NIST NCSTAR 1-4B
Federal Building and Fire Safety Investigation of the
World Trade Center Disaster
Fire Suppression Systems
Mark Hopkins John Schoenrock Edward Budnick
NIST NCSTAR 1-4B
Federal Building and Fire Safety Investigation of the
World Trade Center Disaster
Fire Suppression Systems
Mark Hopkins John Schoenrock Edward Budnick
Hughes Associates, Inc.
September 2005
U.S. Department of Commerce
Carlos M. Gutierrez, Secretary
Technology Administration
Michelle O’Neill, Acting Under Secretary for Technology
National Institute of Standards and Technology
Disclaimer No. 1
Certain commercial entities, equipment, products, or materials are identified in this document in order to describe a procedure or concept adequately or to trace the history of the procedures and practices used. Such identification is not intended to imply recommendation, endorsement, or implication that the entities, products, materials, or equipment are necessarily the best available for the purpose. Nor does such identification imply a finding of fault or negligence by the National Institute of Standards and Technology.
Disclaimer No. 2
The policy of NIST is to use the International System of Units (metric units) in all publications. In this document, however, units are presented in metric units or the inch-pound system, whichever is prevalent in the discipline.
Disclaimer No. 3
Pursuant to section 7 of the National Construction Safety Team Act, the NIST Director has determined that certain evidence received by NIST in the course of this Investigation is “voluntarily provided safety-related information” that is “not directly related to the building failure being investigated” and that “disclosure of that information would inhibit the voluntary provision of that type of information” (15 USC 7306c).
In addition, a substantial portion of the evidence collected by NIST in the course of the Investigation has been provided to NIST under nondisclosure agreements.
Disclaimer No. 4
NIST takes no position as to whether the design or construction of a WTC building was compliant with any code since, due to the destruction of the WTC buildings, NIST could not verify the actual (or as-built) construction, the properties and condition of the materials used, or changes to the original construction made over the life of the buildings. In addition, NIST could not verify the interpretations of codes used by applicable authorities in determining compliance when implementing building codes. Where an Investigation report states whether a system was
designed or installed as required by a code provision, NIST has documentary or anecdotal evidence indicating whether the requirement was met, or NIST has independently conducted tests or analyses indicating whether the requirement was met.
Use in Legal Proceedings
No part of any report resulting from a NIST investigation into a structural failure or from an investigation under the National Construction Safety Team Act may be used in any suit or action for damages arising out of any matter mentioned in such report (15 USC 281a; as amended by P.L. 107-231).
National Institute of Standards and Technology National Construction Safety Team Act Report 1-4B Natl. Inst. Stand. Technol. Natl. Constr. Sfty. Tm. Act Rpt. 1-4B, 278 pages (September 2005) CODEN: NSPUE2
U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 2005
_________________________________________
For sale by the Superintendent of Documents, U.S. Government Printing Office Internet: bookstore.gpo.gov — Phone: (202) 512-1800 — Fax: (202) 512-2250 Mail: Stop SSOP, Washington, DC 20402-0001
A
BSTRACT
The National Institute of Standards and Technology (NIST) conducted a building and fire safety investigation of the World Trade Center (WTC) disasters. The work documented in this report was performed in support of the investigation of active fire protection systems. Specifically, this effort involved documentation and evaluation of the automatic sprinkler and standpipe/pre-connected hose systems and their associated water supplies in WTC 1, 2, and 7.
An extensive literature review was performed in order to document the installed fire suppression features. Hydraulic analyses were performed to provide estimates of the baseline capabilities of the suppression systems as well as capabilities under different fire incident scenarios, including the events of
September 11, 2001.
In general, the installed water supplies, automatic sprinkler, and standpipe/pre-connected hose systems in WTC 1, 2, and 7 met or exceeded the capabilities of systems typically installed to protect high-rise office buildings. The sprinkler systems were capable of providing adequate water densities to areas as much as two or three times the typical design areas.
Based on initial building damage estimates, the sprinkler and standpipe systems sustained considerable damage in the impact areas of WTC 1 and WTC 2. However, even if the sprinkler systems had remained fully operational and had been designed to protect higher hazard levels (e.g., Extra Hazard), the size, number, and extended area of the initial fires would have opened a large number of sprinklers, involving floor areas significantly larger than those associated with the required water demand for the design area associated with the installed systems.
For the most part, the water supplies provided redundant sources of water for the standpipe and sprinkler system infrastructures. However, the typical floor level sprinkler systems were installed with a single connection to a sprinkler riser, providing the potential for single points of failure.
The standpipe/pre-connected hose systems were consistent with the applicable requirements of the Building Code of the City of New York, but were not consistent with the minimum flow rates and durations required in National Fire Protection Association (NFPA) 14.
In addition, selected areas in all three buildings, including the generator fuel day-tank enclosures on several floors in WTC 7, were not protected by automatic sprinklers.
Keywords: Hoses, hydraulic analyses, spray density, sprinkler systems, standpipes, suppression, water supply, World Trade Center.
Abstract
iv NIST NCSTAR 1-4B, WTC Investigation
T
ABLE OF
C
ONTENTS
Abstract ...iii
List of Figures ... xi
List of Tables ...xiii
List of Acronyms and Abbreviations ... xvii
Preface ... xxi
Executive Summary ... xxxi
Chapter 1 Introduction ... 1 1.1 General... 1 1.2 Scope 1 1.3 Primary Tasks ... 2 1.3.1 Task 1 ... 2 1.3.2 Task 2 ... 2 1.3.3 Task 3 ... 3 1.3.4 Task 4 ... 3 1.3.5 Task 5 ... 4 1.4 General Approach ... 4
