Smoke Explosion in Severally Ventilation Limited Compartment Fires
A smoke explosion is generally considered as a deflagration of the accumulated unburned fuel inside a closed compartment. However, the term smoke explosion has been widely misused for decades with a great deal of confusion, and very little research has been done towards this topic. The purpose of this research is to study the smoke explosion phenomenon in much more detail through the development of a fire scenario under various experimental conditions including ventilation size, fuel elevation and fuel mass, so that a more comprehensive understanding of this phenomenon can be achieved.
A total of twenty experiments are carried out including both exploratory and final experiments. Thirteen experiments result in smoke explosions, among which there are five experiments result in more than one smoke explosion. A phenomenon referred as smoldering decay is observed in all experiments with smoke explosions, making it one of the precursors of the smoke explosion phenomenon. The smoldering decay is often indicated by an exponential decay of the temperature and is caused by the low oxygen concentration within the compartment.
Based on the analysis, it is found that the vent size must be at least 50 mm in diameter in order for smoke explosions to occur. The fuel elevation has no influence on the occurrence of the smoke explosion. However when the fuel is placed near the ceiling, the temperature, the mass flow rate and the heat release rate are all lowered significantly. The size of the fuel also has no significant influence except for the duration of the experiment. The concentration of CO is scattered in the range of 1.9% and 4.3% when explosions occur. Hence, the accumulation of CO is considered not to be the direct cause for the smoke explosion. The triggering factor for smoke explosions is believed to be the flammable limit formed by the mixture of hydrocarbon and CO. The pressure difference caused by the explosion inside the compartment has to be at least 27 Pa for it to be considered as a smoke explosion.