Fire safety challenges and performance based fire engineering design of high-rise buildings

Transcription

1 Tall Buildings: Tall Architectural Buildings: Architectural and Structural and Advances Structural Advances Fire safety challenges and performance based fire engineering design of high-rise buildings Kelvin H.L. Wong 1, Bassem Gamil Farag 2 & Mingchun Luo 1 1 ArupFire, Ove Arup & Partners Hong Kong Ltd, Hong Kong SAR 2 Abu Dhabi Civil Defense, United Arab Emirates ABSTRACT: Highrise buildings are always a major concern to the life safety of building occupants in emergencies such as fire incident due to the elevated height and extended vertical travel distance for the egress and fire-fighting access. In addition, as the industry and the society are becoming more and more interested to design multi-purpose developments which include office, retail, hotel and residential in the same building, additional fire safety hazards may have been imposed due to mixed usage and occupancy. The fire safety challenges of highrise buildings will be summarized in this paper with the introduction of innovative evacuation strategies plus advanced fire safety design method utilizing performance based approach to address those fire safety challenges. A proposed 380m multi-purpose ultra-highrise building in Abu Dhabi will be used to demonstrate how the above fire safety strategy can be practically implemented. It has been demonstrated in the proposed building that the use of performance based fire engineering design plus the innovative evacuation strategies can specifically address the fire safety hazards of highrise buildings and result a safe building design without significant increase in fire safety provisions and construction cost. 1 INTRODUCTION Highrise buildings are always a major concern to the life safety of building occupants in emergencies such as fire incident due to the elevated height and extended vertical travel distance for the egress and fire-fighting access. Although statistics suggested that highrise buildings have a lower risk of fire per unit floor area (Hall 1994), highrise buildings account for a very large share of people and property exposed, especially for a large number of modern highrise and ultra-highrise buildings designed and constructed in the Middle East and Asia with office, retail, hotel and residential in the same development. The multi-purpose highrise building design may impose additional fire safety hazards due to the mixed usage and occupancy. Since highrise buildings are unique regarded to their elevated height from conventional low rise buildings, different design considerations including design method and fire safety provision would be required. In this paper, the fire safety challenges of highrise buildings will be discussed. Advanced performance based fire engineering design method with phased and lift evacuation strategies will also be proposed to address the fire safety challenges of highrise buildings. Finally, a proposed 380m multi-purpose ultra-highrise building in Abu Dhabi will be used to demonstrate how the above fire safety strategy can be practically implemented. This proposed building will be used to demonstrate if the use of performance based fire engineering design and proposed evacuation strategies design can address the fire safety hazards of highrise buildings and result a safe building without significant increase in fire safety provisions and construction cost. 484

2 2 FIRE SAFETY CHALLENGES OF HIGHRISE BUILDINGS The fire safety in highrise buildings has always raised special attention by the general public and authorities. The fire safety challenges related to highrise buildings can be summarized into six major areas: fire department accessibility, egress and people movement, stack effect, increase in occupant and fire load, combination of occupancies, and arrangement of internal utility services. The above fire safety issues have been discussed in NFPA Handbook (Caldwell 1997) and can be summarized below. Due to the height of highrise buildings, it is expected that occupants would take longer time to travel from the level of their original location to the street level. In addition to the horizontal travel time from their initial position to the staircase lobby on the floor, the occupants are required to travel extended vertical distances which can up to a few hundreds meters. As a result, occupants may experience to walk hundreds of flights or thousands of steps in the staircase. Not to mention the tiredness of occupants, the slow discharge time will result in an extensive queuing in the entrance of staircases on each floor. Therefore there is a need to provide the effective means for the evacuation of highrise building occupants in case of fire or emergency situations. The increase in occupant load of highrise buildings is due to the stacking of floor upon floor over a hundred floors for ultra-highrise buildings. When compared with the number of occupants per building footprint and per staircase, the density in highrise buildings are significantly higher than the low rise buildings. In addition to the multi-purpose design of modern ultrahighrise buildings, such as observation