INTRODUCTION
There have been, and remain to be, continuing concerns about the adequacy of structural fire protection in the wake of the 9/11 tragedies. As significant as these events were, they were also clearly not representative of the normal accidental impact of fire on building structures. To assess the extent and nature of structural collapses due to fire in taller buildings, a review of existing information about fire incidents resulting in structural collapse was collected and reviewed.

The survey was international in scope and included building collapses due to fire in structures with four or more stories that had occurred during the 1970-2002 time frame of the survey. Both total and partial collapses were included in the survey. Since no database exists that systematically identifies building collapses due to fire (including the NFIRS system), the survey was necessarily exploratory. The survey methodology included a review of both news sources and technical literature, as well as inter-views with a wide range of individuals knowledgeable in structural fire protection. Twenty-two fires were identified that caused either partial or total collapse of a multistory structure. The adequacy and code compliance of the original structural and fire-resistant design of the identified buildings were beyond the scope of the project and were not assessed. While the number of fire events may appear low (average of one/year), these fire events are high-consequence occurrences with respect to loss of life, injuries, and economic costs.

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This survey of structural building collapses due to fire causes was sponsored in 2002 by the National Institute of Standards and Technology (NIST) as part of a larger project. The complete report is available from NIST.¹

SURVEY RESULTS
For the purposes of this NIST survey, multistory buildings were defined as those having four or more stories. Nonbuilding structures, such as tunnels, bridges, observation or transmission towers, were not included. Either partial or total failure of the structural framing, members, and/or connections was considered to have constituted a collapse, and it was necessary for a fire to have been the direct cause of this failure.

A total of 22 such cases were identified through 2002 after extensive searches of the literature, news, and other contacts, with the Sept. 11 disasters in New York and Washington, DC, counting as five of these incidents [World Trade Center (WTC) 1, 2, 5, and 7, and the Pentagon]. The cases occurred not only in the U.S. and North America, but also internationally. This NIST survey data demonstrated that buildings of all types of construction and occupancies, in the U.S., North America, and abroad, are susceptible to fires, particularly older buildings and those that may be undergoing construction, renovations, or repairs. The total fatalities were dominated by the Sept. 11 WTC disasters, which were unique in that they were precipitated by terrorist attacks that substantially damaged the buildings' structural framing and destroyed their fire protection systems prior to the fires.

The NIST survey of 22 fire-induced building collapses from 1970-2002¹ identified a variety of conditions, materials, locations, and buildings. Fifteen cases were from the U.S., two from Canada, and five from Europe, Russia, and South America. The numbers of fire collapse events can be categorized by building material as follows:

• Concrete: 7 (1 in Pentagon 9-11 event)
• Structural steel: 6 (4 in 9-11 WTC events)
• Brick/Masonry: 5
• Wood: 2
• Unknown: 2

The collapse distribution by building story height was as follows:

• 4-8 stories: 13
• 9-20: 3
• 21 or more: 6

At least four of these fire collapses had occurred during construction or renovations of some kind, when the usual expected architectural, structural, and fire protection functions were still incomplete or temporarily disrupted, and/or potential new fire sources were introduced, such as electrical and gas line repairs, welding, and the presence of other flammable supplies and/or equipment. Partial collapses (14 events) were the most frequent occurrences, and the WTC disasters (listed as four separate events, with three full collapses) dominated the full collapse event total of eight cases. Office and residential were the primary types of occupancy in these 22 buildings, as would be expected in multistory construction, with the occupancy distribution being as follows:

• Office: 9
• Residential: 8
• Commercial: 3
• Combined commercial/residential: 2

