimum temperature was fou nd, below which no initiation of smouldering was observed.