The World Trade Center events of September 11, 2001, focused the world's attention on high-rise buildings. Since that time, there have been several other events that have kept the world's attention on high-rise building fire safety, including fires in Madrid, Venezuela, and two in Chicago.
Major code groups in the United States and around the world have begun to seriously look at high-rise building safety and to question whether enough is being done. The United States Government is conducting a major study, through the National Institute of Standards and Technology (NIST), to evaluate high-rise building safety.
This article looks at some of the events that have occurred, evaluates lessons learned, discusses some of the recommendations currently being considered in high-rise safety design, and suggests ways forward to look at fire safety design and high-rise structures.
Though there is some discussion of the World Trade Center, the intent of this article is to address the other events and reactions as well. It is not the intent to discuss the WTC or 9/11 events in any detail. It should be noted that, though the author chairs the NFPA High-Rise Building Safety Advisory Committee, chairs the NFPA Safety to Life Technical Correlating Committee, and is a principal of a global engineering company, the views expressed in this article are those of the author, not the official views of the aforementioned organizations.
High-Rise Buildings Some History
In the United States prior to the 1970s, there were no specific highrise building criteria in the national codes. In the early 1970s, the Uniform Building Code, the Standard Building Code, and the Basic Building Code (now combined into the International Building Code) developed provisions for high-rises. The NFPA Life Safety Code (NFPA 101) also has provisions, which vary by occupancy, that were inserted into the Code in the 1988 edition. 1
In the United States, the high-rise provisions typically are triggered when an occupied floor is at least 75 feet (23 meters) above the lowest level of fire department access. Several jurisdictions in the United States have amended this threshold to 55 feet (17 meters) and some to as low as 35 feet (11 meters).
The original intent of the high-rise building provisions was to require greater protection in buildings where external rescue was no longer available. At the time, 75 feet (23 meters) was considered to be the longest ladder reach that could be achieved; therefore, better protection was required for the occupants when they could not be rescued from the outside. While other features of high-rise buildings, such as stack effect and delayed evacuation, were recognized as factors, the threshold was based upon this ladder reach concept.
The high-rise building provisions evolved into requirements for automatic sprinklers, voice communication, pressurized stairs, and emergency power. In many locations, smoke control was also required. The smoke control requirements have gone in and out of codes for high-rise buildings as the codes have evolved.
Many codes in the rest of the world also address high-rise buildings, and many apply beginning at about the 75-foot (23-meter) height. Similar provisions apply in those countries. Areas where other countries may be more restrictive are in the number and location of firefighter lifts (elevators); the number, width, and travel distance to escape stairs; compartmentation requirements; and structural fire resistance. In parts of Asia, buildings over a certain height (often in the 15- to 30-story range) also require one or more open air refuge floors.
In recent years in the U.S., there are two areas that have gradually begun to be addressed. The first is that building codes typically apply to new buildings, yet there is a huge stock of existing buildings, particularly in older cities, to which the new building code requirements do not apply. Retrofit sprinkler ordinances have been passed in many U.S. cities, often after a local disaster. These retrofit laws are not consistent in the level of protection they require, in the types of buildings to which they apply (i.e., office, hotel, apartment, condominium), or in the time allowed to complete the retrofit. The NFPA Life Safety Code has gradually added to the types of existing high-rise buildings required to have automatic sprinklers, but its enforcement is sporadic, even in those places that have adopted the code. Therefore, the American public has no easy way of knowing the level of protection they will be afforded in a high-rise building, particularly as they travel from city to city.
There is another series of code changes that have been occurring more recently. Additional protection is required in some buildings as they get higher. Few people, when they walk into a 7- to 10-story building, picture that building as a high-rise. Yet the level of protection traditionally required is the same in that building as in a 50- or 100-story building down the street. Similarities between the two buildings are that exterior rescue above 75 feet (23 meters) is difficult, if not impossible (depending on local fire department apparatus and access to the building). However, the dynamics of air movement (and therefore smoke movement), the viability of total evacuation versus staged evacuation, and the level of information needed by occupants and the fire service are clearly different in a very tall building than in a mid-level, but still "high-rise," building. These ideas are beginning to be addressed in a piecemeal fashion in the codes, but often with little technical analysis or evaluation of risk.
Recent Events
Chicago has had two significant fires in existing high-rise buildings in the last three years, the first at 69 West Washington. 2 In this incident, the fire started in a storage room on the 12th floor of a nonsprinklered building. It was able to spread through the suite of origin, and because corridor walls were not full height, it also spread hot smoke and gases into the corridor system. A stair enclosure, with vestibule, was almost directly across the corridor from the area of incidence, and when the fire department responded and opened the doors from the corridor into the stair, hot smoke and gases flowed into the stairwell. In this building, stairwell doors were locked from the stair side for security, with no automatic or remote unlocking capability. Six people died in the stairwell all of whom were trapped above the 12th floor. 2 Those were the only fatalities in this event. The post-fire analysis concluded that, if the stair doors had not been locked from the stair side, there would likely have been no fatalities. Similarly, if the building had been sprinklered, it is unlikely that the smoke and gases would have been as hot, as buoyant, or in the same quantities. Therefore, the fatalities (and much of the damage) could have been avoided by the presence of sprinklers. What was learned from this fire? Perhaps only that the knowledge that is already known should be applied. Sprinklers greatly increase the safety of buildings, and locked stairwells, even from the stair side, create a hazard.
