Dr. S. Shyam Sunder

Deputy Director and Lead Investigator

Building and Fire Research Laboratory

National Institute of Standards and Techno

U.S. Department of Commerce

NIST Response to the World Trade Center Di

Federal Building and Fire Safety Investiga

of 

the World Trade Center Disaster

Media and Public Briefings

June 23, 2005
NIST WTC Investigation Objectives NIST WTC Investigation Objectives

• Determine:

• why and how the WTC towers collapsed following the 

impact of the aircraft, and 

• why and how the 47-story WTC 7 collapsed

• Determine why the numbers of injuries and fatalities were 

high depending on location, including technical aspects of protection, occupant behavior, evacuation, and emergenc

• Determine the procedures and practices that were used in 

design, construction, operation, and maintenance of the Wbuildings

• Identify, as specifically as possible, areas in current n

building and fire model codes, standards, and practicwarrant revision

Some Specific Questions Some Specific Questions

 How and why did WTC 1 stand nearly twice as long as WTC 2 befo

(102 min. vs. 56 min.) though they were hit by virtually identical aircr

 What factors related to normal building and fire safety consideration

to the terrorist attacks of September 11, 2001, if any, could have del

prevented the collapse of the WTC towers?

 Would the undamaged WTC towers have remained standing in a co

large building fire scenario?

 What factors related to normal building and fire safety consideration

could have saved additional WTC occupant lives or could have minimloss of life among the ranks of first responders?

 How well did the procedures and practices used in the design, const

operation, and maintenance of the WTC buildings conform to accep

practices, standards, and codes?
WTC Investigation Overview WTC Investigation Overview

• $16 million investigation announced August 2002; drew talent from 

NIST, outside experts, and contractors; $5.5 million in contracts.

• Two written public updates (December 2002, December 2003); tw

progress reports issued (May 2003, June 2004). 

• Three public meetings held:

• June 24, 2002 (NYC) to present draft WTC investigation plan and sol

on the plan.

• February 12, 2004 (NYC) to present and solicit comments on (1) tech

of investigation, (2) additional information that NIST might consider, (considered for recommendations.

• August 24, 2004 (Chicago) to observe fire resistance test of WTC floo

Underwriters Laboratories

• Seven media/public briefings on investigation progress, six meetin

National Construction Safety Team Advisory Committee, and one 

solicit public input for first-person interviews of occupants and first 
7A Published

Accounts7B SurveyInstruments

4A FireHistory4B FireSprinklers4C FireAlarms4D SmokeManagement

WTC Investigation Reports WTC Investigation Reports

WTC Towers 

Investigation Report

Building and 

Fire Codes

Baseline 

Performance & 

Aircraft Impact

Steel

Analysis

Active Fire 

Protection

Thermal 

Reconstruction

Occupant 

Behavior & 

Egress

WTC Towers: 

Structural 

Collapse

Emerge

Respon

1A Design andConstruction1B StructuralCode Comparison1C StructuralModifications1D Fire Protection &Life Safety Provisions1E Fire CodeComparison 1F Comparisonof NYC Codes1G Fire Protection& Life Safety Amend.1H Post-Const.Modifications WTC1&21I Post-Const.Modifications WTC 71J WTC 7 FuelSystem 

9 

reports 

totaling 

about 

1,500 

pages

34 

reports 

totaling 

about 

8,000 

pages

43 reports for WTC Towers; 5 reports for WTC 7

3A Contemp.Steel Specs.3B SteelInventory3C SteelDamage3D MechanicalSteel3E PhysicalProperties

2A BaselinePerformance2B AircraftImpact

5A VisualEvidence5B SteelExperiments5C SingleWorkstation5D CeilingTile5E MultipleWorkstation 5F FireSimulation5G FireStructure Interface

6A Passive FireProtection6B FireResistance Test6C ComponentAnalysis6D GlobalAnalysis
Schedule for Reports Schedule for Reports

• The 43 reports for the WTC towers include a summary report, 8 se

reports, and 34 supporting technical reports, totaling some 10,000 

• Today, NIST is releasing a draft of the summary report on the WTC 

public comment along with 5 project reports and 22 supporting techthe summary report contains the principal findings and recommendremaining 15 reports on the WTC towers were released on April 5, 

• Six-week public comment period ending August 4, 2005; NIST plan

the final reports for the WTC towers in September 2005.

