The Future of High-Rise Building Design
By BOM Editorial Staff January 2006 - Commercial Office Facilities
In the weeks following the terrorist attack on the World Trade Center, media reports were filled with as many questions as they were facts. How did terrorists bypass airport security? How did terrorists gain access to airliner cockpits? How did foreigners learn to fly commercial airliners while living in the United States? The answers to most of the questions resulted in changes that were evident in longer airport security lines and the creation of a Department of Homeland Security.
But even as measures to thwart future attacks were put in place, one issue remained shrouded: Why did the towers collapse?
Now, after nearly four and a half years of intensive study, there is consensus about how the towers collapsed. But even today, there is no agreement on the lessons that can be drawn from that tragedy. The most ambitious attempt to define those lessons came in the final report on the collapse of WTC 1 and WTC 2 by the National Institute of Standards and Technology (NIST). That report offered 30 recommendations on ways that tall buildings can be made safer.
Some recommendations are concerned with structural stability. Others discuss how emergency responders should react to situations involving high-rises. Others lay out improved procedures for evacuating buildings.
The most far reaching of the recommendations have provoked a debate among facility executives, code officials and others involved in building, designing and operating high-rise structures.
This series of articles explores some of the issues that will determine how high-rises are constructed in the years to come. The first article looks at the NIST effort as a starting point for the discussion on how high-rises can be made safer. The second article looks at the issues surrounding a single recommendation — full building evacuation — that would change how building occupants and emergency workers respond to emergencies in high-rises. A third article looks at an element of building operations that NIST was not charged with investigating: building security.
As industry bodies grapple with possible changes to codes and standards, they will have to decide what sorts of disasters high-rises should be designed to survive. Although NIST officials say the recommendations were not developed solely on the basis of the terrorist attacks, others question whether they go too far in protecting against other kinds of threats. Those critics say that the World Trade Center attacks are unique, and therefore should not be used to justify taking very costly steps to implement some of the NIST recommendations.
Some industry observers might also use the contents of a forthcoming NIST report investigating the collapse of a third World Trade Center tower — WTC 7. Because that tower was spared the impact of an airliner, many are viewing its collapse as more typical of the type of emergency high-rises around the nation might face. That tower was spared the impact of an airliner. Although the NIST report due out in spring will detail the cause of the tower’s collapse, the agency has already reported fires resulting from the initial attack on the other two towers played a role.
Decisions of whether to require building codes that call for thicker fire-resistive coatings on high-rise structural members, use of redundant sprinkler systems, for example, will be influenced by whether such improvements are worth the expense. Many of the NIST recommendations will cost building owners money. In the case of some recommendations, perhaps a lot of money.
The codes and standards groups reviewing the recommendations face an arduous task. On one side, they’ll hear from a group of people who say nothing in the NIST report is worth implementing. On the other side, they’ll hear that everything in the report is not only valid, but that some specific recommendations don’t go far enough toward protecting buildings.
Code groups will be charged with plotting the middle ground without knowing exactly what future terrorist acts or natural disasters will test the limits of high-rise design. Those groups are charged with finding the elusive answer to the question, “How safe is safe enough?”
forming codes and standards
Speaking In Code
National organizations consider fundamental changes to how
high-rises are designed, built and operated
By Mike Lobash, Executive Editor
The collapse of the World Trade Center towers triggered an investigation unprecedented in cost and scope. Nearly 200 investigators spent more than $40 million and three years to determine why the towers collapsed and to issue recommendations on how to make high-rises safer.
Now, with 43 reports constituting more than 10,000 pages filed, the question has changed. No longer is the question, “Can high-rises be safer?” Rather, it is, “How safe should high-rises be?”
“The bottom line is no one can tell us how safe is safe,” says Gerald Jones, co-chairman of a National Institute of Building Sciences (NIBS) committee reviewing recommendations in the federal government’s final report on the collapse of two of the three World Trade Center towers that were destroyed in the attacks. “Everything is a compromise between safety and economics.”
Code organizations will likely spend the next several years discussing 30 recommendations contained in a National Institute of Standards and Technology (NIST) report aimed at improving the safety of buildings taller than 120 feet. At issue in the discussion will be whether the recommendations — taken individually — should be made part of the model building codes and national standards that govern how buildings are designed and constructed.
