Exploring the Concept of Using Lifts to Assist the Evacuation of Very Tall Buildings
Existing buildings’ procedures are examined, and suggestions for future evacuation plans are made.
This article was first presented at the Sixth Symposium on Lift & Escalator Technologies, www.liftsymposium.org.
Evacuation times for very tall buildings, whether for planned evacuation, fire or non-fire emergencies, can be extreme. This article explores the concept of using lifts to assist the evacuation of tall buildings and discusses the major considerations for building designers.
As buildings are getting taller, there is a need to consider the safety of occupants during evacuation. The physical exertion required to walk down 100-plus flights of stairs and, in some cases, for longer than 2 hr., can be very challenging for many people. This unexpected physical exertion, added to the stress of evacuating a building during an emergency, can lead to tiredness, physical or mental injury and fatality.
The design of buildings and complete lift systems to withstand the effects of fire, smoke, water and loss of power can be very expensive in terms of equipment and in the potential loss of rentable area. However, depending on the fire- and life-safety strategy of a given building, an emergency may not require the simultaneous evacuation of all the occupants; therefore, evacuation by lift may not be required from all levels of a building and may not require the use of all lifts.
While designers are required to consider safe evacuation of occupants from all buildings, conventional stair evacuation of tall and very tall buildings can be hazardous. Designers have been considering the use of lifts to assist the evacuation of tall buildings for some time; first, as a matter of code to enable safe egress of all persons, including persons with disabilities and, secondly, as a means of reducing the overall evacuation time and risk of injury to evacuees.
The premise for most buildings is that lifts shall not be used in case of fire and that there shall be sufficient evacuation stairs to ensure a safe evacuation by all building occupants. The question is: does this current design model best serve the needs of occupants of very tall buildings?
There are two main issues with stair evacuation: does the number of flights of stairs cause undue physical stress to evacuees, considering their size, age and general ambulatory condition, and, does the time required to evacuate by stair lead to fatigue and cause undue physical and mental stress?
Evacuation stairs will always be an essential requirement for the life safety design of buildings, either as the sole means of evacuating the building or as a backup to other means of evacuation. That said, there are obvious benefits of using lifts to assist the evacuation when it is safe to do so.
If lifts are to be used to assist the safe evacuation of buildings, cooperation must be achieved among all persons responsible for the design of a building, including client, architect and engineers, and consent will be required from the local fire authority or building control department. Incorporating lifts into the evacuation strategy of a building should, therefore, begin in the early feasibility and concept design stages of the building. This article considers the options available for the evacuation of very tall buildings by use of lifts and stairs, and discusses the design issues, technical solutions and benefits, in terms of evacuation time and evacuee wellbeing.
As buildings have grown taller, the need to consider efficient and assured access into and around buildings and egress from buildings at all times and for all persons (including persons with disabilities) has grown ever more important. There have been technical discussions, specialist meetings, symposia and a vast number of papers written over the years that give an understanding of the problems to encounter and solutions to be found if lifts are ever going to be used to assist the general evacuation of buildings.
Throughout the 1990s, the American Society of Mechanical Engineers, National Fire Protection Association (NFPA) and National Institute of Standards and Technology (NIST) all held workshops for which papers were submitted to aid discussion on fire evacuation using lifts. At that time, the consensus was not generally in favor, as there was a huge skepticism about the safety of users, mainly due to a number of well-documented disasters, in which people had died while using lifts during building fires. Most of the issues discussed were technical ones and included machine failure, reliability of power supplies, lifts passing through fire and smoke zones, exposure to water and inadequate operation — all of which have since been addressed and can pose little or no problems for today’s design engineers.
One other major concern remained, and a 1997 study by So, Lo, Chan and Liu, considering the issue of human behavior while evacuating from building fires concluded that further research into the subject should be undertaken. The unprecedented attack on the World Trade Center (WTC) in 2001, which led to the collapse of WTC buildings 1, 2 and 7 in less than 2 hr. and to the death of 2,752 people has driven further studies into human behavior in fire emergencies. It is unlikely that the disaster could have been prevented by enhanced design measures, but the sheer length of time it took evacuees to escape the building is a matter for life-safety design and has been the subject of many studies since the 2001 disaster. Egan discovered that fatigue would be experienced in about 5 min., and Pauls discovered that the average speed of evacuation would be one floor per 16 s.
Investigations into the evacuation of WTC 2 have shown times in excess of 60 s. per floor. One of the problems is that, as fatigue sets in, evacuees will stop to rest and cause blockages in the escape stair, thus causing increased evacuation times for all.
