S. Shyam Sunder, Lead Investigato

Building and Fire Research Labo

National Institute of Standards and Tec

U.S. Department of Commerce

sunder@nist.gov

NIST Response to the World Trade Cente

World Trade Center Investigatio

February 12, 2004
Highlights Highlights

• Overall Investigation Goals, Status, and Schedule• Selection of External Experts and Contractors• Update on Data Collection Efforts• Original Aircraft Impact Studies• Assessing the Most Probable Structural Collapse Sequence• Update on Experimental/Field Work• Collection and Analysis of Photographic and Video Images• First-Person Data Collection on Evacuation and Emergency Respons• Analysis of Building and Fire Codes and Practices• Investigation of Active Fire Protection Systems• Considerations for Safety Recommendations
Goals

• To investigate the building construction, the materials 

technical conditions that contributed to the outcome oCenter disaster

• To serve as the basis for national benefits:

• Improvements in the way buildings are designed

maintained, and used

• Improved tools and guidance for industry and saf• Revisions to codes, standards, and practices• Improved public safety
Objectives Objectives

• Determine:

• why and how the WTC Towers collapsed fo

impact of the aircraft, and 

• why and how the 47-story WTC 7 collapsed

• Determine why the numbers of injuries and fata

or high depending on location, including technicprotection, occupant behavior, evacuation, and response

• Determine what procedures and practices were 

design, construction, operation, and maintenanbuildings

• Identify, as specifically as possible, areas in nat

and fire codes, standards, and practices that wa
Important Features of NIST Investi

Important Features of NIST Investi

• NIST investigations are independent, objective, a

• No part of any report resulting from a NIST invest

structural failure or from an investigation under th

Construction Safety Team Act may be used in andamages arising out of any matter mentioned in sUSC 281a; as amended by P.L. 107-231)

• NIST is not a regulatory agency and does not set 

standards

• NIST recommendations are given serious conside

sector organizations that develop national standacodes – which provide minimum requirements for The model codes become regulation when adopte

local governments.
NIST WTC Investigation 

NIST WTC Investigation 

Analysis 

of Steel Structural 

Collapse

Baseline 

Performance

& Impact 

Damage

Analysis of 

Codes and 

Practices

Fire Service 

Response

Active Fire 

Suppression

Thermal and 

Tenability 

Environment

Public InputsDocumentsVideo/ Photographic RecordsOral History DataEmergency Response RecordsRecovered Structural SteelBPAT RecommendationsGovernment, Industry, Professional, Academic InputsPublic Inputs
WTC Investigation Status WTC Investigation Status

• 17 months into investigation; good solid progress • $16 million investigation; $5.5 million awarded in • Drawing on complementary talent from NIST, out

contractors; NIST, not the contractors and expertfor determining investigation findings, conclusionsrecommendations

• Two public updates issued (December 2002 and • One technical progress report issued (May 2003)

release next technical progress report in early Sp

• Draft investigation report planned for completion 
Update on Data Collection Update on Data Collection

• Large amounts of data and information received; summ

http://wtc.nist.gov

• NIST has a few requests for materials that are lost, cu

not yet located; NIST is making efforts to re-create this various sources since much of it was lost when the bu

• NIST has received all of the essential information i

WTC investigation; significant progress achieved sinc

• NIST has received considerable cooperation from PA, 

leaseholders, contractors, suppliers, survivors, and vic
Safety of WTC Towers in Aircraft C

Safety of WTC Towers in Aircraft C

• Buildings are not designed to withstand the impacts of fuel-laden co

• Structural safety of the WTC towers in an aircraft collision was a con

design

• The impact scenario considered a Boeing 707 aircraft traveling at 600 mp

considered an aircraft impact at the 80th floor

• Analysis indicated that such collision would result in only local damage w

collapse or substantial damage to the building

• Fire safety: There are two views on whether the effect of jet fuel an

consideration in the original building design:

• One view suggests that an analysis was done indicating the biggest prob

the fuel would dump into the building and there would be a horrendous fir

• Another view suggests that the fuel load, and the fire damage that it woul

considered.

• Life safety: There are two views on what would be the effect of airc

life safety:

• One view, which did not consider the fires, suggests that the aircraft impa

endangered the lives and safety of occupants not in the immediate area o

• Another view, which considered the fires, recognized that a lot of people 

the building structure would still be there.
Assessing the Most Probable Stru

Assessing the Most Probable Stru

Collapse Sequence Collapse Sequence

• These are based on pho

rigorous computer modesimulations, and well-esand probability-based an

• NIST seeks to determine 

the most probable collapse sequence for each building
Examples of WTC Tower Innovatio

Examples of WTC Tower Innovatio

Exterior Framed-Tube

59 columns per side

Bar Joist

Concrete Slab

Floor

Covering

Trough

Decking

Air-conditioning

Electric DuctDuct

• WTC tower structural system• Composite floor truss system using 

long span open-web bar joists and spray-applied fireproofing

• Design for wind loads and control of 

wind-induced vibrations

• Elevator system design
Analysis of Structural Steel Analysis of Structural Steel