The second Chicago fire had better results. Again, it was a fire in a nonsprinklered high-rise building. This building had operable windows, and several occupants went to their windows for fresh air. There were no fatalities in this fire. The fire was notable nationally because it closely followed the 69 West Washington fire, making it the second significant high-rise fire in the same city in a short period of time. As with 69 West Washington, sprinklers in the building would have greatly reduced the amount of smoke and heat generated, and therefore probably would not have required occupants to rely on operable windows in order to receive their fresh air.
Chicago has since passed a retroactive high-rise sprinkler ordinance and has also outlawed door locks on stairwells, unless there is automatic and remote release. An alternate evaluation system has also been established. This was previously described in an article in this magazine. 3
In October 2004, a fire began on the 34th floor of the Parque Central building in Caracas, Venezuela. This building was a 56-story government office building. The fire did more than U.S. $250 million in damage, burning the structure's contents from the 34th to the 50th floor. The building was fully sprinklered; however, the sprinkler system was inoperable. Post-fire analysis indicates that had the sprinkler system been active, the fire would have been limited to the floor of origin. All that has been learned from this fire is that systems that are provided in buildings should be maintained. 4
Early in January 2005, a nighttime fire in a Madrid office building resulted in significant fire and structural damage to the building. Again, the fire was in a nonsprinklered building, and the results would likely have been very different in a sprinklered building. Therefore, although it is possible to learn from the structural response to this fire from a life safety point of view, sprinkler protection was likely the first and best protective measure that could have been provided. 5
The lessons learned from these fires are simple. It is necessary to make sure that the protection of the structure and the compartmentation of high-rise buildings are satisfactory. That is not enough, however. Buildings should be sprinklered, and if they are, they would be significantly safer. It is recognized that there is no simple means of sprinklering existing high-rise buildings. Therefore, means to encourage sprinkler protection in those buildings, such as tax breaks and extended times for installation, need to be factored into the process of requiring automatic sprinklers. However, until sprinklers are required, there is a risk of significant fire and perhaps life safety issues in nonsprinklered highrise buildings.
The World Trade Center
Much has been written and discussed about the World Trade Center events. This article cannot address the event in any level of depth, given that NIST has written reports totaling over 10,000 pages for World Trade Centers 1 and 2,6 and will have more to say about World Trade Center 7. Neither of the NIST reports addresses all the fire protection design issues that must be considered. Before discussing the NIST recommendations, there are a few thoughts or concepts that bear serious consideration.
First, is the incident involving World Trade Centers 1 and 2 an event that should be considered in high-rise building design? Are buildings, or a subset of landmark buildings, going to be designed to defend against terrorist threats? If so, which threats? What will this design cost, and can society afford it? Also, if buildings are designed to protect against these extreme events, will day-to-day life become more difficult, or will reaction to more typical or equally severe but unusual threats become more hazardous?
For example, one common recommendation coming out of the event is the need to harden stairwells. What does this mean? How hard should they be? If they are hardened, what are the results? For instance, if a bomb were released in this hardened stairwell, is it better or worse than the traditional stairwell? The bottom line is, society cannot react to a single event without understanding that there may be negative implications in the building's response to other events. It is a difficult task to apply rigor to collective thinking, as society responds to events such as security threats which may be very unlikely, impossible to predict, and subject to emotion. If rigor is not applied, however, then the overall performance of a building may be worsened, rather than improved.
A second big question coming out of the World Trade Center (WTC) disaster is whether society is comfortable with the performance of the rest of the World Trade Center complex. There was significant damage to several of the buildings, including the collapse of WTC 7. While the ignition of WTC 7 was due to the attacks on WTC 1 and 2, and the lack of water also due to that event, the fuel and fire causing the collapse was all within the WTC 7 building. There may well be lessons to be learned in this event that can extend to typical high-rise buildings.
The NIST Recommendations
In 2005, NIST issued a series of recommendations on the collapse of the World Trade Center Towers. 6 The report included 30 recommendations in 8 general groups. This article does not attempt to address each of those recommendations. However, to gain a feel for the recommendations, the groupings are described herein. They are as follows:
Group I: Increased Structural Integrity
Group II: Enhanced Fire Resistance of Structures
Group III: New Methods for Fire Resistance Design of Structures
Group IV: Improved Active Fire Protection
Group V: Improved Building Evacuation
Group VI: Improved Emergency Response
Group VII: Improved Procedure and Practices
Group VIII: Education and Training
These recommendations were issued in draft form, and many organizations have responded with comments. Many of the recommendations were logical outgrowths of the event, but some others could lead to substantial changes in building design. NIST has offered to work with the code groups in developing code language to respond to these recommendations. Some of the far-reaching recommendations are considered controversial because they may not necessarily spring from the World Trade Center events or because the recommendation seems to stem from an event that occurred only because of the method of attack. Others will lead to long-term improvements in buildings or building operations, or perhaps will spur industry to develop new products. Still others are things that can be accomplished quite easily with changes in operations or methods.
