A study on fire detection systems for supertall buildings

Abstract

Many supertall buildings of height over 300 m have been constructed all over the world. The fire phenomena associated with such buildings are very different from those for high-rise buildings shorter in height. However, there is no fire code specifically worked out for these supertall buildings in Hong Kong. It has been identified that early fire detection in a supertall building is important and being studied in this thesis. The associated fires codes were reviewed first for supertall buildings except the addition of refuge floors for residential buildings and commercial buildings with more than 40 or 25 storeys respectively. Because of the much longer evacuation paths in supertall buildings, evacuation provisions become essential for the occupants in case of emergency. The adequacy of existing provisions on evacuation for supertall buildings based on existing prescriptive codes specifications were evaluated and lots of problems were found. There are insufficient areas to protect the occupants in smoke free environment with much longer evacuation time according to calculated results for existing supertall buildings than assumed in local codes when the occupant load is over 70 % of the maximum value allowed in local codes. Hence, the integrity of the fire safety design for supertall buildings developed from existing fire codes is questionable. Early fire detection, which is one of the ways specified by local authorities to achieve equivalent performance in fire engineering approach, could help and improve the safety level. However, the working conditions for fire detection systems installed inside supertall buildings depend on many other factors beyond the criteria for developing the published design guides for the fire detection system in shorter buildings. All fire detection systems and technologies were analyzed with reference to physical constraints and environmental influences determined from site surveys. Among numerous impact factors on fire detection system, wind effect is the major one that strongly affects or even disables the detectability of common fire detection system used in supertall buildings with reference to analytical and experimental results. With limited coverage of fire detection within some parts of a building interior required from local codes, the impacts due to smoke and fire from adjacent buildings or fire hazard in densely packed urban cities such as Hong Kong were investigated. The corresponding consequences are far more severe than expected after several big fires were reported in Hong Kong. Some citizens and the management of supertall buildings were interviewed and most of them did not realize the fire safety problems within their buildings and external fire hazards. They were in a dilemma as to whether to reject the nuisances from false alarms or to hesitate for delayed evacuation in real fire cases. Uncertainty on the clearance of evacuation paths would further extend the required safe evacuation time. Improper management and inadequate awareness of the stakeholders were concluded from the interviews conducted for this thesis. In view of this, an effective fire detection system with appropriate fire alarm information and engagement of mutual monitoring for the fire safety level is proposed to resolve the problems mentioned above and minimize loss of life in case of fire. Closed circuit television surveillance should cover all public areas and plants rooms with thermal image cameras. When the video images can be monitored by all stakeholders, such proposal can fulfil the expectations of relevant parties as elaborated in this thesis.