The behavior of human beings under the stressful activity of evacuating buildings in real fire emergencies is something that has been very difficult to model or to predict. However, the evacuation of the WTC complex following the events of 9/11 has presented students and researchers with excellent insights into the factors that assist and hinder egress within the high-rise building environment.
There have been many research papers about human behavior in fires and many that were commissioned following 9/11 to address the issues raised by the evacuation of the WTC complex. Since 1998, the annual International Symposium on Human Behaviour in Fire has given students and researchers a platform to present their work and for delegates to debate the issues raised by research.
Much progress has been made, and more is now known on the behavior of people in fire emergencies and on the likely behavior of people during an evacuation. As such, more people are beginning to see the huge benefits that can be gained by designing lift systems to operate in fire emergencies and to assist the evacuation process.
The design and management of lifts costs more in terms of capital expenditure for both the design and construction phases of a building, but it can also lead to a reduction in income return, due to a likely reduction in the net lettable area through additional space requirements of lifts, refuge spaces and the various other aspects of building design. As such, all parties involved with the design (including client and architect) need consent if the concept of improved life safety through reduced evacuation times is to become a reality.
Since 9/11, many buildings have been designed and constructed with the use of lifts to assist the evacuation strategy, and many more have undergone changes to their original life-safety strategy to enable the use of lifts. One such development is Petronas Towers in Kuala Lumpur, the evacuation strategy of which has changed since the building first went into service.
This article investigates the evacuation strategy of several very tall buildings, including Petronas Towers, and discusses the use of lifts to assist evacuation and life safety in them. Finally, it sets out the general principles of design and issues to be overcome when using lifts to assist the evacuation of very tall buildings.
Existing Building Study
Although evacuation by lift was not always a design priority, the use of lifts to assist the evacuation of buildings in fire and non-fire emergencies has become increasingly more commonplace in recent years. Many of today’s tall and very tall buildings use lifts to assist the evacuation process in some way. A recent technical note by NIST in the U.S. explored the evacuation strategy of 12 high-rise buildings and provided an in-depth discussion of six of them.
This study considers four of the buildings discussed in the NIST paper, three of which have held the title of “world’s tallest building.” All four buildings are over 450 m tall, and as such, are classed as very tall buildings.
The construction of Petronas Towers was completed in 1998, and its height of 451.9 m made it the world’s tallest building at that time. The buildings are primarily office space with a single tenant, Petronas Chemicals Group, occupying one tower, and the other being let to multiple tenants. One unique feature of the towers is the adjoining bridge link at levels 41 and 42.
The fire- and life-safety strategy for the Petronas Towers was designed to meet BS 5588: Part 5. However, the British Standards (BS) code of practice (COP) that gave guidance on the means of escape for disabled people was BS 5588: Part 8, which has since been withdrawn in the U.K. but is often still referenced in other parts of the world. The COP recognized the use of lifts for evacuation of persons with disabilities and gave guidance on refuge spaces, evacuation strategies and lifts.[13 & 14]
The evacuation strategy for persons with disabilities is to wait in a designated refuge space adjacent to a firefighting lift (or other lift suitable for evacuation use) and/or an escape stair and await assisted evacuation by building management or the fire service. The evacuation strategy for persons with disabilities within Petronas Towers is as described in BS 5588: Part 8 and provides refuge space on all levels. The firefighting lifts are then used to evacuate waiting persons with disabilities before the fire service arrives.
The evacuation strategy for able-bodied people has changed since Petronas Towers first opened. At that time, the strategy required occupants below the bridge link (level 41) to use the escape stairs to safety and for occupants above the bridge link to use the escape stairs to reach level 41, then cross the bridge link and use the lifts in the adjacent tower to safety. At that time, an incident requiring simultaneous evacuation of both towers was not considered. Post 9/11, the strategy changed to account for the simultaneous evacuation of both towers.
Today, occupants above the link bridge use stairs to reach levels 41 and 42, where double-deck shuttle lifts are available to transport evacuees to the ground and mezzanine floors and to safety. It is not known if the shuttle lifts have special design features that allow their use when the fire is local to the lifts, or whether, in this case, the lifts shut down, and evacuation reverts to either stairs or the other tower.
Taipei 101 is an office building that also houses retail, a conference center and restaurants. Construction was completed in 2004, when Taipei 101 became the latest building to claim the title of the world’s tallest building.
