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

December 2, 2003
Highlights Highlights

• Release of December 2003 Public Update• Overall Investigation Status, Schedule, and Challenges• 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
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
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

• 15 months into investigation; good solid progress • $16 million investigation; $5.5 million awarded in • Drawing on talent from NIST, outside experts, an• Large amounts of data and information received

available at http://wtc.nist.gov

• Two public updates issued (December 2002 and 

2003); latter being released today

• One technical progress report issued (May 2003

release next technical progress report early in 20
WTC Investigation Schedule WTC Investigation Schedule

0 6 12 18 

Development of Plan

Discovery & Collection of Data

Review of Data & Formulation of

Technical Approach

Modeling, Testing & Field Data

Collection

Analysis of Results & Development

of Findings, Conclusions &

Recommendations

Development of Draft Report

2/1/02 8/1/02 2/1/03 8/1/03 2

8/21/03

8/21/02 
Challenges Previously Identified Challenges Previously Identified

• Massive amounts of data from external sources (affec

5, 6 & 8 most)

• Level of complexity in fire-structure modeling and coll

(affecting projects 2, 5 & 6)

• Scope and scale of occupant behavior, evacuation, a

response study (affecting projects 7 & 8)

• Process and time for acquiring outside expertise (affe

6 & 7 most)

• Administrative requirements to ensure strict adherenc

regulations such as Paperwork Reduction Act and CoProtection of Human Subjects (affecting projects 7 & 
Selection of External Experts and C

Selection of External Experts and 

• Process completed

• Solicitations issued: 16 (1 r• Awards made: 12 contracts

9 experts (3 s

• Four others hired as expert consultants

• V. Junker; K. Malley, V. Dunn, J. Hodgens

• Excellent group of contractors and experts to augm

capabilities

• NIST, not the contractors and experts, is responsible f

investigation findings, conclusions, and recommendati

• Contractors and experts complement the team approa

essence of the NCST Act
11 2 Analysis of Aircraft Impacts into the WTC Towers Awarded 

16 4 Analysis of Smoke Management Systems, WTC 1, 2, and 7 Awarded 

15 4 Analysis of Active Fire Alarm Systems, WTC 1, 2, and 7 Awarded 

Structural Response of WTC Towers to Fire With/Without Impact Awarded Damage

14 6

13 6 Development of WTC 7 Structural Models and Collapse Hypotheses Awarded 

12 4 Analysis of Sprinklers, Standpipe, Pre-Connected Hoses in WTC 1, 2, 7 Awarded 

Awarded 6/23-25/

Outside Experts for Baseline Structural Performance, Impact Analysis, Structural Response to Fire, Collapse Initiation and Probabilistic Assessment of the WTC Investigation

10 2, 5, 6

Awarded Modified 

9 6 Fire Endurance Testing of the WTC Floor System

8 7 World Trade Center Investigation First Person Accounts of Egress Awarded 

7 1 Analysis of Building and Fire Codes and Practices Awarded 

Development of Structural Databases and Baseline Models for the Awarded WTC Towers

6 2

WTC Investigation Survey Administration and Report Delivery: Awarded Questionnaires, Interviews and Focus Group Synopsis

5 7

4 3 Document and Evaluate the Steel Recovered from the WTC Towers Awarded 

Hired exconsulta

Media, Visual and Database Expert with Experience in Obtaining Visual Materials for the World Trade Center

3 5

2 5, 6, 7 Fire Safety Engineering Expertise Awarded 

Awarded and 10/1

1 7 Outside Experts for Occupant Behavior and Evacuation

WTC No. Project Title S

World Trade Center Investigation Contract Solicitatio
Update on Data Collection (1) Update on Data Collection (1)

• Significant progress achieved since August 2003, e

• Supporting documents for McKinsey & Company’s FDNY • Information on the flammable contents of the aircraft from • UL test reports on spray-on fireproofing (W.R. Grace)• Port Authority white paper “Salient points with regard to th

The World Trade Center towers”

• Photos (6194 from over 185 photographers); video clips (5

videotape from over 20 sources)

• NIST continues to seek photos and videos of south • NYC has agreed to provide access to 911 tapes and 

transcripts of about 500 first responder interviews nDecember 31, 2003 

• NIST has received all of the essential information it 

investigation
Update on Data Collection (2) Update on Data Collection (2)