1.5 Document Retrieval and Control ... 5
Chapter 2 Background ... 7
2.1 Site and Building Descriptions ... 7
2.1.1 General Site Descriptions ... 7
2.1.2 WTC 1 and WTC 2 ... 7
2.1.3 WTC 7 ... 8
2.2 Installed Fire Suppression Features ... 9
2.2.1 WTC 1 and WTC 2 ... 9
2.2.2 WTC 7 ... 11
2.3 Incident Description... 11
Chapter 3 Automatic Fire Sprinkler and Standpipe/Pre-Connected Hose Technologies ... 13
Table of Contents
vi NIST NCSTAR 1-4B, WTC Investigation
3.2 Automatic Fire Sprinklers... 13
3.2.1 Overview/General Description ... 13
3.2.2 System Types ... 14
3.2.3 Fire Control vs. Fire Suppression ... 15
3.2.4 The Area/Density Occupancy Hazard Design Approach ... 16
3.2.5 Pipe Schedule Design Method... 17
3.2.6 Hydraulic Calculation Design Method ... 17
3.2.7 Performance Expectations/History ... 18
3.3 Standpipes and Pre-Connected Hoses... 19
3.3.1 Overview/General Description ... 19
3.3.2 Classification of Standpipe Systems ... 19
3.3.3 Design Basis ... 20
3.3.4 Performance Expectations ... 21
Chapter 4 Applicable Codes and Standards ... 23
4.1 General... 23
4.2 High-Rise Fire Suppression Systems... 24
4.3 Code Provisions ... 25
4.3.1 Code Provisions for Sprinkler System Installations, WTC 1 and WTC 2... 25
4.3.2 Code Provisions for Sprinkler System Installations, WTC 7 ... 25
4.3.3 Code Provisions for Standpipe System Installation, WTC 1, 2, and 7 ... 26
4.3.4 Code Provisions for Water Supply, WTC 1, 2, and 7 ... 27
Chapter 5 Task 1: Water Supplies, Automatic Fire Sprinklers, and Standpipes (Pre-Connected Hoses) in WTC 1, 2, and 7 ... 29
5.1 General... 29
5.2 Fire Suppression Systems, WTC 1 and WTC 2... 29
5.2.1 Water Supplies ... 29
5.2.2 Standpipe and Pre-Connected Hose Systems ... 36
5.2.3 Automatic Fire Sprinkler Systems... 42
5.2.4 Electrical Power Supply ... 56
5.2.5 Special Hazard Suppression Systems ... 57
5.2.6 Fire Protection in the Initial Impact Areas ... 58
Table of Contents
5.3.1 Water Supplies ... 60
5.3.2 Sprinkler and Standpipe Systems ... 65
5.3.3 Electrical Power Supply ... 68
5.3.4 Fire Suppression Systems Associated with Fuel Oil Supply Systems ... 69
5.4 Design Basis Review ... 73
5.5 Summary–Task 1 ... 75
5.5.1 Fire Suppression Systems, WTC 1 and WTC 2 ... 75
5.5.2 Fire Suppression Systems, WTC 7 ... 79
5.5.3 Consistency of Suppression System Designs with State-of-the-Art Engineering “Best Practices” ... 80
Chapter 6 Task 2: Evaluation of the Fire Sprinkler Water Supplies ... 83
6.1 General... 83
6.2 Description of the New York City Water Supply ... 83
6.3 Evaluation of Sprinkler Systems Flow Capacity and Duration ... 86
6.3.1 Methodology ... 86
6.3.2 Approach ... 89
6.4 WTC 1 and WTC 2 ... 90
6.4.1 Floor System Layout, WTC 1, Floor 107... 91
6.4.2 Floor System Layout, WTC 2, Floor 107... 91
6.4.3 Representative System Layout for all Other Floors ... 92
6.4.4 High Zone... 93 6.4.5 Mid-Level Zone... 99 6.4.6 Low Zone ... 105 6.5 WTC 7... 112 6.5.1 High Zone... 112 6.5.2 Mid-Level Zone... 115 6.5.3 Low Zone ... 117
6.5.4 Manual Operations and Related Procedures... 119
6.6 Water Supply and Primary Sprinkler System Redundancies ... 120
6.6.1 WTC 1 and WTC 2 ... 120
6.6.2 WTC 7 ... 122
Table of Contents
viii NIST NCSTAR 1-4B, WTC Investigation
Chapter 7
Task 3: Differences in Installed Suppression Systems in WTC 1, 2, and 7 ... 125
7.1 General... 125
7.2 Primary System(s) Features ... 125
7.2.1 Water Supplies ... 125
7.2.2 Sprinkler Systems... 131
7.2.3 Standpipe Systems... 131
7.3 Special Systems Protection ... 132
7.4 Discussion ... 133
7.5 Summary of Task 3... 133
Chapter 8 Task 4: Expected Performance of the Suppression Systems Under Specific Building Fire Scenarios ... 135
8.1 General... 135
8.2 Hydraulic Analysis for Automatic Sprinkler Systems ... 135
8.2.1 WTC 1 and WTC 2 ... 136
8.2.2 WTC 7 ... 143
8.3 Standpipe/Pre-Connected Hose Performance ... 148
8.3.1 General ... 148
8.3.2 WTC 1 and WTC 2 ... 148
8.3.3 WTC 7 ... 149
8.4 Summary of Task 4... 150
Chapter 9 Task 5: Suppression Systems Performance on September 11, 2001 ... 151
9.1 General... 151
9.2 Sequence of Events ... 151
9.3 Basis for Estimating Systems Damage ... 152
9.3.1 WTC 1 Aircraft Strike ... 152 9.3.2 WTC 2 Aircraft Strike ... 156 9.3.3 WTC 2 Collapse ... 161 9.3.4 WTC 1 Collapse ... 161 9.3.5 WTC 7 Collapse ... 162 9.4 Summary of Task 5... 162
Table of Contents
Chapter 10
Summary and Limitations ... 165
10.1Summary ... 165
10.1.1 Scope ... 165
10.1.2 Applicable Codes/Standards... 165
10.1.3 Normal Performance Expectations... 166
10.1.4 Evaluation of Suppression Systems... 166
10.2Limitations ... 170
Appendix A References... 173
Appendix B Figures ... 177
Table of Contents
x NIST NCSTAR 1-4B, WTC Investigation
L
IST OF
F
IGURES
Figure P–1. The eight projects in the federal building and fire safety investigation of the WTC
disaster. ...xxiii
Figure 2–1. Site plan, WTC complex. ... 7
Figure 2–2. Typical floor plan, WTC 1. ... 8
Figure 2–3. Typical floor plan, WTC 7. ... 9
Figure 3–1. Typical sprinkler installed in ceiling. ... 13
Figure 3–2. Area/density curves, NFPA 13, 1987 edition. ... 18
Figure 5–1. Plan of water distribution system surrounding the WTC complex... 30
Figure 5–2. Typical 5,000 gal water storage tank, WTC 1 and WTC 2. ... 31
Figure 5–3. Water storage tanks, high zone sprinkler systems. ... 32
Figure 5–4. Water storage tanks, mid-level zone sprinkler systems... 33
Figure 5–5. Manual standpipe fire pump 294A, WTC 1. ... 35
Figure 5–6. Typical floor control valve assembly. ... 46
Figure 5–7. Examples of groove-type pipe fittings... 47
Figure 5–8. Combination pressure reducing control valve assembly. ... 48
Figure 5–9. Typical floor control valve assembly as installed in WTC 1 and WTC 2. ... 50
Figure 5–10. Typical concealed pendent sprinkler. ... 51
Figure 5–11. Typical standard spray pendent sprinkler. ... 51
Figure 5–12. Typical hanger arrangements... 52
Figure 5–13. Automatic sprinkler system booster pump. ... 53
Figure 5–14. Mid-level zone riser supply configuration, WTC 7... 61
Figure 5–15. High zone riser supply configuration, WTC 7... 62
Figure 5–16. Low zone supply configuration, WTC 7. ... 62
Figure 6–1. Municipal water distribution system surrounding WTC complex... 85
Figure 8–1. Summary of sprinkler systems performance for all zones—calculated average delivered density vs. number of open sprinklers, WTC 1 and WTC 2... 137
List of Figures
xii NIST NCSTAR 1-4B, WTC Investigation
Figure 8–2. High zone sprinkler systems performance—calculated average delivered density vs.