The recommendations are broken into eight subject areas. They are:
- Increased structural integrity.
- Enhanced fire resistance of structures.
- New methods for fire resistant design of structures.
- Improved active fire protection.
- Improved building evacuation.
- Improved emergency response.
- Improved procedures and practices.
- Continuing education and training.
As the recommendations are reviewed, some are likely to become model building codes with little debate. And a few recommendations, particularly those regarding education and training of emergency responders and of architects and engineers, require little or no action by code and standards organizations. One recommendation suggesting that academic, professional short courses and Web-based training materials be offered in the use of computational fire dynamics and thermodynamics, for example, affects professional associations and doesn’t require code changes.
Other recommendations will prove to be more controversial, with the amount of debate surrounding the adoption of each being proportionate to the cost involved with implementing it. Perhaps none of the recommendations are more controversial than the ones that aim to change the way high-rises are evacuated. One recommendation calls for full building evacuations during building-specific and large-scale emergencies, such as widespread power outages, fires, explosions, terrorist attacks and unforeseen natural disasters. Another would require high-rises to contain more remote exits and two sets of structurally hardened elevators. During emergencies, one set of elevators would be used by occupants and the second set by emergency personnel. The exact number of exits and elevators required would depend upon building size and the number of occupants.
Those recommendations constitute a sea change in the approach to the way high-rises are designed to accommodate evacuations. By and large, high-rises are designed to handle the evacuation of a single floor. If necessary, multiple floors are evacuated one at a time in what’s known as a staged evacuation.
That was the design approach at the World Trade Center towers, says Shyam Sunder, deputy director of NIST’s Fire Research Laboratory and lead investigator on the collapse of the towers. Stairwells were designed to be wide enough and positioned so that 390 occupants — the maximum on any one floor — could be evacuated at one time.
On Sept. 11, 99 percent of the people located below the floors of impact were able to escape the World Trade Center towers before they collapsed, even though the building wasn’t designed to accommodate full building evacuations, according to the final NIST report on the collapse of the towers. The story would have been different if the buildings were fully occupied.
Even so, Sunder says the recommendations in the NIST report were not based on the ability of a high-rise to withstand the impact of an airliner or to evacuate occupants after such a terrorist attack. Rather, they were developed to aid the evacuation of buildings for any emergency situation, including earthquakes, widespread power outages, tornadoes and other events.
“The need to evacuate a high-rise might need to happen even without a terrorist attack,” Sunder says. “If you look at the nominal life of a building as 100 years, there are likely emergencies that require full evacuation of buildings.”
If the recommendations will make high-rises safer in case of events other than terrorist attacks, that would help justify their being adopted in model codes. Some perceive the NIST report as being narrowly focused on preventing the catastrophic results of Sept. 11.
Samir Mokashi of the engineering firm IDC says immediately following the terrorist attacks, everybody thought that hardening buildings to withstand the impact of airliners was a potential design goal. But now that the event hasn’t been repeated in more than four years, support for that idea has waned.
“Is a plane going into a building something we need to protect against?” he asks.
Phil DiNenno, one of eight members of the National Construction Safety Team Advisory Committee, which advised NIST in its investigation, says of the 30 recommendations issued by NIST, one requiring additional remote exits might have changed the outcome of the attacks on Sept. 11. The addition of those exits — stairwells on the corners and on the perimeter of the building — might have allowed more occupants located above the floor of impact to evacuate.
“But that is singularly an expensive change,” says DiNenno, who is also president of Hughes Associates, a fire protection engineering firm.
The expense comes not only in the design and construction of additional exits, but in the loss of rentable real estate, most notably, the amount of premier daylit space landlords could lease to tenants along a building’s perimeter.
As the recommendations work their way through the code adoption process, expect debate among code-making bodies, building owners — who will ultimately fund the cost of the new codes through increased high-rise design and construction expenses — and building component and material manufacturers whose businesses stand to benefit or suffer from the adoption of certain recommendations as codes.
NIST has already contracted with NIBS to work on turning the recommendations in the final WTC report into code language that can be adopted by model code groups, including the International Code Council and the National Fire Protection Association (NFPA). Jones’ committee, aptly called the Committee for Translating the NIST WTC Investigation into Model Building Codes, is moving quickly to get at least some changes incorporated into the 2007 supplement to the International Building Code
. The deadline for submitting code change proposals for consideration in the next code cycle is March 24, with final action scheduled for May 2007.
