National Institute of Standards and Techno

Technology Administration

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

Part V – Procedures and Practices

April 5, 2005
• The 110-story WTC towers were among the 

world’s tallest buildings, while the 47-story WTC 7 represented a more typical tall building. 

• These buildings provide case studies to 

document, review, and, if needed, improve the procedures and practices used in the design, construction, operation, and maintenance of tall buildings. 

• This investigation objective is independent of 

other objectives which are focused specifically on the consequences of the attack on September 11, 2001, specifically the building collapses, evacuation, and emergency response. 

• While some findings under this objective are 

directly relevant to the events of September 11, 2001, others are concerned with normal building and fire safety procedures and practices.

Procedures and Practices Procedures and Practices
Procedures and Practices Procedures and Practices

• Applicable building codes and policies

• NYC codes; PANYNJ policy and rationale; PANYNJ MOU wi• Comparison with contemporaneous codes

• Building design and construction

• Structure; fire safety; egress; elevators• Design criteria and requirements• Comparison with code requirements• Innovative features; code variances• Fabrication and construction inspections

• Maintenance and modifications

• Local laws; modifications after 1993 bombing• Tenant alteration review manuals• Condition surveys and structural inspections

• WTC 7 Fuel System
Applicable Building Codes and Policies Applicable Building Codes and Policies

• Although not required to conform to NYC codes, the PANYNJ ele

the provisions of the proposed 1968 edition of the NYC Building Cthan three years before it went into effect. 

• The proposed 1968 edition allowed the PANYNJ to take advanta

restrictive provisions and of technological advances compare1938 edition that was in effect when design began for the WTC to1962. The 1968 code:

• Eliminated a fire tower as a required means of egress;• Reduced the number of required stairwells from 6 to 3 and the size of 

to the stairs from 44 in. to 36 in.;

• Reduced the fire rating of the shaft walls in the building core from 3 h 

• Changed partition loads from 20 psf to loads based on weight of parti

length (that reduced such loads for many buildings including the WTC 

• Permitted a 1 h reduction in fire rating for all structural components (c

h to 3 h and floor framing members from 3 h to 2 h).

• Permitted wind tunnel testing using models to establish design values 

load.
Applicable Building Codes and Policies 

Applicable Building Codes and Policies 

• The NYC Department of Buildings reviewed the WTC tower 

1968 and provided comments to the PANYNJ concerning the plarelation to the 1938 NYC Building Code. The architect-of-record to the PANYNJ responses to those comments, noting how the dconformed to the 1968 NYC Building Code. All of the issues idethe NYC review appear to deal with egress issues, not with any innovative features of the buildings.

• In 1993, the PANYNJ and the NYC Department of Buildings entered into 

memorandum of understanding that:

• Restated the PANYNJ’s longstanding policy to assure that its f

the City of New York meet and, where appropriate, exceed the requirements of the NYC Building Code.

• Provided specific commitments to the NYC Department of Buildings 

procedures to be undertaken by the PANYNJ to assure that buildingoperated by the PANYNJ are in conformance with the Building Stancontained in the NYC Building Code. 
Applicable Building Codes and Policies 

Applicable Building Codes and Policies 

• In 1993, the PANYNJ adopted a policy providing for implementation of fir

recommendations made by local government fire departments after a fire inspection of a PANYNJ facility, and for the prior review by local fire safe

fire safety systems to be introduced or added to a facility. Later in 1993, 

entered into an agreement with FDNY which reiterated the policy adoptePANYNJ and set forth procedures to assure that new or modified fire safare in compliance with local codes and regulations.

• While the PANYNJ entered into agreements with the NYC Department of 

the 1990s with regard to conformance of PANYNJ buildings constructed 

City to the NYC Building Code and sought review and concurrence as reagreements, the PANYNJ was not required to yield, and appears not 

approval authority to New York City. The PANYNJ was created as an entity, a “body corporate and politic”, under its charter, pursuant to Article of the U.S. Constitution permitting compacts between states, and like manongovernmental and quasi-governmental entities in the United States is building and fire safety code requirements of any governmental jurisdictio
Rationale for the Selection of the 1968 N

Rationale for the Selection of the 1968 N

Building Code for the WTC Towers Building Code for the WTC Towers

June 22, 1965 letter from John M. Kyle, Chief Engineer to Malco

Chief, Planning Division, WTC:

“This will confirm my advice that, in view of the more liberal pr

the proposed new New York City Building Code, I feel we shouadvantage of its provisions.

