Around the world, from New York and Chicago to Seoul, Dubai, Hong Kong, and Moscow, new super-tall buildings are (or will soon be) scraping the sky at unprecedented heights and speed of completion. Real estate developers are engaged in a high-stakes, high-rise global competition of who can build the tallest building fastest and claim the coveted title. The Burj Dubai, soon to be completed in Dubai, a major city within the Middle Eastern nation of the United Arab Emirates (UAE), will soon become the world's tallest building, but perhaps not for long. Dubai is expected to have six supertowers of over 100 floors each by 2015.
Meanwhile, based on the events of Sept. 11, 2001, in New York, architects, engineers, government officials, and building code experts worldwide are concerned about the impact a terrorist attack, fire, earthquake, or other disaster will have on public safety, building occupant evacuation, emergency response, and related professional liability issues for high- and mid-rise buildings in urban centers.
Model Code Changes Adopted
Safer buildings, especially tall buildings that are more resistant to fire and more easily evacuated in emergencies, are the goal of the first comprehensive set of building code changes recently approved by the Intl. Code Council (ICC) based on recommendations from the findings of the National Institute of Standards and Technology (NIST). The recommendations were based on NIST's 3-year investigation of the collapse of the World Trade Center (WTC) on Sept. 11, 2001.
The changes will be incorporated into the 2007 supplement to the ICC's Intl. Building Code (IBC), a model code used as the basis for building regulations and enforced by U.S. state and local jurisdictions, which have the option of incorporating some or all of the code's provisions. Typically, most provisions are adopted. The proposed changes were developed and refined by a group of building code experts convened by the National Institute of Building Sciences (NIBS) with NIST support.
The proposals address areas such as increased resistance to building collapse from fire and other incidents, use of spray-on fireproofing, performance and redundancy of fire protection systems (automatic sprinklers), fuel oil storage, elevators for use by first responders and evacuating occupants, the number and location of stairwells, and exit path markings. The full roster of recommendations may be found at http://wtc.nist.gov/. Among the recommendations are the following:
- An additional exit stairway for buildings more than 420-feet high.
- A minimum of one fire service access elevator for buildings more than 120-feet high.
- Luminous markings showing the exit path in buildings more than 75-feet high to facilitate rapid egress and full building evacuation.
Additionally, two more model code changes will be considered as proposals to be submitted by the August 2007 deadline for the next code revision cycle and for the IBC. If adopted, one of the key provisions would recommend that structures be designed to mitigate progressive collapse and ensure minimal structural integrity and robustness requirements for structures as complete systems.
Interviews in June 2007 with two key officials - Dr. S. Shyam Sunder, acting director, building and fire research laboratory at NIST and the lead WTC investigator, and William M. Connolly, RA, director of codes and standards for the New Jersey Department of Community Affairs in Trenton, NJ - provided background on how NIST approached these proposals. Several prominent U.S. architects and engineers who were contacted declined to be interviewed, presumably because of the sensitivity of some of these proposed code changes.
Impact of the NIST Recommendations
According to Dr. Sunder, "The collection of changes includes a specific discussion of the third stair in high-rises. The recommendations are intentionally performance focused, not prescriptive. Official code change proposals may be more prescriptive."
Full evacuation capability from high-rises, and how best to accomplish that, is an industry-wide issue. Additional stairs, and wider stairs, to allow more occupants to descend at once, as well as occupant evacuation elevators, serve specific purposes. This may include a dedicated elevator bank or a designated fraction of elevators for occupant, fire service, and emergency responder access.
Proposals relating to progressive collapse, which concerns structural loads and design, are in the next review cycle. The basis of the NIST recommendations and the codes is in design of structural components, such as floors, columns, girder beams, and the reliability of methods used to design components, not assessing structural systems. Two buildings may have two different structural systems, but there are no metrics to measure the safety factors. With cars, for example, the crash-worthiness of the entire car can be analyzed, but this is not so for buildings.
Providing minimum safety levels in buildings is one of the NIST goals. "We shouldn't stop at one set of elements, but look at system-wide building safety as a whole, which has not been consistently and thoroughly done in codes. We need to ensure safety and system robustness, regardless of the threat," observes Dr. Sunder. This includes minimum robustness and structural integrity in all structures for various threats, hazards, and events that may occur in the normal course of the 100-year life of a building rather than designing against a specific threat, such as blast.
Risk assessments should address specific threats and explicitly account for them, Dr. Sunder adds. Codes apply to all buildings and provide minimum thresholds for robustness and structural integrity. Industry groups are considering whether codes should mention risk assessments in addition to robust requirements as recommended specialized undertakings.
Adding a third stair or multiple stairs appears to be among the most controversial provisions of the recommendations, which were voted on by building code officials. Occupant evacuation elevator standards will be available in the future. When considered together, additional stairs and elevators should allow complete occupant evacuation from high-rises in a coordinated fashion.