number of open sprinklers, WTC 1 and WTC 2... 137
Figure 8–3. Mid-level zone sprinkler systems performance—calculated average delivered density vs. number of open sprinklers, WTC 1 and WTC 2. ... 138
Figure 8–4. Low zone sprinkler systems performance—calculated average delivered density vs. number of open sprinklers, WTC 1 and WTC 2... 139
Figure 8–5. Average delivered density vs. number of open sprinklers, WTC 7. ... 143
Figure 8–6. High zone, average delivered density vs. number of open sprinklers. ... 145
Figure 8–7. Mid-level zone, average delivered density vs. number of open sprinklers... 145
Figure 8–8. Low zone, average delivered density vs. number of open sprinklers. ... 146
Figure 9–1. NIST damage estimates, WTC 1. ... 153
L
IST OF
T
ABLES
Table P–1. Federal building and fire safety investigation of the WTC disaster. ... xxii
Table P–2. Public meetings and briefings of the WTC Investigation... xxv
Table 3–1. Sprinklers operating to control or extinguish fires in NYC, 1969–1978... 19
Table 5–1. Fire pumps, WTC 1 and WTC 2... 34
Table 5–2. FDNY recommended FDC pump pressures. ... 36
Table 5–3. Standpipe designations and locations, WTC 1 and WTC 2... 37
Table 5–4. Typical tower pipe and fitting zones. ... 37
Table 5–5. Standpipe system zones, WTC 1 and WTC 2... 38
Table 5–6. WTC 1 and WTC 2 sprinkler system risers... 45
Table 5–7. Summary of WTC 1 and WTC 2 floor control valve assemblies. ... 49
Table 5–8. Summary of high zone static pressure. ... 53
Table 5–9. Summary of mid-level zone static pressure... 55
Table 5–10. Summary of low zone static pressure. ... 56
Table 5–11. System components, WTC 7. ... 64
Table 5–12. Fuel oil equipment, WTC 7. ... 71
Table 6–1. Average water pressure observed at the 14th Street regulators. ... 84
Table 6–2. Number of operating sprinklers, 107th and 99th floor, Light Hazard cases... 95
Table 6–3. High zone Light Hazard hydraulic calculations summary, WTC 1 and WTC 2. ... 95
Table 6–4. Number of operating sprinklers, 107th and 99th floor Ordinary Hazard calculations. ... 96
Table 6–5. High zone Ordinary Hazard hydraulic calculations summary, WTC 1 and WTC 2. ... 96
Table 6–6. High zone primary water supply duration, WTC 1 and WTC 2... 97
Table 6–7. Comparison of primary and secondary water supplies for high zone... 98
Table 6–8. Light Hazard hydraulic calculations summary, 107th floor, WTC 1 and WTC 2... 99
Table 6–9. Number of operating sprinklers, 98th, 87th, and 32nd floor, Light Hazard calculations, WTC 1. ... 100
Table 6–10. Mid-level zone Light Hazard hydraulic calculations summary, WTC 1 and WTC 2. ... 101
Table 6–11. Number of operating sprinklers, 98th, 87th, 86th and 32nd floor Ordinary Hazard calculations, WTC 1. ... 102
List of Tables
xiv NIST NCSTAR 1-4B, WTC Investigation
Table 6–12. Mid-level zone Ordinary Hazard hydraulic calculations summary, WTC 1
and WTC 2. ... 103
Table 6–13. Mid-level zone primary water supply duration, WTC 1 and WTC 2. ... 104
Table 6–14. Comparison of primary and secondary water supplies for mid-level zone. ... 105
Table 6–15. Number of operating sprinklers, 31st and 2nd floor Light Hazard calculations, WTC 1.... 106
Table 6–16. Low zone Light Hazard hydraulic calculations summary, WTC 1 and WTC 2... 107
Table 6–17. Number of operating sprinklers, 31st, 9th, 7th and 2nd floor Ordinary Hazard calculations, WTC 1. ... 108
Table 6–18. Low zone Ordinary Hazard hydraulic calculations summary, WTC 1 and WTC 2. ... 108
Table 6–19. Low zone primary water supply duration, WTC 1 and WTC 2. ... 109
Table 6–20. Comparison of primary and secondary water supplies for low zone... 110
Table 6–21. Low zone primary water supply duration, WTC 1 and WTC 2. ... 111
Table 6–22. Summary of manual fire pump pressure limitations at rated flow (750 gpm), WTC 1 and WTC 2. ... 112
Table 6–23. Number of operating sprinklers for hydraulic supply calculations, 47th and 40th floors, WTC 7. ... 114
Table 6–24. High zone hydraulic calculations summary, WTC 7... 115
Table 6–25. Number of operating sprinklers for hydraulic supply calculations, 39th and 21st floors, WTC 7 ... 116
Table 6–26. Mid-level zone hydraulic calculations summary, WTC 7. ... 117
Table 6–27. Number of operating sprinklers for hydraulic supply calculations, 1st and 20th floors, WTC 7. ... 118
Table 6–28. Low zone hydraulic calculations summary, WTC 7. ... 118
Table 7–1. Summary of active fire suppression system features, WTC 1, 2, and 7 ... 126
Table 8–1. High zone average delivered density per floor vs. number of floors flowing (four sprinklers/floor), WTC 1 and WTC 2... 140
Table 8–2. Mid-level zone average delivered density per floor vs. number of floors flowing (four sprinklers/floor), WTC 1 and WTC 2... 140
Table 8–3. High zone and mid-level zone average delivered density per floor vs. number of floors flowing (four sprinklers/floor), WTC 1 and WTC 2. ... 141
Table 8–4. High zone average delivered density per floor vs. number of floors flowing (eight sprinklers/floor), WTC 1 and WTC 2... 142
Table 8–5. Mid-level zone average delivered density per floor vs. number of floors flowing (eight sprinklers/floor), WTC 1 and WTC 2... 142
List of Tables
Table 8–7. Average delivered density per floor vs. number of floors flowing (four
sprinklers/floor). ... 146 Table 8–8. Average delivered density per floor vs. number of floors flowing (nine
sprinklers/floor). ... 147 Table 9–1. Timeline and summary of major events. ... 151 Table 9–2. Summary of estimated initial damage, sprinkler and standpipe systems, 96th floor,
WTC 1. ... 154 Table 9–3. Summary of estimated initial damage, sprinkler and standpipe systems, 95th floor,
WTC 1. ... 155 Table 9–4. Summary of estimated initial damage, sprinkler and standpipe systems, 94th floor,
WTC 1. ... 155 Table 9–5. Summary of estimated initial damage, sprinkler and standpipe systems, 81st floor,
WTC 2. ... 158 Table 9–6. Summary of estimated initial damage, sprinkler, and standpipe systems, 80th floor,
WTC 2. ... 159 Table 9–7. Summary of estimated initial damage, sprinkler and standpipe systems, 79th floor,
WTC 2. ... 159 Table 9–8. Summary of estimated initial damage, sprinkler and standpipe systems, 78th floor,
List of Tables
xvi NIST NCSTAR 1-4B, WTC Investigation
L
IST OF
A
CRONYMS AND
A
BBREVIATIONS
Acronyms
AA American Airlines
AHJ authority having jurisdiction ASTM ASTM International
BCNYC Building Code of the City of New York BPS Building Performance Study
BWS Bureau of Water Supply
BWSO Bureau of Water and Sewer Operations Con-Ed Consolidated Edison Company
DTAP dissemination and technical assistance program EH Extra Hazard
FCA floor control assembly FDC fire department connection
FDNY The Fire Department of the City of New York FEMA Federal Emergency Management Agency FHC fire hose cabinets
FHV fire hose valves
HAI Hughes Associates, Inc.
