Terrorist resistant buildings

By Richard Schulte

Schulte & Associates, Evanston, Ill.

September 11, 2001 -- Just the mention of the date brings back vivid memories. It has been six and one-half years since the terrorist attack on the World Trade Center (WTC) towers. The National Institute of Standards and Technology (NIST) investigation into the collapse of the WTC towers was completed in the fall of 2005; yet the recommendations of the NIST investigation are still being discussed.

In my estimation, the NIST investigation into the collapse of the towers was "top-notch." Unfortunately, the NIST report included not only the results of the investigation but also recommendations on how to make buildings "safer." The question that wasn't clearly answered in the NIST investigation report was "safer from what?"According to the lead investigator for NIST, Dr. Shyam Sunder, the recommendations contained in the report on the WTC towers collapse are not intended to address the issue of terrorism and building design, but rather the issue of the exposure of tall buildings to simultaneous "multi-hazards" (i.e. seismic events followed by fire or simultaneous high wind events and fire).

While NIST suggests the need to design tall buildings for simultaneous, or near simultaneous, "multi-hazards," the investigation report provides no rationale or justification for "multi-hazard" design, other than the mantra "to make buildings safer." In my opinion, this lack of discussion of the need for "multi-hazard" design in the report means that, overall, the NIST report should be judged to be a failed effort. Of course, the NIST investigation report with its recommendations on how to make buildings "safer" is history now. Now what do we do with those recommendations?

The International Code Council's (ICC) answer to that question was to form a committee to develop code change proposals intended to implement NIST's recommendations. This committee was given the name of the Ad Hoc Committee on Terrorism Resistant Buildings, TRB for short. Just the name of the ad hoc committee suggests a misunderstanding of NIST's recommendations, since those recommendations are not intended to address the terrorism issue.

The TRB committee has developed a number of building and fire code change proposals and has submitted these code changes for inclusion in the International Building Code (IBC) and the International Fire Code (IFC). While many of these proposals were rejected for inclusion in the 2007 supplement to the International Building Code, they have once again been submitted for inclusion in the 2009 edition of the IBC and IFC. In addition, the TRB's proposals that were approved for inclusion in the building code have been challenged with proposals to strike these provisions from the 2009 edition of the IBC.

The ICC assigns alphanumeric designations to proposals that will be discussed and voted upon in public hearings. The TRB's code change proposals for the 2007/2008 code change cycle and proposals to strike previously approved TRB code change proposals include the following code changes: G45, G51, G52, G54, G55, G56, G57, G58, G61, G62, G63, G65, G66, G67, G69, G108, G197, E14, E23, E135 and E149. (The letter "G" refers to the general sections of the IBC, while the letter "E" refers to the egress sections of the IBC.)

Following is a brief summary of each of these code change proposals.

Code Change G45. This proposal will mandate the use of the ICC Performance Code for Buildings and Facilities for the design of tall buildings. (Proponent: Lawrence Perry, Building Owners and Managers Association (BOMA))

Code Change G46. This proposal addresses the reliability of sprinkler systems for tall buildings. The proposal will require control valves in sprinkler risers at three-story intervals and require a minimum of two connections to the municipal water supply system. (Proponent: TRB committee)

Code Change G51. This proposal will require tall buildings to be designed to prevent collapse under the conditions of "total burnout," assuming failure of the sprinkler system. (Proponent: TRB committee)

Code Change G52. This proposal will require that the structural frame and floor construction in tall buildings develop a minimum four-hour fire resistance rating or be designed to prevent collapse under the conditions of "total burnout," assuming failure of the sprinkler system. (Proponent: Ramon Gilsanz, Gilsanz Murray Steficek LLP)

Code Change G54. This proposal will require that a minimum of three elevators be provided as fire service access elevators, rather than one elevator, in buildings that have occupied floors more than 120 feet above the lowest level of fire department vehicle access. (Proponent: Ed Donoghue, Edward Donoghue Associates Inc.)

