|Title:||Fire safety concerns for new architectural features|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Fire risk assessment
|Department:||Department of Building Services Engineering|
|Pages:||1 v. (various pagings) : ill. ; 30 cm|
|Abstract:||As experienced, many buildings with new architectural features have difficulties in complying with the prescriptive fire codes in Hong Kong. Active updating to the existing prescriptive codes and adopting the new approach of performance-based design are essential in the new century. However, both approaches cannot be achieved with a good understanding on the problems inside. Therefore, fire safety concerns associated with the new architectural features was studied and being the focus of this thesis. Four popular innovative architectural features including atrium design, double-skin facade (DSF), internal building void (IBV) and ultra high-rise building design were identified to study their hidden fire risks. Methodology included analysis of numerical experiments, critical review on fire codes and fire incidents, application of fire engineering tools including fire models, and full-scale burning tests at a remote site in Northeastern China. The current fire regulations, particularly requirements on fire resisting construction such as providing intumescent protective coating for steel structure were reviewed first with their deficiencies identified. The rationale behind the development and some standard fire tests and equal area hypothesis of the fire codes for high-rise buildings were analyzed. The review study would give a basis for revising existing codes. It was found that the existing prescriptive-based fire codes with objectives only on protecting against accidental fires. There might not be adequate for some premises as shown in the World Trade Center (WTC) incident. Further, it would take time, say a few years, on revising current codes and developing new codes. An immediate action is to protect those buildings with higher chance to have non-accidental fires. A new fire risk assessment scheme was proposed to identify those different buildings for immediate upgrading their fire safety provisions. The contrast to other common fire safety assessment scheme, the total fire safety concept is included in this new system. The likelihood of a building in having non-accidental fires can be assessed. In this thesis, fire safety aspects of atrium buildings were discussed. By studying the configuration of an atrium in a site survey, it was revealed that fire and smoke could spread rapidly in the huge atrium space and adjacent levels, leading to life losses, human injuries and property damaged. After the review on the existing codes, it was found that there are no tailor-made codes or regulations specifying the fire safety requirements for atrium. Having considered three fire scenarios, including fire at the atrium level; fire at a shop adjacent to the atrium at lower levels; and fire at a shop adjacent to atrium at upper levels, high headroom sprinkler following the fire services installation code was found not necessarily be capable of controlling an atrium fire. Fire safety of the IBV design for high-rise buildings was studied by covering the following three areas, including fire in a room adjacent to the internal void; spreading of smoke from the fire level to adjacent levels; and fire resistance provisions for windows. For a typical bathroom in a domestic building in Hong Kong, of size 2.25 m x 1.55 m x 3 m with an opening 0.6 m wide and 1 m high, the heat release rate (HRR), from Thomas equation, needed for such small room is only 0.5 MW which is a value easily obtained by materials stored inside the room. Fire models including application of Computational Fluid Dynamics (CFD) were used for the analysis of an IBV connected with 2 levels of bathroom. The CFD study from the literature includes five scenarios varied with opening conditions and pressure differential. The most undesirable fire scenarios happened when there was a negative pressure imposed at the door of the upper room. Results of the study indicated that there might be possibility of spreading hot smoke or even flame from the fire level to adjacent levels through the IBV. Further studies should be carried out to investigate the problem. Fire hazard of another new architectural feature - DSF was examined experimentally. Flame impingement onto the inner glass panes on the adjacent floors and cracking appeared on the internal layer of a DSF would be the most undesirable scenario. Full-scale burning tests on part of a full-scale DSF design were carried out in a facility developed in Northeast of China. A total of four sets of tests were performed to demonstrate how the depth of cavity of a DSF affects the smoke movement. Cavity depths of 1.5 m, 1 m and 0.5 m were examined. Surface temperature and heat flux received on the test panels were recorded. By comparing the measured surface temperature of the inner and outer glass panels, the possible smoke movement pattern inside the air cavity could be estimated. Cracking patterns found on the glass panels were also observed. The first cracking occurred when the bulk glass temperature was ranging from 120 C to 350 C and the heat flux was higher than 3 kWm-2. It has good agreement with the overseas studies in which the first cracking occurred when the bulk glass temperature was at about 110 C and the heat flux was about 3 kWm-2. Results showed that a deeper cavity might give better safety under the scenario studied. The outer glass panel would be broken rapidly for the cavity of 0.5 m deep but DSF with a cavity of 1.0 m deep appeared to be the most risky as glass panels above broke the most frequent among the different cavity depths. The inner glass panel might be broken before the outer panel, leading to an undesirable fire scenario. Possible collapse scenarios of the WTC twin towers assessed by local and international experts were studied and reported. Investigational results on the collapse mechanism were reviewed. Failure of end connections, dislodgment of fireproofing, insufficient thickness of insulation materials and higher heat release rate than a normal accidental fire were considered to be the possible factors to give total failure within one and a half hours. The fire resistance provided for the structural steel members were discussed. Uncertainties in the standard practice on fire testing conditions were pointed out. The mass needed for four fireballs generated at the twin towers was 12,000 kg of jet fuel. The possible heat release rate of the big fire triggered by burning huge amount of fuel was also estimated. The jet fuel carried by the planes would lead to HRR of up to 8 GW, a thousand time of a common design fire, on the typical floor area of WTC. Consequent to the WTC incident, the existing standards and codes were discovered to have problems in dealing with non-accidental fires. Further investigations are urged to carry out. Prior to that, a fire risk assessment scheme was proposed to identify buildings requiring more fire safety provisions. Having studied the four new architectural features of interest in this thesis by full-scale experiment, application of fire engineering tools, critical reviews on statutory requirements and literatures, and analysis of fire incidents, it was revealed that the new generation of architecture was usually associated with some hidden fire risks which had not been paid adequate attention before. By analyzing the development and establishment of the existing codes, including the standard fire tests and equal area hypothesis, their inadequacy in protecting new buildings against fires was unveiled. The fire safety objectives of the existing codes only taking accidental fires into account were evident to be insufficient in defeating non-accidental fires. In view of these findings, the existing fire codes would require major revisions and performance-based codes are needed to take non-accidental fires into consideration to protect new architectural features against fires. As these exercises would take time, a Fire Risk Assessment Scheme, including total fire safety concept, was therefore proposed in this thesis to provide quicker estimate for those buildings most likely to encounter non-accidental fire risks. By making reference to the prevailing fire risk indexing system and considering total fire safety concept, 24 parameters in the areas including passive building design, fire services installation, fire safety management, political stability and social stability were included in the assessment. From which, the relative fire risk the building encountered could be evaluated and prompt remedial measures for improving fire safety provisions could be thus determined. The diversified investigation results of this study can be unified to provide a checklist for designers' consideration when planning for innovative designs for which fire safety aspects should be paid extra attention. The checklist could become a good start in handling the brand new building designs and maintaining the fire safety level of our built environment.|
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