The NIST reports can be found on the NIST Web site (wtcdata.nist.gov). This Web site includes all of the research reports that have led up to the recommendations, as well as the recommendations themselves.
Items to Consider
There are several areas where the design and code communities should give serious consideration with respect to high-rise buildings. Some of these are as follows:
Risk Evaluations: Very large buildings should not be designed by a cook book method, but by an integrated, holistic, and rational engineering approach. While there are not sufficient events in high-rise buildings to do statistical analysis of the risks, there are many ways to look at risk as it relates to high-rise buildings. As a building gets taller, the number of occupants increases, and the potential for disaster increases. Engineering decisions should be based upon such factors as potential occupant load, whether a building may be a target, potential contents and businesses within the building, the capability and effectiveness of other suppression efforts, and other unique features in the building. Without this type of analysis, the rigor that the building demands and the public deserves will not be included in the design process. This rigor should lead to an informed design, which is well documented, so that the thought process can be followed in the future. Only then will high-rise buildings truly be engineered, rather than pieced together using codes which were never meant to apply to a very tall building. Such an approach exists today in the form of performance codes, but their use has been limited, particularly in the United States.
Thresholds: While the codes are gradually grappling with the concept that not all high-rise buildings are the same, it may make sense to develop some thresholds of protection. For instance, high-rise requirements may start at 75 feet (23 meters or 7 to 8 stories) based upon the reach of fire apparatus. The next threshold may occur at about 20 stories, where fullbuilding evacuation has become unwieldy, and where stack effect can begin to have a significant effect on smoke movement. Subsequent thresholds may be at 40, 60, or 100 stories, where the time to evacuate may exceed the fire resistance of a structure, where elevators may need to be considered in building evacuation, where special provisions for firefighter access may be needed, where mechanical systems alone may not be able to overcome stack effect, and where people movement and psychology may have to be factored into how messages are transmitted and received. At one of these thresholds, it may well be that prescriptive codes no longer apply and that a performance code approach utilizing engineered systems is the only allowed alternative. Once this analysis is done, it may also be that requirements can be relaxed somewhat in the 7- to 20-story building range. As an example, in China, buildings over 820 feet (250 meters) are considered as super high-rise buildings, and approval involves the central government authorities.
Structural Fire Resistance: The current code methods of evaluating structural fire resistance are archaic. There are simulation techniques available that can tell much more about a building's potential behavior than a 1-, 2-, or 3-hour rating. In the automotive industry, physical crashes and crash simulations are used on new car models to determine how a vehicle will respond to a series of events. Those same models can be used (and are starting to be used) in the building industry to judge structural and fire performance.
Another aspect of structural fire resistance in tall buildings is the need for a building to withstand an event for long periods of time. In a medium height building, the current building codes reasonably match full evacuation time with structural fire resistance. For very tall buildings, however, should a change in fire resistance be considered? If so, how much (given that fires will only burn a finite amount of time)? A balance on this item has not yet emerged. It is also necessary to discuss costs and acceptable endpoints if sprinklers fail. Surely, total building collapse is unacceptable, but is localized collapse or deflection over small areas acceptable in the rare event of a fire and sprinkler failure? With more stringent provisions come more costs.
Financial Incentives: In the building energy field, there are minimum codes for energy usage. However, a voluntary system for evaluating buildings' energy usage has emerged, which has caused many owners to choose to develop more energy-efficient buildings. They can use this increased energy efficiency as a means of marketing to potential tenants and as a means of evaluating how their building uses energy compared to others. This results in lower operational costs, as well as increased marketability.
There is an opportunity being considered by the NFPA and the Council on Tall Buildings to look at the potential of a similar voluntary system for life safety. This is currently proposed to be a points-based system, similar to the LEED system used for energy-efficient buildings. This would allow building owners to decide to improve the safety in their building, to have a means of measuring and marketing that, and perhaps to result in a safer group of structures than is available today. Often, it is preferable to let market influence create change rather than legislation.
James Quiter, is with Arup.
References
- NFPA 101, Life Safety Code , National Fire Protection Association, Quincy, MA, 1988.
- Report of the Cook County Commission Investigating the 69 West Washington Building Fire of October 17, 2003, Cook County Board, Cook County, IL, 2004.
- Baldassarra, C., "Fire Safety Meets Economics 101 - How Chicago Achieved Balance in Its High-Rise Building Ordinance," Fire Protection Engineering, 26, Spring 2005, pp 22-28.
- Moncada, J.A., "Fire Unchecked," NFPA Journal, March/April 2005, pp 46-52.
- Madrid Windsor Fire - The Arup View, www.arup.com/fire.
- NIST NCSTAR 1, Final Report on the Collapses of the World Trade Center Towers, National Institute of Standards and Technology, Gaithersburg, MD, 2005.