Code Change G55. This proposal will require that wall assemblies that enclose elevator hoistways in tall buildings be fire tested with the hose stream test conducted at the end of the test, rather than at one-half of the fire rating period. (Proponent: Greg Lake, Sacramento Metropolitan Fire District, California Fire Chiefs Association)

Code Change G56. This proposal will require that exit stair enclosures be designed to resist a pressure of 2 psi applied in a perpendicular direction to the enclosure. (Proponent: TRB committee)

Code Change G57. This proposal will require that wall assemblies that enclose exit stairs in tall buildings be fire tested with the hose stream test conducted at the end of the test, rather than at one-half of the fire-rating period. (Proponent: Greg Lake, Sacramento Metropolitan Fire District, California Fire Chiefs Association)

Code Change G58. This proposal will require that elevator lobbies, elevator hoistways and elevator equipment rooms in all high-rise buildings be provided with a video surveillance system to allow remote monitoring of these spaces during a fire or other emergency event. (Proponent: TRB committee)

Code Change G61. This proposal will require that the enclosure walls of exit stairs be located a minimum of one-third the diagonal distance of the floor apart. (Proponent: TRB committee)

Code Change G62. This proposal will require that all exit stairs in high-rise buildings that serve the highest story be extended to the roof and be provided with roof access. (Proponent: Ken Kraus, Los Angeles Fire Department, Calif.)

Code Change G65. This proposal will require exit stair and elevator hoistway enclosures in tall buildings to comply with a minimum of Soft Body Impact Classification Level 2 when tested per ASTM C1629/C1629M. (Proponent: Michael Gardner, Gypsum Association)

Code Change G66. This proposal will modify the requirement that each floor in a tall building be provided with access to three enclosed exit stairs by permitting any acceptable exit to be used as an alternative to providing a third stair. (Proponent: Jeff Harper, Rolf Jensen and Associates)

Code Change G67. This proposal will eliminate the requirement that each floor in a tall building be provided with access to a minimum of three exit stairs. (Proponents: Kim Clawson, Chicago Committee on High-rise Buildings, (CCHRB); David Frable, U.S. General Services Administration and David S. Collins, AIA, The Preview Group Inc., representing the American Institute of Architects Codes and Standards Committee; Raymond A. Grill, P.E., Arup, representing himself; Lawrence G. Perry, AIA, Building Owners and Managers Association (BOMA) International)

Code Change G69. This proposal will eliminate the requirement that higher bond strength fireproofing materials be utilized to protect structural steel members in high-rise buildings. (Proponent: David Frable, U.S. General Services Administration)

Code Change G108. This proposal will require a "risk assessment" analysis for tall buildings, buildings with a design occupant load greater than 10,000 people or buildings that may be a higher than normal risk of terrorist attack. (Proponent: Ronald O. Hamburger, S.E., Simpson Gumpertz & Heger Inc., representing the National Council of Structural Engineers Association Ad Hoc Joint Industry Committee on Structural Integrity)

Code Change G197. This proposal will require that lobbies serving fire service access elevators be a minimum of 150 SF in floor area. (Proponent: Ken Kraus, Los Angeles Fire Department, Calif.)

Code Change E14. This proposal will allow elevators to be designed to be part of the egress system serving a building. (Proponent: David W. Frable, U.S. General Services Administration, Gerald H. Jones, representing himself.)

Code Change E23. This proposal will permit emergency exit stair lighting to be eliminated in exit stairs that are provided with photo-luminescent exit path markings. (Proponent: Lawrence G. Perry, AIA, representing Building Owners and Managers Association (BOMA) International)

Code Change E135. This proposal will limit the length of horizontal transfer corridors provided within exit stair enclosures to a maximum of 50 feet in high-rise buildings. (Proponent: TRB committee.)

Code Change E149. This proposal will eliminate the requirement for photo-luminescent exit path markings in exit stairs. (Proponent: Lawrence G. Perry, AIA, representing Building Owners and Managers Association (BOMA) International)

Note: The term "tall building" as used above refers to buildings that have occupied floors that are more than 420 feet above the lowest level of fire department vehicle access.