• WTC 7 report will be issued as a supplement to the main report: dr

for October 2005; final for December 2005.

• Decoupling of WTC 7 report necessary to accommodate overlapping st

for work on WTC towers.

• This change affects mainly the collapse analysis; other WTC 7 work rep

other Investigation reports.

• WTC Conference: Putting Recommendations into Practice, Septem

2005.
Approach to Recommendations Approach to Recommendations

• NIST is issuing recommendations in accordance with the 

Construction Safety Team Act.

• NIST considered:

• Findings from the investigation;• If findings were unique to the terrorist attacks or relate

normal building and fire safety considerations;

• What technical solutions are needed to address poten

identifiable risks; and

• Whether the risks apply to all buildings or are limited t

types of building (e.g., iconic status, critical function, o
Context for Recommendations Context for Recommendations

• The tragic consequences of the September 11, 2001, attacks were d

attributable to the fact that terrorists flew large jet-fuel laden commairliners into the WTC towers. 

• Buildings for use by the general population are not designed to wit

aircraft attacks; building codes do not require building designs to consi

impact. 

• In our cities, there has been no experience with a disaster of such m

has there been any in which the total collapse of a high-rise building occrapidly and with little warning.

• NIST is making recommendations based on its findings related to proce

practices that are commonly used for buildings under normal cond

• Public officials and building owners will need to determine appropriate p

requirements for buildings that are at higher risk due to their iconic 

critical function, or design.
Context for Recommendations (2) Context for Recommendations (2)

• NIST believes that the recommendations are realistic and achieva

a reasonable period of time.

• Implementation of the recommendations would make buildings, 

occupants, and emergency responders safer in future emergenc

 The recommendations do not prescribe specific systems, materi

technologies. Instead, NIST encourages competition among alternacan meet performance requirements. 

 The recommendations do not prescribe specific threshold levels

responsibility falls within the purview of the public policy setting procewhich standards and codes development plays a key role.
Recommendations: Call to Action Recommendations: Call to Action

• NIST strongly urges:

• The building and fire safety communities to give immediate an

consideration to these recommendations in order to achieve aimprovements in the way buildings are designed, constructedand used and in evacuation and emergency response procedu

• Building owners and public officials to:

1. evaluate the safety implications of these recommendations to thei

inventory of buildings; and

2. take the steps necessary to mitigate any unwarranted risks withou

changes to occur in codes, standards, and practices.

• State and local agencies, well trained and managed, to rigorou

building codes and standards since such enforcement is criticthe expected level of safety. 

• NIST is assigning top priority to work vigorously with the building 

safety communities to assure that there is a complete understandirecommendations and to provide needed technical assistance.
Federal Building and Fire Safety Investi

Federal Building and Fire Safety Investi

of the World Trade Center Disaste

of the World Trade Center Disaste

Recommendations Recommendations
Group 1: Increased Structural Integrity Group 1: Increased Structural Integrity

The standards for estimating the load effects opotential hazards (e.g., progressive collapse, wand the design of structural systems to mitigateffects of those hazards -- should be improved enhance structural integrity.
Increased Structural Integrity Increased Structural Integrity 

Recommendation 1. NIST recommends that:

1. progressive collapse should be prevented in buildings through the de

and nationwide adoption of consensus standards and code provisionthe tools and guidelines needed for their use in practice; and

2. a standard methodology should be developed—supported by analytic

tools and practical design guidance—to reliably predict the potential ffailures in structural systems subjected to multiple hazards. 

