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

U.S. Federal Building and Fire Safety Investi

of 

the World Trade Center Disaster

WTC Technical Conference

September 13, 2005
National Context for WTC Investigation National Context for WTC Investigation

• The collapse of the World Trade Center structures followi

terrorist attacks of September 11, 2001 was among the wbuilding disasters in recorded history – killing 2749 people

• More than 400 emergency responders were among those 

the largest loss of life for this group in a single incident.

• Strong private sector, public, and Congressional demand 

comprehensive response to the World Trade Center disas

• Congress passed and the President signed into law on O

2002, the National Construction Safety Team (NCST) Act

• Gives NIST authorities to investigate building failure• Modeled after the NTSB, with some differences.
Fire & Emergency 

Service

IAFC, NASFM,

IAFF, FDNY, NYPD,...

Academics

IAFSS, ASME, 

LANL, MIT, 

Princeton, 

Northwestern, UT 

Austin, Georgia 

Tech, Penn State, 

Drexel, Wharton, 

Columbia, Lehigh, 

UMd, WPI,...

Industry Suppliers

W.R. Grace,

United Technologies, Sensors, Controls,...

Stakeholders and Partners Stakeholders and Partners

Public-Private 

Response Plan

Construction Industry

CII, IAI, CERF, 

FIATECH, NIBS, AGC

Fire Safety 

Engineering

Private 

Consultants, 

SFPE,...

Codes 

Org

ASCE, A

NFPA

ASTM

Structu

an

AIA, C

Buildi

Habitat, 

NCS

NYC/D

A

Other Governm

FEMA, ATF

USACE, DOE, D

CDC, GSA, Stat

IRC/NRCC, 

Insurance/

Testing labs

UL, FM Global, 

SwRI, IRI

Public/Groups

Skyscraper Safety,..

Occupants/Witnesses

Entrepreneurs/Inventors

Small Businesses, 

Students,... 
Dissemination

and Technical

Assistance Program

Dissemination

and Technical

Assistance Program

BPAT

Recommendations

BPAT

Recommendations

Govt.

Industry

Professional

Academic

Inputs/Actions

Govt.

Industry

Professional

Academic

Inputs/Actions

Public Inputs/

Efforts

Public Inputs/

Efforts

Technical Basis fo

Building and Fi

and Stand

Technical Basis fo

Building and Fi

and Stand

Standards and C

Org

Owners, Contractors, Designers,

Emergency Responders and

Regulatory Authorities

Guidance and Tools for

Improved Practices

Guidance and Tools for

Improved Practices

Research &

Development

Research &

Development

WTC

Investigation

WTC

Investigation

WT

Respons

Respon
Investigation Objectives 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?
Analysis of Probable Collapse Sequence

Analysis of Probable Collapse Sequence

NIST developed and used a series of rigorous and comprehensto determine the probable collapse sequence for the WTC toweaircraft impact to collapse initiation. The approach:

 Analyzed the complete sequence of events from aircraft impact to the 

jet-fuel-ignited multi-floor fires, thermal weakening of structural compothe progression of local structural failures that ultimately initiated collabuildings.

 Combined mathematical modeling, well-established statistical and 

probability-based analysis methods, laboratory experiments, and ana

and physical evidence—significantly advancing the current state-oand testing the limits of current computational capabilities.

 Required use of advanced strategies for managing computational 

due to unprecedented analysis complexity and sophistication; ad

captured the physics of phenomena essential to determining the collapse sequence.
WTC 1 Tower Model for Aircraft Impact Analysis WTC 1 Tower Model for Aircraft Impact Analysis
WTC 1
WTC 1 Damage: Composite Summa

WTC 1 Damage: Composite Summa

for Floors 93 to 98 for Floors 93 to 98

Column DamageSeveredHeavy DamageModerate DamageLight DamageSevere Floor DamageFireproofing and partitionsFloor system structural damage Floor system removed
WTC 1 Damage by Floor WTC 1 Damage by Floor

Floor 94 

Floor 96 Floor 97 

Floors 93 to 98 Floor 93

Cumulative Damage

Column DamageSeveredHeavy DamageModerate DamageLight DamageSevere Floor DamageFireproofing and partitionsFloor system structural damage Floor system removed
WTC 2
WTC 2 Damage: Composite Summary fo

WTC 2 Damage: Composite Summary fo

78 to 83 78 to 83

Column DamageSeveredHeavy DamageModerate DamageLight DamageFloor DamageFireproofing and partitionsFloor system structural damage Floor system removed
Enhancements added by NIST.