“We’re going to do our best to get at least some of the recommendations adopted in the current code process,” Jones says.
Some of the measures recommended by NIST began working their way into codes and standards even before the agency completed its investigation. For example, NFPA included a provision in its 2003 edition to require wider stairwells for buildings with more than 2,000 occupants. In the 2006 code cycle, there were no dramatic code changes based on the NIST report, says Gary Keith, vice president of building and life safety for NFPA.
For the 2009 code cycle, which will be available for public comment in 2007, Keith says the association’s High-Rise Safety Advisory Committee will review the recommendations and monitor proposals for code changes.
“The questions will be whether anyone looking at the report sees recommendations that are worthy of code changes,” he says.
Shortly after NIST’s final report was issued, BOMA International, representing building owners and managers, issued a statement calling for further study, including a risk-benefit analysis, into some of the recommendations. One comment took issue with a NIST recommendation calling for the development of national standards and codes to prevent the progressive collapse of buildings.
“The big issue here would be to what extent it would be required to prevent progressive collapse?” wrote BOMA’s David Johnston, a member of the organization’s advocacy staff, in submitting written comments to NIST. “How many column failures (specific number, a percentage of a floor, etc…) would need to be able to be withstood? ‘Progressive collapse should be prevented’ is a pretty vague goal without a better explanation of what factors must be considered.”
Another recommendation that has drawn early criticism from BOMA is one requiring the fire resistance performance of structures. NIST recommends that uncontrolled building fires result in burnout without a structure suffering either partial or total collapse.
“The effort is a bit unrealistic and unwarranted,” BOMA wrote. “NIST assumes the complete loss of the sprinkler system, and no intervention by fire departments.”
As the process of reviewing the recommendations moves forward, code-making bodies will likely hear those types of comments as well. While the arguments might not be geared at questioning whether a certain code will make buildings safer, they will be pointing out that the cost of implementing a code might not be worth the expense.
“The real question as the process moves forward is how much will a change cost,” DiNenno says. “That’s the real world where code is written.”
elements of future high-rises
click on image for a PDF version
new evacuation procedures proposed
Full building evacuations and use of elevators during emergencies are among sweeping proposals for egress procedures
By Brandon Lorenz, Senior Editor
After more than four years, it’s possible to forget not only how tragic the events of Sept. 11, 2001, actually were, but also how much more tragic they could have been. Had the buildings been fully occupied, the National Institute of Standards and Technology (NIST) has estimated that it would have taken more than three hours to fully evacuate the buildings. In the process, 14,000 people — 28 percent of the occupants — would have died because of insufficient stairwell capacity.
Those stark numbers prompted NIST to call for changes in high-rise building design to improve evacuation time in an emergency. If the recommendations are adopted, facility executives could one day oversee high-rise buildings that have timely full building evacuation plans for non-fire emergencies. The buildings would have hardened elevators and stairwells. Stairwells would be wider and spaced farther apart, and upgraded elevators would be used for evacuation and for emergency responders.
But the NIST recommendations are both controversial and broadly defined, which means industry code bodies will have a significant role to play shaping the recommendations into code — if they are adopted at all.
New Approach to Evacuation
High-rises have been built assuming that the entire building wouldn’t need to be evacuated at once. Instead, during a fire on one floor, occupants evacuate to adjacent floors until it is safe to return.
What does timely full building evacuation entail? NIST’s recommendation says that a building’s size, population, function and iconic status should be taken into account in designing an egress system. “The key question is how much time should be allowed or specified for total safe evacuation,” says Milosh Puchovsky, principal fire protection engineer for the National Fire Protection Association (NFPA).
There is little agreement about how much time should be allowed for a full building evacuation because the topic is relatively new, says Ron Klemencic, chairman of the Council on Tall Buildings and Urban Habitat. “Clearly, if you put in 10 stairwells, you could get people out of the building much faster,” he says. “But how fast is fast enough?”
A full building evacuation during a prolonged power outage, for example, would not necessarily need to be rapid. An explosion, however, might require faster evacuation.
Even if there is disagreement regarding how fast a full building evacuation should be, elevators, stairwells and evacuation plans will all need major revisions to make full evacuation practical.