• NIST believes the collection of steel 

from the WTC towers is adequate for purposes of its investigation

• NIST is documenting failure mechanisms 

and damage via an extensive visual analysis of the WTC steel and enhanced image analysis of photographs of the damaged buildings

• Preliminary results show that the 

measured room temperature steel strength met relevant ASTM specifications; in many instances exceeding the specifications by 5,000 to 15,000 psi

• Work is ongoing to evaluate the design of 

the steel building components and system and their performance under impact and fire conditions up until the time of collapse initiation

Simula
Fireproofing and Fire Rating of Flo

Fireproofing and Fire Rating of Flo

• There appears to have been no technical basis for: 

• selection of fireproofing material for the WTC floor system• specified fireproofing thickness to achieve the expected 2

• Project specific fire endurance testing was not and is not norm

conducted when circumstances warrant it, e.g., in a new or inn

• In 1966, the Architect of Record and, in 1975, the Structural En

that the fire rating of the floor system could not be determined 

• NIST has not found any evidence indicating that a test based o

been conducted to determine the fire rating of the WTC floor syinformed NIST that “there are no test records in our files”

• NIST has awarded a contract to Underwriters Laboratories to d

of typical WTC floor systems under both as-built and specified are expected to be conducted in Spring 2004

• Origins of current fire endurance rating test method nearly a ce

are relative and apply to subassemblies tested in a standard firfor major fires and the building as a complete system; NIST is 

improved methods to determine the fire endurance of builfires
WTC Fire Model Validation Experim

Prediction of steel temperatures through fireproofing

Assess th

damage to 

Multiple work

validation of f

Single workstation burn tests for input to fire dynamics simulator
Reco

Rec

of th

of th
Collection and Analysis of Photog

Collection and Analysis of Photog

Video Images Video Images

• Visual database now contains:

• 6,194 photographs taken by more 

than 85 photographers

• 150 hours of videotape (5,726 

video clips) representing more than 20 sources

• From the analysis of the visual 

images to date, NIST has identified significant events for WTC 1 and 2 related to aircraft impact, fire development, and building damage

• NIST has developed detailed 

mappings for the fire, smoke, and the condition of windows at several specific times for each WTC tower; work is underway for WTC 7
Fire Dynamics

Structure Response 

and Collapse

Proposed Method:

Probabilistic, Nonlinear, Coupled Analy

of Collapse Induced by Fire-Structure Inte

Radiative Heat Transfer

Boundary Conditions

Vents

Fire Growth and Spread

Load Redistribution

Coupled Analyses Coupled Analyses
First-Person Data on Occupant Be

Person Data on Occupant Be

Evacuation, and Emergency Respo

Evacuation, and Emergency Respo

• Buildings are designed for fire protection and evacuation under nor

conditions found in major emergencies

• Critical lack of information on which to base evacuation and emerg

standards, and codes in such conditions

• First-person interviews of occupants, current and retired first 

members in contact with victims are providing valuable informemergencies in tall buildings.

• Firefighting (access time, physiological factors, fight fires versus evacua

• Evacuation in tall buildings (defend-in-place, phased versus full, counte

• Emergency command, control, and communications in major events (in

coordination, repeaters, overload, technology, interoperability)

• Building design features to support such operations (stairs, elevators, in

• NIST has made good progress in its first-person data collectio

• Telephone interviews: completed all 800 planned• Face-to-face interviews: completed about one-third of approximately 45

• Focus groups: in process

• The personal privacy and confidentiality of individual respondents w

maximum extent permitted by law
Multiple Data Sources Multiple Data Sources

• Existing published first-person accounts of WTC evacuation; ove

collected and analyzed

• Communication tapes from Port Authority of NY & NJ and NYPD

taped recordings

• Filings with the Occupational Safety and Health Administration b

families of victims; about 60 written statements

• Documents from Port Authority, FDNY, NYPD, and others on de

emergency communication systems; WTC evacuation history; Wplanning and drills; emergency response preparedness and ope

• Photographic and video data on occupant behavior, evacuation, 

response

• First-person data collection from survivors, current and retired fi

families of victims

• Access to NYC 9-1-1 tapes and logs, and transcripts of about 500 int

employees involved in WTC emergency response activities
Occupant Behavior, Evacuation, an

Emergency Response Study 

• NIST is developing a detailed chronology of events re

emergency response and evacuation

• NIST is analyzing the contents of emergency commun

already received to:

• better define the events of September 11, 2001• document the performance of the emergency communi

• NIST is using computer egress modeling to better und

evacuation experience on September 11, 2001:

• Obtained three existing computer models• Supporting information from evacuation history of WTC • Supporting information from first-person accounts
First-Person Interviews: Prelimina

