A critical study on performance-based fire safety design in Hong Kong with timber perforated ceilings as an example

Abstract

Fire engineering approach has been adopted in Hong Kong for many years in unusual or complex buildings. The approach is officially allowed by Buildings Department since 1995/96. Fire Safety Committee is an advisory panel for the assessment of fire engineering design proposal. The Government has appointed a Consultant in 2002 to develop the Performance-based Building Fire Safety Code. The aim of this study is to better understand the fire safety design and control environment in Hong Kong and hence to make recommendations to improve the performance-based design application. The research objectives are to study the local building fire safety design and control environment with exploration of the possible and usual applications; to identify the issues, constraints and concerns along with the performance-based design process with the review of relevant overseas practices; to discuss and evaluate the adopted design process focusing on Fire Hazard Aspects and Evacuation Safety Aspects; with timber perforated ceiling as an example in real-life application, to study its effect to the fire environment by carrying out a series of full-scale burning tests; and to recommend ways in practicing performance-based design. The development of performance-based building fire safety code in both Hong Kong and in some selected overseas countries is reviewed. Possible, usual and common design applications are surveyed. Issues and concerns including technological aspects and administrative aspects are identified, which topics cover fire safety management, technology transfer, fire hazard analysis and evacuation safety analysis. Specifications for the means of escape design and the fire services installations in the prescriptive codes are reviewed in-depth. Discussions are made to the commonly adopted engineering methods for fire hazard analysis and evacuation safety analysis. Timber perforated ceiling, an interior decoration, is selected as an example to verify the realized technological concern that is not easily reflected in the design process. Three sets of experimental studies were carried out to study its effect to room air temperatures, room heat contribution (heat release rate) under two fire sources (small fire 235 kW and flashover fire 2400 kW) and sprinkler water deflection. Based on the above study, the recommendations are made as follows: Firstly, a local Code/Guidance which states the Deem-to-Satisfy solutions, the fire safety objectives, the functional/performance requirements and the analyzing approach is required. Secondly, mechanism to assure the fire engineering design proposal is undertaken by competent fire engineering practitioners is recommended to establish. Thirdly, mechanism to assure fire safety management is continuously implemented throughout the life-time of the buildings is recommended to establish. Fourthly, control on combustible interior decoration is recommended to review and may be required for all premises, not only for some premises subject to licenses for operation. Fifthly, experimental studies showed that the design fire size based on the time of sprinkler activation may not be always applicable as sprinkler water may not always control growth of the fire. Extended time for fire growth after sprinkler activation should be considered. Thorough considerations on the fuel type and orientation, any obstruction to prevent water from reaching the fuel should be included in the design documentation. Lastly, heat release rate is an important input parameter in engineering analysis, wherever appropriate (e.g. unusual fuel types with limited past research on heat output) full-scale burning test may be useful to support and verify the design assumption.