Structural Changes Required
The final NIST report on the collapse of the World Trade Center towers indicated that the overall evacuation rate in WTC 2 was 108 survivors per minute, about 50 percent faster than WTC 1 at 73 survivors per minute. That’s because occupants in WTC 2 used the elevators in the 16 minutes before the second tower was struck.
For more than 30 years, building occupants have been told not to use an elevator during a fire. With new recommendations from NIST for full building evacuation, the American Society of Mechanical Engineers (ASME) is examining whether elevators could safely be used to evacuate high-rises during an emergency.
Designing elevators that could safely be used during a fire or other emergency is a serious challenge, says Edward Donoghue, administrator for the National Elevator Industry Inc. (NEII) and a safety and codes consultant. For example, one hazard that needs to be overcome is keeping water used during firefighting out of the hoistway, Donoghue says. ASME is conducting separate hazard analyses to see whether elevators can safely be used by occupants for evacuation and whether they can also be used for emergency responders during a fire or other emergency. The NIST report also recommends emergency responders have access to a dedicated elevator.
“It’s a very extensive analysis,” Donoghue says. “It’s probably going to take another couple of years to complete.”
Upsides and Downsides
While elevators factor into the timely evacuation of high-rise buildings, NIST has not ignored stairwells. NIST recommends designing stairwells wide enough to accommodate both descending occupants and ascending emergency responders. That means wider stairwells. “For certain size buildings, provisions have already been implemented in NFPA 101 and NFPA 5000 that require additional stair width to accommodate the counterflow of emergency responders,” says Puchovsky. NFPA 101 is a life safety code. NFPA 5000 is a model building code.
The 28-story Cira Centre in Philadelphia, for example, has stairwells that are 50 inches wide, as opposed to the 44 inches required by code. Construction on the building began in 2003, and the stairwells were voluntarily widened, says Stephen Rush, leasing agent for Brandywine Realty Trust.
NIST has also recommended that stairwells be marked with consistent signage, be located farther apart without increasing average travel distance and maintain their integrity under foreseeable building-specific or large-scale emergencies. Each World Trade Center tower had three emergency stairwells, but only one stairwell in WTC 2 remained passable after the towers were struck, according to NIST. Increasing stairwell distance means more stairwells could move from the building core to the perimeter.
However, maximizing the distance between stairwells could slow evacuation as it takes longer for occupants to reach a stairwell, Klemencic says.
New York City’s World Trade Center Building Code Task Force issued a variety of recommendations in 2003 that are now required by the city’s Local Law 26. Three requirements regarding stairwells apply to buildings 75 feet and higher and are retroactive. Photoluminescent markings are required in all exit doors and exit stairs. Additional signage is required when the exit path is not clear and such signs must have battery or generator power.
Disaster planning in a post-9/11 world means evacuation plans should move beyond fires. Power outages, earthquakes, tornadoes, fires, explosions and terrorist attacks should all be taken into account when evacuation plans are formulated, according to NIST.
“When we are talking about full building evacuation, we are talking about evacuation for potentially any type of situation,” says Jim Carrigan, supervising engineer for fire and life safety for the Syska Hennessy Group. Prior to 9/11, for example, facility executives really didn’t talk about hazardous material issues when formulating evacuation plans.
Unlike NIST’s recommendation for full building evacuation, the recommendation for better evacuation planning appears to be gaining traction.
In one case, a tenant occupying multiple floors in a high-rise paid to have its evacuation plan reviewed and upgraded after the developer declined, says Carrigan. The original plan only contained provisions for a fire emergency, while the revised evacuation plan was broadened to take other potential emergencies into account. It was later adopted by all 40 building tenants, Carrigan says.
In New York City, Local Law 26 requires that emergency evacuation plans include non-fire-related events. “The idea was that while the codes have had sufficient fire protection and fire safety plans, the conditions of other emergencies that are not directly related to a fire have not been considered,” says Ronny Livian, chairman of the World Trade Center Building Code Task Force.
In earthquake-prone Seattle, a full building evacuation plan doesn’t necessarily make sense, says Ben Barron, vice president of development for Clise Properties, which manages 1700 Seventh Avenue, a 23-story office building. “We feel that the tenants are safer in our building than out on the street, at least until we analyze what is going on.”
