The National Commission on Terrorist Attacks Upon the United States, also known as the 9/11 Commission, was set up on November 27, 2002 "to prepare a full and complete account of the circumstances surrounding the September 11, 2001 attacks", including preparedness for and the immediate response to the attacks.
NIST NCSTAR 1: Federal Building and Fire Safety Investigation of the World Trade Center Disaster
This is the final report on the National Institute of Standards and Technology (NIST) investigation of the collapse of the World Trade Center (WTC) towers, conducted under the National Construction Safety Team Act. This report describes how the aircraft impacts and subsequent fires led to the collapse of the towers after terrorists flew jet fuel laden commercial airliners into the buildings; whether the fatalities were low or high, including an evaluation of the building evacuation and emergency response procedures; what procedures and practices were used in the design, construction, operation, and maintenance of the towers; and areas in current building and fire codes, standards, and practices that warrant revision.
Extensive details are found in the 42 companion reports. (The final report on the collapse of WTC 7 will appear in a separate report.) Also in this report is a description of how NIST reached its conclusions. NIST complemented in-house expertise with private sector technical experts; accumulated copious documents, photographs, and videos of the disaster; established baseline performance of the WTC towers; performed computer simulations of the behavior of each tower on September 11, 2001; combined the knowledge gained into a probable collapse sequence for each tower; conducted nearly 1,200 first-person interviews of building occupants and emergency responders; and analyzed the evacuation and emergency response operations in the two high-rise buildings.
The report concludes with a list of 30 recommendations for action in the areas of increased structural integrity, enhanced fire endurance of structures, new methods for fire resistant design of structures, enhanced active fire protection, improved building evacuation, improved emergency response, improved procedures and practices, and education and training.
NIST NCSTAR 1-1: Design, Construction, and Maintenance of Structural and Life Safety Systems
The collapse of World Trade Center (WTC) 1, 2, and 7 resulted from structural damage from direct and indirect effects of aircraft impact and the ensuing fires. Thus, for collapse analyses of these buildings, knowledge of the physical state of the structural and fire safety systems prior to the aircraft impact is essential. To obtain information for the collapse analysis of the buildings, National Institute of Standards and Technology reviewed design and construction documents, correspondence, and memoranda related to the building projects; interviewed individuals involved in the design, construction, and maintenance of the buildings; obtained information from regulatory and emergency services agencies of New York City; and reviewed books and published journal and magazine articles related to the WTC building projects.
Information obtained from various sources are synthesized and summarized in this report. Specifically, this report presents (1) provisions used to design and construct the structural, fire protection and egress systems of the buildings; (2) tests performed to support the design of these systems; (3) criteria that governed the design of the structural and fire protection systems; (4) methods used to proportion structural members and other components of the buildings; (5) innovative features, technologies and materials that are incorporated in design and construction of the structural and fire protection systems; (6) details of deviations to the contract documents granted by Port Authority of New York and New Jersey; (7) fabrication and inspection requirements at the fabrication yard; and (8) inspection protocols during construction.
NIST NCSTAR 1-2: Baseline Structural Performance and Aircraft Impact Damage Analysis of the World Trade Center Towers
The baseline structural performance and aircraft impact damage analysis of the National Institute of Standards and Technology (NIST) Investigation of the World Trade Center (WTC) disaster had two primary tasks: (1) to develop reference structural models of the WTC towers and use these models to establish the baseline performance of each of the towers under gravity and wind loads, and (2) to estimate the damage to the towers due to aircraft impacts and establish the initial conditions for the fire dynamics modeling and the thermal-structural response and collapse initiation analysis. This report provides the technical approach, methodology, and results related to both tasks.
The focus of the analysis was to analyze the aircraft impacts into each of the WTC towers to provide the following: (1) estimates of probable damage to structural systems, including exterior walls, floor systems, and interior core columns; (2) estimates of the aircraft fuel dispersion during the impact; and (3) estimates of debris damage to the building nonstructural contents, including partitions and workstations. The results were to be used to estimate the damage to fireproofing based on the predicted path of the debris field inside the towers. This analysis thus estimated the condition of the two WTC towers immediately following the aircraft impacts and established the initial conditions for the fire dynamics modeling and the thermal-structural response and collapse initiation analysis. The impact analyses were conducted at various levels of complexity including: (1) the component level, (2) the subassembly level, and (3) the global level to estimate the probable damage to the towers due to aircraft impact.
NIST NCSTAR 1-3: Mechanical and Metallurgical Analysis of Structural Steel
This report is an overview of the results of the mechanical and metallurgical analysis of structural steel from the World Trade Center (WTC), part of the National Institute of Standards and Technology Investigation of the WTC disaster of September 11, 2001. The goal of the study was threefold: Determine mechanical properties of WTC structural steel, Determine the quality of the steel and if design requirements were met, and Analyze the recovered steel to provide insight into failure mechanisms to guide and/or validate models of building performance. Structural steel recovered from the WTC site was analyzed for composition, microstructure, and mechanical properties, including room temperature properties (for modeling baseline building performance), high temperature properties (for modeling structural response of the building to fire), and behavior at high strain rates (for modeling airplane impact). Failure analysis of the recovered steel, complemented by pre-collapse photographs of the damaged building, was used to establish failure modes and temperature excursions experienced by the steel. In addition, documents from the construction era covering issues ranging from steel specifications to engineering design drawings were used to help interpret the results and supplement models of mechanical properties used in the models of building performance.
