Ignition signatures of a downward smolder reaction

An experimental study has been conducted to determine signatures that will describe the onset of self-sustained downward smolder. The fuel used is polyurethane foam, mainly due to its common occurrence in households and thus its importance in fire scenarios linked with smoldering combustion. The polyurethane foam is subject to a constant heat flux imposed by a cone heater for different time periods. Temperature and mass loss rate measurements together with visual observations serve to determine specific events that can be considered signatures of the onset of a self-sustained smolder reaction. Three stages were identified in the ignition process: the warm-up stage and unsteady smolder stage, both controlled by external heat flux, and the self-sustained smoldering stage controlled by the heat generation by the smolder reaction. Each stage is characterized by a change in the temperature and mass loss rate histories (signatures). It was observed that self-sustained smolder could only occur in an external heat flux window corresponding to 6.1 kW/m 2< q ̇ ′′ e