The designers of Taipei 101 originally planned for traditional stair evacuation, but an evacuation conducted prior to completion took approximately 2 hr. to complete. Aware of the research undertaken after 9/11, the authorities decided to try another evacuation, but this time with the passenger lifts remaining in service. The evacuation using lifts and stairs took 57 min.
The decision to include evacuation by lift in the Taipei 101 evacuation strategy was made after the final design and construction stages, so only limited modifications could be made to enhance the reliability and safe operation of the lifts. However, the enhanced features were only applied to special emergency/service and firefighting lifts.
The building was designed with special refuge areas every eight floors to allow persons who could not use the stairs to wait in a fire-protected area to be evacuated by either the special evacuation/service or firefighting lifts. The firefighting and special evacuation/service lifts are the only lifts used in a fire emergency; all other lifts, including the main passenger lifts, are shut down. Although the full evacuation strategy is unknown, it is stated that refuge areas and lifts are available to assist the evacuation of all persons who cannot use the stairs, which may be targeted at persons with disabilities but does not discount other occupants. The designers considered the evacuation by lifts for persons who have difficulties using the stairs, although this strategy could not accurately quantify the number of persons who may need to use the refuge spaces and lifts.
Shanghai World Finance Centre (SWFC)
SWFC in Shanghai is a mixed-use development mainly consisting of offices, a hotel and a conference center. Construction was complete in 2007, and, although the design intent had been to construct a 510-m-high tower, due to restrictions on the height of the roof, the building was constructed to a final height of 492 m.
SWFC was designed to surpass the 1995 Chinese code for the fire-protection design of tall buildings (GB 50045-95), which required a refuge floor every 15 floors. Its design included a refuge floor every 12 floors.
Two special lifts were originally designed to serve the observation deck at the top of the tower but were modified to support evacuation from each of the refuge floors in an emergency. Occupants with disabilities and other occupants who cannot use the stairs to reach a refuge floor are required to wait adjacent to one of the firefighting lifts for evacuation by building management or the fire service.
The refuge areas serve two purposes: evacuees can wait and rest in a safe place before continuing their journey on foot, or they can wait for a lift to transport them directly to the ground floor. Evacuation by lift is a managed strategy: priority is given to persons with disabilities and others who find it difficult to manage conventional stair evacuation.
The Burj Khalifa is a mixed-use tower in downtown Dubai incorporating offices, a hotel and residential apartments. Construction of the tower was complete in 2009 to a height of 828 m, which made it the world’s tallest building from that date. The building was opened to the public in 2010. It was constructed to IBC: 2003 and to NFPA 101 fire and life safety code and was designed for the use of some lifts to assist the evacuation process. A full building evacuation uses 10 of the 58 lifts installed in the building.
Burj Khalifa has 163 floors and fully fire-protected and pressurized refuge spaces on levels 43, 76 and 123. Occupants are expected to leave the fire-affected floors via the emergency stairs and walk to one of these refuge spaces, where they will be transported via lifts to the exit floor and safety. Design information states that total estimated evacuation time using a mixture of stairs and lifts is 90 min., with 55% of the 19,000 occupants using stairs, and 45% using lifts.
Summary of Existing Building Evacuation Strategy
The aforementioned buildings use lifts to assist the evacuation strategy, but each uses them in a slightly different way. The evacuation strategy for Petronas Towers is different for occupants of the upper and lower zones of the building. Occupants of the lower floors are expected to use the stairs to reach the building exit, while occupants of floors above level 42 use the stairs to reach level 42 before transferring to shuttle lifts.
Taipei 101 has special service/evacuation lifts to transport evacuees from refuge areas located every eight floors to the main exit floor. The lifts were designed for evacuation after the construction stages, so only limited modifications to enhance reliability could be made. As such, it is unknown whether the available lifts provide sufficient capacity for the expected number of users.
Like Taipei 101, SWFC has special evacuation lifts to transport evacuees from refuge areas to the main exit, but, in this case, the refuge areas are every 12 floors. SWFC has only two lifts designed to assist evacuation, so the evacuation strategy is unlikely to make provision for all occupants.
Burj Khalifa uses 10 lifts to assist the evacuation of the tower. They operate between three specially designed refuge floors and the main exit. Occupants use the stairs to reach the nearest refuge floors, where they wait to be evacuated by lift. The building design and evacuation-lift configuration are unknown, but 45% of occupants being evacuated by lift equates to 8,550 people.
Irrespective of whether the building evacuation strategy makes provision for the evacuation of all occupants or for disabled and injured persons only, lifts used to assist evacuation will have to be specially designed for the purpose and should be installed in a fire and smoke protected core.