This decision is based on the following:

1. The new code has received thorough review by interes

technical groups and representatives of the City and hmodified to meet all major objections.

2. It is scheduled to be officially submitted to the City in Septe

should be approved well before we construct our buildings

3. The Commissioner has stated that he favors the appro

by the Port Authority in using advanced techniques in of the World Trade Center. He also stated that the Port A

not subject to the provisions of the Building Code.”
Rationale for the Selection of the 1968 N

Rationale for the Selection of the 1968 N

Building Code for the WTC Towers Building Code for the WTC Towers

September 29, 1965 letter from Malcolm P. Levy, Chief, Plannin

WTC to Minoru Yamasaki, Architect:

“... Generally the tower core should be redesigned to eliminate 

tower and to take advantage of the more lenient provisions regstairs...”

May 19, 1966 memorandum from Guy F. Tozzoli, Director, Wor

Department to John M. Kyle, Chief Engineer:

“The decision to follow the new Code was, as you pointed out, 

memorandum to Mr. Levy of June 22, 1965, based on the fact thatnew Code had been thoroughly reviewed by interested technicand was modified to meet all major objections; (2) it would probadopted before we constructed our buildings; and (3) the Commisfavored the approach of using advanced techniques in the desWorld Trade Center and that the Port Authority, according to him, subject to the provisions of the Building Code.”
Rationale for the Selection of the 1968 N

Rationale for the Selection of the 1968 N

Building Code for the WTC Towers Building Code for the WTC Towers

Memorandum dated January 15, 1987, from Lester S. Feld (

Structural Engineer, World Trade Department, PANYNJ) to J. Linn (Deputy Director for Physical Facilities, WTD, PANYSubject: The World Trade Center – Towers and Plaza BuiFire Rating per NYC Building Code Revision Effective 12-6

Paragraph 2. B. of the memo states:

“For office buildings there is no economic advan

using Class 1A Construction, and ER&S used Class 1B Construction for the WTC Towers and Plaza Buildings are Occupancy Group “E” (Business) with a fire index hours. As such, columns must have a three hour rating anconstruction with a 2 hour rating.”
Condition Surveys and Structural Inspe

Condition Surveys and Structural Inspe

• PANYNJ developed the Standards for Structural Integrity Inspection 

Trade Center Towers A & B in 1986.

• Beginning in 1990, PANYNJ implemented a systematic facility cond

program for the WTC Towers. Prior to 1990, both WTC 1 and WTC inspected occasionally.

• WTC 7, which was not owned by PANYNJ, was also inspected base

criteria in the Standards.

• The condition survey program included:

• WTC 2 condition survey, 1990, PANYNJ Engineering Quality Assuranc• WTC 1 condition survey, 1991, Office of Irwin G. Cantor, Consulting Eng• WTC 7 survey, 1997, Ammann & Whitney• Due diligence physical condition survey of WTC 1 and WTC 2, 2000, Me

• Periodic inspections under the Structural Integrity Inspection Progra

conducted by LERA and other engineering firms.
Standards for Structural Integrity Inspec

Standards for Structural Integrity Inspec

• Statistical inspections:

• Periodic visual inspection of selected structural components in “high

trouble prone areas” supplemented by occasional visual inspections 

structure was exposed during tenant remodeling or general mainten

• Review of maintenance and tenant complaint reports:

• Examination of various reports to shed light on underlying structura

maintenance reports of non-structural repairs; water leakage; and tecomplaints about unusual building movements, vibration, noise, etc

• Building movement and deformation measurements:

• Performance of systems within buildings evaluated through measur

movement or deformation using appropriate tests and instruments.Measurements were to be performed on individual components in twell as on the entire towers themselves.
Structural Integrity Inspection Program Structural Integrity Inspection Program

• In general, the structural integrity inspections (SII) found that the structur

WTC 1, 2, and 7 were in good condition. The inspection consultants made 

routine and some priority recommendations for repairs to the PANYNJ. 