NIST NCSTAR 1-4: Active Fire Protection Systems
The National Institute of Standards and Technology investigation of active fire protection systems in World Trade Center (WTC) 1, 2, and 7 included the design, installation, capabilities, and performance on September 11, 2001, of the automatic fire sprinkler, standpipe, standpipe preconnected hoses, fire alarm, and smoke management systems. The purpose and normally expected performance of each active fire protection system in the buildings are described, as well as details about the systems installed in WTC 1, 2, and 7. Using fire protection engineering methods, the capabilities of the installed systems to respond to various fire threats from normal office fires up to and including the extraordinary challenge of the fires ignited by the aircraft impacts on September 11, 2001, were assessed. Information from The Fire Department of the City of New York records was used to document the history of significant fire events in WTC 1, 2, and 7. Findings of the investigation are presented with regard to the fire suppression, fire alarm, and smoke management systems installed on the day the buildings collapsed.
NIST NCSTAR 1-5: Reconstruction of the Fires in the World Trade Center Towers
The collapses of the World Trade Center towers on September 11, 2001, resulted from a combination of aircraft impact damage and the ensuing fires.
NIST NCSTAR 1-6: Structural Fire Response and Probable Collapse Sequence of the World Trade Center Towers
One of the four main objectives of the National Institute of Standards and Technology (NIST) investigation of the collapse of the World Trade Center (WTC) towers was to determine why and how the two towers collapsed. Events that played a significant role in the structural performance of the towers were the aircraft impact, the rapid ignition of fires on multiple floors, the growth and spread of fires and the structural weakening resulting from effects of high temperatures. The passive fire protection applied to the steel structural components in the WTC towers was investigated to provide information on the in place condition of the fire protection before and after aircraft impact. Standard fire resistance tests were conducted to establish the appropriate classification (fire resistance rating) of the original design of the WTC floor system and to develop insight into the structural performance of the composite steel and concrete floor system under exposure to a standard fire. Results of simulations of the aircraft impacts were used to predict damage to the structure, fire protection, and partition walls in the path of the debris field. Characterization of the temperatures of the structural components, determined from simulated WTC fires, allowed the calculation of the performance of major subsystems constituting the structural system of the towers including the core framing, the exterior wall (columns and spandrels), and full tenant floors. Insights gained from these analyses were used, in turn, to formulate and execute nonlinear, temperature-dependent finite element analyses of global structural systems to predict the collapse sequence of each tower. The structural analyses were guided, and where possible validated, by observations made from the review of thousands of photographs and video recordings. This report covers the characterization of the conditions of the WTC towers before the attacks, their weakening due to the aircraft impacts, the response of the structural systems to the subsequent growth and spread of fires, and the progression of local failures that led ultimately to the total collapse of both towers.
NIST NCSTAR 1-7: Occupant Behavior, Egress, and Emergency Communication
This report describes the occupant evacuation of World Trade Center (WTC) 1 and WTC 2 on September 11, 2001. Multiple sources of information were collected and analyzed: over 1,000 new interviews with survivors (including 803 telephone interviews, 225 face-to-face interviews, and 5 focus groups); over 700 published interviews; 9-1-1 emergency calls; transcripts of emergency communications, historical building design drawings, memoranda, and calculations; formal complaints filed with the Occupational Safety and Health Administration; and other relevant materials. The egress system, including stairwells and elevators, was described and compared to requirement of both contemporary and current code requirements. This report documents the emergency procedures, both as they were designed to be implemented, as well as how they were actually implemented on September 11, 2001.
NIST NCSTAR 1-8: The Emergency Response Operations
The September 11, 2001, attack on the World Trade Center (WTC) caused the deaths of 2,749 people. Included in the group were approximately 421 emergency responders from The Fire Department of the City of New York (FDNY), The New York City Police Department (NYPD), the Port Authority Police Department (PAPD), The Port Authority of New York and New Jersey (PANYNJ), from WTC security firms, and volunteer emergency responders who were in the WTC area of the city when the attack occurred. This report addresses the operations of these emergency responders, the technologies used during WTC operations, and the guidelines and practices that governed these operations. The objectives of this study were to 1) fully document what happened during the response by the emergency services to the attacks on the WTC, up to the time of collapse of WTC 7; (2) identify issues that need to be addressed in changes to practice, standards, and codes; (3) identify alternative practices and/or technologies that may address these issues; and (4) identify R&D needs that advance the safety of the fire service in responding to massive fires in tall buildings.
NIST NCSTAR 1A: Final Report on the Collapse of World Trade Center Building 7
This is the final report on the National Institute of Standards and Technology (NIST) investigation of the collapse of World Trade Center Building 7 (WTC 7), conducted under the National Construction Safety Team Act. This report describes how the fires that followed the impact of debris from the collapse of WTC 1 (the north tower) led to the collapse of WTC 7; an evaluation of the building evacuation and emergency response procedures; what procedures and practices were used in the design, construction, operation, and maintenance of the building; and areas in current building and fire codes, standards, and practices that warrant revision. Extensive details are found in the companion reports, NIST NCSTAR 1-9 and NIST NCSTAR 1-9A.
NIST NCSTAR 1-9: Structural Fire Response and Probable Collapse Sequence of World Trade Center Building 7 (two volumes)
This is the primary technical report on the investigation of the collapse of World Trade Center Building 7 (WTC 7), providing technical details of all aspects of the investigation. This report also contains five appendices, which provide supporting background information on the Con Edison substation in WTC 7, analysis of the September 11, 2001 seismogram data recorded near the WTC site, video analysis of WTC 7 building vibrations before its collapse, analyses of hypothetical blast scenarios, and plasticity and creep models for WTC 7 steels.
Post 9/11 World Re: Terrorism