Recommendation 2. NIST recommends that nationally accepted performa

be developed for: (1) conducting wind tunnel testing of prototype structures sound technical methods that result in repeatable and reproducible results testing laboratories; and (2) estimating wind loads and their effects on tall buse in design, based on wind tunnel testing data and directional wind speed Recommendation 3. NIST recommends that an appropriate criterion shoul

developed and implemented to enhance the performance of tall buildings bmuch they sway under lateral load design conditions (e.g., winds and earth
Group 2: Enhanced Fire Resistance of 

StructuresThe procedures and practices used to ensure tresistance of structures should be enhanced b

• improving the technical basis for construction 

classifications and fire resistance ratings,

• improving the technical basis for standard fire 

resistance testing methods, 

• use of the “structural frame” approach to fire 

resistance ratings, and 

• developing in-service performance requiremen

conformance criteria for spray-applied fire resimaterials.
Enhanced Fire Resistance of Structures

Recommendation 4. NIST recommends evaluating, and where needed improving, the 

for determining appropriate construction classification and fire rating requirements (esp

buildings greater than 20 stories in height)—and making related code changes now as 

possible—by explicitly considering factors including: 

 timely access by emergency responders and full evacuation of occupants, or the 

for burnout without local collapse;

 the extent to which redundancy in active fire protection (sprinkler and standpipe, 

smoke management) systems should be credited for occupant life safety;

 the need for redundancy in fire protection systems that are critical to structural in

 the ability of the structure and local floor systems to withstand a maximum credib

without collapse, recognizing that sprinklers could be compromised, not operatioexistent;

 compartmentation requirements (e.g., 12,000 ft2) to protect the structure, includi

doors and automatic enclosures, and limiting air supply (e.g., thermally resistant 

assemblies) to retard fire spread in buildings with large, open floor plans;

 the impact of spaces containing unusually large fuel concentrations for the expe

of the building; and

 the extent to which fire control systems, including suppression by automatic or m

should be credited as part of the prevention of fire spread.
Enhanced Fire Resistance of Structures 

Recommendation 5. NIST recommends that the technical basis for the cen

standard for fire resistance testing of components, assemblies, and systemimproved through a national effort. Necessary guidance also should be deextrapolating the results of tested assemblies to prototypical building systeRecommendation 6. NIST recommends the development of criteria, test m

standards:

1. for the in-service performance of spray-applied fire resistive materials 

also commonly referred to as fireproofing or insulation) used to proteccomponents; and

2. to ensure that these materials, as-installed, conform to conditions in t

establish the fire resistance rating of components, assemblies, and sy

Recommendation 7. NIST recommends the nationwide adoption and use o“structural frame” approach to fire resistance ratings (structural members cthe columns carry the high fire resistance rating of the columns). 
Group 3: New Methods for Fire Resistan

Design of Structures

Procedures and practices used in the fire resistance desstructures should be enhanced by requiring an objective uncontrolled fires result in burnout without local or globcollapse. Performance-based methods are an alternativprescriptive design methods. This effort should include the development and evaluatio

• new fire resistive coating materials and technologie• evaluation of the fire performance of conventional a

performance structural materials. 

Technical and standards barriers to the introduction of nmaterials and technologies should be eliminated.
New Methods for Fire Resistance Desig

StructuresRecommendation 8. NIST recommends that the fire resistance of structure

enhanced by requiring a performance objective that uncontrolled building fi

burnout without local or global collapse. Recommendation 9. NIST recommends the development of:

1. performance-based standards and code provisions, as an alternative 

prescriptive design methods, to enable the design and retrofit of struc

resist real building fire conditions, including their ability to achieve the performance objective of burnout without structural or local floor colla

2. the tools, guidelines, and test methods necessary to evaluate the fire 

performance of the structure as a whole system. 

