A study on the smoke filling process for a forced ventilation fire

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A study on the smoke filling process for a forced ventilation fire


Author: Chang, Wing-cheong
Title: A study on the smoke filling process for a forced ventilation fire
Degree: M.Sc.
Year: 1997
Subject: Fire prevention
Fire prevention -- China -- Hong Kong -- Case studies
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Pages: 1 v. (various pagings) : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1250483
URI: http://theses.lib.polyu.edu.hk/handle/200/4698
Abstract: This work aims to contribute the knowledge to understand better the smoke filling process inside a small compartment during a fire, and the smoke propagation through a ventilation system under natural and forced ventilation conditions for a preflashover fire. A series of full-scale burning tests were performed using a full-scale burning room of size 6.1m x 3.5m x 2.8m and two adjacent rooms of size 3m x 4.2m x 2.8m at the Department of Building Services Engineering of The Hong Kong Polytechnic University. Nine ventilation rates, they were 0.53 m3s-1, 0.48 m3s-1 and 0.3m3s-1 when the system damper was fully opened; 0.49 m3s-1, 0.42 m3s-1 and 0.25m3s-1 when the system damper was partially opened; 0.44 m3s-1, 0.32 m3s-1 and 0.18m3s-1 when the system damper was slightly opened; were adopted in nine groups of burning tests respectively to study the smoke filling process and smoke propagation under forced ventilation fire. Two groups of tests when the fan was stopped and the system damper was set at either fully open or slightly open position were also performed. Finally two additional groups of tests when the fan was stopped and the horizontal opening connected to a ventilation system which area was reduced from 600 mm x 600 mm to either 400 mm x 400 mm or 300 mm x 300 mm with system damper fully open were performed. The smoke layer temperatures inside the burning room, average room temperatures inside the adjacent rooms, smoke temperatures in the air duct before and after the obstacle (system air damper), pressures inside the rooms and air duct, smoke flow, optical density, and the smoke flow rate through the horizontal opening at the ceiling of the burning room, which was connected to the ventilation system, were measured. The smoke layer interface heights in the burning room under different ventilation conditions were estimated. The related fire hazard under different ventilation fires at different ventilation rates was also discussed. Based on the experimental results, a relationship between the estimated safe egress time and the air change rate per hour (ACH) was established. It was found that when a fire was generated and developed in a small compartment, the safe egress time for the occupants to leave before the smoke was developed to an untenable condition ranged from was 120 to 390 seconds under forced ventilation fires, and 120 to 225 seconds under natural ventilation fires. The safe egress time was as long as 290 to 390 seconds when the forced ventilation fires had high air change rate per hour (ACH) ranging from 26.5 to 31.9.

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