Real Fires for the Safe Design of Tall Buildings

A Fire Safety Strategy is an essential component of the design for a building. It ensures that in the event of a fire, building occupants can be evacuated safely. The main consideration in these strategies is time. The engineer must show that all occupants can evacuate the building without being exposed to the fire. This is particularly difficult in the case of tall buildings where occupants must travel long distances downward before they can exit the building. A rule of thumb to estimate total building evacuation time is one minute per floor. By this rule the 828m, 162 floor Burj Khalifa in Dubai would take more than 2.5 hours to fully evacuate. The 159m, 31 storey TVCC tower in Beijing was engulfed in a fire which spread up the entire height of the building within 15 minutes of ignition. Clearly, it would not have been possible to evacuate occupants in sufficient time to save them from this fire. It is therefore necessary to have a specific Fire Safety Strategy for these unique buildings.Firstly, the fire must be prevented from spreading vertically, confined to one floor for as long as possible, so occupants on floors far enough from the fire can remain safely in the building until the fire is extinguished or runs out of fuel. Secondly, the building must remain standing, again so that people still in the building and the emergency responders that enter it to fight the fire do not perish as in the World Trade Center disaster. Thirdly, the vertical escape routes must remain structurally intact and smoke free to allow safe passage of occupants from the building. If occupants cannot reach the outside of the building in a timely fashion, then the vertical escape routes must act as the outside and once reached, guarantee safety. To provide these three crucial elements and ensure the safety of occupants of tall buildings, designers must be able to approximate in a quantitative manner the fires expected to occur in these buildings. With optimal use of space being the driving force behind these designs, floors often consist of large, open plan compartments. According to the CTBUH, 82% of the tallest 100 buildings are partially or completely office use (62% completely). Fires in large open plan spaces tend not to cover the entire area of the compartment at any instant but instead propagate across it. These fires have been labelled "travelling fires" and given the statistics, it should be expected that these would be typical fires for tall buildings. Despite this, current methods of prescribing fires are based on data obtained with small homogeneously heated 4mx4m (approx) compartments. These methods, used since the beginning of the 20th Century, are still applied to all structures irrespective of their nature.Current state-of-the-art research shows that a realistic definition of the fire is essential to safely provide all three critical components of the Fire Safety Strategy but also that our current analytical and computational tools cannot provide this. This means we cannot provide an adequate quantitative assessment of the Fire Safety Strategy for tall buildings. Designers are thus not capable of assessing if safety measures introduced result in an under or over dimensioned building. Given the level of optimisation required for tall buildings, this is clearly an important weakness in the design process. As large-scale fire testing cannot be done for all possible building configurations, safe designs can only be achieved using properly validated tools. With no sufficiently detailed test data, fire models cannot be said to have been performance assessed, verified and validated for these scenarios. Real data is needed to establish modelling capabilities and identify problems, thus an integrated modelling/testing programme is essential. This project will conduct a series of tests and modelling studies to establish a methodology that generates real fire inputs for the safe definition of a Fire Safety Strategy for tall buildings.

This research will provide data to enable the improvement and validation of methodologies for design of tall buildings. Specifically, it will provide a fit for purpose design fire methodology to enable designers to develop robust Fire Safety Strategies. Despite the Fire Strategy for tall buildings being a unique problem, a specific methodology does not exist. The quantitative data and validated methods will be used by engineers worldwide to provide a quantitative assessment of the performance of different construction and architectural options. This will have a deep impact on sustainability, energy conservation, safety, definition of space, emergency response, security and the indoor air quality management. The beneficiaries will be built environment designers at all levels, from architects to building services, developers of prefabricated building components, urban planners, building standards developers, building authorities, the fire service and the public at large.The data and validation methodologies part of this project will provide an invaluable input for structural modellers and researchers who currently rely on an unrepresentative fire definition. Structural analysis from connection performance to global building behaviour will be done on the basis of a proper fire input. It is explicitly stated in the most advanced design methodologies (Eurocodes) for structural design for fire that the thermal input is not valid for compartments typical of most modern tall buildings. Elimination of this uncertainty will result in a more accurate quantification of factors of safety, thus the potential for improvement and Optimisation of tall building design. This will have a positive economic impact on the construction industry and provide a competitive edge for UK designers.This proposal has support from beneficiaries including governmental organisations, code developers, emergency responders, architects, engineering consultancies, and insurance providers (see letters of support). Communications to date have initiated a great deal of thought and concern within the industry on current design practices, which has led to collaboration between interested parties by way of providing resources for the research.Knowledge gained from this work will enable regulators to assess robustness when presented with such a strategy. The Scottish Building Standards Division has given support to the project, which will give direct access to the building regulator industry in Scotland, and provide an avenue to regulators both in the UK and abroad.The work will greatly impact the developers of fire modelling software by supplying a hereto unavailable set of data with which to validate the various models for fires of the size deemed typical of tall buildings. With a notable amount of data available for small sized compartments, this work will provide the opposite bound of data for the validation of these models.Given the multidisciplinary audience for this research, attention has been paid to modes of communication. It is envisaged that during the project the number of partners will increase, something that the communication and engagement strategy will actively target. The dissemination strategy will consider five target communities for direct dissemination, Architects, Civil Engineers, Fire Safety & Rescue Services, Tall Buildings community, Standards Developers & Government, accessed by publishing of articles in peer reviewed journals, industry magazines and technical conferences, and also through leadership and participation in the communities' interest groups. The CTBUH will serve as a vehicle to produce guidelines for tall building designers and has offered to dedicate a session on the research findings at one of its annual worldwide conferences. The BRE Centre for Fire Safety Engineering will dedicate its yearly conference, FireSEAT, with the resulting proceedings providing the technical underpinnings of the CTBUH guidelines.