• The SII reports identify some of the same deficiencies from report to repo

missing fireproofing on structural steel members. 

• According to the PANYNJ, all of the construction records on repairs following th

were lost on September 11, 2001. Thus, it cannot be determined whether all orecommended repairs were performed.

• Fireproofing was reported to be missing or damaged in the floors below the Pla

B1 to B6 of WTC 1 and WTC 2) and in the hat-truss zone. 

• Fireproofing on beams and columns was also found missing or damaged in ele

The causes for missing and damaged fireproofing were attributed to high-speed elevator cabs and elevator cables hitting fireproofing on structural members. It that a large portion of missing or damaged fireproofing in elevator cores occurrlevels of the towers.
Retention of Building Documents Retention of Building Documents

• State and local jurisdictions do not require retention of documen

the design, construction, operation, maintenance, and modificatbuildings, with few exceptions. These documents are in the posbuilding owners, contractors, architects, engineers, and consulta

• Building documents are not archived for more than about 6 

and there are no requirements that they be kept in safe custphysically remote from the building throughout its service l

• In the case of the WTC towers, the PANYNJ and its contract

consultants maintained an unusually comprehensive set of documents, a significant portion of which had not been desthe collapse of the buildings but could be assembled and pthe NIST investigation.

• In the case of WTC 7, several key documents could not be revie

they were lost in the collapse of the building. 
Roles of Architects and Engineers Roles of Architects and Engineers

• Consistent with the practice at the time, the code architect was responsible for spe

protection and designing the egress system for the WTC Towers in accordance wiprescriptive provisions of the NYC building code. 

• The architect and owner engaged the services of structural engineers to perfo

structural design and to ensure that his/her design was properly implemented

• At that time the fire protection engineering profession was not sufficiently mat

the same standard of care employed with the structural design. 

• There is no reason to believe that the involvement of a fire protection enginee

would have resulted in any differences in the design or performance of the fire 

systems. 

• Today, particularly when designing a building employing innovative features

involvement of a fire protection engineer in a role similar to the structural en

under the overall coordination of the Design Professional in Responsible Chto the standard of care.

• The technical base and sophistication of the practice of fire protection engine

well advanced of where it was during the design and construction of the WTC 

• When designing the structure of selected tall buildings or selected other buil

fires, or evaluating the fire resistance of such structures, it is essential for th

engineer and the fire protection engineer to jointly provide the needed stand
Mitigation of Progressive Structural Col

Mitigation of Progressive Structural Col

• Building codes lack explicit structural integrity provisi

mitigate progressive collapse. 

• Federal agencies have developed guidelines to mitigate pr

collapse and routinely incorporate such requirements in thconstruction of new federal buildings. 

• The United Kingdom incorporates such code requirements 

buildings. 

• New York City adopted by rule in 1973 a requirement f

buildings to resist progressive collapse under extreme loads. The rules, which were adopted after the WTC towere built but before WTC 7 was built, applied specificbuildings that used precast concrete wall panels and nother types of buildings. 
Structural Integrity of Means of Egress Structural Integrity of Means of Egress

• Building codes lack minimum structural integrity provisions for the means o

(stairwells and elevator shafts) in the building core that are critical to life safe

• In most tall buildings the core is designed to be part of the vertical gravity load carr

the structure. However, in many of those buildings, especially in regions where ea

not dominant, the core may not be part of the lateral load carrying system of the stthe core may be designed to carry only vertical gravity loads with no capacity to reloads, i.e., overturning moment and shear loads. In such situations, the structural prefer the use of partition walls over structural walls in the core area to reduce buil

• The decision to have the core carry a specified fraction of the lateral design loads o

of a dual system to carry lateral loads, each of which would enhance the structural core if structural walls were used, is left to the discretion of the structural engineer. 

