| Author: | Shang, Dongyu |
| Title: | Fire spread in underground spaces in the presence of mechanical ventilation |
| Advisors: | Usmani, Asif (BSE) |
| Degree: | M.Eng. |
| Year: | 2020 |
| Subject: | Fire prevention Tunnels -- Fires and fire prevention Ventilators, Mechanical Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Building Services Engineering |
| Pages: | viii, 57 pages : color illustrations |
| Language: | English |
| Abstract: | Over recent decades, a large number of cities of various countries have engaged in building metro lines, huge underground garages and tunnels, in order to enhance transportation capacity and address car-parking problems. In this paper, a simulation studies on the optimal ventilation system for the control of fire spread in underground space will be conducted, especially in tunnels. A suitable Mechanical ventilation system is selected to address the fire prevention and protection problem of the smoke and fire spread representation. Based on the working experience in designing the metro stations, in this paper, the mechanical ventilation system is reorganized to reduce the length of smoke layering and the time of smoke chaos following the operation of the ventilation system in underground spaces. In this study, a six-tunnel mechanical ventilation system model is established by applying the fire dynamic simulator Pyrosim 2019. Statistically, it has been found that the height of the underground space is one of the most important parameters for the underground spaces without mechanical ventilation. The smoke layer on the altitude depends mostly on the heat release rate of the fire source. When increasing the height of the underground spaces, the storage capacity of the smoke will be larger than the underground spaces with a lower height. Focusing on the mechanical ventilation in underground spaces, especially tunnels, six models is conducted to search for the relationship between the control of fire spread and the various parameters including ventilation volume, critical velocity, the concentration of toxic gases and the heat release rate. Among these six models, the function of model F shows prefect representation. Model F is designed as 120×20×5 (L×W×H) with the mechanical ventilation system. The thickness of the ceiling and floor is 0.5m. Depending on the demand of the fire dynamic simulator, this tunnel will be divided into several small cells to operate and cumulate, with the diameter of the cells as 0.5 m³ per cell. The total cell of this model is 115200. Four lines of the jet fan are installed in the tunnel, two of which are set in the middle beneath the ceiling, with the other two installed at the sidewall with the height of 3m. When the heat release rate from the fire source is 16MW, and the volume of the jet fans is 60 m³/s per unit, the velocity of the fan outlet will reach 11m/s, below 25% than model C with single line of mechanical ventilation. Meanwhile, it takes 6 seconds for the transverse section to approach the critical velocity, which is the fastest response time among the six models. Compared with the tunnels without mechanical ventilation model A and B, the model C to F is advantageous in preventing the flue gas from flowing upstream, indicating that the trapped person and vehicles have much more time to evacuate from the burning underground space. |
| Rights: | All rights reserved |
| Access: | restricted access |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| 5339.pdf | For All Users (off-campus access for PolyU Staff & Students only) | 3.21 MB | Adobe PDF | View/Open |
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