Broken 

Column Longitu

Panel JuObscure

Relative Roles of Aircraft Impact and Fir

Relative Roles of Aircraft Impact and Fir

• Fires played a major role in further reducing the structural capacity o

buildings, initiating collapse. While aircraft impact damage did not, b

initiate building collapse, it contributed greatly to the subsequent firethermal response of the structures by:

• Compromising the sprinkler and water supply systems;• Dispersing jet fuel and igniting building contents over large areas;• Creating large accumulations of combustible matter containing aircraft 

building contents;

• Increasing the air supply into the damaged buildings that permitted sig

higher energy release rates than would normally be seen in ventilation building fires, allowing the fires to spread rapidly on multiple floors; 

• Damaging and dislodging fireproofing from structural components in th

of the debris and due to the strong vibrations generated by aircraft imp

• Damaging ceilings that enabled “unabated” heat transport over the floo

partition walls and to structural components.
Relative Roles of Aircraft Impact and Fir

Relative Roles of Aircraft Impact and Fir

• The jet fuel, which ignited the fires, was mostly consumed w

first few minutes after impact. The fires that burned for almoentire time that the buildings remained standing were due mburning building contents and, to a lesser extent, aircraft cojet fuel.

• Typical office furnishings were able to sustain intense fires f

an hour on a given WTC floor. No structural component, howevsubject to intense fires for the entire period of burning. The duraintense burning impacting any specific component was controlled 

• The availability of combustible materials• Fuel gases released by those combustibles• Combustion air in the specific area

• The typical floor had on average about 4 psf of combustible 

on floors. Mass of aircraft solid combustibles was significant in immediate impact region of both WTC towers.
Initial Fire and Smoke Simulations: Fall 

Initial Fire and Smoke Simulations: Fall 
Reconstruction of the WTC Fires Reconstruction of the WTC Fires
Upper Layer Temperatures (WTC 1, Floo
Structural Analysis Progression Structural Analysis Progression

Component Analyses Knuckle Truss seat connections Single truss and 

concrete slab

 Full floor Column splice 

connection

 Single story column Nine story column Nine story-nine column 

exterior wall panel

Subsystem Analyses WTC 1

• Isolated Core• South Exterior Face• Floors 93 to 99

 WTC 2

• Isolated Core• East Exterior Face• Floors 79 to 83

Glob WT WT

Detailed nonlinear analyses to determine component behaviors and failure mechanisms

Nonlinear analyses with component simplifications and failure mechanism simplifications to determine major subsystem behavior and sequential failure mechanisms.

Nonlindetermbehavsequemecha


Critical Analysis Inter Critical Analysis Inter

-Dependencies Dependencies

Collapse Seq

Reference 

Structural 

Models 

SAP 2000 

SAP to ANSYS 

Conversion

SAP to LS-DYNA 

Conversion

Compartment Damage

Debris and Fuel 

Distribution

SFRM Damage

Structural 

Damage

Gas Temperat

Time-Historie

(FSI)

Structural

Temperature T

Histories

Resolution1-4 in.10-6 s

Aircraft Impact 

Damage

LS-DYNA

Fire Dynam

(FDS)

Thermal Ana

ANSYS v.8

Structural Res

and Failure An

ANSYS v.8

Time scale: 10 orders of magnitudeLength scale: 5 orders of magnitude

Baseline Performance Analysis
South Face of WTC1

• Maximum = 55 inches

(uncertainty ~ +/- 6 inches)

• Time: 10:22 AM• Measurements of inward

bowing (inches)

• Floor locations approximate• Blue tinted region digitally

enhanced
WTC2: East Face

Time: 9:21:29 AM ~18 minutes post impact

Maximum inward bowing of columns approximately 10 inches
Inward Bowing of Perimeter Columns A

Inward Bowing of Perimeter Columns A

Minutes Prior to Collapse: WTC 2 East 

Minutes Prior to Collapse: WTC 2 East 
Tilting of Building Tilting of Building 

Sections Sections

Initiation of glowas first obsertilting of buildinabove the impaof both WTC to

WTC 1 tilted to the south; WTC 2 tilted to the east and south.

© 2001 Dean Riviere
Factors that Enhanced Building Perform

Factors that Enhanced Building Perform

on September 11, 2001 on September 11, 2001

• The unusually dense spacing of perimeter columns, coupled with deep s

that was an inherent part of both the architectural and structural design 

walls, resulted in a robust building that was able to redistribute loads froperimeter columns to adjacent intact columns.

• The wind loads used for the WTC towers, which governed the design of 

frame-tube system, significantly exceeded the prescriptive requirements 

York City building code and selected other building codes of the era (Ch

York State), including the relevant national model building code (BOCA)

• The robustness of the perimeter frame-tube system and the large dimen

the WTC towers helped the buildings withstand the aircraft impact. 