facilities on the building top, hotel or service apartment on higher levels, office floors on lower levels, and retail or exhibition facilities in the podium, different usages and occupancies exist. The difference in occupancies which will have different familiarity with the buildings and alertness further complicates the evacuation behaviour in addition to the high occupant load. Stack effect is the induced natural air movement within the vertical shafts inside building which was created by the pressure differential due to temperature difference. Stack effect can become very significant in highrise buildings, which was capable of moving large volumes of uncontrolled heat and smoke from the fire floor to the whole building. The architectural atrium, lift shafts and internal utility ducts running through the building will further worsen the situation. There is a need to quantify the smoke spread behaviour within the building in order to address the static effect effectively. From the fire department s perspective, highrise fire can also present serve challenges and more complicated operational approaches in emergency response, include locating and attacking the fire, evacuating occupants, performing ventilation and fire fighting command (USFA 1996). Access to floors beyond the reach of ladder can only be limited to the building staircases. The large number of evacuating occupants due to the high occupant load as discussed above may occupy all the stairway widths, which are also the only access for firefighters coming up to assist the evacuation and fighting the fire. Therefore the ability to control and fighting the fire at the early stage would heavily be dependent on the building construction and the existing sprinkler system to deliver water to the fire area. The installed building fire protection system is essential for fire fighters to control the fire and its reliability is critical for highrise buildings fire safety. There are some major highrise fires where fire protection systems did not work properly at the time of fire and creating extreme challenges to even experienced and well equipped fire departments (NFPA 1988, USFA 1991). In terms of fire fighting, ventilation is an important issue to remove the heat and smoke in fire room. Ventilation to the highrise buildings during or after fire will be vertically limited and any horizontal ventilation will present the risk of falling glass from high level to the perimeters of buildings. The amount of time it takes to reach and take action for fire fighting would also be much higher in highrise buildings since it often takes longer path from the ground to the fire floor. Firefighters have to climb dozens of floors before they reach the fire floor. In highrise buildings, the fire fighting communication, command and control will become very difficult due to the large building size and complex building structure. Extra effort would be required to coordinate the fire fighting operations in addition to the extra personnel in fighting the fire for the fire department. 485

3 3 PROPOSED FIRE SAFETY SOLUTIONS In order to tackle the fire safety challenges of highrise buildings, performance based fire safety design method which is becoming widely accepted due to their clear advantages over the prescriptive code based design has been proposed for the fire safety design. In addition, among the fire safety challenges discussed in the above section, most of them are directly or indirectly related to the evacuation of building occupants. Therefore innovative evacuation strategies will also be proposed to facilitate the evacuation of highrise buildings. 3.1 Holistic Performance Based Approach for Fire Safety Design Performance based design of a building is to use a fire engineering approach to design the fire safety systems by taking into consideration of fire growth and spread, smoke movement, tenability or toxicity analysis, fire detection and suppression, means of escape, human behavior, fire hazard, fire safety management, etc. to achieve specified fire and life safety objectives. It is a new discipline and also a multi-discipline field which can specifically address the above listed fire safety challenges of ultra-highrise buildings discussed in Section 2. As a comparison to the traditional approach, fire safety design has been by reference to prescriptive guidance within building codes. These codes are generally developed in response to major fire incidents and drafted to be generic for all building types and functions. In another words it has been assumed by the prescriptive codes that the fire risks are the same for all building types and the same fire protection measures would be sufficient. For the highrise buildings in hundreds meter high and multi purpose usages, it is expected that the prescriptive approach to fire safety design of buildings may not be sufficient to address these complex building design. An alternative performance based fire engineering approach would be needed to better address and enhance the life safety in tall and complex developments. Performance based fire engineering can lead to new solutions and innovative development in fire safety system design. In