• NIST requests for materials that are currently pending 

• Original contract specifications for WTC towers (lost in th

buildings)

• Construction logs and maintenance logs for WTC 1, 2, a

collapse of the buildings)

• Calculations and analyses that supported the original air

(lost in the collapse of the buildings)

• Descriptions of partitions and furnishings in most of the t

2 & 7 in the fire and impact zones

• Shop drawings showing connection details of WTC 7

• NIST is making efforts to re-create this information fro

since much of it was lost when the buildings collapsed

• NIST will pursue other materials that could assist in th

NIST has received all of the essential information it neinvestigation
Safety of WTC Towers in Aircraft C

Safety of WTC Towers in Aircraft C

• Buildings are not normally designed to withsta

of fuel-laden commercial airliners.

• Safety of the WTC towers and their occupants 

collision was a consideration in the original de

• NIST needs information to understand what w

• What was the type and speed of aircraft consid• Where was the impact considered to have occu• Would the tower remain standing after aircraft i• What would be the effect of the jet fuel and airc

fire safety? 

• Would there be loss of life among the tower occ
Sources of Available Information Sources of Available Information

• Port Authority (February 1964), three-page white paper, “Sal

to the structural design of The World Trade Center towers,” d

• Port Authority (March 1964), three-page document, “period o

plane crash at 80th floor.”

• Alternative Insurance Works (2001), World Trade Center Pro

Prepared for Silverstein Properties, Inc.

• The New Yorker (11/19/2001), “The Tower Builder” by Jo

Interview with Leslie Robertson.

• FEMA 403 (2002), World Trade Center Building Performance 

Collection, Preliminary Observations, and Recommendations

• Glanz and Lipton (2003), City in the Sky – The Rise and the F

Trade Center, Times Books, 2003.
Available Information on Safety of 

Available Information on Safety of 

Towers in Aircraft Collision (1) Towers in Aircraft Collision (1)

Type of Aircraft: Boeing 707 (largest jet aircraft in 

DC-8

Speed of Aircraft: 600 mph (Port Authority, Februa

180 mph (FEMA 403, 2002)

Location of Impact: 80th floor (Port Authority, March 

Structural design: It appears that the design of the 

considered the impact of 707 airindicated that such collision woulocal damage which could not casubstantial damage to the buildi
Available Information on Safety of 

Available Information on Safety of 

Towers in Aircraft Collision (2) Towers in Aircraft Collision (2)

Fire safety: There are two views on whether the effect of jet f

was a consideration in the original building design

• One view suggests that an analysis was done indicating the 

the fact that all the fuel would dump into the building and thefire.

• Another view suggests that the fuel load, and the fire damag

not have been considered.

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

occupant life safety.

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

have endangered the lives and safety of occupants not in the 

• Another view, which considered the fires, recognized that a l

even though the building structure would still be there.

• NIST continues to be interested in available information re

calculations and analyses that supported the original airc
Assessing the Most Probable Stru

Assessing the Most Probable Stru

Collapse Sequence (1) Collapse Sequence (1)

• Overall analysis objectives:

• What is the most probable collapse sequence?

• What confidence levels are associated with it?• What is the probability of other collapse sequences?

• What parameters influence the most probable collaps

• NIST has developed a comprehensive approach 

most probable structural collapse sequence, froto collapse initiation

• NIST has made significant progress in:

• Defining the requirements for these complex series of 

• Formulating detailed technical modeling approaches• Augmenting in-house expertise with contractors and e

• Commencing technical work in all of these areas
Assessing Most Probable Structura

Assessing Most Probable Structura

Sequence (2) Sequence (2)

• NIST is developing a rigorous technical approach t

of fireproofing in the collapse of the WTC towers, c

• As-built condition of the fireproofing prior to September 1

• Mechanical and thermal properties of the fireproofing mat

• Extent to which fireproofing may have been dislodged du

debris impact and local deformation/acceleration

• NIST is developing a number of simplified modeling ap

insights and bases to evaluate results from detailed mo

• Integration of impact damage, fire dynamics, thermal resp

response, collapse initiation analyses

• Performance of connections, components and subsystem

• Effect of key components and subsystems on structural s

• NIST is working with commercial software developers t

conversion of geometry, finite element meshing, materinformation between different computer programs in a s
Fire Dynamics

