EXPERIMENTAL STUDIES ON SMOKE CONTROL WITH MECHANICAL EXHAUST AT LOW LEVEL IN A CABIN FIRE

Although the cabin design is widely used for providing fire safety in big and tall public transport terminals in the Far East, there are many debates on its performance. Very few experimental studies with big fires in a cabin were reported in the literature. In many applications, smoke exhaust was at low level in the cabin. The performance of such systems has to be justified. Full-scale burning tests were carried out to study smoke exhaust at low levels in a cabin fire. A cabin of length 3 m, width 4 m and height 3 m was constructed. Smoke temperature, average smoke layer height in the cabin, and velocity in the fan duct were measured with different heat release rates and heights of the ventilation opening. Eight sets of tests were carried out with results reported in this paper. For smoke exhaust at low level, the interface of smoke layer was low, usually lower than the height of the ventilation opening. The fire plume was then at the continuous flame zone. The interface of the smoke layer would be tilted. The smoke layer near the mechanical exhaust ventilation was lower than that at the opposite wall. The calculated smoke production rate would then be lower than the mechanical exhaust rate, as air would be extracted directly from the lower layer. In designing mechanical exhaust system in a cabin, the plume coefficient should be tuned up by a factor. In this paper, the mechanical exhaust rate used in cabin design at low levels would be estimated by changing the coefficient concerned. Plume correlation expression due to McCaffrey was taken as an example. Semi-empirical correlation of the flow rates of the fan in controlling smoke not to spill out was derived based on the experimental data