• The composite floor system with open-web bar joist elements, framed to 

way flat plate action, enabled the floors to redistribute loads without collaplaces of aircraft impact damage to other locations, avoiding larger scale 

upon impact.
Factors that Enhanced Building Perform

Factors that Enhanced Building Perform

on September 11, 2001 (2) on September 11, 2001 (2)

• The hat truss resisted the significant weakening of the core, due 

impact damage and subsequent thermal effects, by redistributinfrom the damaged core columns to adjacent intact columns andby redistributing loads to the perimeter walls from the thermally wcore columns that lost their ability to support the buildings’ weigh

• The buildings would likely not have collapsed under the com

effects of aircraft impact and the subsequent jet-fuel ignited floor fires, if the fireproofing had not been dislodged or had minimally dislodged by aircraft impact. The existing conditfireproofing prior to aircraft impact and the fireproofing thicthe WTC floor system did not play a significant role in initiacollapse on September 11, 2001.
Innovative WTC Tower Structural System Innovative WTC Tower Structural System

• Innovative structura

when built; incorpornew and unusual ferequire additional co

• Composite flo

system using open-web baspray-applied 

• Design for wi

and control of induced vibra
Fire Performance of Composite Floor Sy

Fire Performance of Composite Floor Sy

• Fire-protection of a truss-supported floor system with spray-on 

was innovative and not consistent with then-prevailing practice

• No evidence found of technical basis in the selection of fir

thickness to meet 2 h fire rating:

 1/2 in. specified when WTC towers were built to maintain Clas

fire rating requirement of the NYC Building Code 

 1-1/2 in. specified for upgrades some years prior to 2001 2 in. for similar floor system in an unrestrained test (model cod

service recommendation in June 2001, unrelated to WTC build

• No evidence that full-scale fire resistance test of the WTC 

was conducted to determine the required fireproofing thicknes

the Architect of Record and, in 1975, the Structural Engineer o

stated that the fire rating of the WTC floor system could not be without testing.
Results From NIST Sponsored Tests at 

Results From NIST Sponsored Tests at 

___________________________________________________(1) Imminent collapse(2) Vertical displacement exceeded capability to measure accurately(3) Did not occurThe end-point criterion that determined the rating is shown in matching color.

--- 58 66 58 (3) 120(1)

3⁄4

17 ft, restrained, 1⁄2 in fireproofing

4

210

2

(2) 180 157 86 76 (3) 17 ft, restrained, 3⁄4 in fireproofing

3

146

2 

(2) --- --- 76 62 (3)

35 ft, unrestrained,

3⁄4 in fireproofing

2

116 11⁄2 

(1) --- 111 66 62 (3) 35 ft, restrained, 3⁄4 in fireproofing 1

Rating

(hr)

Maximum

(1300oF)

Average

(1100oF)

Maximum

(Ambient

+325oF)

Average

(Ambient

+250oF)

ASTM

E 119-

Failure 61

to

Support 

Load

Steel Temperatures Temperature on Unexposed Surface

Standar

Test

Terminated

(min)

Times to Reach End-Point Criteria (min)

Test Description
Wind Load Estimates for WTC 2

1960’s 13.1 10.1 16.5 8.8 12

Original WTC Design (Clarified by designer in July 2004)

2004 12.2 14.0 15.6 12.8 11

NIST / third-party SOM review / ASCE 7-02

CPP / ASCE 7-98 2002 15.1 15.3 17.1 15.5 14

*

2002 NA NA NA NA N

CPP / NYC Building CodeRWDI / ASCE 7-98 2002 10.6 12.2 13.5 11.1 10

2002 9.7 11.1 12.3 10.1 9

RWDI / NYC Building Code

9.3 9.3 7.6 7

1968 - 2001 NYC Building Code

5.3 5.3 4.2 4

Prior to 1968 NYC Building Code

Ab

E

About NS N-S E-W Resultant

Base Mome

Base Shear 10 

3 kips

Source Year

* Using ASCE 7-98 sections 6.5.4.1 and 6.6
Results and Findings of Drift Analysis Results and Findings of Drift Analysis

70.6 H/244 83.9 H/205 75.6 H/227 71

Refined NIST case

SOP case 56.8 H/303 68.1 H/253 59.7 H/287 56

56.6 H/304 55.7 H/309 51.2 H/335 65

Original design case

Tot

Dr

(in

Drift 

Ratio

Total 

Drift 

(in.)

Drift 

Ratio

Total 

Drift 

(in.)

Drift 

Ratio

Total 

Drift 

(in.)

E–W N–S E–W 

WTC 1 WTC 2

Loading Case

 The calculated drift ratios correspond to a damping ratio of 2.5% in es

loads.

 Typical drift ratios considered in practice (not required by building co

• H/500 (~ 32.9 in.)

 Under the original design wind loads, the WTC towers would need to h

between 1.5 to 1.9 times stiffer to achieve a H/500 drift limit; this can bachieved by increasing exterior column areas in the lower stories andadditional damping.
Evacuation and Emergency Response Evacuation and Emergency Response

Based on 1,056 interviews of surviving WTC occupants ainterviews of emergency responders.

• It is estimated that 17,400 occupants (± 1,200) were present in th

towers on the morning of September 11, 2001. The initial populat

tower was similar: 8,900 (± 750) in WTC 1 and 8,500 (± 900) in WTC present on 9/11, 16 percent were also present during the 1993 bomb

• About 6 percent of the surviving occupants reported a pre-e

limitation to their mobility. These limitations included obesity, condition, needing assistance to walk, pregnancy, asthma, being 

chronic condition, recent surgery or injury, and other.

