Experimental stuidies on forced ventilation fires

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Experimental stuidies on forced ventilation fires


Author: Tang, Ho-ming
Title: Experimental stuidies on forced ventilation fires
Degree: M.Sc.
Year: 1997
Subject: Fire prevention -- China -- Hong Kong -- Case studies
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Pages: xvi, 64, [112] leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1410638
URI: http://theses.lib.polyu.edu.hk/handle/200/3312
Abstract: Fire occurred in a ventilation chamber is very different from those in a room with natural ventilation. For a fire under natural ventilation, the burning rate is related to the ventilation factor of the opening, but operating the ventilation system might give a bigger fire due to higher air entrainment rate. This would prolong the egress time of the occupants. Also, a stable hot smoke layer is not formed if air is supplied from a higher level. The smoke layer and temperature for a forced-ventilated compartmental fire were studied in this project. A series of 16 full-scale burning tests with different ventilation arrangements was carried out. The fire chamber of size 4.2 m by 3.0 m by 2.8 m, at the Department of Building Services Engineering, The Hong Kong Polytechnic University was used. Three different ventilation rates, of 0.5 m3 s-1, 0.25 m3 s-1 and 0.17 m3 s-1 were adopted to study the fire behaviours under different arrangements of the flow rates of air intake and exhaust vents, as well as mechanical/natural - intake/exhaust combinations. Comparison was made with the fire under natural ventilation condition. Propanol was used as the fire source. For each test, the mass consumption rate of the fuel and the temperature profiles inside the chamber were recorded. The temperature profiles were utilised to investigate the establishment of a smoke layer and the time taken to reach a quasi-steady state. The smoke layer interface heights under different ventilation conditions were estimated. Empirical relations between the safe egress time and the ventilation rate were derived. The safe egress time for the occupants to leave before the smoke is developed to an untenable condition ranged from 0 to 100 seconds under natural ventilation fires, and 0 to 400 seconds under forced ventilation fires. The safe egress time can be up to 400 seconds when the ventilation rate is high, say 40 to 50 air changes per hour. Distinct hot and cool layers are when mechanical air supply is at mid-level and exhaust is at high level, or for the case when mechanical air supply is at low level, the layer interface height is at a higher position.

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