Recommendation 10. NIST recommends the development and evaluation 

resistive coating materials, systems, and technologies with significantly enhperformance and durability to provide protection following major events.
New Methods for Fire Resistance Desig

Structures (2)Recommendation 11. NIST recommends that the performance and suitabi

advanced structural steel, reinforced and pre-stressed concrete, and other performance material systems should be evaluated for use under conditionin building fires.
Group 4: Improved Active Fire Protectio

Active fire protection systems (i.e., sprinklers, standphoses, fire alarms, and smoke management systems) be enhanced through improvements to:

• Design• Performance• Reliability, and• Redundancy 

of such systems.
Improved Active Fire Protection

Recommendation 12. NIST recommends that the performance and redund

fire protection systems (sprinklers, standpipes/hoses, fire alarms, and smokmanagement systems) in buildings should be enhanced to accommodate thrisks associated with increasing building height and population, increased uspaces, available compartmentation, high-risk building activities, fire departmresponse limits, transient fuel loads, and higher threat profile.Recommendation 13. NIST recommends that fire alarm and communication

buildings should be developed to provide continuous, reliable, and accurate 

on the status of life safety conditions at a level of detail sufficient to manage evacuation process in building fire emergencies, and that standards for theibe developed. Recommendation 14. NIST recommends that control panels at fire/emerge

stations in buildings should be adapted to accept and interpret a larger quanreliable information from the active fire protection systems that provide tactic

aids to fireground commanders, including water flow rates from pressure anmeasurement devices, and that standards for their performance be develop
Improved Active Fire Protection (2)

Recommendation 15. NIST recommends that systems should be develope

implemented for:

1. real-time off-site secure transmission of valuable information from fire 

other monitored building systems for use by emergency responders, location, to enhance situational awareness and response decisions asafe and efficient operations; and

2. preservation of that information either off-site or in a black box that w

fire or other building failure for purposes of subsequent investigations analysis. 

Standards for the performance of such systems should be developed, and should be required.
Group 5: Improved Building Evacuation

Building evacuation should be improved to include:

• system designs that facilitate safe and rapid egres• methods for ensuring clear and timely emergency 

communications to occupants, 

• better occupant preparedness for evacuation duri

emergencies, and 

• incorporation of appropriate egress technologies
Improved Building Evacuation

Recommendation 16. NIST recommends that public agencies, non-profit o

concerned with building and fire safety, and building owners and managers develop and carry out public education campaigns, jointly and on a nationwimprove building occupants’ preparedness for evacuation in case of buildinemergencies.Recommendation 17. NIST recommends that tall buildings should be desig

accommodate timely full building evacuation of occupants due to building-s

large-scale emergencies such as widespread power outages, major earthqtornadoes, hurricanes without sufficient advanced warning, fires, accidentaand terrorist attacks. Building size, population, function, and iconic status s

taken into account in designing the egress system. Stairwell and exit capabe adequate to accommodate counterflow due to access by emergency res
Improved Building Evacuation (2)

Recommendation 18. NIST recommends that egress systems should be d

1. to maximize remoteness of egress components (i.e., stairs, elevators

without negatively impacting the average travel distance;

2. to maintain their functional integrity and survivability under foreseeab

specific or large-scale emergencies; and

3. with consistent layouts, standard signage, and guidance so that syste

intuitive and obvious to building occupants during evacuations. 
Improved Building Evacuation (3)

Recommendation 19. NIST recommends that building owners, managers, a

responders develop a joint plan and take steps to ensure that accurate emerinformation is communicated in a timely manner to enhance the situational a

building occupants and emergency responders affected by an event. This shaccomplished through:

• better coordination of information among different emergency responde• efficient sharing of that information among building occupants and eme

responders, 

• more robust design of emergency public address systems, • improved emergency responder communication systems, and • use of the Emergency Broadcast System (now known as the Integrated 

and Warning System) and Community Emergency Alert Networks. 