• Alternatively, stairway/elevator cores built with concrete or reinforced concrete bloc

not part of the lateral load carrying system, may be able to provide sufficient struct

they meet, for example, ASTM E1996-03, or other more appropriate tests for impa

• In the case of the WTC towers, the core had 2 h fire-rated partition walls with little 

integrity, and the core framing was required to carry only gravity loads. Had there minimum structural integrity requirement to satisfy normal building and fire 

considerations, it is conceivable that the damage to stairways in the WTC towespecially above the floors of impact, may have been less extensive.
Standards for Estimating Design Wind L

Standards for Estimating Design Wind L

• Standards and code provisions do not exist for conducting wind tun

for the methods used in practice to estimate design wind loads from 

• Building codes allow the determination of wind pressures from wind tunn

in design. Such tests are frequently used in the design of tall buildings. 

• Results of two sets of wind tunnel tests conducted for the WTC tow

by independent commercial laboratories as part of insurance litigat

voluntarily provided to NIST by the parties to the litigation, show lardifferences, of as much as about 40 percent, in resultant forces on tstructures, i.e., overturning moments and base shears.

• Independent reviews by a leading engineering design firm contracte

and a NIST expert on wind effects on structures indicated that the documentation of the test results did not provide sufficient basis to major differences.

• Wind loads were a major governing factor in the design of structural com

made up the frame-tube steel framing system.
Sources of Major Differences in Wind Lo

Sources of Major Differences in Wind Lo

Estimation Methods Used in Current Pra

Estimation Methods Used in Current Pra

• Design wind speed (codes, standards, site-specific e• Hurricane wind profile (whether or not hurricane wind 

are flatter than the profiles for extratropical windstorm

• Estimation of “component” wind effects with a specifi

recurrence interval by integrating wind tunnel data wispeed and direction information (e.g., up-crossing mesector-by-sector method, storm passages approach)

• Estimation of “resultant” wind effects using load comb

methods (e.g., principle of companion loads, companin-time loads)
Standard Fire Standard Fire-Resistance Tests Resistance Tests

• Code provisions with detailed procedures do not exist to analyze an

data from fire resistance tests of other building components and asqualify an untested building element. 

• Based on available data and records, no technical basis was found 

the spray-applied fire resistive material (SFRM) used (two competinwere under evaluation) or its thickness for the large-span open-web of the WTC towers. 

• The assessment of the fireproofing thickness needed to meet the 2 h fire 

requirement for the untested WTC floor system evolved over time:

• In October 1969, the PANYNJ directed the fireproofing contractor to appl

fireproofing to the floor trusses. 

• In 1999, the PANYNJ issued guidelines requiring that fireproofing be upg

for full floors undergoing alterations. 

• Unrelated to the WTC buildings, an International Conference of Building 

Evaluation Service report (ER-1244), re-issued June 1, 2001, using the srecommends a minimum thickness of 2 in. for “unrestrained steel joists” w

concrete” slab.
Standard Fire Standard Fire-Resistance Tests (2) Resistance Tests (2)

• Code provisions are needed to require the conduct of a fire 

test if adequate data do not exist from other building compoassemblies to qualify an untested building element.

• Instead, several alternate methods based on other fire-resistanc

calculations or alternative protection methods are permitted with guidance on detailed procedures to be followed. 

• Both the architect-of-record (in 1966) and the structural-eng

record (in 1975) stated that the fire rating of the floor system WTC towers could not be determined without testing. 

• NIST has not found evidence indicating that such a test was 

to determine the fire rating of the WTC floor system. The PAinformed NIST that there are no such test records in its files
Fire-Resistance Ratings (1) Resistance Ratings (1)

• Use of the “structural frame” approach, in conjunction with the prescript

would have required the floor trusses, the core floor framing, and perimethe WTC towers to be 3 h fire-rated, like the columns for Class 1B constru1968 NYC Building Code. 

• Neither the 1968 edition of the NYC Building Code which was used in the 

WTC towers, nor the 2001 edition of the code, adopted the “structural frarequirement. 

