Scale modeling study on flame colour in a ventilation-limited train car pool fire

Scale modeling experiments were carried out to investigate flame colour of train car fire under limited ventilation. A 1:15 scale model car with adjustable openings was constructed to study train car fire in the subway system in Hong Kong. Ventilation was provided by opening different numbers of doors of the model car. The fire load was taken to be 10 ml of propanol, simulating the possible bags and luggage allowed to be carried by a passenger in train. As the size of the luggage carried by passengers in the train may be different from each other, two fire pans of different shapes and surface areas, namely a 75 mm × 75 mm square pan with a surface area of 5625 mm² and a 38-mm diameter circular container having a surface area of 1135 mm² for containing the same amount of propanol were used in the tests. Differences in flame colour of a train car fire under limited ventilation were studied. Seven ventilation scenarios with various door openings were investigated. In the tests with all doors closed, the flame colour changed significantly when the fire progressed from the fully-developed to decay stages. Pale-blue flame with light-orange colour in the upper part was observed in the scenario with all doors closed at the decay stage of the fire for both square pan and circular container. In addition, the flame began to oscillate when the oxygen concentration decreased to 14.3% and 16.2% for the square pan and circular container respectively. When the oxygen concentration further dropped to 12.5% (square pan) or to 16.0% (circular container), the pale-blue flame detached completely from the fuel surface and was then self-extinguished with a large quantity of propanol (50% in the square pan and 70% in the circular container) left behind.