addition, this new design approach gives a number of advantages over the prescriptive code as discussed below Flexibility in design For architectural and functional reasons, complex structures such as ultra-highrise buildings or shopping centers are frequently designed to incorporate large uncompartmented space in terms of atrium. A fire safety engineering design can justify the safety and risks and provide adequate protection to make the design feasible. It also allows the retail space or large carpark in a single fire compartment without fire separation in the present of suitable fire safety provisions High level of safety A fire engineering design is based upon the fundamental principles in fire safety, such as the analysis of fire load, fire scenario and risk using the latest research results and technology. A performance based approach in fire engineering design also takes into account the prescriptive code requirements and past fire incident statistics. This approach will provide an equivalent or higher level of safety compared with a prescriptive code approach Cost effective fire safety solution A performance based fire engineering approach uses design fires scenarios for fire safety system design and provides fire protection systems to meet the performance requirements. This approach optimizes the fire services system throughout the development and prevents oversupplying of fire protection provisions. Thus it can lead to a significant savings in capital investment and future maintenance cost. 486

4 3.1.4 Quantification of risks A fire engineering design will carry out analysis of fire load, fire development, smoke spread, tenability or toxicity of smoke and evacuation, which will quantify risks of people including occupants and firemen and risks to properties. A fire safety engineering design will ensure that the risks are under an acceptable level. Figure 1. The use of computer models to quantify the fire risk to people and properties 3.2 Phased Evacuation for Highrise Fires In highrise buildings with large number of occupants, it would take excessive time for occupants to evacuation if a single staged total building evacuation is initiated. Therefore an alternative phased evacuation has been proposed in case of highrise building fire to facilitate the evacuation of fire floor occupants. In phased evacuation, the occupants on the most critical floors like fire floor and floors nearby will be prioritized to evacuate first as shown in Figure 2. Therefore the queuing time into staircases for fire floors occupants can be reduced and occupants can leave the fire floors more quickly. The remaining occupants of the building are evacuated subsequently as necessary. The concept of phased evacuation relies on adequate fire compartmentation such that any fire occurring will be contained within the fire compartment prior to the arrival of the fire brigades. It means that only the occupants within the floor on fire need to be evacuated from the building immediately, whilst the remaining occupants only need to be alerted to an incident. Figure 2. The concept of phased evacuation Early detection of a fire and the raising of an alarm, together with a suitable automatic fire extinguishing installation for controlling the size of a fire, are important additional criteria. Facilities like stairs or fireman s lifts should also be provided to enable the fire brigades to have quick access to the location of fire origin. Similarly, well management control with trained fire marshals or fire wardens and well trained and disciplined staff, together with adequate means of communication within the building like addressable public address system on each floor, are essential to achieve safely and orderly evacuation. It is also important that people remaining in a building in fire are given appropriate information relating to the nature of the incident and the 487

5 action being taken to render it safe. Guideline is also available to provide the relevant principles and appropriate recommendations in phased evacuation for office buildings (LDSA 1990). 3.3 Emergency Lift Evacuation for Highrise Building Extreme Emergencies During the last thirty more years, extensive researches (Pauls 1977, Groner & Levin 1992, Klote et al. 1993a) has been made on the feasibility of using lift as a means of evacuation in case of emergency to facilitate building evacuation. Without imposing a height limitation or providing more and wider stairs, lift evacuation can be an important part of the solutions to effectively evacuate highrise building occupants. The development of using protected/hardened lift has already been recommended by National Institute of Standards and Technology (NIST) in US as the next generation of evacuation technology to be evaluated. In fact, lifts have already become a means of evacuating mobility impaired occupants (BSI 1999) since it is not realistic to expect the fire services personnel to carry people to safety via what may be hundreds of stair flights. Lifts have also been used in a number of tower structures for evacuating general public such as British Telecom Tower (Howkins 2001) in London and the Stratosphere Tower (Quiter 1996) in Las