HASS Hydraulic Analyzer of Sprinkler Systems LH Light Hazard
MER mechanical equipment room NCST National Construction Safety Team NFPA National Fire Protection Association
NIST National Institute of Standards and Technology
NYC DEP New York City Department of Environmental Protection NYC New York City
NYPD New York City Police Department O&M operations and maintenance OEM Office of Emergency Management
List of Acronyms and Abbreviations
xviii NIST NCSTAR 1-4B, WTC Investigation
OH Ordinary Hazard OS&Y outside screw and yoke
PANYNJ Port Authority of New York and New Jersey PRV pressure relief valve
R&D research and development
RASCO Reliable Automatic Sprinkler Corporation of America, Inc. RJA Rolf Jensen & Associates
RS Reference Standards
SEAoNY Structural Engineers Association of New York UA United Airlines
USC United States Code WTC World Trade Center
WTC 1 World Trade Center 1 (North Tower) WTC 2 World Trade Center 2 (South Tower) WTC 7 World Trade Center 7
Abbreviations °C degrees Celsius °F degrees Fahrenheit μm micrometer CO2 carbon monoxide ft foot ft2 square foot gal gallon
gpm gallons per minute h hour in. inch kW kilowatt L liter m meter min minute
List of Acronyms and Abbreviations
s second V volt
List of Acronyms and Abbreviations
xx NIST NCSTAR 1-4B, WTC Investigation
P
REFACE
Genesis of This Investigation
Immediately following the terrorist attack on the World Trade Center (WTC) on September 11, 2001, the Federal Emergency Management Agency (FEMA) and the American Society of Civil Engineers began planning a building performance study of the disaster. The week of October 7, as soon as the rescue and search efforts ceased, the Building Performance Study Team went to the site and began its assessment. This was to be a brief effort, as the study team consisted of experts who largely volunteered their time away from their other professional commitments. The Building Performance Study Team issued its report in May 2002, fulfilling its goal “to determine probable failure mechanisms and to identify areas of future investigation that could lead to practical measures for improving the damage resistance of buildings against such unforeseen events.”
On August 21, 2002, with funding from the U.S. Congress through FEMA, the National Institute of Standards and Technology (NIST) announced its building and fire safety investigation of the WTC disaster. On October 1, 2002, the National Construction Safety Team Act (Public Law 107-231), was signed into law. The NIST WTC Investigation was conducted under the authority of the National Construction Safety Team Act.
The goals of the investigation of the WTC disaster were:
• To investigate the building construction, the materials used, and the technical conditions that contributed to the outcome of the WTC disaster.
• To serve as the basis for:
− Improvements in the way buildings are designed, constructed, maintained, and used; − Improved tools and guidance for industry and safety officials;
− Recommended revisions to current codes, standards, and practices; and − Improved public safety.
The specific objectives were:
1. Determine why and how WTC 1 and WTC 2 collapsed following the initial impacts of the aircraft and why and how WTC 7 collapsed;
2. Determine why the injuries and fatalities were so high or low depending on location, including all technical aspects of fire protection, occupant behavior, evacuation, and emergency response;
3. Determine what procedures and practices were used in the design, construction, operation, and maintenance of WTC 1, 2, and 7; and
4. Identify, as specifically as possible, areas in current building and fire codes, standards, and practices that warrant revision.
Preface
xxii NIST NCSTAR 1-4B, WTC Investigation
NIST is a nonregulatory agency of the U.S. Department of Commerce’s Technology Administration. The purpose of NIST investigations is to improve the safety and structural integrity of buildings in the United States, and the focus is on fact finding. NIST investigative teams are authorized to assess building performance and emergency response and evacuation procedures in the wake of any building failure that has resulted in substantial loss of life or that posed significant potential of substantial loss of life. NIST does not have the statutory authority to make findings of fault nor negligence by individuals or
organizations. Further, no part of any report resulting from a NIST investigation into a building failure or from an investigation under the National Construction Safety Team Act may be used in any suit or action for damages arising out of any matter mentioned in such report (15 USC 281a, as amended by Public Law 107-231).
Organization of the Investigation
The National Construction Safety Team for this Investigation, appointed by the then NIST Director, Dr. Arden L. Bement, Jr., was led by Dr. S. Shyam Sunder. Dr. William L. Grosshandler served as Associate Lead Investigator, Mr. Stephen A. Cauffman served as Program Manager for Administration, and Mr. Harold E. Nelson served on the team as a private sector expert. The Investigation included eight interdependent projects whose leaders comprised the remainder of the team. A detailed description of each of these eight projects is available at http://wtc.nist.gov. The purpose of each project is summarized in Table P–1, and the key interdependencies among the projects are illustrated in Fig. P–1.
Table P–1. Federal building and fire safety investigation of the WTC disaster.
Technical Area and Project Leader Project Purpose
Analysis of Building and Fire Codes and Practices; Project Leaders: Dr. H. S. Lew and Mr. Richard W. Bukowski
Document and analyze the code provisions, procedures, and practices used in the design, construction, operation, and maintenance of the structural, passive fire protection, and emergency access and evacuation systems of WTC 1, 2, and 7. Baseline Structural Performance and
Aircraft Impact Damage Analysis; Project Leader: Dr. Fahim H. Sadek
Analyze the baseline performance of WTC 1 and WTC 2 under design, service, and abnormal loads, and aircraft impact damage on the structural, fire protection, and egress systems.
Mechanical and Metallurgical Analysis of Structural Steel; Project Leader: Dr. Frank W. Gayle
Determine and analyze the mechanical and metallurgical properties and quality of steel, weldments, and connections from steel recovered from WTC 1, 2, and 7.
Investigation of Active Fire Protection Systems; Project Leader: Dr. David D. Evans; Dr. William Grosshandler
Investigate the performance of the active fire protection systems in WTC 1, 2, and 7 and their role in fire control, emergency response, and fate of occupants and responders.
Reconstruction of Thermal and Tenability Environment; Project Leader: Dr. Richard G. Gann
Reconstruct the time-evolving temperature, thermal environment, and smoke movement in WTC 1, 2, and 7 for use in evaluating the structural performance of the buildings and behavior and fate of occupants and responders.
Structural Fire Response and Collapse Analysis; Project Leaders: Dr. John L. Gross and Dr. Therese P. McAllister
Analyze the response of the WTC towers to fires with and without aircraft damage, the response of WTC 7 in fires, the performance of composite steel-trussed floor systems, and determine the most probable structural collapse sequence for WTC 1, 2, and 7. Occupant Behavior, Egress, and Emergency
Communications; Project Leader: Mr. Jason D. Averill
Analyze the behavior and fate of occupants and responders, both those who survived and those who did not, and the performance of the evacuation system.
Emergency Response Technologies and Guidelines; Project Leader: Mr. J. Randall Lawson
Document the activities of the emergency responders from the time of the terrorist attacks on WTC 1 and WTC 2 until the collapse of WTC 7, including practices followed and technologies used.
Preface
NIST WTC Investigation Projects
NIST WTC Investigation Projects
Analysis of
Steel Structural Collapse
Evacuation Baseline Performance & Impact Damage Analysis of Codes and Practices Emergency Response Active Fire Protection Thermal and Tenability Environment Video/ Photographic Records Oral History Data Emergency Response Records Recovered Structural Steel WTC Building Performance Study Recommendations Government, Industry, Professional, Academic Inputs Public Inputs
Figure P–1. The eight projects in the federal building and fire safety investigation of the WTC disaster.
National Construction Safety Team Advisory Committee
The NIST Director also established an advisory committee as mandated under the National Construction Safety Team Act. The initial members of the committee were appointed following a public solicitation. These were:
• Paul Fitzgerald, Executive Vice President (retired) FM Global, National Construction Safety Team Advisory Committee Chair
• John Barsom, President, Barsom Consulting, Ltd. • John Bryan, Professor Emeritus, University of Maryland • David Collins, President, The Preview Group, Inc.
• Glenn Corbett, Professor, John Jay College of Criminal Justice • Philip DiNenno, President, Hughes Associates, Inc.
Preface
xxiv NIST NCSTAR 1-4B, WTC Investigation
• Robert Hanson, Professor Emeritus, University of Michigan
• Charles Thornton, Co-Chairman and Managing Principal, The Thornton-Tomasetti Group, Inc.
• Kathleen Tierney, Director, Natural Hazards Research and Applications Information Center, University of Colorado at Boulder
• Forman Williams, Director, Center for Energy Research, University of California at San Diego
This National Construction Safety Team Advisory Committee provided technical advice during the Investigation and commentary on drafts of the Investigation reports prior to their public release. NIST has benefited from the work of many people in the preparation of these reports, including the National Construction Safety Team Advisory Committee. The content of the reports and recommendations, however, are solely the responsibility of NIST.
