Studying the extinguishing performance of a water mist system under different ventilation conditions

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Studying the extinguishing performance of a water mist system under different ventilation conditions

 

Author: Woo, Chun-kit
Title: Studying the extinguishing performance of a water mist system under different ventilation conditions
Degree: M.Eng.
Year: 2005
Subject: Hong Kong Polytechnic University -- Dissertations
Pressurized water reactors
Fire extinction
Fire extinguishers
Department: Dept. of Building Services Engineering
Pages: 1 v. (various pagings) : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1810031
URI: http://theses.lib.polyu.edu.hk/handle/200/3425
Abstract: Water mist suppression system is a potential replacement for Halon fire suppression agents. Water mist system has already demonstrated its efficacy for fire protection in a wide range of applications. However, there are no existing standard and design guideline for water mist system application under the ventilation conditions. The size of water mist droplet is very fine. It is easily affected by the air movement. This dissertation investigates the extinguishing performance of water mist system under ventilation conditions. The recommended points for the design of a water mist system are pointed out with the mechanical ventilation and air-conditioning system. A series of experiments were conducted to investigate the effects of ventilation on the water mist extinguishing of two fires with 50kW and 100kW under different conditions in the fire chamber in the department of BSE at The Hong Kong Polytechnic University. The experiments were conducted in a simulated typical office room under three ventilation conditions: no ventilation, natural ventilation and forced ventilation in 3 m/s, two operating pressure: 12bar and 16bar and the three fire locations: 0m, 0.5m and 1m from the water mist nozzle. A single-fluid and low pressure water mist system was used in the experiments. The test results showed that water mist suppression effectiveness was dependent on the ventilation conditions and the relative fire location. The water mist system effectively extinguished fires under no ventilation and the 0m distance from the nozzle axis. The fire took the longest extinguishing time under the forced ventilation and 1m distance from the nozzle. The extinguishing mechanisms including flame cooling and oxygen depletion and displacement are discussed in the report. In addition, the ventilation condition and the distance between the flame and the nozzle are two main factors which influence the effectiveness of the water mist system. The ventilated and air-conditioning system should be shut down and the opening of the room should be closed when the water mist system is operating and the spacing of the water mist nozzle should be reduced in the design of water mist system.

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