Vegas. From our experience, lift is an efficient means of evacuation during emergencies, which can reduce the total building evacuation time. When lifts are used in conjunction with stairs, it could reduce the amount of time for total building evacuation significantly (Wong & Luo 2005a). Interviews have shown that it took an hour to descend downwards from 91/F of World Trade Centre to street level using stairs (Fahy & Proulx 2002). Given that this was not at the peak hour, additional queuing time would need to be included in the evacuation time. Lifts could be used to evacuate occupants with disabilities who cannot descend stairs without assistance. Even for people without disabilities, descending many flights of stairs is an onerous task in highrise buildings. Furthermore, people evacuating by stairs could be exposed to other kinds of dangers such as tiredness, becoming dizzy, slipping on surfaces or experiencing fatigue. A reduced number of occupants using stairs can also help to free up space in the stairs for more efficient fire fighting access on upper floors (Burns, D.J. 1993). A refined lift evacuation strategy which consists of combining stair evacuation from a group of occupied floors to a protected area on transfer floor followed by lift evacuation from the transfer floor to street level is proposed as shown in Figure 3. The proposed lift evacuation strategy can prevent the major problems in traditional lift evacuation design including smoke spread into lift shafts, water spillage and fire hazard to occupants in lobbies (Klote 1982, 1986, 2004, Klote et. al. 1993b). For the proposed lift evacuation strategy, occupants on each floor will evacuate through the stairs to the protected area first, where the occupants can choose to travel down to the street level by using shuttle lifts or stairs. The comparison on the proposed lift evacuation strategy with the traditional method has been discussed in detail in the literature (Wong et. al. 2005). This refined lift evacuation strategy has also been adopted and approved in the 492m Shanghai World Financial Center (Guo et. al. 2004) in China. Figure 3. Proposed lift evacuation strategy in simulation model: transfer floor (left) and street level (right) 488

6 4 DESIGN EXAMPLE The above proposed fire safety solutions for highrise buildings have also been implemented in the design of an ultra-highrise building in Abu Dhabi. The purpose of this real project example is to demonstrate if the use of performance based fire engineering design can specifically address the fire safety hazards of highrise buildings and result a safe building design without significant increase in fire safety provisions and construction cost. 4.1 Building Descriptions The proposed development consists of a 380m ultra-highrise building with luxury residential and office floors on upper and lower portion of tower respectively. This building will sit on a large scale retail podium and basement carpark. Together with other highrise towers within the same development, this ultra-highrise building will become the landmark structure in that district. Due to the height and the multi-purpose design of this prestige building, special fire safety considerations are required. In addition, there is an architectural inspiration to create a vertical void penetrating all residential floors with a total height of 160m. Additional fire safety challenge has been created due to this vertical void for building. In order to enhance the fire safety design of this landmark building in Abu Dhabi, a performance based fire engineering design has been used with the above proposed fire safety strategy to address the special fire safety issues in this building. 4.2 Proposed Fire Safety Strategies The fire safety design of buildings can be classified in the areas of means of escape, smoke management, fire control and suppression, detection and notification, fire fighting provisions, fire resistance rating and fire safety management. Emphasis has been put in the means of escape and smoke management in this building due to the long evacuation time for this tall building and the present of 160m vertical void space. In order to facilitate the evacuation of building occupants for this mixed use building, the original requirement is to provide separate staircases between the office and residential occupants or increase the number or width of stairs in building. Both of the above proposals will cause a substantial increase in core size and reduction in office floor efficiency. In order to address the evacuation safety of occupants without significant increase in construction cost, phased evacuation for accidental fire scenarios and total evacuation with the assistance of shuttle lifts for extreme scenarios have been proposed. The residential floors and office floors can be shared with the same staircase shafts for evacuation instead of providing dedicated staircase for the residential floors. The use of phased evacuation involves the additional requirement that the fire alarm system should be addressable on every floor. For the use of shuttle lifts to assist building evacuation, the lifts need to be upgraded to the fireman s lift standard. When