Recommendation 20. NIST recommends that the full range of current and n

evacuation technologies should be evaluated for future use, including protec

elevators, exterior escape devices, and stairwell navigation devices, which moccupants an equal opportunity for evacuation and facilitate emergency resp
Group 6: Improved Emergency Respon

Group 6: Improved Emergency Respon

Technologies and Procedures Technologies and Procedures

Technologies and procedures for emergency rshould be improved to enable better access to buildings, response operations, emergency communications, and command and control in scale emergencies
Improved Emergency Response Techno

Techno

and Procedures and ProceduresRecommendation 21. NIST recommends the installation of fire-protected a

structurally hardened elevators to improve emergency response activities in 

by providing timely emergency access to responders and allowing evacuatimpaired building occupants. Such elevators should be installed for exclusemergency responders during emergencies. In tall buildings, consideration be given to installing such elevators for use by all occupants. Recommendation 22. NIST recommends the installation, inspection, and t

emergency communications systems, radio communications, and associatprotocols to ensure that the systems and protocols:

1. are effective for large-scale emergencies in buildings with challenging 

frequency propagation environments; and

2. can be used to identify, locate, and track emergency responders with

building environments and in the field. 
Improved Emergency Response Techno

and Procedures (2)Recommendation 23. NIST recommends the establishment and implemen

detailed procedures and methods for gathering, processing, and delivering 

information through integration of relevant voice, video, graphical, and writtenhance the situational awareness of all emergency responders. An informintelligence sector should be established to coordinate the effort for each in

Recommendation 24. NIST recommends the establishment and implemen

codes and protocols for ensuring effective and uninterrupted operation of th

command and control system for large-scale building emergencies. 
Group 7: Improved Procedures and Pra

The procedures and practices used in the designconstruction, maintenance, and operation of buildshould be improved by: 

• encouraging code compliance by nongover

and quasi-governmental entities, 

• adoption and application of egress and spri

requirements in codes for existing buildings

• retention and availability of building docum

over the life of a building.
Improved Procedures and Practices

Recommendation 25. Nongovernmental and quasi-governmental entities t

lease buildings -- and are not subject to building and fire safety code requir

any governmental jurisdiction -- are nevertheless concerned about the safe

building occupants and the responding emergency personnel. 

• NIST recommends that such entities should be encouraged to provid

safety that equals or exceeds the level of safety that would be provide

compliance with the code requirements of an appropriate governmenjurisdiction. 

• To gain broad public confidence in the safety of such buildings, NIST 

recommends that it is important that as-designed and as-built safety 

by a qualified third party, independent of the building owner(s). The p

should not use self-approval for code enforcement in areas including interpretation of code provisions, design approval, product acceptanccertification of the final construction, and post-occupancy inspections 

of the buildings. 
Improved Procedures and Practices (2)

Recommendation 26. NIST recommends that state and local jurisdictions s

adopt and aggressively enforce available provisions in building codes to en

egress and sprinkler requirements are met by existing buildings. Further, o

requirements should be modified where needed (such as when there are ause spaces within an office building) to meet the requirements in model bui

Recommendation 27. NIST recommends that building codes should incorp

provision that requires building owners to retain documents, including supp

calculations and test data, related to building design, construction, mainten

modifications over the entire life of the building. Means should be develope

storage and maintenance of the documents. In addition, NIST recommendrelevant building information should be made available in suitably designed or electronic format for use by emergency responders. Such information seasily accessible by responders during emergencies.
Improved Procedures and Practices (3)

Recommendation 28. NIST recommend that the role of the “Design Profes

Responsible Charge” should be clarified to ensure that:

1. all appropriate design professionals (including, e.g., the fire protection 

are part of the design team providing the standard of care when desigbuildings employing innovative or unusual fire safety systems, and

2. all appropriate design professionals (including, e.g., the structural eng

the fire protection engineer) are part of the design team providing the 

care when designing the structure to resist fires, in buildings that emp

innovative or unusual structural and fire safety systems. 
Group 8: Education and Training Group 8: Education and Training

The professional skills of building and fire safprofessionals should be upgraded through a neducation and training effort for fire protection engineers, structural engineers, and architect
Education and Training 

Recommendation 29. NIST recommends that continuing education curric

be developed and programs should be implemented for:

• training fire protection engineers and architects in structural engin

principles and design, and 

• training structural engineers, architects, and fire protection engine

modern fire protection principles and technologies, including fire-rdesign of structures. 