Safe and Reliable Operation
Many studies have considered the design issues relating to the safe use of lifts in a fire emergency. One very early study in this regard was by So, et al (1997), who listed a number of areas of concern needing further research if lifts were ever to be used as part of an evacuation plan. The following discusses the areas of concern.
The danger of machine failure can be brought about by: loss of power, non-fire-related failure of equipment or fire-related damage to equipment, and can occur whether the lifts are in normal service, or in firefighting or evacuation mode. With an unprotected lift, there would certainly be an increased risk of failure during a building fire; the main issue here is to try to minimize the risk of failure through good design.
A building and lift installation designed and constructed in line with the requirements of BS 9999 (2008) and BS EN 81-72 (2015) should have a reduced risk of loss of power or machine failure due to the effects of fire, smoke or water. This COP recommends that machine rooms be constructed within firefighting shafts, defining a firefighting shaft as “a protected enclosure containing a firefighting stair, firefighting lobbies and, if provided, a firefighting lift together with its machine room.” When considering the possible failure of the main power supply, the COP recommends the use of a backup power supply from an alternative source. Such a source could be either a separate substation or a generator-driven supply.
Research shows that lifts have a likely breakdown rate of one every 62-1/2 days, equating to one breakdown every 90,000 min. The likelihood of a breakdown in a 10-min. evacuation period would, therefore, be considered as 9,000:1. Since this is a case of balancing the possibility of smoke breaking through to the firefighting shaft against that of the lift breaking down, two simple control measures that would reduce the risk could be put into place. First, the breakdown rate could be improved by employing a more rigorous maintenance program for lifts that may be used for evacuation. Second, by monitoring for signs of smoke within the firefighting shaft, the lift could be forced to the evacuation floor and out of service at the first signs of danger; in this case, evacuation would revert to stairs only.
Obstruction of the fire service would only become an issue if the firefighting lifts were used as the main evacuation lifts. As previously discussed, firefighting lifts can be used before the fire service arrives on site to assist the evacuation of disabled persons. Once it arrives, it would take control of the lift and the operation of assisting injured and disabled persons out of the building.
It is recommended that, in line with the current COP, the evacuation strategy only consider the use of firefighting lifts for injured persons and persons with disabilities. If the evacuation strategy requires the use of lifts for the evacuation of other occupants, then lifts designed for the specific purpose of evacuation should be used. In this case, the risk of obstructing the fire service from going about its duty is reduced.
The evacuation of a building may require many people to be transported from specific floors of the building to an exit level in a very short time. Lift groups are not normally configured for this type of traffic and may have inadequate configuration and operation for it.
For office buildings, the main passenger lifts are generally configured to provide acceptable performance during the morning or lunchtime peaks, up-peak and two-way peak, respectively. Lift systems for hotels and residential buildings may also be configured for acceptable performance during two-way peaks but at different times of day. In all cases, the lift configuration will be designed for a peak period of operation other than evacuation.
This does not mean that lifts cannot be configured with evacuation in mind or that the control system cannot incorporate adequate evacuation software. Whatever configuration of lifts is eventually used to assist the evacuation will require calculations to be performed to understand the likely evacuation time when using lifts.
Lifts used during a fire emergency could be exposed to the effects of the fire while passing through zones of danger. One solution to prevent smoke from entering the fire-protected core or lift shaft would be to pressurize the core and/or lift shaft. The need for and extent of pressurization would depend on the evacuation strategy, building arrangement and lift configuration, but, in all cases, the evacuation lifts, lift lobbies and refuge areas should be protected against smoke and the effects of fire much the same as any other escape route or stair.
All lifts use electrical circuits – on the lift car, in the hoistway and in the machine room – and as such, should be protected from exposure to water. Water from sprinkler systems and direct from fire-service hose pipes could cause electrical failure if allowed to enter the hoistway or machine room. Firefighting lifts are designed to prevent water entering the lift shaft by ramps or gullies, and to detect and remove any water that finds its way into the lift shaft by sump pumps or drains in the lift pit. In addition, wiring and equipment should be protected against the effects of water by being installed in a minimum of IPX3-rated enclosures.
