Flame stretching and swirling in a room fire with natural vents will be studied with scale models in this paper. Experiments were carried out in two models of same size 18 cm by 15 cm by 15 cm with or without a movable wall. A total of 16 tests were carried out with different ceiling vent sizes and ventilation arrangement. Different propanol pool fires of diameters 0.11 m to 0.2 m were set up. Volume of propanol varied from 30 ml to 500 ml to give different burning durations. Two pool fires of same volume of fuel and diameter were used in each test, one put in the model and the other burnt outside. The flame lengths of the two fires inside and outside the room model were measured and compared. Two fire regimes under limited ventilation were observed in this scale modeling studies. Firstly, the pool fire inside the model burnt for a longer time with a taller flame when there is no ventilation provided to the model. At the later stage of the fire, the flame height inside the model stretched by over 20% taller than that for the pool fire outside the model. This fire scenario of having tall flame for a long time is very hazardous and should be considered in designing natural vents. Secondly, providing ventilation at the side wall of the model might induce swirling motion inside. Air will be supplied into the model to burn the pool fire faster with short duration. The flame swirled up to a tall height fast but not stretching up slowly as in the case with limited ventilation. The additional air intake flow can be taken as air pumping action.

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