Theoretical analysis and experiments on the effect of fire source location on maximum ceiling excess smoke temperature in Z-shaped passage fires with natural ventilation

The maximum ceiling excess smoke temperature is a critical parameter for assessing fire safety in Z-shaped passages. These passages are long and narrow spaces formed by two horizontal segments connected by an inclined passage. Smoke movement in such passages significantly differs from traditional confined spaces due to the stack effect and the presence of corners where the horizontal and inclined segments meet. Previous empirical formulas for evaluating the maximum ceiling smoke temperature rise are not applicable to Z-shaped passages. Therefore, this study experimentally explored the impact of fire location, both longitudinally and vertically, on the flame shape and ceiling excess smoke temperature profile of the Z-shaped passage. The results revealed a strong correlation between the stack effect and smoke plume impinging position. By considering the smoke plume deflection angle and fire location, the position of the maximum ceiling smoke temperature rise was determined. Moreover, a new variable, the effective height (he) was introduced to replace the passage height. Various heat release rates (HRRs) and fire locations were taken into account in the development of a modified model to determine the maximum ceiling smoke temperatures rise in Z-shaped passages. Experimental data from this work and others were used to verify the model's accuracy; the results showed greater accuracy in the absence of smoke backflow in the passage.