• Approximately 87 percent of the WTC tower occupants, including 

99 percent of those below the floors of impact, were able to evac

successfully. 

• Rough estimates indicate that about 20 percent or more of the 2,56

occupants and emergency responders who were in the WTC towtheir lives may have been alive in the buildings just prior to thei
Evacuation Rates in the WTC Towers Evacuation Rates in the WTC Towers

• The overall evacuation rate in WTC 2 (108 survivors per min) was a

percent faster than that in WTC 1 (73 survivors per min).

• After the first airplane struck WTC 1 and before the second airplan

2, the rate of evacuation completion in WTC 2 was twice the rate in 

• Functioning elevators allowed many (roughly 3,000) survivors 

evacuate WTC 2 during the 16 minutes prior to aircraft impact.

• Soon after WTC 2 was struck by the airplane until about 20 min before e

collapsed, the survivors in WTC 2 and WTC 1 exited at about the same evacuation rate of WTC 1).

• During the last 20 min before each building collapsed, the evacuation ra

buildings slowed to about one-fifth the immediately prior evacuation ratesuggests that for those seeking and able to reach and use undamagstairways, the egress capacity (number and width of exits and stairadequate to accommodate survivors.
Evacuation Rates in the WTC Towers (2

Evacuation Rates in the WTC Towers (2

• Based on use of existing egress models and actual evacuation time on S

2001, it is estimated that a full capacity evacuation of each WTC towe

people—three times the number present on September 11, 2001—wrequired about 4 hours. 

• Had the buildings been full, it is possible that as many as 14,000 peo

lost their lives based on rough estimates using existing models.

• To achieve a significantly faster total evacuation at full capacity wou

required increases in egress capacity (number and width of exits and 

• The egress capacity required by current building codes and practice 

“phased” evacuation strategy, not “full” evacuation. 

• The average surviving occupants moved slower down stairs and thr

exits than previously reported for non-emergency evacuations.

• In WTC 1, the average surviving occupant spent 48 seconds pe

descending the stairwell. This is about 50% of the slowest spee

measurement reported for non-emergency evacuations (e.g., dr
Occupant Preparedness Occupant Preparedness

• Two-thirds of surviving occupants reported having participated in 

in the 12 months prior to September 11, 2001, while 17 percent rethey received no training during that same period.

• Of those participating in fire drills, 93 percent were instructed abo

location of the nearest stairwell.

• Overall, slightly over half of the survivors, however, had never 

stairwell at the WTC prior to September 11, 2001 (NYC Local Larequiring occupants to practice stairwell evacuation.)

• Occupants were often unprepared for the physical challenge of fu

evacuation. Numerous occupants required one or more periods of restairwell descent or turned to elevators after finding the stairwells stren

• Occupants were often unprepared to encounter transfer hallways 

stairwell descent. Groups of evacuees occasionally hesitated or debof action upon encountering a transfer hallway. 
Condition of Stairwells Condition of Stairwells

• The stairwells, with partition wall enclosures that provided a 2 h fire-rating but little s

integrity, were damaged in the region of the aircraft impacted floors. 

• One of the stairwells in WTC 2 (Stairwell A on the Northwest side) was passab

of aircraft impact for some period of time after WTC 2 was attacked.

• All three stairwells in WTC 1 and the two other stairwells in WTC 2 were rendered im

the region of aircraft impact.
• After aircraft impact, only two elevators out of 198 w

operating inside the two WTC towers. WTC 1, from t

lobby to the 16th floor. WTC 2, from the lobby to the 40t

• The stairways were filled with occupants evacuating the 

buildings. FDNY personnel and other emergency 

responders reported difficulty attempting to climb thstairs due to this counterflow.

• Counter flow in the staircases made it difficult for emerg

responders to carry equipment up the stairways.

• Counter flow in the staircases caused teams of emerge

responders to become separated, causing delays and disrupting team operations.

FDNY Access to the WTC Towers FDNY Access to the WTC Towers
Emergency Responders & High Emergency Responders & High

-Rise Buildin

Rise Buildin

• First responding FDNY units took from 4 to 10 minutes to get to 

complex. They then got their equipment and received assignmeanother 3 to 5 minutes. Time to begin operations 7 to 15 minute

• Of the 27 emergency responders interviewed that were inside W

maximum floor height achieved before WTC 2 collapsed, a time hour 13 minutes.

1 – A police officer carrying no extra equipment and in a patrolman’s 

uniform climbed to the 44th floor.

8 – Emergency responders (FDNY, PAPD, NYPD) climbed to the 30’s

Two FDNY took an elevator to the 16th floor.

16 – Emergency responders (mostly FDNY) climbed to the 20’s.2 – Emergency responders (NYPD) climbed to the teens.