• The “structural frame” approach to fire resistance ratings requires structural me

than columns, that are essential to the stability of the building as a whole to be the same rating as columns. 

• This approach, which appeared in the Uniform Building Code (a model building 

as 1953, was carried into the 2000 International Building Code (one of two curcodes) which states: 

“The structural frame shall be considered to be the columns and the girde

trusses and spandrels having direct connections to the columns and braci

designed to carry gravity loads.” 

• The WTC floor system was essential to the stability of the building as a whole s

lateral stability to the columns and diaphragm action to distribute wind loads to the frame-tube system. 
Fire-Resistance Ratings (2) Resistance Ratings (2)

• A technical basis is needed to establish whether the construction classification an

requirements in modern building codes are risk-consistent with respect to the desiand the consequences of that hazard.

• The fire rating requirements, which were originally developed based on experience with b

about 20 stories in height, have generally decreased over the past 80 years since historicbuildings suggested considerable conservatism in those requirements. 

• For tall buildings, the likely consequences of a given threat to an occupant on the u

more severe than the consequences to an occupant, say, on the first floor. 

• It is not apparent how the current height and area tables in building codes con

technical basis for the progressively increasing risk to an occupant on the up

buildings, that are much greater than about 20 stories in height, where access 

without the availability of firefighter elevators is limited by physiological facto

• The maximum required fire rating in current codes applies to any building more than 

in height. There are no additional categories for buildings above, for example, 40 ststories, where different building classification and fire ratings requirements may be arecognizing factors such as the time required for stairwell evacuation without functio(e.g., due to power failure or major water leakage), the time required for first respon

without functioning elevators, the presence of sky lobbies and/or refuge floors, and l

height of elevator shafts. 

• The 110-story WTC towers, initially classified as Class IA based on the 1938 NYC Buildin

classified as Class 1B before being built to take advantage of the provisions in the 1968 eThis re-classification permitted a reduction of 1 h in the fire rating of the components (coluh and floor framing members from 3 h to 2 h).
Fire-Resistance of Structural Connectio

Resistance of Structural Connectio

• Code provisions are needed to ensure that struc

connections are provided the same degree of fire protection as the more restrictive protection of thconnected elements.

• The provisions that were used for the WTC towers a

7 did not require specification of a fire rating requiremconnections separate from those for the connected e

• It is not clear what the fire rating of the connectio

the WTC towers were when the connecting elemedifferent fire ratings and whether the applied fireachieved that rating. 
Fireproofing: Field Application and Inspe

Fireproofing: Field Application and Inspe

• Rigorous field application and inspection provisions and reg

requirements are needed to assure that the as-built conditiopassive fire protection, such as SFRM, conforms to conditiofire-resistance tests of building components and assemblies

• Provisions are not available to ensure that the as-applied ave

fireproofing thickness and variability (reflecting the quality of is thermally equivalent to the specified minimum fireproofing 

• Requirements are not available for in-service inspections of p

protection during the life of the building. 

• The adequacy of the fireproofing of the WTC towers posed an iss

concern to the PANYNJ over the life of the buildings, and the avaaccepted requirements and procedures for conducting in-service would have provided useful guidance.
Fireproofing: Requirements for In Fireproofing: Requirements for In

-Servic

Servi

Performance Performance

• A technical basis is needed to establish whether the m

mechanical and durability related properties of SFRM sufficient to ensure acceptable in-service performancbuildings. 

• While minimum bond strength requirements exist, the

serviceability requirements for such materials to withtypical shock, impact, vibration, or abrasion effects ov

of a building. 

• There are existing testing standards for determining many 

properties, but the technical basis is insufficient to establis

serviceability requirements. Knowledge of such serviceabrequirements would have assisted in assessing the post-ifireproofing condition of the WTC towers. 
Performance Performance-Based Design for Fire Based Design for Fire-Res

Res

of Structures of Structures

• Structural design does not consider fire as a design condition, as it does the ef

loads, live loads, wind loads, and earthquake loads.

• Current prescriptive code provisions for determining fire resistance of structures—use

of the WTC towers and WTC 7— are based on tests using a standard fire that may b

many simple structures and for comparing the relative performance of structural com

complex structures. 