Recommendation 30. NIST recommends that academic, professional sho

and web-based training materials in the use of computational fire dynamicthermostructural analysis tools should be developed and delivered to stren

base of available technical capabilities and human resources. 
Recommendations: Call to Action Recommendations: Call to Action

• NIST strongly urges:

• The building and fire safety communities to give immedia

serious consideration to these recommendations in order appropriate improvements in the way buildings are designconstructed, maintained, and used and in evacuation and emergency response procedures.

• Building owners and public officials to:

1. evaluate the safety implications of these recommendations to 

existing inventory of buildings; and

2. take the steps necessary to mitigate any unwarranted risks w

waiting for changes to occur in codes, standards, and practic

• State and local agencies, well trained and managed, to rig

enforce building codes and standards since such enforcecritical to ensure the expected level of safety. 
Recommendations: NIST Actions Recommendations: NIST Actions

• After issuance of the final report, the National Construction 

Team Act requires NIST to:

• Conduct, or enable or encourage the conduct of, appro

research recommended by the NCST Team; and

• Promote the appropriate adoption of the recommendat

Federal Government and other agencies and organizati

 NIST is assigning top priority to work vigorously with the b

and fire safety communities to assure that there is a complunderstanding of the recommendations and to provide neetechnical assistance.
Recommendations: NIST Actions (2) Recommendations: NIST Actions (2)

• As part of NIST’s overall WTC response plan, the Institute has b

reach out to the building and fire safety communities to pave the timely, expedited consideration of recommendations stemming finvestigation. 

• Outreach to:

• model code organizations (ICC, NFPA)• standards development organizations (e.g., ASCE, NFPA, ASTM, ASME

• state and local building officials (NCSBCS, AMCBO, NYC DOB) 

• the professional community, including presentations at major conference

ASCE, AIA, CTBUH, Chicago Committee on High-Rise Buildings, Struct

Foundation of Chicago, NCSBCS/AMCBO, CII, CERF Corporate Adviso

• Detailed briefing for designers of the WTC redevelopment (including Silverste

Authority, and NYC DOB officials).

• WTC Technical Conference: Putting Recommendations into Practice, Septem

2005.

• NIST will establish a web-based system to track the status of the recommend
Recommendations: NIST Actions (3) Recommendations: NIST Actions (3)

• NIST also has expanded its research in areas of high priority ne

Examples include:

• Prevention of Progressive Collapse• Fire Resistance Design and Retrofit of Structures• Fire Resistive Coatings for Structural Steel• Fire Resistance of Uncoated Structural Steel with Improved Therm• Fire Resistance of Building Partitions• Occupant Behavior and Egress • Emergency Use of Elevators• Equipment Standards for First Responders• Standard Building Information Models for Vulnerability Assessmen• Technologies for Building Operations in CBR Attacks• Cost-effective Risk Management Tools
Process for Submitting Public Commen

Process for Submitting Public Commen

• NIST welcomes comments from the public on the dra

investigation reports for the WTC towers. 

 The public is welcome to comment on any of the 43 d

reports issued by NIST, totaling about 10,000 pages. 

 NIST especially encourages public comment on t

approximately 200-page draft summary report, whcontains the principal findings and recommendatchanges to codes, standards, and practices. 

 NIST will consider all comments received from the pu

the 43 draft reports before they are issued in final for
Process for Submitting Public Commen

Process for Submitting Public Commen

 Comments must be as specific as possible. Provide a short reason for any suggested change. Provide suggested language for the requested revision. All comments shall include the following information: 

Name:Affiliation:Contact: Phone number or e-mail address where you can be contact

of questions.