Generally, passenger lifts are not designed to operate in the presence of water, and additional features should be installed to ensure that casual water from building fire-prevention systems does not affect the reliability of lifts that are to be used for evacuation. Consideration should be given to the design of fire-protection systems that do not require sprinklers in lift shafts, lift lobbies and ramps, and gullies should be installed at convenient locations to prevent water entering the lift lobby and shaft. Preventing water entering the lift lobby and lift shaft would be a better solution than providing the aforementioned water protection for firefighting lifts, but it is unlikely that prevention methods can be assured, so, a level of protection will also be required.
One other non-technical point of concern was raised by So, et al (1997), who foresaw problems relating to the complex psychological reaction of the evacuees to a building fire and a forced evacuation of the building. Evacuees may suffer an inability to understand and follow evacuation guidelines in the stressful environment of a fire emergency. Apart from the stress, anxiety and possible panic evacuees may experience when the fire alarm is raised, they are likely to struggle to carry through any preplanned evacuation routine. There is a recognized theorem that people require information to prevent the onset of panic. Research in the field of human behavior in fires has shown that panic is not inevitable, and that clear and precise information can help people remain calm.
So, et al (1997) were concerned about lift operation in an evacuation and suggested lift control systems with “computer vision” would be better and that modern systems were more than capable of this type of operation. From this approach, it would seem they were advocating some type of crowd control by vision-adjusted elevator control operation.
This concept is not only possible, but such equipment is available and adaptable for use on lift control systems. It is recommended that all evacuation control systems use a type of information fire warning system to pass lift and evacuation status information to evacuees waiting at upper floors to stop the onset of panic. This does not mean that evacuation operation should be by automatic or any other type of control, just that the progress of the evacuation and lift operation should be made visually and audibly available for building occupants waiting to be evacuated.
Each of the existing buildings presented here uses a different strategy for evacuation, and each strategy requires a different number of lifts to meet the expected demand. However, some of those buildings had a different evacuation strategy in place at the design stage than they have in place today, and, as such, it is uncertain whether the lifts have sufficient design features to ensure reliable operation or to ensure their use in all types of emergency.
It is important that the strategy is set early in the design life of the building, and it can be met by the existing lift configuration. Otherwise, additional lifts may be required. Additional lifts mean less rentable area and could affect the viability of the project.
The right lift configuration to assist the evacuation of any given building may be inappropriate for another building and will depend on the type and use of the individual building and existing lift arrangement.
The design issues to be overcome if lifts are to provide safe and reliable operation during a building evacuation and lift performance during evacuation mode have been discussed here. The right solution is one that provides sufficient lift capacity to meet the needs of the evacuation strategy and a robust design that ensures each of the design issues is met.
Theoretical Lift Performance
Table 2 depicts a lift arrangement for a typical tall building. High-level calculations have been performed to determine how many and which type of lifts are required to meet the expected demand, given the occupancy in the table. The low, mid and high zones are served by double-deck lifts, the sky lobby by double-deck shuttle lifts and super-high-rise zones by single-deck lifts. Table 3 contains high-level results for the stated typical building arrangement and for an assumed 12% demand during an up-peak period.
Assuming the lifts for the above typical tall building meet the performance requirements for up and two-way peak traffic, it is almost certain they will provide sufficient capacity for down-peak traffic; evacuation can be considered a form of down-peak demand. A potential evacuation strategy for such a building would be for all persons below the sky lobby to use the stairs and for all occupants of the super-high-rise zone to use the stairs to the sky lobby at levels 49 and 50, and, from there, use the shuttle lifts to exit the building. If we assume a worst case of a total evacuation (1,920 persons) of the super-high-rise zone and that the evacuation demand will be 100% down traffic, the round-trip time (RTT) and handling capacity of a given lift arrangement can be determined by:
RTT = (Equation 1)
Equation 1, presented by Barney, is for a double-deck lift with multiple stops. However, if we assume the shuttle lifts will travel between two set stops, we can state that each trip would include only one stop, with one period of loading, one period of unloading and two high-speed journeys between the ground floor and the sky lobby. The RTT equation can be simplified for the proposed manual evacuation and become:
RTT sky lobby shuttle) =
where S = average number of stops; P = average number of passengers; tT = single-journey travel time, which can be calculated by kinematics for each journey to and from the sky lobby; tS = time, associated with each stop: (door open time + door close time + start delay); and tP = period of time for a single passenger to enter or leave the car.
Using Equation 2, with rated capacity per car (CC) = 24 persons; average number of passengers per car (P) = 24 X 0.8 = 19.2; and passenger average transfer time (tp) = 0.8 s.:
RTT (sky lobby shuttle) = (2 X 40) + (1 + 1)(1.9 + 2.9 + 0.5) + (2 X 19.2 X 0.8)
RTT (sky lobby shuttle) = 121.32 s.
