A study on enclosure fires with mechanical ventilation system.

摘要

Enclosure fires with forced ventilation were studied in this thesis with three stages. Stage one is on reviewing fire codes in China, Hong Kong, USA and other countries for identifying the fire safety aspects in enclosures with mechanical ventilation. Theoretical background of airflow induced by mechanical ventilation system appeared in the literature was studied. New concepts on performance-based fire codes were discussed. Stage two is on evaluation of different system designs. Possible fire hazard scenarios in relation to ventilation requirements were identified. Consequences of those hazard scenarios on the occupants, the building and its contents were assessed by fire models. Results are useful for designing appropriate fire services systems to provide better fire safety. Stage three is on developing a practical air flow model for forced ventilated fire.; Cabin design, a safety concept commonly used in big halls in Hong Kong, was selected for a more detailed evaluation. This was taken as an example with provision of mechanical ventilation system. Concepts of zone models with some fire plume equations available in the literature were studied. Models were then applied for scenario analysis. The principles of ventilation system design and aspects of smoke movement in a chamber were studied. In the zone model simulations, both natural ventilation and forced ventilation conditions in a cabin were considered. The associated developed equations were solved by symbolic mathematics which have greater flexibility in changing the parameters concerned; and more transparent to the users. The two-layer zone model ASET was used for enclosures without openings. ‘Bare cabin’ fires with operation of smoke extraction system were solved by FIREWIND program. The Computational Fluid Dynamics (CFD) package PHOENICS was also applied to simulate several cases of cabin fire. In verifying the model, CFD results are compared with those experimental results reported in the literature including the ISO room-corner fire test and other compartment fires. Simulations with different geometrical aspects of the chamber, fire sizes, zone models, and plume models were carried out. Results are useful to identify the possible fire hazards, as well as to determine the zone model with suitable sub-models such as the plume model for different types of chamber. (Abstract shortened by UMI.)