compared with the lost in efficiency of all office floor plates or additional staircase shafts, the cost of the proposed fire safety enhancement measure is considered minimal. The effectiveness of the above proposed evacuation strategies will be characterized using a performance based approach in the Section 4.4. For the void space penetrating the residential floors, the original proposal was to use fire rated materials to enclose all the openings facing the void. This will create substantial impact to the architectural expression of the void. In addition, the use of fire rated materials such as fire rated glass would be excessive when compared with the dilution of hot smoke by the cool air in the large atrium void. It has been proposed to use toughened glass without fire rating to protect the openings around the void. A mechanically assisted smoke clearance system is also proposed for post fire clean up within the void. The effectiveness of the proposed toughened glass to remain intact for any hot smoke within the void will also be investigated using a performance based fire engineering approach with computer software for analysis as discussed in Section

7 The use of toughened glass can significantly reduce the construction cost and maximize design feasibility of building. 4.3 Performance Based Fire Engineering Design Performance based fire engineering design has been used to investigate if the proposed means of escape and smoke management strategies can ensure the fire safety of building. Computational software (Wong & Luo 2005b) has been used as the tool for the analysis due to the large scale and complex configuration of this building. An agent-based evacuation model STEPS (Simulation of Transient Evacuation and Pedestrian movements), which can take into account the human factors and floor plan layout, has been selected for the means of escape analysis. Computational fluid dynamics software Fire Dynamics Simulator (FDS) v.4.0 (McGrattan 2005), which is appropriate for low speed, thermally-driven flow like the smoke and heat transport from fire, has also been used for the smoke management analysis. STEPS is designed to simulate how people move in both normal and evacuation situations within complex building structures. Other agent-based models are also available for evacuation modeling, but STEPS can model a large-scale evacuation in terms of tenths of thousand occupants with multi floors 3-D visualization. Human factors can also be inputted in STEPS for more realistic simulation. FDS is a computer program that solves the governing equations of fluid dynamics with a particular emphasis on fire and smoke transport. FDS was developed and is currently maintained by the Fire Research Division in the Building and Fire Research Laboratory at the NIST sponsored by Department of Commerce in US. It is widely used throughout the world as the CFD model for fire safety applications due to the large number of verification and validations by the academics and research institutes. 4.4 Means of Escape Analysis A number of evacuation scenarios have been simulated to investigate the efficiency of the proposed phased evacuation and emergency lift evacuation strategies in this building. The evacuation simulation scenarios are summarized in Table 1. Table 1. Evacuation simulation scenarios Scenarios Remarks Total Building Evacuation Phased Evacuation Use stairs only Use stairs and lifts High zone office floors Low zone office floors Total building evacuation Total building evacuation has been simulated in a way that all occupants start evacuation at the same time. This is the worst scenario as far as stair usage is concerned. Two scenarios, traditional evacuation using stairs only, and the proposed lift evacuation strategy of using lifts and stairs together, have been simulated. The comparison of total building evacuation time is listed in Table 2. A number of trials have been simulated for the stair plus lift scenario until the times for the last person from stairs and lifts to reach ground floor are the same in the model, which is the case that the discharge capacities of both stairs and lifts are fully utilized. The cumulative percentages of occupants evacuated from the building have been plotted against time in Figure 4. For the case of any undetermined human factors, such as occupants hesitating and refusing to take the evacuation lifts and insisting to use stairs for evacuation, the evacuation times should be bounded by the two cumulative percentage curves in Figure