INT (sky lobby shuttle) = RTT/no lifts = 121.32/4 = 30.33 s.
Number of trips = super-high-rise occupancy/persons per trip (2P) = 1920/38.4 = 50
Evacuation time (super-high-rise zone) = (INT X number of trips)/60
Evacuation time (super-high-rise zone) = (30.33 X 50)/60 = 25.275 min.
The calculation is very simplistic but gives an idea of the possibilities of using lifts for evacuation. The example lifts are shuttle lifts designed to meet performance targets for the morning up-peak and could theoretically evacuate the total super-high-rise zone in approximately 25 min.
The above tall-building example may have an evacuation strategy that also requires the use of lifts for persons in the mid- or high-rise zones, for which there would be numerous options to execute the evacuation. Each option would require consideration for the design of lifts, the building environment in which the lifts operate and the performance of the group in evacuation mode.
A decision needs to be made for whether the lifts are to operate on normal control, under management control or with some special, bespoke evacuation control. The current COP for reference to means of escape for disabled people is BS 9999 (2008), the COP for the design, management and use of buildings. The COP recommends adopting a management strategy for evacuation and suggests that lifts used to assist the evacuation of disabled people should be operated under the direction and control of the fire-safety manager. The previous (now withdrawn) COP for means of escape for disabled people, BS 5588: Part 8, also recommended to adopt a management strategy for evacuation and to avoid automatic operation of lifts.
Lift lobbies and refuge areas should be considered fire protected cores with access to escape stairs and with minimal risk of fire and smoke infiltration. Information fire warning systems should be incorporated into the refuge areas and lift lobbies to provide up-to-date information on lift arrival and departure status and to keep the evacuees informed as to the progress of the evacuation.
As discussed, the lift shafts should be designed with a minimal risk of smoke infiltration by considering the fire loads of the lower ground and mezzanine floors and by avoiding the need for pressure-release holes in lift shafts. Sky lobby lift lobbies should be designed without sprinkler systems or provided with a means to prevent water entering the lift lobbies and lift shafts.
Building Design Implications
Every solution is different, but, in this case, the only implication on building design is the requirement for a refuge area at the sky-lobby level, which will reduce rentable area and increase design costs.
Lift Design Implications
The shuttle lifts should have additional features to enable safe and reliable use in fire or non-fire emergency evacuation.
Normally only firefighting lifts require emergency power supplies, but, in this case, an additional supply would be required for the four double-deck lifts serving the sky lobby. In addition, there may be a need to pressurize the shuttle lift lobbies, although it may be possible to achieve this through natural means.
The evacuation strategy for a design similar to the above example would require management control of the evacuation, emergency telephones at the lift lobbies, refuge areas and emergency command center, and a number of trained staff in the refuge areas and lift lobbies.
The intent of this paper was to discuss the implications of using lifts to assist the evacuation of tall and very tall buildings. The paper investigated the evacuation strategies of four existing tall buildings, including three that have held the title of the world’s tallest building. With reference to previous papers on the subject, the main design issues were discussed and solutions presented for design requirements that would ensure safe and reliable use of lifts during evacuation.
A typical building was presented as an example, showing that, generally, lifts configured to meet performance requirements during a main traffic peak would normally provide acceptable performance during evacuation mode. In this case, shuttle lifts designed to transport 12% of occupants of a super-high-rise zone in 5 min. during a morning up-peak were capable of evacuating the entire super-high-rise zone in less than 25 min.
It is important that if lifts are to be used to assist the evacuation of a building that they are part of the overall life-safety strategy for the building. Many modern buildings have compartmentalized construction and employ phased evacuation, in which only floors immediately adjacent to the fire floor are evacuated. However, in cases where the fire spreads, and the phased evacuation is escalated, it may become necessary to evacuate a complete zone or even complete building. This is why a total evacuation should always be modeled.
Every building is different, but, if consideration is given to the design of lift systems to assist the evacuation strategy at the building concept stage, all parties to the design process can have input. The use of lifts to assist either a full or partial evacuation of any building is possible but depends on early cooperation among the client, architect and design engineers. There will always be sufficient lifts in a building to evacuate the total occupancy in a reasonable time. The question is, can the building afford a design that would make it safe to use the lifts?
Many buildings currently under design have accepted principles of design that will enable lifts to be used to assist evacuation, and it is hoped that presentation of case studies for these buildings will be possible at a future Lift Symposium.