• Estimated climbing rate based on a 60 minute climbing perio

maximum height: 1.4 to 2 minutes/floor
High-Rise Buildings & Emergency Resp

Rise Buildings & Emergency Resp

Example: Fire department response to a 60 story high-rise building

trapped above fires on the 58th floor and no operating eleva

Lobby

Firefighters begin to climb 10 minutes

Fire department arrival 4 minutes 

Firefighters carrying equipment and

wearing PPE ~ 70 minutes

Firefighters carrying no equipment and not

wearing PPE ~ 50 minutes

Fires Firefighters carrying equipment and wearing PPE ~ 125 minutes

Firefighters carrying no equipment and not

wearing PPE ~ 90 minutes
Radio Communications in High Radio Communications in High

-Rise Bu

Rise Bu

• Challenging radio-f

propagation enviroand reinforced conbuildings.

• Large scale operat

• Number of first • Communication

and protocols.

• Surge in traffic; 

• Interoperability of r

communication tecamong different emresponder organiza

• Identification, locat

Schematic of WTC Radio Repeater System first responders.
Mobility Impaired Occupants Mobility Impaired Occupants

• As the emergency responders started evacuating WTC 1 after th

of WTC 2, they found mobility impaired occupants still in the stairdown.

• Ambulatory mobility impaired occupants typically walked down th

one hand on each hand rail and took one step at a time going doaddition, they were typically accompanied by one person, anothe

or an emergency responder. This blocked others behind them frmore rapidly down the stairs.

• FDNY and PAPD personnel found 40 to 60 mobility impaired 

on the 12th floor of WTC 1 as they went down and attempted 

each floor on their way out. These impaired individuals had be

on this floor in an attempt to clear the stairways.

• Emergency responders were assisting approximately 20 of t

mobility impaired people down the staircase just prior to the of WTC 1. It is unknown how many fatalities occurred with this g
Key Findings Key Findings

• The buildings would likely not have collapsed due to aircraft impa

subsequent jet-fuel ignited multi-floor fires, if the fireproofing had dislodged or had been only minimally dislodged by aircraft impact

• The existing condition of the fireproofing prior to aircraft impact a

fireproofing thickness on the WTC floor system did not play a govin initiating collapse on September 11, 2001.

• Since the buildings were occupied by only about 1/3 of the building’s fu

of 25,000 occupants, approximately 87 percent of the WTC tower oc

including more than 99 percent below the floors of impact, were aevacuate successfully.

• A full capacity evacuation of each WTC tower with 25,000 people w

required about 4 hours and as many as 14,000 people may have lolives.

• Documents suggest that the WTC towers generally were designed 

maintained consistent with the requirements of the 1968 New York Building Code.
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
Submission Process for Public Commen

Submission Process for Public Commen

 NIST released the draft WTC Towers report and 42 supp

draft reports on June 23, 2005 for public comment.

 Six week period for public comment; all comments due to 

August 4, 2005.

 Comments encouraged on the WTC Towers Report but w

on all reports.

 NIST requested comments be specific in nature with 

recommendations for change.

 Comments were accepted via web site, e-mail, fax, and r

mail.
Summary of Comments Received Summary of Comments Received

Total number of submissions: 469Number of Organizations Responding: 22Number of Individuals Responding: 58 Nearly all major building and fire safety organization

submitted comments: (e.g., ICC, NFPA, ASCE/SEINCSEA, PCA, AIA, BOMA, ACI, NASFM, AFSC, NCAMCBO, CRSI, UL, ASTM, SPI, NFSA, NRMCA)
Appreciation Appreciation

 NIST appreciates the desire of organizations and individu

state their positions on the draft WTC Reports.

 NIST was gratified by the industry interest in the WTC 

Investigation and our findings and recommendations and quality and quantity of the comments received.

 Most of the pros and cons of issues raised in the comme

been debated by the NIST team and already considered findings and recommendations contained in the draft repo

 The comments have resulted in a wealth of information a

that will guide not only follow-on work by NIST, but also ton work of the standards and codes organizations, indusorganizations, and academic researchers. 
Nature of Changes Nature of Changes

 Multiple additions and wording changes to emphasize an

clarify aspects

 Numerous editorial changes Clarified a finding Modified six recommendations (3 amendments, 3 clarifica Clarified the back-up text for several of the recommendat

including definition of tall buildings used in the report

 Greatly enhanced index of topics covered in the report
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.
Definition of Tall Buildings Definition of Tall Buildings

 From:

 Buildings over 20 stories in height: NIST has found that the physiolog

on emergency responders of climbing 20 or more stories makes it diff

conduct effective and timely firefighting and rescue operations in buildemergencies without functioning elevators. Better knowledge of the p

impacts through research could refine the definition of tall buildings us

 To:

 NIST has found that the physiological impacts on emergency respond

climbing numerous (e.g., 15 to 20 or more) stories makes it difficult to effective and timely firefighting and rescue operations in building emewithout functioning elevators. Consideration and better knowledge of as ladder height, physiological factors involving emergency responde

building occupants, use of working elevators, and installation and use elevators could refine the currently used definition of tall buildings to i

multiple threshold levels.
Clarification to Findings Clarification to Findings

Inserted a clarification into the Executive Summary and (Outcome of the Investigation):

