In this study, full-scale experiments were conducted to observe the influence of a natural ventilation shaft on smoke layer descent in room fires. An oil pan with a heat release rate of 50 kW was ignited in a model space to generate fire smoke for the observation of smoke layer descent and flow conditions under various natural ventilation conditions. It is found that when there is no natural ventilation shaft available in a room that is on fire, the height of the descending smoke layer in the

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... re room has nothing to do with whether the natural ventilation shaft has been set up or not in the adjacent non-fire room. However, when a natural ventilation shaft has been set up in the fire room, it is able to effectively raise the smoke layer height.