8 100% % of occupants evacuated 90% 80% 70% 60% 50% 40% 30% 20% Lifts + Stairs Stairs 10% 0% Time (mins) Figure 4. Cumulative percentages of occupants evacuated from the building When comparing the total building evacuation times, it can be seen that using lifts plus stairs can reduce the evacuation time by 32%. Besides the total evacuation time, the time for a certain percentage of occupants who evacuated from the building can be another indicator to quantify the evacuation efficiency. In most cases, the total evacuation time is dominated by a few occupants who leave the building very late. From Table 2, it is apparent that the evacuation time can also be shortened by up to 33% at the early stage if a combined lift and stair evacuation strategy is adopted. This shows that the proposed lift evacuation strategy for this ultra-highrise building is also effective in evacuating a large number of occupants at the early stage of evacuation. Table 2. Time for different percentages of occupants discharged from the building Percentage Discharged Time (min) Stair Stair + Lift Change 25% (32%) 50% (32%) 75% (32%) 90% (33%) 100% (32%) Phased evacuation Phased evacuation has also been proposed in this building for office fire. Simulations on phased evacuation have been carried out on the high zone and low zone office floors. Comparisons have been made with the traditional total building evacuation strategy to characterize the benefit to adopt the phased evacuation. In this section, occupants are regarded to be evacuated when they enter the office floor protected stairs, where is the place of temporary safety leading to the outside of building. The floors involved in the evacuation process for different scenarios are listed below: Total Evacuation: all office floors evacuate simultaneously using stairs Phased Evacuation: fire floor plus one floor up and one floor down evacuate simultaneously Table 3. Evacuation time for total and phased evacuations Fire Floor Time (min:sec) Total evacuation Phased evacuation Change Low Zone 7:30 2:40 4:50 (64%) High Zone 39:05 3:30 35:35 (91%) 491

9 For both upper and lower office floors, it can be shown that the use of phased evacuation can shorten the evacuation time significantly. The time difference is more significant for the higher floor levels due to the blockage of staircases by the large number of occupants on the lower floors. Phased evacuation initiates the evacuation from the floors in immediate danger, that is the fire floor and floors immediately above and below fire floor. Therefore the fire floor occupants are prioritized to evacuate first and the required time to enter protected areas can be shortened significantly. 4.5 Smoke Management Analysis The purpose of the smoke movement simulations is to investigate if the hot smoke from lower level will break the upper floor windows and spread to the upper floors, which will breach the floor by floor fire compartmentation and endanger the life safety of upper level occupants. All apartment units in this building will be sprinkler protected due to the highrise building requirements. For a sensitivity study, additional scenario has been simulated to ignore the sprinkler cooling effect on the fire and smoke temperature. Local weather conditions and the combustion properties of design fire have been considered and inputted into the model carefully Apartment fire with the sprinkler cooling effect considered With the consideration of sprinkler system, the first head was actuated at around 113s. It can be found that most of the hot smoke has been cooled to below 100 C immediately after the sprinkler actuation as shown in Figure 5. The temperature of hot smoke in the fire apartment was limited and there was no breakage of glazing panel facing the residential void for the simulated time period. Figure 5. The actuation of sprinkler head (left) and cooling of room temperature within 100 C (right) At the time when sprinkler actuated, the water spray will cool most of the smoke layer to below 100 C (CIBSE 2003). Therefore it can be seen that the hot smoke layer in the fire room shall be cooled by the sprinkler spray to a temperature which is not likely to break the fire room glazing and affect the upper floors, as demonstrated in the simulation model Apartment fire with the sprinkler cooling effect ignored For a sensitivity analysis, it has been conservatively assumed that the sprinkler spray cooling effect in the room is ignored. The fire room temperature was raised to 200 C at 3.8mins and the glazing panel was fall off. Hot smoke spilled from the window opening to the residential void. It was observed that the hot smoke can rise to higher levels up to the roof of building in the simulation. Although there was cooling of hot smoke from the surrounding air, the temperature of hot smoke was high enough (3-4 C temperature difference to the surrounding air at high level of 492

10 void) to get the sufficient buoyancy to rise to the top. In order to investigate if the hot smoke spilled to the void will break the glazing panel facing the void on the higher floors, thermocouples have been installed in the FDS model to measure the higher level temperature. The measured glazing surface temperature on top of the fire floor by thermocouple is plotted in Figure Temperature (deg C) Time (mins) Figure 6. Measured glazing temperature on top of fire floor It can be shown from the above simulation results that the glazing temperature right on top of the fire room is generally below 150 C (with a few spots at 180 C) for the design fire in simulation. The proposed use of toughened glass, which is able to withstand an exposured temperature of about 350 C (Kim & Taber 1989) for toughened glass panel, should be sufficient to withstand without cracking or fall off. Therefore it can be demonstrated that it is unlikely the smoke from the fire on