NIST found no corroborating evidence for alternativhypotheses suggesting that the WTC towers were down by controlled demolition using explosives plaprior to September 11, 2001. NIST also did not finevidence that missiles were fired at or hit the towerInstead, photos and videos from several angles cleshowed that the collapse initiated at the fire and imfloors and that the collapse progressed from the infloors downward, until the dust clouds obscured the 
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 

Consensus standards and code provisions for preventing progressive colla

developed and adopted nationwide – along with tools and guidelines for thea standard methodology be developed to reliably predict the potential for cofailures in structural systems subjected to multiple hazards. Rec. #1

Nationally accepted performance standards be developed for: 

 wind tunnel testing of prototype structures based on sound technica

that result in repeatable and reproducible results; and 

 estimating wind loads and their effects on tall buildings, based on w

testing data and directional wind speed data. Rec. #2

Appropriate criterion be developed and implemented to enhance performan

buildings by limiting how much they sway under lateral load design conditiowinds and earthquakes). Rec. #3
Group 2: Enhanced Fire Resistance of 

StructuresThe procedures and practices used to ensure tresistance of structures be enhanced by:

• improving the technical basis for construction 

classifications and fire resistance ratings and tmethods, 

• using the “structural frame” approach to fire re

ratings, and 

• developing in-service performance requiremen

conformance criteria for sprayed fire resistive (commonly known as fireproofing).
Enhanced Fire Resistance of Structures

Evaluate -- and where needed improve -- the technical basis for determining classification and fire rating requirements (especially for tall buildings)...and 

code changes now as much as possible by explicitly considering: 

 timely access by emergency responders and full evacuation of occupa

required for burnout without local collapse;

 extent to which redundancy in active fire protection (sprinkler and stan

alarm, and smoke management) systems should be credited for occup

safety;

 need for redundancy in fire protection systems critical to structural inte

 ability of the structure and local floor systems to withstand maximum c

scenario without collapse -- recognizing that sprinklers could be comp

operational, or non-existent; (continued)
Enhanced Fire Resistance of Structures 

 compartmentation requirements to protect the structure, including:

 fire rated doors and automatic enclosures, and 

 limiting air supply (e.g., thermally resistant window assemblies) 

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

 effect of spaces containing unusually large fuel concentrations for the 

occupancy of the building; and

 extent to which fire control systems -- including suppression by autom

manual means -- should be credited as part of the prevention of fire s
Enhanced Fire Resistance of Structures 

Improve the technical basis for century-old standard for fire resistan

of components, assemblies, and systems and... develop guidance fextrapolating results of tested assemblies to prototypical building sy

principal step in fulfilling this recommendation is to establish a capability for studying and testing components, assemblies, ansystems under realistic fire and load conditions. Rec. #5

Develop criteria, test methods, and standards:

 for in-service performance of fireproofing to protect structural 

components; and

 to ensure that these materials, as-installed, conform to conditio

tests used to establish the fire resistance rating. Rec. #6 

Adopt and use “structural frame” approach (structural members con

the columns carry the high fire resistance rating of the columns). Rec
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 partial or glo

collapse. 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. 
New Methods for Fire Resistance Desig

Structures

Require that uncontrolled building fires result in burnout without partial or (total) collapse. Rec. #8Develop:

 performance-based standards and code provisions -- as an alternat

current prescriptive design methods -- to enable design and retrofit to resist real fire conditions

 tools, guidelines, and test methods to evaluate fire performance of t

as a whole system. Rec. #9
New Methods for Fire Resistance Desig

Structures (2)

Develop and evaluate new fire resistive coating materials, systems, and technologies with significantly enhanced performance and durability to prprotection following major events. Rec. #10Evaluate performance and suitability of advanced structural steel, reinforc

pre-stressed concrete, and other high-performance material systems for conditions expected in building fires. Rec. #11
Group 4: Improved Active Fire Protectio

Active fire protection systems (i.e., sprinklers, standpipehoses, fire alarms, and smoke management systems) shenhanced through improvements to:

• Design• Performance• Reliability, and• Redundancy 

of such systems.
Improved Active Fire Protection

Enhance performance and possibly the redundancy of active fire protec

systems to accommodate higher risks associated with tall buildings. 

Develop advanced fire alarm and communication systems that provide 

continuous, reliable, and accurate information on life safety conditio

manage the evacuation process; all communication and control p

buildings need to be designed and installed to have the same r

to failure and increased survivability above that specified in prstandards. Rec. #13

Adapt advanced fire/emergency control panels to accept and interpret 

and more reliable -- information from the active fire protection systeprovide tactical decision aids. Rec. #14

Develop and require systems for improved transmission to emergency 

responders, and off-site or black-box storage, of information from bumonitoring systems. Rec. #15
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 regarding their role

duties for evacuation during emergencies, and 

• incorporation of appropriate egress technologies
Improved Building Evacuation

Develop and carry out public education and training campaigns to improvoccupants’ preparedness for evacuation in case of building emergencies. Design tall buildings to accommodate timely full building evacuation of occ

to building-specific or large-scale emergencies such as widespread power major earthquakes, tornadoes, hurricanes, fires, explosions, and terrorist a

 Building size, population, function, and iconic status should be tak

account in designing the egress system. 