Public Outreach
During the course of this Investigation, NIST held public briefings and meetings (listed in Table P–2) to solicit input from the public, present preliminary findings, and obtain comments on the direction and progress of the Investigation from the public and the Advisory Committee.
NIST maintained a publicly accessible Web site during this Investigation at http://wtc.nist.gov. The site contained extensive information on the background and progress of the Investigation.
NIST’s WTC Public-Private Response Plan
The collapse of the WTC buildings has led to broad reexamination of how tall buildings are designed, constructed, maintained, and used, especially with regard to major events such as fires, natural disasters, and terrorist attacks. Reflecting the enhanced interest in effecting necessary change, NIST, with support from Congress and the Administration, has put in place a program, the goal of which is to develop and implement the standards, technology, and practices needed for cost-effective improvements to the safety and security of buildings and building occupants, including evacuation, emergency response procedures, and threat mitigation.
The strategy to meet this goal is a three-part NIST-led public-private response program that includes: • A federal building and fire safety investigation to study the most probable factors that
contributed to post-aircraft impact collapse of the WTC towers and the 47-story WTC 7 building, and the associated evacuation and emergency response experience.
• A research and development (R&D) program to (a) facilitate the implementation of
recommendations resulting from the WTC Investigation, and (b) provide the technical basis for cost-effective improvements to national building and fire codes, standards, and practices that enhance the safety of buildings, their occupants, and emergency responders.
Preface
Table P–2. Public meetings and briefings of the WTC Investigation.
Date Location Principal Agenda
June 24, 2002 New York City, NY Public meeting: Public comments on the Draft Plan for the pending WTC Investigation.
August 21, 2002 Gaithersburg, MD Media briefing announcing the formal start of the Investigation. December 9, 2002 Washington, DC Media briefing on release of the Public Update and NIST request
for photographs and videos.
April 8, 2003 New York City, NY Joint public forum with Columbia University on first-person interviews.
April 29–30, 2003 Gaithersburg, MD NCST Advisory Committee meeting on plan for and progress on WTC Investigation with a public comment session.
May 7, 2003 New York City, NY Media briefing on release of May 2003 Progress Report.
August 26–27, 2003 Gaithersburg, MD NCST Advisory Committee meeting on status of the WTC investigation with a public comment session.
September 17, 2003 New York City, NY Media and public briefing on initiation of first-person data collection projects.
December 2–3, 2003 Gaithersburg, MD NCST Advisory Committee meeting on status and initial results and release of the Public Update with a public comment session. February 12, 2004 New York City, NY Public meeting on progress and preliminary findings with public
comments on issues to be considered in formulating final recommendations.
June 18, 2004 New York City, NY Media/public briefing on release of June 2004 Progress Report.
June 22–23, 2004 Gaithersburg, MD NCST Advisory Committee meeting on the status of and preliminary findings from the WTC Investigation with a public comment session.
August 24, 2004 Northbrook, IL Public viewing of standard fire resistance test of WTC floor system at Underwriters Laboratories, Inc.
October 19–20, 2004 Gaithersburg, MD NCST Advisory Committee meeting on status and near complete set of preliminary findings with a public comment session. November 22, 2004 Gaithersburg, MD NCST Advisory Committee discussion on draft annual report to
Congress, a public comment session, and a closed session to discuss pre-draft recommendations for WTC Investigation. April 5, 2005 New York City, NY Media and public briefing on release of the probable collapse
sequence for the WTC towers and draft reports for the projects on codes and practices, evacuation, and emergency response. June 23, 2005 New York City, NY Media and public briefing on release of all draft reports for the
WTC towers and draft recommendations for public comment. September 12–13,
2005
Gaithersburg, MD NCST Advisory Committee meeting on disposition of public comments and update to draft reports for the WTC towers. September 13–15,
2005
Gaithersburg, MD WTC Technical Conference for stakeholders and technical community for dissemination of findings and recommendations and opportunity for public to make technical comments.
• A dissemination and technical assistance program (DTAP) to (a) engage leaders of the construction and building community in ensuring timely adoption and widespread use of proposed changes to practices, standards, and codes resulting from the WTC Investigation and the R&D program, and (b) provide practical guidance and tools to better prepare facility owners, contractors, architects, engineers, emergency responders, and regulatory authorities to respond to future disasters.
The desired outcomes are to make buildings, occupants, and first responders safer in future disaster events.
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xxvi NIST NCSTAR 1-4B, WTC Investigation
National Construction Safety Team Reports on the WTC Investigation
A final report on the collapse of the WTC towers is being issued as NIST NCSTAR 1. A companion report on the collapse of WTC 7 is being issued as NIST NCSTAR 1A. The present report is one of a set that provides more detailed documentation of the Investigation findings and the means by which these technical results were achieved. As such, it is part of the archival record of this Investigation. The titles of the full set of Investigation publications are:
NIST (National Institute of Standards and Technology). 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Final Report on the Collapse of the World Trade Center Towers. NIST NCSTAR 1. Gaithersburg, MD, September.
NIST (National Institute of Standards and Technology). 2008. Federal Building and Fire Safety
Investigation of the World Trade Center Disaster: Final Report on the Collapse of World Trade Center 7. NIST NCSTAR 1A. Gaithersburg, MD, November.
Lew, H. S., R. W. Bukowski, and N. J. Carino. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Design, Construction, and Maintenance of Structural and Life Safety Systems. NIST NCSTAR 1-1. National Institute of Standards and Technology. Gaithersburg, MD, September.
Fanella, D. A., A. T. Derecho, and S. K. Ghosh. 2005. Federal Building and Fire Safety
Investigation of the World Trade Center Disaster: Design and Construction of Structural Systems.
NIST NCSTAR 1-1A. National Institute of Standards and Technology. Gaithersburg, MD, September.
Ghosh, S. K., and X. Liang. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Comparison of Building Code Structural Requirements. NIST
NCSTAR 1-1B. National Institute of Standards and Technology. Gaithersburg, MD, September. Fanella, D. A., A. T. Derecho, and S. K. Ghosh. 2005. Federal Building and Fire Safety
Investigation of the World Trade Center Disaster: Maintenance and Modifications to Structural Systems. NIST NCSTAR 1-1C. National Institute of Standards and Technology. Gaithersburg, MD, September.
Grill, R. A., and D. A. Johnson. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Fire Protection and Life Safety Provisions Applied to the Design and Construction of World Trade Center 1, 2, and 7 and Post-Construction Provisions Applied after Occupancy. NIST NCSTAR 1-1D. National Institute of Standards and Technology. Gaithersburg, MD, September.
Razza, J. C., and R. A. Grill. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Comparison of Codes, Standards, and Practices in Use at the Time of the Design and Construction of World Trade Center 1, 2, and 7. NIST NCSTAR 1-1E. National Institute of Standards and Technology. Gaithersburg, MD, September.
Grill, R. A., D. A. Johnson, and D. A. Fanella. 2005. Federal Building and Fire Safety
Preface
York City Building Code Provisions. NIST NCSTAR 1-1F. National Institute of Standards and Technology. Gaithersburg, MD, September.
Grill, R. A., and D. A. Johnson. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Amendments to the Fire Protection and Life Safety Provisions of the New York City Building Code by Local Laws Adopted While World Trade Center 1, 2, and 7 Were in Use. NIST NCSTAR 1-1G. National Institute of Standards and Technology. Gaithersburg, MD, September.
