A study on fires and associated provisions in open kitchens in small residential units of tall buildings

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A study on fires and associated provisions in open kitchens in small residential units of tall buildings


Author: Liu, Jing
Title: A study on fires and associated provisions in open kitchens in small residential units of tall buildings
Degree: Ph.D.
Year: 2016
Subject: Kitchens -- Fires and fire prevention.
Dwellings -- Fires and fire prevention.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xix, 107, 8, 73, 3, 10 pages : color illustrations
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2925525
URI: http://theses.lib.polyu.edu.hk/handle/200/8694
Abstract: Open kitchens are adopted in small residential units in tall buildings to make room spacious. These residential flats characterized by small floor area and high fire load density in tall buildings pose serious fire hazards. In this thesis, the fire hazards associated with open kitchens were first studied. Then, fire resulting environments of kitchen fires were examined. And at last, the application and effectiveness of water mist fire suppression system in these kitchens were evaluated. Fire hazards originating from cooking area were reviewed and analysed. The leading cause of home cooking fires was identified. A scenario with special hazards was also identified. When frozen food is dipped into hot oil, the water turns into steam instantly and can violently explode hot oil in many directions with large volume of flames. In this case, the fire may spread out of the cooking area and ignite surrounding combustibles, resulting in a big fire. Water and ice were used to simulate the water content in frozen foods and experiments were conducted under varying ratio of water or ice to oil to evaluate the associated hazards. In the experiments, an induction cooker was used to heat the oil which is allowed to use in open kitchens. Temperature and characteristics of flames were obtained and discussed. Flashover is a big concern in small units with a high fire load density. Nonlinear dynamics was applied to study flashover in flats with an open kitchen. Evolution equation was developed based on a two-layer zone model. The upper smoke temperature was taken as the system state with selected control parameters. The effect of heat release rate, floor geometry, thermal properties of wall material and other parameters on the occurrence of flashover was investigated. It was proved that flashover can be demonstrated by the model developed, though the results are sensitive to the parameters selected.
Kitchen fires were then investigated numerically by the Computational Fluid Dynamics software Fire Dynamics Simulator (version 6.0). Fire source was determined based on the plate size of the induction cooker and heat release rate per unit surface area of canola oil. Common household furnishings in a typical layout were input to the model. Then, the fire environment was evaluated under various scenarios. The presence of combustibles in the immediate vicinity of the cooker, state of the exhaust hood fan, fire barrier required to install adjacent to the exit and wind effect were taken into consideration. The extinguishment of cooking oil fires is very challenging. Water mist fire suppression system is one of the alternative protection measures in open kitchen. The effectiveness of water mist fire suppression system depends on the fire scenario. Full-scale fire extinguishment experiments were conducted in a mock-up open kitchen. The suppression performance of water mist system was examined under different types of nozzle head, various system operating conditions and different oil depths. Parameters such as free burning time, discharge duration, extinguishing time, quantity of water used and temperatures were recorded and measured. The suppression of cooking oil fire by water mist was also numerically studied. The cooking oil fire was modelled in different ways and the water mist system was modeled with varying spray characteristics. The numerical results were compared with the experimental data.

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