Given the number of code change proposals directed toward high-rise and tall buildings, one would probably conclude that high-rise buildings, particularly those that are more than 420 feet in height, are dangerous buildings, but the fire safety statistics for high-rise buildings indicate otherwise. Statistically speaking, high-rise office and residential buildings, including hotels, are the safest buildings that we construct. There is simply no comparison between the safety record of high-rise buildings and one- and two-story family dwellings in the United States.

According to the National Fire Protection Association (NFPA), the average number of fire fatalities that occurred in office buildings, both high rise and low rise, in the United States between 2000 and 2004 was one per year (excluding 9/11). Yes, that's correct, one per year. The fire safety record of high-rise apartment buildings and high-rise hotels protected by a sprinkler system is similar to that of office buildings. If this is the case, what is the reason for all of the code change proposals addressing high-rise building construction?

The answer to that question is simply, "the NIST WTC towers investigation recommendations." But if NIST didn't include a specific rationale or justification for each of its recommendations, should the ICC's TRB committee have used the NIST recommendations as the basic justification for its proposals? Simply because a federal government agency puts together recommendations, should these recommendations be implemented if the agency can't provide any rationale for their recommendations? Utilizing the NIST recommendations as the basis for code change proposals doesn't seem to be a rational way to proceed until NIST justifies its recommendations.

From my perspective, designing high-rise buildings to survive simultaneous "multi-hazards" doesn't make a whole lot of sense, given that the probability that these multi-hazards will actually occur simultaneously is practically nil. The NIST recommendations do not provide any discussion or guidance as to what is an acceptable risk versus an unacceptable risk. Hence, the NIST recommendations are, actually, simply opinions. In the 21st century, NIST should be able to do better than that.

Also from my perspective, designing buildings to be resistant to acts of terrorism does not appear to be a cost-effective approach to building design. Given the number of "targets" in the United States and around the globe, the civilized world simply doesn't have the means to protect every potential target of terrorism. While it makes sense to protect some targets to prevent mass havoc (i.e. nuclear power plants), playing defense in the "war on terror" is a losing proposition, just as playing the "prevent" defense is a good way to lose a football game in the final minutes of the game. In my opinion, the way to protect our citizens and civilization from terrorism is to play offense and keep the terrorists on the defensive.

With respect to designing buildings for simultaneous hazards, there are some risks that simply have to be accepted, and there is little that we can do to prevent a calamity from perhaps occurring sometime in the future. To fret and worry over whether a building is susceptible to simultaneous multiple hazards that have never occurred in history, nor are they likely ever to occur, is simply a waste of both capital and, even more precious, a waste of time. Certainly, citizens such as the investigators at NIST, who are concerned with the occurrence of improbable events, have the option of avoiding living, working in or entering high-rise buildings. There is plenty of open land in the Midwest, where there are no high-rise buildings for hundreds of miles. For the rest of us, there are more important things to accomplish than worrying about freak events. It simply makes little sense to "saddle" the American public with the cost of complying with regulations that will likely accomplish nothing other than making high-rise buildings more costly to construct and satisfying our emotional response to 9/11.

High-rise buildings built to comply with the high-rise provisions presently contained in the International Building Code are already "safe" buildings. You are much more likely to die in your home or in your automobile than in a high-rise building, yet most Americans consider their home and their automobiles to be "safe." If the American people consider the level of safety provided in their homes and in their automobiles to be adequate, then surely the present level of safety provided in our high-rise buildings should be acceptable to most Americans, NIST's and the TRB committee's opinions not withstanding.

Richard Schulte is a 1976 graduate of the fire protection engineering program at the Illinois Institute of Technology. After working in various positions within the fire protection field, he formed Schulte & Associates in 1988. His consulting experience includes work on the Sears Tower and numerous other notable structures. He has also acted as an expert witness in the litigation involving the fire at the New Orleans Distribution Center. He can be contacted by sending e-mail to rschulte@plumbingengineer.com.