Report Number: (e.g., NCSTAR 1-1)

Page Number:Paragraph/Sentence: (e.g., paragraph 2/sentences 2-4)Comment:Reason for Comment:Suggestion for Revision:
Process for Submitting Public Commen

Process for Submitting Public Commen

 NIST will accept public comments on any of the dra

until 5 pm EDT August 4, 2005.

 Comments may be submitted:

 through a link on the WTC Investigation web site: 

http://wtc.nist.gov

 Via e-mail to wtc@nist.gov By fax to 301-975-6122 By mail to: 

WTC Technical Information RepositoryAttention: Mr. Stephen CauffmanNational Institute of Standards and Technology100 Bureau Drive Stop 8610Gaithersburg, MD 20899-8610
WTC Technical Conference: Putting WTC Technical Conference: Putting 

Recommendations into Practice Recommendations into Practice

 Objectives: 

 To present the technical foundation for the NIST recommendations f

building and fire codes, standards, and practices.

 To solicit feedback on the NIST Investigation Reports from the techn

community, with an emphasis on spurring action on recommendation

 Presenters:

 NIST WTC Investigation Team Project Leaders. Key NIST team members. Selected contractors and experts who contributed to the WTC Invest

 Other Presenters:*

 Technical representatives from standards and codes development a

regulatory organizations.

 Technical experts from academia and industry not involved in the NI

investigation.

 Members of the general public.

________________________

* Selected based upon relevance of technical comments (250 to 500 words) received by Augu
WTC Technical Conference (2) WTC Technical Conference (2)

 Dates: September 13-15, 2005 Location: National Institute of Standards and Technology, Gaithersburg, MD Registration Fee: $110 Registration: Online registration is available through the WTC Investigation 

http://wtc.nist.gov

 For those wishing to present their comments at the Conference, a 250-500 w

should be submitted by August 1, 2005 to:

WTC Conference, MS 8610 100 Bureau Drive Gaithersburg, MD 20899-8610, USAEmail: wtc@nist.gov

fax: (301) 975-6122
Disclaimer No. 1

Certain commercial entities, equipment, products, or materials are identifiedocument in order to describe a procedure or concept adequately or to tracof the procedures and practices used. Such identification is not intended to recommendation, endorsement, or implication that the entities, products, mequipment are necessarily the best available for the purpose. Nor does suidentification imply a finding of fault or negligence by the National Institute oand Technology.Disclaimer No. 2The policy of NIST is to use the International System of Units (metric units) publications. In this document, however, units are presented in metric units 

pound system, whichever is prevalent in the discipline. Disclaimer No. 3:

Pursuant to section 7 of the National Construction Safety Team Act, the NIhas determined that certain evidence received by NIST in the course of this Investigation is “voluntarily provided safety-related information” that is “not 

related to the building failure being investigated” and that “disclosure of tha

would inhibit the voluntary provision of that type of information” [15 USC 73

In addition, a substantial portion of the evidence collected by NIST in the co

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 bcompliant with any code since, due to the destruction of the WTC buildings

not verify the actual (or as-built) construction, the properties and condition o

materials used, or changes to the original construction made over the life obuildings. In addition, NIST could not verify the interpretations of codes us

applicable authorities in determining compliance when implementing buildinWhere an Investigation report states whether a system was designed or insrequired by a code provision, NIST has documentary or anecdotal evidence 

whether the requirement was met, or NIST has independently conducted te

analyses indicating whether the requirement was met.Use in Legal Proceedings

No part of any report resulting from a NIST investigation into a structural fa

an investigation under the National Construction Safety Team Act may be usuit or action for damages arising out of any matter mentioned in such repo281a, as amended by P.L. 107-231).
Web site Web site http:// http://wtc.nist.gov wtc.nist.gov

Email to Email to wtc@nist.gov wtc@nist.gov

Facsimile to (301) 975 Facsimile to (301) 975-6122

Regular mail: Regular mail:

WTC Technical Information Repository, Stop 8

Technical Information Repository, Stop 8

100 Bureau Drive, Gaithersburg, MD 20899 Bureau Drive, Gaithersburg, MD 20899-86