Grill, R. A., and D. A. Johnson. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Post-Construction Modifications to Fire Protection and Life Safety Systems of World Trade Center 1 and 2. NIST NCSTAR 1-1H. National Institute of Standards and
Technology. Gaithersburg, MD, September.
Grill, R. A., D. A. Johnson, and D. A. Fanella. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Post-Construction Modifications to Fire Protection, Life Safety, and Structural Systems of World Trade Center 7. NIST NCSTAR 1-1I. National Institute of Standards and Technology. Gaithersburg, MD, September.
Grill, R. A., and D. A. Johnson. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Design, Installation, and Operation of Fuel System for Emergency Power in World Trade Center 7. NIST NCSTAR 1-1J. National Institute of Standards and Technology. Gaithersburg, MD, September.
Sadek, F. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Baseline Structural Performance and Aircraft Impact Damage Analysis of the World Trade Center Towers. NIST NCSTAR 1-2. National Institute of Standards and Technology. Gaithersburg, MD, September.
Faschan, W. J., and R. B. Garlock. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Reference Structural Models and Baseline Performance Analysis of the World Trade Center Towers. NIST NCSTAR 1-2A. National Institute of Standards and Technology. Gaithersburg, MD, September.
Kirkpatrick, S. W., R. T. Bocchieri, F. Sadek, R. A. MacNeill, S. Holmes, B. D. Peterson,
R. W. Cilke, C. Navarro. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Analysis of Aircraft Impacts into the World Trade Center Towers, NIST
NCSTAR 1-2B. National Institute of Standards and Technology. Gaithersburg, MD, September. Gayle, F. W., R. J. Fields, W. E. Luecke, S. W. Banovic, T. Foecke, C. N. McCowan, T. A. Siewert, and J. D. McColskey. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Mechanical and Metallurgical Analysis of Structural Steel. NIST NCSTAR 1-3. National Institute of Standards and Technology. Gaithersburg, MD, September.
Luecke, W. E., T. A. Siewert, and F. W. Gayle. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Contemporaneous Structural Steel
Specifications. NIST Special Publication 1-3A. National Institute of Standards and Technology. Gaithersburg, MD, September.
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xxviii NIST NCSTAR 1-4B, WTC Investigation
Banovic, S. W. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Steel Inventory and Identification. NIST NCSTAR 1-3B. National Institute of Standards and Technology. Gaithersburg, MD, September.
Banovic, S. W., and T. Foecke. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Damage and Failure Modes of Structural Steel Components. NIST
NCSTAR 1-3C. National Institute of Standards and Technology. Gaithersburg, MD, September. Luecke, W. E., J. D. McColskey, C. N. McCowan, S. W. Banovic, R. J. Fields, T. Foecke,
T. A. Siewert, and F. W. Gayle. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Mechanical Properties of Structural Steels. NIST NCSTAR 1-3D.
National Institute of Standards and Technology. Gaithersburg, MD, September.
Banovic, S. W., C. N. McCowan, and W. E. Luecke. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Physical Properties of Structural Steels. NIST NCSTAR 1-3E. National Institute of Standards and Technology. Gaithersburg, MD, September. Evans, D. D., R. D. Peacock, E. D. Kuligowski, W. S. Dols, and W. L. Grosshandler. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Active Fire Protection Systems. NIST NCSTAR 1-4. National Institute of Standards and Technology. Gaithersburg, MD, September.
Kuligowski, E. D., D. D. Evans, and R. D. Peacock. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Post-Construction Fires Prior to September 11, 2001. NIST NCSTAR 1-4A. National Institute of Standards and Technology. Gaithersburg, MD, September.
Hopkins, M., J. Schoenrock, and E. Budnick. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Fire Suppression Systems. NIST NCSTAR 1-4B. National Institute of Standards and Technology. Gaithersburg, MD, September.
Keough, R. J., and R. A. Grill. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Fire Alarm Systems. NIST NCSTAR 1-4C. National Institute of Standards and Technology. Gaithersburg, MD, September.
Ferreira, M. J., and S. M. Strege. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Smoke Management Systems. NIST NCSTAR 1-4D. National Institute of Standards and Technology. Gaithersburg, MD, September.
Gann, R. G., A. Hamins, K. B. McGrattan, G. W. Mulholland, H. E. Nelson, T. J. Ohlemiller,
W. M. Pitts, and K. R. Prasad. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Reconstruction of the Fires in the World Trade Center Towers. NIST NCSTAR 1-5. National Institute of Standards and Technology. Gaithersburg, MD, September.
Pitts, W. M., K. M. Butler, and V. Junker. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Visual Evidence, Damage Estimates, and Timeline Analysis. NIST NCSTAR 1-5A. National Institute of Standards and Technology. Gaithersburg, MD, September.
Preface
Hamins, A., A. Maranghides, K. B. McGrattan, E. Johnsson, T. J. Ohlemiller, M. Donnelly, J. Yang, G. Mulholland, K. R. Prasad, S. Kukuck, R. Anleitner and T. McAllister. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Experiments and Modeling of Structural Steel Elements Exposed to Fire. NIST NCSTAR 1-5B. National Institute of Standards and Technology. Gaithersburg, MD, September.
Ohlemiller, T. J., G. W. Mulholland, A. Maranghides, J. J. Filliben, and R. G. Gann. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Fire Tests of Single Office Workstations. NIST NCSTAR 1-5C. National Institute of Standards and Technology. Gaithersburg, MD, September.
Gann, R. G., M. A. Riley, J. M. Repp, A. S. Whittaker, A. M. Reinhorn, and P. A. Hough. 2005.
Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Reaction of Ceiling Tile Systems to Shocks. NIST NCSTAR 1-5D. National Institute of Standards and Technology. Gaithersburg, MD, September.
Hamins, A., A. Maranghides, K. B. McGrattan, T. J. Ohlemiller, and R. Anleitner. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Experiments and Modeling of Multiple Workstations Burning in a Compartment. NIST NCSTAR 1-5E. National Institute of Standards and Technology. Gaithersburg, MD, September.
McGrattan, K. B., C. Bouldin, and G. Forney. 2005. Federal Building and Fire Safety
Investigation of the World Trade Center Disaster: Computer Simulation of the Fires in the World Trade Center Towers. NIST NCSTAR 1-5F. National Institute of Standards and Technology. Gaithersburg, MD, September.
Prasad, K. R., and H. R. Baum. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Fire Structure Interface and Thermal Response of the World Trade Center Towers. NIST NCSTAR 1-5G. National Institute of Standards and Technology. Gaithersburg, MD, September.
Gross, J. L., and T. McAllister. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Structural Fire Response and Probable Collapse Sequence of the World Trade Center Towers. NIST NCSTAR 1-6. National Institute of Standards and Technology. Gaithersburg, MD, September.
Carino, N. J., M. A. Starnes, J. L. Gross, J. C. Yang, S. Kukuck, K. R. Prasad, and R. W. Bukowski. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Passive Fire Protection. NIST NCSTAR 1-6A. National Institute of Standards and Technology.
Gaithersburg, MD, September.
Gross, J., F. Hervey, M. Izydorek, J. Mammoser, and J. Treadway. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Fire Resistance Tests of Floor Truss Systems. NIST NCSTAR 1-6B. National Institute of Standards and Technology. Gaithersburg, MD, September.
Zarghamee, M. S., S. Bolourchi, D. W. Eggers, Ö. O. Erbay, F. W. Kan, Y. Kitane, A. A. Liepins, M. Mudlock, W. I. Naguib, R. P. Ojdrovic, A. T. Sarawit, P. R Barrett, J. L. Gross, and
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xxx NIST NCSTAR 1-4B, WTC Investigation
T. P. McAllister. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Component, Connection, and Subsystem Structural Analysis. NIST NCSTAR 1-6C. National Institute of Standards and Technology. Gaithersburg, MD, September.
