Numerical study of smoke and fire confinement using air curtains in shopping malls

Abstract

Fire incidents in densely populated urban areas can rapidly results in a catastrophicmulti-death scenario, in absence of adequate fire-fighting equipment. As smoke generatedduring fire hazards is predominantly responsible for loss of life, confining smokeand heat at the source of fire is essential to facilitate safe evacuation. Shopping malland marketplace fires represent a high percentage (18%) of the total number of fireincidents that occur in the country. The use of air curtains is quite common in the manyshopping malls, especially in the typical, old-fashioned ones in both staircases/exitsand in storefronts, for the purpose of acting as aerodynamic sealing. The present studyaims to examine the effects of air curtains in confining the propagation of fire andsmoke from a source of fire in the event of a typical shopping mall fire in the contextof Bangladesh. Smoke and flame propagation through shopping malls with air curtains are analyzednumerically from evacuation perspective, with strategic variations of operatingconditions, and compared with the no air curtain case. Three different designs ofshoppingmalls with distinct geometric and architectural features, two fuel types, andthree distinctfuel arrangements are examined to imitate the diversities present inactual shopping malls.The parametric variation of air curtain operating parametersincludes the variation of air curtain jet velocity in the range of 3 m/s to 10 m/s, jetangles from 0o to 60o, with a flow rate of 1250 m3/h to 5000 m3/h, and jet width of7.62 cm to 30.48 cm. Single and twin jet configuration of air curtains, with 0 to 4 jetdistance between two jets, and placement of air curtain in different combinations, atcritically appraised positions during evacuation, are also examined. The numericalstudies are conducted in PyroSim, a graphical user interface (GUI) for Fire DynamicsSimulator (FDS), a widely accepted fire simulation tool. The proposition of injecting additional oxidizers into flame is more involved than common understanding and the phenomenon is addressed comprehensively. An off-the-shelfair curtain installed at fire source shop door can confine the fire generated heat and smoke inside source shop substantially for all fuel type and arrangements considered,enabling crucial increment in safe evacuation time. About 37.1% of the fire generatedheat could be confined within the source and the flashover event could be delayed for18s with air curtain at fire source. Use of air curtains with a reduction in the actual,extremely dense, arrangements of fuels, typically present in shops of Bangladesh, to astandard amount and arrangement is found to be beneficial to mitigate devastationduring a fire incident. The flashover event can be further delayed with air curtainsin combination with standard fuel arrangements but cannot be completely avoided incase of stores with high fuel density. The effectiveness of air curtains in confining the heat and smoke transfer from thesource as observed from the findings of the present study are quite encouraging. Aircurtains operated at optimum parameters and placed at multiple critical positions arefound to be even more beneficial to the evacuation process. A maximum of 59.4%heat confinement at source and about 120s increment in safe evacuation time throughstaircase could be achieved for the best-case scenario. The findings of the presentstudy provide a comprehensive insight into the role and effectiveness of air curtainsin confining the heat and smoke and hence assisting safe evacuation in case of fireincidents in typical shoppingmalls in Bangladesh.