Partial Failure

Load Redistribution

Time-Temperature Curve 

ASTM E 119 Test

Uncoupled Uncoupled 

Analysis Analysis

Current Method:

Deterministic, Linear and Sequential Ana

of Collapse Induced by Fire-Structure Inte
Fire Dynamics

Structure 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
Projects 2, 5 & 6 Interfaces Projects 2, 5 & 6 Interfaces

0 6 12 

Simplified Approach

Project 2Project 5Project 6

2/1/03 8/1/03 2/1/04 

Simplified Structural-Fire Modeling Effort to 

Integrate & Test Coupled Failure Analyses

Structural 

Databases

Component 

Structural 

Analysis

w

Fire w/o 

Impact

Computational 

Interface SAPANSYS

Baseline 

Performan

Analysis

Visual 

Assessment

Draft 

Structural 

Models
Update on Analysis of Structural S

Update on Analysis of Structural S

• NIST has 236 pieces of WTC steel in its possession; NIST be

of steel from the WTC towers is adequate for purposes o

• regions of impact and fire damage emphasized in selection o

• NIST has all 14 specified steel grades for exterior panels; 2 s

represent 99 percent of core columns; and both specified gr

• NIST is documenting failure mechanisms and damage via an 

analysis of the WTC steel and enhanced image analysis of p

damaged buildings

• Preliminary results show that the measured room tempe

met relevant ASTM specifications; in many instances excspecifications by 5,000 to 15,000 psi

• Ongoing work to evaluate the design of the steel building com

and their performance under impact and fire conditions up un

initiation
WTC Fire Model Validation Experim

• NIST has completed experiments for validation of WTC fir

• Fire tests in large compartments to measure the heat rele

compartment gases and steel components (steel truss anwithout fireproofing). NIST reported on these tests in May 

• Shake table experiments to determine the magnitude of i

in damage to the ceiling tile systems, increasing the acce

to the ceiling/floor membranes. These tests are now com

• Office work station fire tests, based on descriptions of fur

office space, to input thermo-physical properties to the firon these tests in August 2003.

• Fire tests of multiple (three) workstations to validate mode

sensitivity of fire intensity, duration, and spread to the disthe ventilation of the fire, and the effect of jet fuel. These completion.
Update on Fireproofing and Fire R

Update on Fireproofing and Fire R

WTC Floor System WTC Floor System

• May 2003 progress report: NIST has not been able to determ

for the selection of fireproofing material for the WTC floor systdetermination of the thickness of fireproofing to achieve the sp

• NIST found no documentary evidence indicating that a test ba

been conducted to determine the fire rating of the WTC floor s

informed NIST that “there are no test records in our files.”

• Project specific fire endurance testing was not and is not 

may be conducted when circumstances warrant it, e.g., in 

• A composite bar joist floor system with spray-applied fireproof

innovative application in the 1960s.

• Use of bar joists in the floor system of high rise buildings such as 

• Long unsupported span of the floor system (60 ft and 35 ft in the t• Role of floor system in ensuring stability of the WTC structural sys

• Floor diaphragm action to transfer lateral (wind) loads to the colum

• NIST has awarded a contract to Underwriters Laboratorie

rating of typical WTC floor systems under both as-built an
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 photographer

• 5,726 video clips from 150 hours of videotape representi

sources

• NIST has determined the exact times for the major 

September 11, 2001 (aircraft strike, building collap

• NIST has developed detailed mappings for the fire

condition of windows at several specific times for Work is underway for WTC 7

• From the analysis of the visual images to date, NIST h

significant events for WTC 1 and 2 related to aircraft imdevelopment, and building damage
First-Person Data on Occupant Be

Person Data on Occupant Be

Evacuation, and Emergency Respo

Evacuation, and Emergency Respo

• Buildings are not normally designed for fire protection and ev

extreme conditions

• Critical lack of information on which to base evacuation 

response practice, standards, and codes in such conditi

• First-person interviews will provide valuable information to im

during extreme events in tall buildings. Specifically in the follo

• Firefighting in tall buildings• Evacuation in tall buildings• Emergency communications in extreme events• Building design features to support such operations

• NIST has now received all necessary approvals and has 

first-person data collection efforts

• The personal privacy and confidentiality of individual respond

to the 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
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
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
Bottom Line Bottom Line

Make all buildings safe

for occupants and first respo

Better evacuation systems 

emergency response capabil

future disasters