 Stairwell capacity and stair discharge door width should be ade

accommodate counterflow due to emergency access by responde
Improved Building Evacuation (2)

Design egress systems:

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

without negatively impacting the average travel distance;

 to maintain their functional integrity and survivability under foreseea

building-specific or large-scale emergencies; and

 with consistent layouts, standard signage, and guidance so that sys

become intuitive and obvious to building occupants during evacuati

Rec. #18
Improved Building Evacuation (3)

Building owners, managers, and emergency responders should develop and ensure accurate emergency information is communicated in a timely enhance awareness of occupants and emergency responders through:

 better coordination of information among different emergency resp

groups,

 efficient sharing of that information among building occupants and 

responders, 

 more robust design of emergency public address systems, 

 improved emergency responder communication systems, and  use of the Emergency Broadcast System (the Integrated Public Ale

Warning System) and Community Emergency Alert Networks. Rec
Improved Building Evacuation (4)

Evaluate the full range of current and next generation evacuation techno

future use, including:

 protected/hardened elevators, 

 exterior escape devices, and  stairwell descent devices, 

which may allow all occupants an equal opportunity for evacuation and f

emergency response access. Rec. #20
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 Procedures

Install fire-protected and structurally hardened elevators in tall buildings to 

timely emergency access to responders and allow evacuation of mobility ibuilding occupants. 

 Such elevators should be for exclusive use by emergency responde

emergencies. 

 In tall buildings, consideration also should be given to installing such 

for use by all occupants. Rec. #21

Install, inspect, and test emergency communications systems, radio command associated operating protocols to ensure that the systems and protoc

 are effective for large-scale emergencies in buildings with challengin

frequency propagation environments, and 

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

building environments and in the field. Rec. #22
Improved Emergency Response Techno

and Procedures (2)

Establish and implement detailed procedures and methods for gathering, 

processing, and delivering critical information through integration of relev

video, graphical, and written data to enhance situational awareness of all emergency responders. Establish an information intelligence sector to co

each incident. Rec. #23

Establish and implement codes and protocols for ensuring effective and 

uninterrupted operation of the command and control system for large-sca

emergencies. Rec. #24
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

Nongovernmental and quasi-governmental entities that own or lease buildare not subject to building and fire safety code requirements of any goverjurisdiction -- should provide a level of safety that equals or exceeds the lsafety that would be provided by strict compliance with the code requirem

appropriate governmental jurisdiction. 

 As-designed and as-built safety should be certified by a qualified th

independent of the building owner(s). 

 The process should not use self-approval for code enforcement in a

including:

 interpretation of code provisions,  design approval,  product acceptance,  certification of the final construction, and 

 post-occupancy inspections over the life of the buildings. #25
Improved Procedures and Practices (2)

State and local jurisdictions adopt and aggressively enforce building codes ensure that egress and sprinkler requirements are met by existing building

Further, occupancy requirements should be modified where needed (such there are assembly use spaces within an office building) to meet the modecodes. Rec. #26

Building codes should require building owners to retain documents related building design, construction, maintenance and modifications over the ent

the building. Means should be developed for offsite storage and maintenathe documents. Relevant information should be easily accessible by respoduring emergencies. Rec. #27
Improved Procedures and Practices (3)

The role of the “Design Professional in Responsible Charge” be clarified to 

all appropriate design professionals (including the fire protection and structengineers) are part of the team designing buildings that employ innovative 

structural and fire safety systems. Rec. #28
Group 8: Education and Training Group 8: Education and Training

The skills of building and fire safety professioshould be upgraded through a national educaand training effort for fire protection engineersstructural engineers, and architects. The skillbuilding regulatory and fire service personnel also be upgraded to provide sufficient undersand skills to conduct the review, inspection, aapproval tasks for which they are responsible
Education and Training 

Continuing education curricula should be developed and programs be implemented for: 

 training fire protection engineers and architects in structural eng

principles and design, and 

 training structural engineers, architects, fire protection engineers

code enforcement officials in modern fire protection principles technologies, including fire-resistance design of structures. 

 training building regulatory and fire service personnel to up

their understanding and skills to conduct the review, inspecapproval tasks for which they are responsible. Rec. #29

Academic, professional short-course, and web-based training materials of computational fire dynamics and thermostructural analysis tools be deRec. #30
Dissemination

and Technical

Assistance Program

Dissemination

and Technical

Assistance Program

BPAT

Recommendations

BPAT

Recommendations

Govt.

Industry

Professional

Academic

Inputs/Actions

Govt.