Person Interviews: Prelimina

• Evacuation

• Most people had participated in evacuation training and knew whe

located; most respondents indicated that they had not ever used th

people found stairwell transfer floors confusing on 9/11

• Ingress/egress was a tremendous physical challenge for both first 

occupants; inadequate footwear presented a mobility challenge, pa

as discarded shoes often littered the stairwells, leaving many peop

• Emergency Response

• All radio communications evaluated so far (PANY&NJ, NYPD, and 

experienced surge load conditions after the attack; as a result roug

communications were not complete; traffic volume made it difficult 

of information; multiple concurrent transmissions on the same freq

it more difficult

• First responders – including key incident commanders -- did not ha

(voice, video, and data) on and an overall perspective of the condit

what was happening elsewhere at the WTC site; interagency inform

inadequate

• Building Damage

• Multiple first responders – including those with command authority 

large gouge on the south face of WTC 7; the gouge appeared to exthe 10th floor and covered roughly a third of the length of the south 

of the building depth; possible implications for structural weakening 
Analysis of Building and Fire Code

Analysis of Building and Fire Code

Practices Practices

• Procedures and practices of interest:

• Design and construction of WTC towers and WTC 7• New and innovative design features, technologies and m• Passive and active fire safety systems • Emergency access and egress systems• Structural modifications, inspection, and maintenance

• NIST has completed a preliminary comparison of t

building regulatory and code requirements

• Provides context to study specifications and criteria used 

construction, operation, and maintenance of the WTC bu

• NIST has completed preliminary documentation of 

for emergency power in WTC 7

• Fuel tanks, fuel distribution system, control system, fire p
Code Comparison: Preliminary Fin

Code Comparison: Preliminary Fin

Floors

3

2 

Columns

4

3

1938 1968 

Fire Resistance (hours)

• PONYA adopted 1968 NYC Building Code for final design of WT

WTC 7

• Designers were allowed to use “acceptable engineering practices

PONYA where code provisions were obsolete (1963 directive) 

• All five codes reviewed have similar wind pressure distributions; 

over 1000 ft), the largest base shear is obtained from BOCA (196

• NYC introduced progressive collapse resistance requirement by 

• 1968 NYC Code reduced fire resistance ratings from 1938 edition

further from 1968 edition
Investigation of Active Fire Protect

Investigation of Active Fire Protect

Systems Systems

• NIST is investigating the design, capabilities, an

of the active fire-protection systems in the WTC WTC 7:

• Sprinkler system, including fire standpipes, pre-c

water supply

• Fire alarm systems, including provisions for redu

modifications made after the 1993 bombing

• Smoke management systems, including reviews 

the 1993 bombing

• NIST has completed a review of the history o

occupancy fire incidents and has identified 

were large enough to activate more than one sprinklers were not present, events judged t
• NIST gathered information on significant fires in t

occupancy and prior to 9-11-01

• The extensive records of fire incidents kept in the 

the PANYNJ were lost in the collapse

• Information was collected from FDNY [434 Burea

Fire Reports (1970-2001) and 87 Bureau of Fire Records (1977-2001)]

• There were 12 significant fires defined by NIST a

multiple sprinklers or equivalent in addition to the fire starting on floor 11 of WTC 1 and 1993 parkinbombing

Fire History of WTC Buildings 1, 2, 

Fire History of WTC Buildings 1, 2, 
Considerations for Safety Recomm

Considerations for Safety Recomm

• Recommendations based on the findings of the inv

seek to enable:

• making buildings safer• improving safety of occupants and first respond• improving evacuation systems and emergency 

capabilities

• Distinguish unique circumstances related to the ter

from more common building and fire safety issues

• Emphasis on needed performance-based, not pres

solutions
Purpose of Public Meeting Purpose of Public Meeting

To solicit comments from the public on: (1) specific technical aspects of the individual projects as re

December 2003 progress update and presentations to tConstruction Safety Team Advisory Committee (availabInvestigation Web site http://wtc.nist.gov); 

(2) information that NIST might consider in the time remaini

scope of the eight projects described in the investigation available at the same Web site); and 

(3) areas that NIST should consider, within the scope of its 

order to make recommendations for specific improvemefire practice, standards, and codes, and their timely adoAll comments received will be given serious consideappropriate investigator.
Contact Information Contact Information

• Anonymous tip line: 888-804-7581 (toll free)

• WTC web site: http://wtc.nist.gov

• Mail address: NIST World Trade Center Investiga

100 Bureau Drive, Stop 8610Gaithersburg, MD 20899-8610

• E-mail: wtc@nist.gov

• Facsimile: 301-975-6122• Survivors, families, and retired first responders may volunteer to partici

interviews by contacting:

877-221-7828 (toll free)

• Alternately, families of victims may volunteer to participate in the face-t

following web site:

https://wtc.nist.gov/family
Thank You Thank You