Energy balance equation for pressure in air-tight compartment fires: detailed discussion and experimental validation

Abstract

In order to better interpret the fire-induced pressure variation in air-tight compartment fires, the present paper discusses the energy balance equation starting from a commonly used form, taking into account the mutual influence between compartment pressure and ventilation behavior. The obtained pressure formulation, under certain assumptions, can explain the observed linear relationship between pressure variation and fire evolution. Based on the mathematical development, the difference between fire-induced pressure and initial compartment pressure is expected to depend on the net heat gained in the gas phase. This is subsequently validated by experimental results. Differences in heat losses through walls, acquired by varying the fire duration, are illustrated to influence the pressure variation during the fire decay phase, while they hardly affect the pressure during the fire growth phase. Besides, it is found from the theoretical reasoning that the mass flow rate difference between admission and extraction ducts depends on the net heat gained in the gas phase, and is not strongly related to the ventilation resistance. This is also confirmed by the experiments. However, a higher ventilation resistance results in higher compartment pressure variations and longer development time of the pressure.