Two large department store fires in Athens, Greece, in 1980 are documented in the paper by Kyriakos Papaioannoa, 1986.⁴ These fires began at 3 a.m. on Dec. 19, 1980, with arson being suspected as the cause. The Katrantzos Sport Department Store was an 8-story reinforced concrete building. Its fire started at the 7th floor and rapidly spread throughout the building, due to lack of vertical or horizontal compartmentation and the absence of sprinklers. Collected evidence indicated that the fire temperatures reached 1000°C over the 2- to 3-hour fire duration, and the firefighters concentrated on containing the fire spread to the adjacent buildings. Upon termination of these fires, it was discovered that a major part of the 5th to 8th floors had collapsed. Various other floor and column failures throughout the Katrantzos Building were also observed (see Figure 1). The cause of these failures was considered to be restraint of the differential thermal expansion of the structure that overloaded its specific elements or connections. On May 21, 1987, Sao Paulo had one of the biggest fires in Brazil, which precipitated a substantial partial collapse of the central core of the tall CESP Building 2.⁵ This was a 21-story office building, headquarters of the Sao Paulo Power Company (CESP), after whom the building was named. Buildings 1 and 2 of this office complex were both of reinforced concrete framing, with ribbed slab floors. These two buildings had several unique internal features and contents. Both buildings still retained their original wood forms used for pouring the concrete floor slabs, which were never removed. Low-height plywood partition walls were also used in the interiors. Approximately two hours after the beginning of the fire in CESP 2, its structural core area throughout the full building height collapsed. This collapse was attributed to the thermal expansion of the horizontal concrete T-beam frames under the elevated fire temperatures, which led to the fracture of the vertical framing elements and their connections in the middle of the building, and the consequent progressive loss of gravity load-carrying capacity (see Figure 2).

A fire-initiated full collapse of a textile factory occurred in Alexandria, Egypt, on July 19, 2000.⁶ This 6-story building was built of reinforced concrete, and its fire started at about 9 a.m. in the storage room at the ground floor. Fire extinguishers were nonfunctional, and the fire spread quickly before the firefighters could arrive. An electrical short-circuit accelerated the fire spread. At about 6 p.m., nine hours after the start of the fire, when the blaze seemingly was under control and subsiding, the building suddenly collapsed, killing 27 people. Figure 3 shows a photograph of this collapse.

CONCLUSIONS
Past experience and this 2002 NIST collapse survey confirm that fires, and the related damage, deaths, casualties, and any collapses, are essentially rare and random events, whose effects depend highly on the time, nature, and circumstances of the fire occurrence. Thus, fires represent a hazard to all building types, materials, and occupancies. Likewise, the added fire-fighting difficulty in all taller buildings must be recognized, given the longer times needed to escape or access the higher floors. Many of the past major fires in tall buildings fortunately occurred in the evenings or weekends, when the office buildings were almost vacant, thereby, minimizing their potential dangers to human life. Automatic sprinkler systems are a very effective means to suppress a fire, but if the system is being repaired, or is nonexistent or nonfunctional for other reasons, the threat of fire growth increases.

Another important finding of this study was the lack of readily available, and well-documented, information on partial or total structural collapse due to fire. Unless the fire event was significant for other reasons, e.g., loss of life, very little information was available. It is recommended that a centralized database be developed, whereby structural damage and collapse can be investigated and systematically reported in the future. The current lack of systematic information on fire-induced collapses seriously limits the profession's understanding of the scope and nature of the real structural fire protection problem.

Jesse Beitel and Nestor Iwankiw are with Hughes Associates, Inc.

REFERENCES

1. Iwankiw, N., and Beitel, J., "Analysis of Needs and Existing Capabilities for Full-Scale Fire Resistance Testing," Hughes Associates, Report NIST GCR 02-843, December 2002.
2. 2 FEMA 403, World Trade Center Building Performance Study: Data Collection, Preliminary Observations, and Recommendations, Federal Emergency Management Agency, Washington, DC, May 2002.
3. ASCE-SEI, The Pentagon Building Performance Report, ASCE, Reston, VA, January 2003.
4. Papaioannoa, K., "The Conflagration of Two Large Department Stores in the Centre of Athens," Fire and Materials, Vol. 10, 1986, pp. 171-177, John Wiley and Sons, Ltd.
5. Berto, A.F., and Tomina, J.C., "Lessons From the Fire in the CESP Administration Headquarters," IPT Building Technologies, 1988, Sao Paulo, Brazil.
6. BBC News, "Factory Fire Kills 15 in Egypt," World: Asia-Pacific, July 20, 2000.