Not everyone in the building industry is pleased with these recommendations, nor will they openly discuss them. For example, before the City of New York adopted Local Law 26, revisions to the New York Building Code in 2004, an industry-wide task force of more than 400 representatives in design, construction, real estate, emergency services, and other trade groups was formed to review various proposals based on lessons learned from the collapse of the World Trade Center. Some of the most powerful New York real estate and construction groups participated and, despite concerns about additional costs and lost rentable space, consensus was achieved regarding wider stairs and other provisions.
Outside New York, Washington, D.C., and major cities where perceived risks and threats may be lower, mid-rise buildings might be more common, and developers are less willing to pay for safety enhancements when they believe the risks and threats are low, such code proposals may not be well received.
Real estate interests have typically opposed wider or additional stairwells and elevators not required by building codes because they reduce rentable area in commercial high-rises and may result in additional costs; however, construction costs in major cities, escalating costs of steel, oil, and other building materials, far outpace the relatively minor costs which may accrue from loss of area dedicated to vertical circulation elements intended to enhance occupant safety. Such security enhancements often serve as marketing tools. Developer Larry Silverstein's World Trade Center Seven in Lower Manhattan exceeded the New York Building Code, to ensure tenants would have a safe and secure building overlooking the World Trade Center site.
Code Official Viewpoint
New Jersey code official Bill Connolly was surprised at "the degree of resistance to the NIST proposals, which are prudent and responsible. NIST performed a thorough and painstaking analysis of building failure evidence. The recommendations focused on a multi-hazard approach, not terrorism."
At issue, says Connolly, is the full evacuation of high-rises, circumstances which were not historically considered. Traditionally, codes addressed moving people to safe places until a fire was controlled. The collapse of the Twin Towers illustrated the need for rapid evacuation of all building occupants, especially when elevators are not working.
The two big changes are the fire service elevator, hardened, near stairs and the standpipe, allowing firefighters to reach any floor, not just 30 floors per hour. The need for an extra stair is important because, traditionally, firefighters take over a stair and leave the door open to access the hose. In a two-stair building, one stair is then lost for occupant evacuation. The extra stair allows basic egress capacity when the fire department is operating.
According to Connolly, NIST performed modeling studies on the impact of an extra stair vs. widening existing stairs for evacuating a building when firefighters are responding to fires on low or high floors. The findings indicated the extra stair performs better than a wider stair when occupant evacuation and firefighting occur simultaneously.
Fireproofing specifications should include higher bond strength to increase the probability it will stay in place. Performance standards will address installation practice and special inspections. Better oversight will determine if installations comply with standards.
Photoluminescent markings on exit stairs are useful during power outages to help occupants find their way out of buildings. These strips were installed in the World Trade Center in 1993, before the bombing that year, and during the Pentagon renovations before 9/11, and proved useful for occupant evacuation during both events. New York's Local Law 26 includes provisions for photoluminescent markings in stairwells.
"The United States has no code provisions addressing progressive collapse, unlike the U.K., which has had them since the 1970s. We are the only country in the Western world without such provisions," notes Connolly. He attributes this to resistance by American engineering societies. The ICC Ad Hoc Committee has drafted comprehensive progressive collapse provisions designed to motivate engineering societies to accept them for the August 2007 code cycle.
Connolly believes the objections by engineers relate to "an additional skill to be learned, additional analysis which may not be reflected in higher buildings, additional liability, and more work on each job that may add to construction costs. Learning new technology is not a good reason to object to these provisions. The U.K. has been doing this for 30 years. We are committed to seeing this proposal in the next cycle."
Global Impact
The NIST recommendations adopted by the Intl. Code Council will have worldwide implications. "U.S. codes have impact and will help raise the standard of care around the world. Other countries look to U.S. codes for guidelines," notes Connolly.
American architects and engineers are designing high-rise projects in China, the Middle East, and elsewhere. Countries that lack adequate codes for high-rises and super-tall buildings often rely on standards from the United States and the U.K. Other locations, such as Hong Kong, have codes comparable to the United States and U.K., but there is no time for some countries to catch up in creating their own codes while major construction is under way, says Dr. Sunder. Thus, leading architects and structural engineers are in a position to influence building codes and revisions around the world, including in China and the UAE, where unprecedented development is planned for Abu Dhabi, as well as ongoing work in Dubai.
Next Round
The next round of code reviews will address enhanced video monitoring in building stair towers, especially when wired to the command center. In this issue, the Federal Bureau of Investigation (FBI) is concerned about privacy - especially identities of informants who they don't want appearing on video; however, says Connolly, firefighters need to know what's going on and have the best tools during emergencies. "Why deprive the entire U.S. of video monitoring in stairwells because the federal government doesn't want it, especially when they don't have to comply with building codes?"
These issues, and several others noted on the NIST site, will be reviewed in the months ahead. Stay tuned.
Internet Resources
- National Institute of Standards and Technology (NIST) and the World Trade Center
- National Institute of Building Sciences (NIBS) Building Code Experts and ICC Code Change Proposals
- NIST's Recommendations Following the Federal Building and Fire Investigation of the World Trade Center Disaster