• A building system with 3 h rated columns and 2 h rated girders and floors could l

3 h or shorter than 2 h depending upon the performance of the structure as a 3-d

system in a real fire. 

• The standard tests cannot be used to evaluate the actual performance (i.e., load 

capacity) in a real fire of the structural component, or the structure as a whole sythe connections between components. 

• Performance-based code provisions and standards are not available for use by 

an alternative to the current prescriptive fire rating approach to:

• evaluate the system performance of tall-building structures under real fire 

• enable risk consistent design with appropriate thickness of passive protec

provided where it is needed on the structure. 

• Standards development organizations, including the American Institute of Steel Cons

initiated development of performance-based provisions to consider fire effects in stru
Design-Basis Fire Scenarios Basis Fire Scenarios

• Detailed procedures are needed to select appropriate design-basis fire scenario

considered in the performance-based design of the sprinkler system, compartmpassive protection of the structure. 

• The standard fire in current prescriptive fire resistance tests is not adequate for use in 

based design. While the NFPA 5000 model building code contains general guidance 

scenarios (the IBC Performance Code contains no such guidance), the details of the to the fire engineer and regulatory official. 

• The three major scenarios that are not considered adequately are: 

• frequent but low severity events (for design of sprinkler system)• moderate but less frequent events (for design of compartmentation)• a maximum credible fire (for design of passive fire protection on the structure). 

• The maximum credible fire scenario for passive protection of structures would assum

sprinkler system is compromised or overwhelmed and that there is no active firefighticonsidered for U.S. Department of Energy facilities. 

• These building-specific representative fire scenarios are similar in concept, though no

approach used in building design where the performance objectives and design-basis are better defined (e.g., a two-level design that includes an operational event with a 1

probability of occurrence in 50 years and a life safety event with a 2 percent probabili

in 50 years). 

• The design-basis fire hazards for the WTC towers are unknown, and it is difficu

the performance of fire protection systems in these buildings under specific fir
Performance Performance-Based Design Tools to Eva

Based Design Tools to Ev

Fire-Resistance of Structures Resistance of Structures

• Validated and verified tools are needed for use in performa

design practice to analyze the dynamics of building fires aeffects on the structural system that would allow engineers evaluate structural performance under alternative fire scenfire protection strategies. 

• Existing tools are either too simplified to adequately capture the 

performance of interest or too complex and computationally demand lack adequate validation. 

• While considerable progress has been made in recent years, s

work remains to be done before adequate tools are availabin routine practice. 

• NIST had to further develop and validate existing tools to invest

fire performance of the WTC towers and WTC 7.
Compartmentation Compartmentation to Mitigate Fire Spre

to Mitigate Fire Spre

• Building fire protection is based on a four-level hierarchical strategy compris

suppression (sprinklers and firefighting), compartmentation, and passive pro

structure. 

• Detectors are typically used to activate fire alarms and notify building o

emergency services. 

• Sprinklers are designed to control small and medium fires and to preve

beyond the typical water supply design area of about 1,500 ft2.

• Compartmentation mitigates the horizontal spread of more severe but l

fires and typically requires fire-rated partitions for areas of about 12,000 

firefighting measures also cover up to about 5,000 ft2 to 7,500 ft2. 

• Passive protection of the structure seeks to ensure that a maximum cre

scenario, with sprinklers compromised or overwhelmed and no active fresults in burnout, not overall building collapse. The intent of building cfor the building to withstand local structural collapse until occupants cathe fire service can complete search and rescue operations. 
Compartmentation Compartmentation to Mitigate Fire Spre

to Mitigate Fire Spre

• The NYC Building Code and PANYNJ practice required partitions to se

spaces from each other and from common spaces such as the corridserved the elevators, stairs and other common spaces in the building cor

• Local Law 5 (1973) required compartmentation of unsprinklered spaces i

office buildings over 100 ft in height “having air-conditioning and/or mechventilation systems that serve more than the floor on which the equipmento be subdivided by 1 hour fire separations into spaces or compartmexceed 7,500 ft2. Floor areas could be increased up to 15,000 ft2 if p

hour fire resistive construction and smoke detectors. 