Zarghamee, M. S., Y. Kitane, Ö. O. Erbay, T. P. McAllister, and J. L. Gross. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Global Structural Analysis of the Response of the World Trade Center Towers to Impact Damage and Fire. NIST NCSTAR 1-6D. National Institute of Standards and Technology. Gaithersburg, MD, September. Averill, J. D., D. S. Mileti, R. D. Peacock, E. D. Kuligowski, N. Groner, G. Proulx, P. A. Reneke, and H. E. Nelson. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Occupant Behavior, Egress, and Emergency Communication. NIST NCSTAR 1-7. National Institute of Standards and Technology. Gaithersburg, MD, September.
Fahy, R., and G. Proulx. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Analysis of Published Accounts of the World Trade Center Evacuation. NIST NCSTAR 1-7A. National Institute of Standards and Technology. Gaithersburg, MD, September. Zmud, J. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Technical Documentation for Survey Administration. NIST NCSTAR 1-7B. National Institute of Standards and Technology. Gaithersburg, MD, September.
Lawson, J. R., and R. L. Vettori. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: The Emergency Response Operations. NIST NCSTAR 1-8. National Institute of Standards and Technology. Gaithersburg, MD, September.
McAllister, T., R. G. Gann, J. D. Averill, J. L. Gross, W. L. Grosshandler, J. R. Lawson, K. B. McGrattan, H. E. Nelson, W. M. Pitts, K. R. Prasad, F. H. Sadek. 2008. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Structural Fire Response and Probable Collapse Sequence of World Trade Center Building 7. NIST NCSTAR 1-9. National Institute of Standards and Technology. Gaithersburg, MD, November.
MacNeill, R., S. Kirkpatrick, B. Peterson, and R. Bocchieri. 2008. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Global Structural Analysis of the
Response of World Trade Center Building 7 to Fires and Debris Impact Damage. NIST NCSTAR 1-9A. National Institute of Standards and Technology. Gaithersburg, MD, November.
E
XECUTIVE
S
UMMARY
E.1 INTRODUCTION
The National Institute of Standards and Technology (NIST) conducted a building and fire safety investigation of the World Trade Center (WTC) disaster. The work documented in this report was performed in support of the investigation of active fire protection systems. This effort involved
investigation of the performance of pre-connected hoses, standpipes, and automatic fire sprinkler systems, and the associated water supplies for WTC 1, 2, and 7.
There was very little eyewitness or communications information regarding the performance of the fire suppression systems on September 11, 2001. The descriptions of the systems and their inherent
operational capabilities described in this report are considered reasonably accurate. The performance of the individual suppression systems on September 11, 2001 was based on review of the incident
information accumulated by NIST, analysis of the likely initial impact effects on the systems, and
historical performance records for automatic sprinklers. Where possible, significant events and/or effects were determined based on information from more than one source. However, due to the fragmentation of available information regarding the events of September 11, this could not always be accomplished. Descriptions of suppression systems, likely events or actions, and subsequent effects were based on, and/or deduced from, available information. Events or effects that were considered “likely” or “probable,” based on the accumulated information, were considered appropriate for inclusion.
E.1.1 Incident Description
On September 11, 2001, WTC 1 was struck by a hijacked commercial aircraft. The impact occurred between the 93rd and 99th floors. Subsequently, WTC 2 was struck by a second hijacked aircraft. The impact of this second aircraft was between the 77th and 85th floors. Extensive impact damage occurred on multiple floors of both buildings. Fires extended over multiple floors in each building with a
significant initial contributor to fire spread being the aviation fuel from the two aircrafts (McAllister 2002).
WTC 2 was the first building to collapse. Collapse occurred approximately 56 min after impact. WTC 1 collapsed approximately 1 h and 43 min after impact. Both buildings suffered total, progressive collapse, resulting in exposure of surrounding buildings to debris and burning materials.
WTC 7 burned for over 7 h before collapsing. The working hypothesis at the time this study was completed, involved an initial local failure of the structure below the 13th floor due to fire and/or debris induced structural damage of a critical column. This incident resulted in a number of fires burning uncontrollably and global structural collapse of the building.
The collapses of the two tower buildings also caused damage to the New York City (NYC) water system in the streets surrounding the WTC complex.
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xxxii NIST NCSTAR 1-4B, WTC Investigation
E.1.2 Scope and Objectives
Five specific objectives associated with this effort included the following:
1. Documentation of the design and installation of the fire sprinkler systems, standpipe systems, and pre-connected hoses and comparison of the designs to applicable code and standards requirements (Task 1).
2. Documentation of the design and capacity of the water supply to the fire sprinklers including provisions for redundancy (Task 2).
3. Identification and documentation of the differences in the design of the water supply, fire sprinkler systems, standpipe systems, and pre-connected hoses among WTC 1, 2, and 7 (Task 3).
4. Documentation of the normal operation and effect of fully functional fire sprinkler system, standpipe system, and pre-connected hoses for fire control (Task 4).
5. Documentation of the performance of the sprinkler systems, standpipe systems, and pre-connected hoses on September 11, 2001 in WTC 1, 2, and 7 (Task 5).
E.1.3 General Approach
A literature review was performed in order to document the installed fire suppression features in WTC 1, 2, and 7 as well as to provide any information regarding the performance of these systems on
September 11, 2001. The primary source of documents and related information (e.g., drawings,
specifications, procedures, etc.) were the documents collected and maintained by NIST during the WTC investigation. NIST had been accumulating information related to the design, construction, and operation of WTC 1, 2, and 7 as well as information related to the incidents on September 11. The information available from NIST was supplemented by information in the open literature, information from the Hughes Associates, Inc. (HAI) technical library, and inquiries by NIST to appropriate organizations in New York City. In addition, information related to applicable codes and standards of record was provided in studies performed by Rolf Jensen and Associates (RJA) as part of the NIST investigation (Razza and Grill 2005).
Based on available information and codes and standards documentation, the fire suppression features that existed in WTC 1, 2, and 7 were reconstructed and documented. Once this was completed, hydraulic analyses were performed to provide estimates of the baseline capabilities of the suppression systems as well as capabilities under different fire incident scenarios, including the events of September 11, 2001. Performance criteria for the suppression systems were selected based on requirements in National Fire Protection Association (NFPA) 13, Standard for the Installation of Sprinkler Systems, and NFPA 14, Standard for the Installation of Standpipe, Private Hydrant, and Hose Systems, the primary design and installation standards for fire suppression systems in high-rise buildings.
Executive Summary
E.2
SITE AND BUILDING DESCRIPTIONS
E.2.1 General Site Descriptions
The WTC complex consisted of seven buildings located on 16 acres in lower Manhattan in New York City. WTC buildings 1 through 6 were constructed on the primary WTC Plaza. WTC 7, completed in the mid-1980s, was the last building constructed, just north of the WTC Plaza. A six-level structure below the ground floor of the main WTC Plaza included utilities, parking, and subway stations.
E.2.2 WTC 1 and WTC 2
WTC 1 (North Tower) and WTC 2 (South Tower) were each 110 stories in height above the plaza level, and 7 stories below. For the most part, the two towers were similar in size and layout. Each floor was approximately 207 ft by 207 ft, providing nearly an acre of floor area. A service core (approximately 87 ft by 137 ft) was located in the center of each tower. The elevators, stairwells, primary piping, and
ventilation duct systems were located in this service core.