Industry

Professional

Academic

Inputs/Actions

Public Inputs/

Efforts

Public Inputs/

Efforts

Technical Basis fo

Building and Fi

and Stand

Technical Basis fo

Building and Fi

and Stand

Standards and C

Org

Owners, Contractors, Designers,

Emergency Responders and

Regulatory Authorities

Guidance and Tools for

Improved Practices

Guidance and Tools for

Improved Practices

Research &

Development

Research &

Development

WTC

Investigation

WTC

Investigation

WT

Respon

Respon
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, IAFF, CTBUH, Chicago Committee on High-Rise Buildings, Engineers Foundation of Chicago, NCSBCS/AMCBO, CII, CERF CorpoBoard)

• Detailed briefing for designers of the WTC and lower Manhattan redevelopme

Silverstein, Port Authority, NYC DOB officials, and Goldman Sachs).

• WTC Technical Conference: Putting Recommendations into Practice, Septem

2005.

• NIST will establish a web-based system to track the status of the recommend
Strategy for Recommendations Strategy for Recommendations

Separate plan for each of the 30 recommendations:

 Team leader (responsible for proactive pursuit and schedul

support staff 

 Concise objective Needs to meet objective (NIST and others) Strategy (research, consensus, public policy) Workshops to facilitate consensus (NIBS) Schedules and required format for submitting proposals to t

codes and standards

 Technical and position papers to build support
Proposals for Changes to Codes Proposals for Changes to Codes

 NIST has contracted the National Institute of Building Sci

(NIBS) to coordinate preparation of code change proposaselected recommendations.

 NIBS is organizing a panel of recognized experts to:

 Prioritize the recommendations (e.g., those that can b

translated directly into code change proposals, those require changes to standards, and those that will requadditional research).

 Develop proposals for changes to building codes.

 Panel will prepare proposals for ICC and NFPA 5000 and 

coordinate submission with code update cycles. 
Dissemination

and Technical

Assistance Program

Dissemination

and Technical

Assistance Program

BPAT

Recommendations

BPAT

Recommendations

Govt.

Industry

Professional

Academic

Inputs/Actions

Govt.

Industry

Professional

Academic

Inputs/Actions

Public Inputs/

Efforts

Public Inputs/

Efforts

Technical Basis fo

Building and Fi

and Stand

Technical Basis fo

Building and Fi

and Stand

Standards and C

Org

Owners, Contractors, Designers,

Emergency Responders and

Regulatory Authorities

Guidance and Tools for

Improved Practices

Guidance and Tools for

Improved Practices

Research &

Development

Research &

Development

WTC

Investigation

WTC

Investigation

WT

Respon

Respon
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
Publication of Reports on the WTC Tow

Publication of Reports on the WTC Tow

 43 reports to be downloadable from the NIST WT

site by late September or early October 2005

 43 reports to be available on two CDs in October  Limited number of hard copies of NIST NCSTAR 

available in October, 2005
Tentative Schedule for WTC 7 Reports Tentative Schedule for WTC 7 Reports

 January 2006 Completion of technical w March 2006 Draft reports for review April 2006 Draft reports to NCST AC May 2006 Reports for public comm June 2006 Publication
Web site Web site http:// http://wtc.nist.gov

Email to Email to 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

NCST Advisory Committee NCST Advisory Committee

Members Members

Dr. Charles Thornton, Co

Thornton-Tomasetti

Tomasetti

Dr. Robert Hanson, Profe

Dr. Robert Hanson, Profe

University of Michig

University of Michig

Mr. Philip DiNenno, Pres

Mr. Philip DiNenno, Pres

Associates. Associates.

Professor Glenn Corbett

College, NYC. College, NYC.

Dr. Kathleen Tierney, Un

Dr. Kathleen Tierney, Un

Colorado, Boulder. Colorado, Boulder.

Mr. Paul Fitzgerald, FM G

Mr. Paul Fitzgerald, FM G

(retired). (retired).

Mr. David Collins, Mr. David Collins, The Pr

The P

Professor Forman William

Professor Forman William

of California at San 

of California at San 

Dr. John Barsom, Presid

Dr. John Barsom, Presid

Consulting. Consulting.

z Appointed by the NIST Director.z Functions...

• Review procedures and reports• Evaluate activities of teams• Assess implementation of 

recommendations

• Annual report to Congress

z Reviewed WTC Investigation plan, 

progress, findings, and draft recommendations at 6 meetings. 

z Reviewed all WTC progress reports and 

final reports

z Membership balances broad scope of 

disciplines and interests
WTC Investigation Overview WTC Investigation Overview

• Investigation announced August 2002; drew talent from about 20

outside experts, and contractors.

• Two written public updates, two technical progress reports.• Three public meetings:

• June 24, 2002 (NYC) to present and solicit comments on draft inves• February 12, 2004 (NYC) to solicit comments on (1) technical aspec

investigation, (2) additional information that NIST might consider, (3) considered for recommendations.

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

Underwriters Laboratories.

• Seven media/public briefings on progress, seven meetings of the 

Construction Safety Team Advisory Committee, and one meeting public input for first-person interviews of occupants and first respo