• Shortly after the adoption of LL 5 (1973), the PANYNJ began to add the 

compartmentation as a part of new tenant layouts as evidenced by sever

alteration contracts at the time. 

• Following the 1975 fire a fire safety consultant report recommended to 

the buildings be retrofit with sprinklers to address possible smoke pr

the PANYNJ realized that this would also obviate the need for compartand permit the unobstructed views for which the buildings were known. Tsprinkler the buildings left the arrangement again with only partitions setenant spaces from each other and from exit access corridors or cospaces in the core, and with shaft enclosures.
Compartmentation Compartmentation to Mitigate Fire Spre

to Mitigate Fire Spre

• Building codes typically require 1 h fire-rated tenant separations but do not im

compartmentation requirements (e.g., 12,000 ft2) for buildings with large open 

mitigate the horizontal spread of fire. This was the case with both the 1968 NYC which did not require sprinklers in occupied spaces on or above the ground floor, anBuilding Code, which requires sprinklers in Group E (Business) buildings over 100 f

• The sprinkler option was chosen for the WTC towers in preference to the compartm

in meeting the subsequent requirements of Local Law 5, adopted by New York City 

• If there was only one tenant on a WTC floor, there would be no horizontal com

requirement. Conversely, if there were a large number of tenants on a WTC flhighly compartmented with separation walls. 

• The fire-affected floors in the WTC towers were mostly open—with a modest n

perimeter offices and conference rooms and an occasional special purpose afloors had two tenants, and those spaces, like the core areas, were partitioned (slab 

• Photographic and videographic evidence confirms that even non-tenant spac

(such as those that divided spaces to provide corner conference rooms) provsubstantial resistance to fire spread in the affected floors. 

• For the duration of about 50 to 100 min prior to collapse of the WTC towers th

were active, the presence of undamaged 1 h fire-rated compartments may hav

mitigating fire spread and consequent thermal weakening of structural compo
Tenant Separation Walls Tenant Separation Walls

• The 1968 NYC Building Code required that tenant spaces be separated “

separations having at least the fire resistance rating prescribed in Table 5case less than 1 hr, and shall continue through any concealed spaces or roof construction above.” 

• The PANYNJ chose to stop tenant (demising) partitions (walls separa

occupied by different tenants) at the bottom of the suspended ceilin10 ft strips of 1 h rated ceiling on either side of the partition (Solomogeneral contractor stated in a letter to the Port Authority “...we have been find any precedent for the fire rated ceiling 10’ on either side of the demis

beyond the one you described from your construction experience on Por

hangers [sic]” (Endler 1969).

• In a code compliance evaluation report written in 1997, it was stated “T

demising partitions, including separations from the public corridor, do not 

meet the requirement of being built to the slab above” (Coty 1997). The areport recommended that: “Generally, this condition has been and will c

remediated as a requirement of new tenant alterations. However, it irecommended that the Port Authority develop and implement a survey prassure that this remediation process occurs as quickly as possible.
Tenant Separation Walls (2) Tenant Separation Walls (2)

• It appears that with few exceptions, nearly all of the fl

upgraded were occupied by a single tenant, and it is nwhether separation walls would have mattered in termconsistency with the 1968 code. 

• The PANYNJ commissioned a due diligence study in 1996 w

indicated that the issue of tenant demising walls not running included some of the corridor separation walls. This was a mrequirement since the corridor walls were required to meet a rating while the demising walls were required to be 1 hour fir

• The tenant alteration guidelines issued in 1998 required that 

partitions have a 1 h fire rating, and the standard details for f

partitions indicated a continuous fire barrier from top of floor 

slab (PANYNJ 1998). There were no requirements in the cothe PANYNJ guidelines for partitions wholly within tenant spa
Sprinkler Systems Sprinkler Systems

• State and local building regulations are needed that require installation of s

existing buildings on a reasonable time schedule, not as an option in lieu of compartmentation.

