Chow W.K.,Research Center for Fire Engineering |
Wong K.Y.,Research Center for Fire Engineering |
Chung W.Y.,Research Center for Fire Engineering
Tunnelling and Underground Space Technology | Year: 2010
Longitudinal ventilation systems are commonly installed in new tunnels in large cities of the Far East including Mainland China, Hong Kong and Taiwan. Many tunnels are found in big cities and some of them are inclined at an angle to the horizontal. However, smoke movement in tilted tunnels is not fully understood. In some of the tunnels, the ventilation system was designed based on presumed smoke movement pattern without experimental demonstration. Smoke movement pattern in a tilted tunnel model was studied by using a scaled model. A 1/50 tunnel model of length 2 m with adjustable angle to the horizontal was constructed by transparent acrylic plastics. A small 0.097 kW propanol pool fire was used as the heat source combined with burning pellets generating smoke. A fan placed at the upstream end was used to create longitudinal ventilation. Different ventilation rates were set using a transformer to control or adjust the fan speed. Experiments were performed with the tunnel angle varying up to 30° to the horizontal. Effect of smoke screens was also studied. The observed smoke movement patterns indicated that the shape of the buoyant plume inside the tunnel depends on the tilted angle. Smoke would flow along the tunnel floor due to gravity. The bending angle of the plume depends on the tunnel angle. Tunnel inclined at greater angles to the horizontal would give larger amount of smoke flow. Smoke movement pattern for a tilted tunnel with smoke screens was observed to be very different from some design projects. All results will be reported in this paper. © 2009 Elsevier Ltd. All rights reserved.
Chow C.L.,University of Cambridge |
Chow W.K.,Research Center for Fire Engineering
Building and Environment | Year: 2010
Residential highrise building fire of height above 200 m is now a concern in the Far East. Long-term survey study on fire load density indicated that high amount of combustibles over the local upper limit of 1135 M Jm-2 used to be stored in residential flats. Wind-induced air-flow rates through openings at upper levels of those tall buildings can be very high. Stack effect in areas with large indoor and outdoor temperature differences (such as 14 °C indoor and - 30 °C outdoor at Harbin, Heilongjiang, China) will also give high ventilation rate through leakage areas. Adequate oxygen is then supplied to burn up all stored combustibles to give a big fire. In applying performance-based design to determine the fire safety provisions, heat release rate of the design fire is the first parameter to decide. In this paper, stack effect and wind action on possible increase in the heat release rate for fires in supertall residential buildings will be explored. Air intake rates through openings to rooms at high levels due to stack effect and wind action are estimated by simple empirical formula. The maximum heat release rates for well-developed room fires in these tall buildings under different stack and wind conditions are determined by varying two parameters. Air flow rate through openings in an 800 m tall building induced by wind gust can be over 20 times the value at ground level. Consequently, heat release rate can be much higher, confirming experimental studies on building fires under wind action. © 2010 Elsevier Ltd. All rights reserved.
Chow W.K.,Research Center for Fire Engineering |
Chow W.K.,Hong Kong Polytechnic University |
He Z.,Harbin Engineering University |
Gao Y.,Harbin Engineering University
Journal of Fire Sciences | Year: 2011
Internal fire whirls induced by a pool fire in a vertical shaft of height 15 m with different ventilation conditions are studied experimentally. Ventilation is provided through a rectangular gap at the side wall with varying widths. Gasoline pool fires with diameters up to 0.46 m are set up at the center of the floor. Flame height and burning duration of the pool fire are measured. Average flame height ranged from 1 to 4.5 m when whirling is onsetted in the vertical shaft. Experimental studies indicate that air supply to the upper part of the shaft is a key factor for onsetting internal fire whirls. Oxygen is required to sustain combustion to generate heat for inducing whirling motions. Therefore, flame will not whirl without adequate oxygen supply. In this study, the flaming zone in a vertical shaft is divided into four stages: the initial stage, flame rising-up stage, stable flame, whirling stage and decay stage. Based on the flame height correlations for free burning pool fires, the fuel consumption rate of the pool fire in the shaft at each stage is estimated. Correlations of the whirling flame height with fuel mass and other key parameters are then derived. Computational fluid dynamics is applied to examine the validity of the derived correlation expressions. © The Author(s), 2011.