lower level spread to the floors above by cracking the upper floor glass panels, and the separation of 160m vertical void opening with toughened glass instead of fire rated enclosure is not likely to cause fire spread within the void. 5 CONCLUSIONS The fire safety challenges of highrise buildings have been reviewed in this paper. With the fire safety design of an ultra-highrise building as an example, it has been shown from the analyses that the proposed phased evacuation for accidental fire scenarios and total evacuation with the assistant of shuttle lifts for extreme scenarios can effectively reduce the highrise building e- vacuation time. The use of toughened glass in atrium void would also sufficient to withstand during the worst credible fire scenario and limit the spread of smoke in highrise building atrium void. With the use of performance based fire engineering analysis, the actual performance of the above proposed fire safety strategies specifically designed for highrise buildings can be quantified and investigated in detail, especially for the ultra-highrise buildings which have a number of fire safety challenges over the traditional buildings. In addition, it has been demonstrated that the use of performance based fire engineering design plus the new evacuation strategies can address the fire safety hazards of highrise buildings effectively and result a safe building design without significant increase in fire safety provisions and construction cost. 6 REFERENCES Pauls, J Management and Movement of Building Occupants in Emergencies. Proc. of 2 nd Conf. on Designing to Survive Severe Hazards, IIT Research Institute, Chicago: Klote, J.H Elevators as a Means of Fire Escape. Gaithersburg: National Institute of Standards and Technology. 493

11 Klote, J.H Elevator Piston Effect and the Smoke Problem. Fire Safety Journal Vol.11 No.2: NFPA Fire Investigation, Fire Intestate Bank Building Fire. Maryland: National Fire Protection Association. LDSA, Fire Safety Guide No.3 Phased Evacuation from Office Buildings. London: London District Surveyors Association. USAF High-rise Office Building Fire One Meridian Plaza Philadelphia, Pennsylvania. Maryland: United States Fire Administration. Groner, N.E. & Levin, B.M Human Factors Considerations in the Potential for Using Elevators in Building Emergency Evacuation Plans. Gaithersburg: National Institute of Standards and Technology. Burns, D.J Operation in Tower 1, The World Trade Centre Bombing: Report and Analysis. Maryland: United States Fire Administration. Klote, J.H. et al. 1993a. Workshop on Elevator Use During Fires. Gaithersburg: National Institute of Standards and Technology. Klote, J.H. et. al. 1993b. Fire Evacuation by Elevators. Elevator World, Vol.41 No.6: 66-70, Hall, J.R US Highrise Fires: The Big Picture, NFPA Journal 88 (2): Quiter, J.R An Application of Performance Based Concepts at the Stratosphere Tower Las Vegas Nevada. Proc. of Fire Risk and Hazard Assessment Sym., Research and Practice: Bridging the Gap, National Fire Protection Research Foundation: USFA, Operational Considerations for Highrise Firefighting Special Report. Maryland: United States Fire Administration. Caldwell, C Occupancies in Special Structures and Highrise Buildings, Section 9-1, Fire Protection Handbook, 18 th ed., Cote. E.A. ed. Quincy: National Fire Protection Association. BSI BS5588 8:1999 Fire Precautions in Design, Construction and Use of Buildings Part 8; Code of Practice for Means of Escape for Disabled People. London: British Standards Institution. Howkins, R Lift Modernization BT Tower London. The Arup Journal 3/2001: Fahy R.F. & Proulx G A Comparison of the 1993 and 2001 Evacuations of the World Trade Center. Proc. of Fire Risk and Hazard Assessment Sym., Baltimore, MD, CIBSE, CIBSE Guide E Fire Engineering. London: Chartered Institution of Building Services Engineer. Guo, D.G. et. al Lift Evacuation Design of Ultra High Rise Building. Proc. of the Fire Conf Total Fire Safety Concept, Hong Kong, Hong Kong Polytechnic University: Hong Kong. Klote, J.H Analysis of the Lift Safety Consequences of Smoke Migration Through Elevator Shafts, Atlanta Workshop On the Use of Elevator in Fires and Other Emergencies, Atlanta, American Society of Mechanical Engineer. Wong, H.L.K. & Luo, M.C. 2005a. Total Building Evacuation Strategy for High Rise Buildings. Tall Buildings, Proc. of 6 th Int. Conf. on Tall Buildings, Hong Kong, Hong Kong: World Scientific. Wong H.L.K. & Luo M.C. 2005b. Computational Tool in Infrastructure Emergency Total Evacuation Analysis. Lecture Notes in Comp. Science, Vol. 3495/2005, ISI IEEE Intern. Conf. on Intelligence and Security Informatics, May 2005, USA. Berlin: Springer-Verlag. Wong, H.L.K. et. al. 2005, A Refined Concept on Emergency Evacuation by Lift. Proc. of 8 th Intern. Sym. on Fire Safety Science, Beijing, London: International Association for Fire Safety Science. McGrattan, K.B Fire Dynamics Simulator (Version 4) Technical Reference Guide. Gaithersburg: National Institute of Standards and Technology. Kim, A.K. & Taber, B.C The effects of sprinkler location and activation time on the protection of glazing systems. Canada: National Research Council of Canada. 494