Barron says that a man threatened to blow himself up while standing in the lobby of a nearby courthouse. Rather than completely evacuate the 1700 Building, tenants were moved away from the side of the building nearest the courthouse. The reason? Tenants who left the building likely would have gathered in a courtyard near the courthouse, placing them in danger.
Beyond the Exits
Facility executives can’t forget about occupants once they leave a building. Proper planning means making sure occupants remain safe once they are evacuated, says Livian.
“In a larger building, you may have an occupant load of 10,000 or 20,000,” he says. “Where do you put them and still be safe? You can’t just leave them out in the street.”
To be successful, full building evacuation plans must be tailored for specific buildings and the types of occupants in the buildings, says Carrigan. In addition, the plans require training so that facility executives know when it is appropriate to call for a full evacuation and when to call for a phased evacuation. What’s more, facility executives should not call for a full-building evacuation by paging the entire building and asking occupants to leave, as was the case on 9/11, Carrigan says.
“The purpose of a full building evacuation is to do a staged evacuation in a controlled manner,” he says. “With the current buildings, if the stairwells haven’t been widened, you have to do a staged evacuation or there will be a bottleneck.”
Comprehensive disaster planning also means accounting for mobility-impaired occupants. According to NIST, 6 percent of the occupants in the World Trade Center were mobility-impaired. In a traditional phased evacuation, mobility-impaired occupants can be moved away from a fire or other emergency with relatively little difficulty. A full building evacuation is more troublesome. Knowing which occupants are impaired and where they are located is key. Ideally, an evacuation plan also takes into account visitors and occupants who are temporarily impaired because of illness. In the case of non-fire emergencies, Carrigan recommends using elevators to evacuate mobility-impaired occupants.
In Seattle, Clise Properties has identified mobility-impaired tenants. In case of an emergency, a “buddy system” has been arranged to make sure the mobility-impaired tenants can get the assistance needed to evacuate, if necessary. The company has ordered an evacuation chair that will allow occupants to be evacuated down a stairwell, Barron says.
Even if the NIST recommendations governing full building evacuation and elevators are approved by code bodies, implementation will likely take years. While not all cities require high-rises to develop separate emergency action plans for fire and non-fire events, a proper plan that considers fire and non-fire-related emergencies can ensure that a building disaster doesn’t become a greater tragedy.
“In a post-9/11 world, everybody needs to have an emergency evacuation plan for fire and non-fire events,” says Carrigan. “We have different threats today.”
security guidelines to keep high-rises safe
De Facto Standards
Although codes don’t govern building security systems,
these high-rise systems have been upgraded across the board
By Greg Zimmerman, Managing Editor
Designing and maintaining high-rise security following 9/11 represents a multifaceted challenge to building owners. Absent a report like the one the National Institute of Standards and Technology produced with its list of recommendations for fire safety, evacuation procedures and technologies, high-rise building owners are largely on their own to determine how best to protect people and property at their buildings.
The need for particular high-rise security measures depends on a building’s location, proximity to other types of buildings, tenants, purpose and visibility, among other things. However, access control is one area of security that building owners have ramped up in high-rises nearly across the board since 9/11.
In the past, standard operating procedure had been to control access in many high-rises only after business hours, says Carlos Villarreal, vice president, national security and life safety for Trizek. Many high-rises had a single card reader in the elevator vestibule that wasn’t turned on until the close of the business day. While some access control was usually in place at the building’s main entrance, once a visitor or occupant made it through the first point, the person was free to wander.
“Traditional high-rise buildings were much like schools before Columbine,” says Sean Ahrens, senior security consultant at Schirmer Engineering and a member of the ASIS commercial real estate council. “They were open and people could walk around at will.”
Since 9/11, that has changed. Access is controlled 24/7 at elevators, including freight and service elevators. Visitors and occupants may need specific permissions tied to their credentials to gain access to certain floors. Also, gone are the days of flashing a badge to a security guard at a building’s main entrance.
“Optical turnstiles are being used more in large buildings,” says Geoff Craighead, vice president of high-rise and real estate services at Securitas and chair of ASIS commercial real estate council. “It’s all very well to have card readers at elevators, but if you can’t control piggy-backing at the main access points, then you’re not controlling access at all.”
