Experimental investigation of underventilated fires in enclosures with two front vertical openings and occurrence of smoke explosions

Abstract

In addition to classical compartment fire development stages, smoke explosions can occur for underventilated conditions while the ventilation openings remain the same. Smoke explosions are different from backdrafts, involving changes in ventilation by additional openings. In this study, the burning history of medium-density fibre (MDF) cribs located at three different elevations has been investigated for the first time in an underventilated enclosure having two vertical openings at the front wall. The effects are examined of different fuel locations, the crib geometry and the ventilation on the mass loss and heat release rates. The fuel mass loss and heat release rates being nearly independent of the crib location and type depend on a new ventilation parameter determined from the distance between the two openings in a simplified way including effects of mass pyrolysis rate and gas temperatures. The mass air inflow is also proportional to this ventilation parameter and independent of the gas temperatures. In some experiments, however, the fires produced single or multiple smoke explosions after a dip in the heat release rate ejecting flames outside. The occurrence of a smoke explosion in relation to the porosity of crib, appearance of smouldering and the vitiated environment is also discussed.