• Functioning sprinklers can provide significant improvement in safety from most co

fires and can prevent them from becoming large fires. 

• NYC promulgated local laws in 1973 and 1984 to encourage installation of s

new buildings and is now considering a law to require sprinklers in existing 

• The WTC towers were fully sprinklered by 2001, about 30 years after their constru

Sprinklering of the tenant floors in the WTC towers was completed by October 19sprinklering of the sky lobbies was still underway at that time. 

• The sprinkler system in the WTC towers was installed in three phases:

• Phase 1 was completed during initial building construction and included the 

areas. 

• Phase 2 was completed in 1976, consistent with Local Law 5, and included s

corridors, storage rooms, lobbies, and certain tenant spaces. 

• Phase 3 was begun in 1983 and completed in 2001 and resulted in fully spri

buildings.
Sprinkler Systems (2) Sprinkler Systems (2)

• Modern building codes allow a lower fire rating for structural elements when a b

sprinklered. This trade-off provides an economic incentive to encourage installsprinklers. 

• Sprinklers provide better intervention against small and medium fires, fires whic

likely to occur than a WTC disaster, as long as the water supply is not comprom

is redundant technology in place. 

• The required technical basis is not available to establish whether the “spr

trade-off” in current codes adequately considers fire safety risk factors su

• the complementary functions of sprinklers and fire-protected structur

• the different fire scenarios for which each system is designed to prov

and 

• the need for redundancy should one system fail. 

• The British Standards Institution (BSI) has established a group to review a

sprinkler trade-offs contained in their standards. No such formal review hinitiated in the United States.

• Although the classification and fire rating of the WTC towers did not take 

the sprinkler trade-off since such provisions were not contained in the 19Building Code, had such provisions existed, they would have permitted a rating for many WTC building elements. 
Use of Elevators in Emergencies Use of Elevators in Emergencies

• With a few special exceptions, building codes in the United States do not perm

protected elevators for routine emergency access by first responders or as a 

method (after stairwells) for emergency evacuation of building occupants. Th

by emergency responders would additionally mitigate counterflow problems i

• While the United States conducted research on specially protected elevators 

the United Kingdom along with several other countries that typically utilize Brhave required such “firefighter lifts,” located in protected shafts, for a numbe

• Without functioning elevators, emergency responders carrying between 50 to 

gear required about 1.4 minutes to 2 minutes per floor when using the stairs i

• While it is difficult to maintain this pace for more than about the first 20 s

take an emergency responder between 1-1/2 to 2 hours to reach, for exam

floor of a tall building if that pace could be maintained. 

• Such a delay, combined with the resulting fatigue and physical effects on 

responders that were reported on September 11, 2001, would make firefig

rescue efforts difficult even in tall building emergencies not involving a t

• Each of the WTC towers had 106 elevators, and WTC 7 had 38 elevators. By code, 

could not be used for fire service access or occupant egress during an emergency s

not fire-protected, nor were they located in protected shafts. The elevators were eq

normal modernization with fire service recall. All but one of the elevators were dam

WTC tower by the aircraft impacts; though prior to the impact in WTC 2 the elevatorfunctioning and contributed greatly to the much faster initial evacuation rate in WTC 
Selected Findings on Codes and Practic

Selected Findings on Codes and Practic

• The 1968 New York City Building Code was comparable to other co

era (1964 New York State, 1967 Chicago, and 1965 BOCA/BBC nacode).

• Documents suggest that the WTC towers generally were design

maintained consistent with the requirements of the 1968 New YBuilding Code. Areas of concern included fireproofing of WTC system, height of tenant separation walls, and egress requiremassembly use space for the Windows of the World in WTC 1 anWorld observation deck in WTC 2.

• The PANYNJ developed and periodically updated a Tenant Alteratio

Manual that contained the technical criteria, standards, and requiremguide modifications and alterations over the life of the buildings.

• The PANYNJ developed and implemented a formal facility condition 

structural integrity inspection program. The buildings generally were in good condition. Frequent recommendations were made to repair missing fireproofing at different locations, particularly in elevator sha

below the plaza level.
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