Visitor management policies have also become more sophisticated. Gone is the simple sign-in sheet. In its place are automated systems that allow occupants to pre-register visitors, who are then given a badge, which must be returned when they leave. In many federal high-rises, or other buildings with many visitors, a dedicated visitor management station exists so as not to slow the entry of regular building occupants.
And it’s not just visitor management that’s getting its own lobby space. In general, experts say high-rise building lobbies are becoming more segmented and compartmentalized.
“It’s important to separate people that haven’t been screened yet,” says Lauris Freidenfelds, vice president at Sako & Associates. “Lobbies are getting bigger, too. The lobby is the area where there is most likely to be an incident. If there is an incident, it’s essential that the lobby is designed so the incident has the least impact on the rest of the building.”
Security by Design
To make controlling access easier, many high-rise buildings, including newly designed ones, are cutting back on the number of places people are able to get in and out. In addition, many high-rises have designated a single entry for mail, packages and large deliveries. New high-rises are being designed so that the mailroom is situated at the exterior of the building and can be cordoned off at a moment’s notice in case of a threat, says Ahrens.
Policies that govern vehicle access are receiving new scrutiny as well. It’s become common to design new structures with lower deck parking — structures with smaller floor to ceiling distances — near the building so that only small vehicles can fit. Higher deck parking for large vehicles that could potentially carry large amounts of explosives is farther away from the building. Also, experts suggest locating occupant parking near the building, with visitor or public parking located farther away. If the high-rise is serviced by underground parking, Ahrens warns that building owners should make sure measures are taken so that the building above is properly protected. “There needs to be increased vehicle screening,” he says. “That means putting mirrors under the cars as they come in and opening trunks.”
Other exterior measures intended to mitigate the effects of bombs include bollards, concrete barriers and even sculptures or artwork. Tiered landscaping or ponds, when the site allows, can also make approaching the building by vehicle more difficult.
However, if the high-rise’s site limits stand-off distances or physical measures, window film and blast-resistant glass can help reduce the impact of a bomb. New high-rises are sometimes being designed with fewer windows near grade. For instance, the new Freedom Tower, which will be built on the World Trade Center site, is being designed with no windows on the first 20 floors of the building, says Craighead.
Concerns about a possible chemical, biological or radiological (CBR) attack have led many building owners to monitor access to a once-ignored part of the building: grade-level exterior and interior air intakes. The danger is that a terrorist could dump into the air intakes an agent that is circulating through the building’s HVAC system within minutes. To combat that threat, some high-rise building owners are installing CCTV cameras with intelligent video algorithms on the air intakes. If a video frame is broken by motion, a security staff member is alerted automatically and can determine whether there is danger and, if so, begin evacuation procedures. This strategy probably won’t prevent an attack, but it can help speed the response and evacuation.
However, if the vulnerability is deemed severe enough, Craighead says some high-rise building owners have undertaken the significant cost of relocating the air intakes out of pedestrian reach.
Also, many new high-rise buildings are being designed so that exterior air intakes are at least 75 feet above ground.
In the case of an outside or nearby CBR attack, many building owners have instituted defend-in-place procedures, which were nearly nonexistent before 9/11. “Traditionally, tenants had been trained to evacuate,” says Villarreal. “But now we’re seeing seminars on how to shelter in place, and how to completely seal off a building so no one can get in or out.”
Freidenfelds says that practicing a procedure is just as important as instituting a procedure in the first place. “Make sure that response plans are exercised,” he says. “We don’t want to be dusting off these plans when there is an emergency.”
Guidelines for Securing Facilities
Several documents produced since 9/11 aim to provide direction to building owners on improving security. While these documents are all applicable to high-rise buildings, and security personnel responsible for those structures, none was developed specifically for tall buildings. They apply to a range of occupancies.
Instead of Code
Currently, no regulations or codes exist that govern how building security should be planned and executed. That’s because creating security codes would be like creating separate fire codes for each building, says William Sako, executive vice president of RJA Group and chairman of the board for Sako & Associates. A central challenge for a high-rise building owner is determining what risks or threats exist for a specific property. Identifying where dollars should be spent to address the most urgent vulnerabilities and selecting systems that best mitigate threats are the other critical challenges.
—Greg Zimmerman, managing editor