E.2.3 WTC 7
WTC 7 was a 47-story office building with nearly two million square feet of office space. Floors 8 through 47 were primarily office spaces. The elevators, stairwells, primary piping, and ventilation duct systems were located in the core of the building. Loading docks and an electrical substation that provided power to lower Manhattan were located in the lower part of the building at the ground level. Switchgear, generators, transformers, management offices, and transformer vaults were located on floors one through nine. Two 12,000 gal fuel tanks were located below the first floor loading dock, and one 6,000 gal fuel tank was located above ground on the first floor. These tanks supplied the 275 gal day tanks on the fifth, seventh, and eighth floors and a 50 gal day tank on the ninth floor. Also, there were two 6,000 gal tanks located below the first floor that supplied the fifth floor. A pressurized fuel distribution system extended to the fifth floor, supplied from these tanks.
E.3
DESCRIPTION OF THE NYC WATER SUPPLY
The primary source of water for the WTC complex was the NYC water supply and distribution system. This system was operated by the New York City Department of Environmental Protection (NYC DEP). Two separate divisions (bureaus) of the DEP were responsible for the water supply and distribution system: The Bureau of Water Supply (BWS) and the Bureau of Water and Sewer Operations (BWSO) (LZA 2002).
The NYC water distribution system in lower Manhattan surrounding the WTC complex was composed of a complex gridded network of 20 in. and 12 in. ductile iron mains. A 20 in. loop was located beneath the streets surrounding the main WTC complex where towers WTC 1 and WTC 2 were located. The mains were beneath Vesey Street to the north, Liberty Street to the south, Church Street to the east, and West Street to the west. These mains were inter-connected to a series of 20 in. and 12 in. mains. This
permitted water to flow along a large number of flow paths, minimizing the effects of friction loss while flowing a large volume of water. The large volume of water within the distribution system mains,
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xxxiv NIST NCSTAR 1-4B, WTC Investigation
transmission mains, and at the source (watersheds in upstate New York) allowed for a large capacity of water to be available for fire fighting capabilities.
A 20 in. water main was located beneath West Broadway, immediately to the east of WTC 7. This main supplied water to the 20 in. loop around the WTC plaza. A 12 in. main to the west of WTC 7 beneath Washington Street supplied two parallel 8 in. diameter lead-ins (feeder mains) for WTC 7 and connected to a 12 in. main at the north side of WTC 7 beneath Barclay Street and the 20 in. main beneath Vesey Street. The 12 in. main on Barclay Street increased to a 20 in. diameter pipeline near the center of WTC 7 at Greenwich and interconnected to the 20 in. main on West Broadway. A 12 in. main and a separate 20 in. parallel main connected to the 20 in. water main on Barclay and continued to the north on Greenwich.
This arrangement of the water distribution system provided a near constant pressure for all flows that are normally anticipated for fire protection system demands, with a residual pressure that was nearly identical to the static pressure. Standard practice in New York City was to flow 500 gpm to 750 gpm through the 12 in. and 20 in. mains, respectively. Such flows typically would not cause a recognizable drop in the system pressure.
E.4
INSTALLED FIRE SUPPRESSION FEATURES
The scope of Task 1 included a detailed reconstruction and documentation of the water supplies,
automatic sprinkler systems, standpipe, and pre-connected hose systems and any special fire suppression features or systems that existed in WTC 1, 2, and 7 on September 11, 2001.
E.4.1 WTC 1 and WTC 2
WTC 1 and 2 were protected by automatic fire sprinkler systems, essentially throughout. The sub-grade areas of the complex were provided with sprinkler systems during the initial construction. The systems were not installed in the towers during construction of the two buildings, but retrofit installations were carried out in two phases. The first phase included the installation of the sprinkler system infrastructures and sprinklers in common areas and certain tenant and Port Authority of New York and New Jersey (PANYNJ or Port Authority) spaces in response to the adoption of Local Law 5 (New York 1973). The second phase included the installation of the sprinkler systems throughout the remaining areas of the complex during the period from 1983 to 2001. The retrofit program had been completed prior to September 11, 2001.
In addition to automatic fire sprinkler systems, each building was configured with four vertical water supply zones that included three vertical standpipe risers in the stairwells of each zone. The standpipes provided fire suppression water to pre-connected hoses located in the stairwells at each floor. The standpipe systems were equipped with Class III pre-connected hose stations in all exit stair enclosures and in certain corridors and tenant spaces. Each hose station had a standpipe hose control valve, a 125 ft long fire hose and a nozzle for use by a trained fire brigade or The Fire Department of the City of New York (FDNY).
The primary water supply for the standpipe systems was initially gravity-fed from reserve water storage tanks located above the standpipe system zone. Also, a series of manually operated fire pumps provided
Executive Summary
water supplied by the NYC water distribution system. The primary water supply consisted of a fire main that looped the WTC complex. The 12 in. diameter main was supplied directly from the municipal water supply by two redundant 16 in. diameter connections. Operating pressures were maintained by two 750 gpm high-pressure electric pumps that supplied the sub-grade loops and were located beneath the towers on the B1 level of the complex.
Each tower had three 750 gpm manually operated electrical fire pumps, located on the 7th, 41st and 75th floors, to supplement standpipe pressures. Each pump provided sufficient pressure for the standpipes to skip the next sequential pump above it if any failed to operate. In addition to the pumps, a single 500 gpm automatic fire pump was provided in each tower on the 108th floor for the sprinkler systems located on the 99th through 107th floors and the hose stations in the mechanical rooms on the 108th through 110th floors. Six emergency power generators were located in the basement at the B-6 level. These generators provided back-up power to the fire pumps, as well as to communications equipment, elevators, and emergency lighting.
Additional components of the water supply were 5,000 gal storage tanks, filled from the building’s domestic water system. Tanks were located on the 20th, 41st, 75th and 110th floors in each tower. Although these tanks served as the secondary water supply, the tanks supplied the initial water supply to the fire brigade or the FDNY. Without supplemental water supplied by the domestic water system, the tanks provided approximately 10 min for the PANYNJ maintenance staff to manually start the fire pumps.
The tank on the 20th floor directly supplied the main loop.
Fourteen fire department connection (FDC) stations were located at ground level for use by the FDNY to supplement the water supply and pressure to the fire suppression systems in the buildings. Any of the FDC stations could be used to supply the standpipe systems throughout the complex of sprinkler systems in WTC 1 and WTC 2 above the 32nd floor level. Isolation valves were installed between each
consecutive FDC station. This provided independent supply and operation of the standpipe systems throughout the WTC complex. Two additional express FDC stations were provided to supply only the sprinkler systems in WTC 1 and WTC 2 above the 32nd floor level, and, two separate FDC stations were provided for the sprinkler systems in WTC 1 and WTC 2 below the 31st floor level.
Several types of special suppression systems were used in WTC 1 and WTC 2. These systems included (a) kitchen ventilation, dry chemical and steam smothering systems, (b) carbon dioxide (CO2) systems, and (c) Halon 1301 total flooding systems. These systems were supervised by the fire alarm systems at WTC 1 and WTC 2 and were designed to transmit signals to FDNY upon operation.
The Operations & Maintenance (O&M) manual for WTC 1 and WTC 2 indicated that ventilation and grease extraction systems were installed in restaurant kitchens above fryers, griddles, ranges, boilers, and ovens, but did not provide specific locations where these systems were installed (PANYNJ 1987a). The O&M manual identified that steam smothering systems were installed in the kitchens at the following locations:
• PA Cafeteria • The “Big Kitchen”