Influences of inclined tunnel ceiling on plug‐holing phenomenon and mechanical smoke exhaust efficiency in tunnel fires

Abstract

SummaryIn this paper, the effect of inclined tunnel ceiling on the characteristic of smoke extraction and the efficiency of mechanical smoke exhaust is studied. The parameters of different ceiling inclination angles, exhaust velocities, and heat release rates in the tunnel fire are taken into account. The results demonstrate that for the given smoke exhaust velocity and heat release rate, as the ceiling inclination angle increases, the smoke flow tends to accumulate toward the centerline of the tunnel ceiling, which increases the temperature of the smoke layer and relieves the phenomenon of plug‐holing beneath the shaft. The applicability of previous Fr criterion for predicting whether the plug‐holing phenomenon occurs is also verified. It is shown that the Fr criterion of Fr = 1.5 can also be applicable to the tunnel with different inclination angles. In addition, a predicted correlation for the mechanical smoke exhaust efficiency is established by taking the effect of inclined tunnel ceiling into account, and the predicted value is in good agreement with the results in this paper. This work provides an improved understanding of mechanical smoke extraction in tunnel with inclined ceiling. It may also serve as a reference for the design of a mechanical smoke exhaust system.