Statement of
William Jeffrey
Director
National
Technology Administration
On
The Building and Fire Safety Investigation into the
Before the
House Committee on Science
Mr. Chairman, and members of the Committee, I am William Jeffrey,
Director of the National Institute of Standards and Technology. I am pleased to appear today and testify on
the building and fire safety investigation of the
NIST announced its building and fire safety investigation
of the World Trade Center (WTC) disaster on
The goals of the investigation of the WTC disaster were:
· To investigate the building construction, the materials used, and the technical conditions that contributed to the outcome of the WTC disaster after terrorists flew large jet-fuel laden commercial airliners into the WTC towers.
· To serve as the basis for:
— Improvements in the way buildings are designed, constructed, maintained, and used;
— Improved tools and guidance for industry and safety officials;
— Recommended revisions to current codes, standards, and practices; and
— Improved public safety
The specific objectives were:
1. Determine why and how WTC 1 and WTC 2 collapsed following the initial impacts of the aircraft and why and how WTC 7 collapsed;
2. Determine why the injuries and fatalities were so high or low depending on location, including all technical aspects of fire protection, occupant behavior, evacuation, and emergency response; and
3. Determine what procedures and practices were used in the design, construction, operation, and maintenance of WTC 1, 2, and 7.
4. Identify, as specifically as possible, areas in current building and fire codes, standards, and practices that warrant revision
APPROACH
To meet these goals, NIST complemented its in-house expertise with an array of specialists in key technical areas. In all, over 200 staff contributed to the Investigation. NIST and its contractors compiled and reviewed tens of thousand of pages of documents; conducted interviews with over a thousand people who had been on the scene or who had been involved with the design, construction, and maintenance of the WTC; analyzed 236 pieces of steel that were obtained from the wreckage; performed laboratory tests, measured material properties, and performed computer simulations of the sequence of events that happened from the instant of aircraft impact to the initiation of collapse for each tower.
Cooperation in obtaining the resource materials and in interpreting the results came from a large number of individuals and organizations, including The Port Authority of New York and New Jersey and its contractors and consultants, Silverstein Properties and its contractors and consultants, the City of New York and its departments, the manufacturers and fabricators of the building components, the companies that insured the WTC towers, the building tenants, the aircraft manufacturers, the airlines, and the media.
The scarcity of physical evidence that is typically available in place for reconstruction of a disaster led to the following approach:
· Accumulation of copious photographic and video material. With the assistance of the media, public agencies and individual photographers, NIST acquired and organized nearly 7,000 segments of video footage, totaling in excess of 150 hours and nearly 7,000 photographs representing at least 185 photographers. This guided the Investigation Team’s efforts to determine the condition of the buildings following the aircraft impact, the evolution of the fires, and the subsequent deterioration of the structure.
·
Establishment of the baseline performance of the
WTC towers, i.e., estimating the expected performance of the towers under
normal design loads and conditions. The
baseline performance analysis also helped to estimate the ability of the towers
to withstand the unexpected events of
·
Conduct of simulations of the behavior of each
tower on
1. The aircraft impact into the tower, the resulting distribution of aviation fuel, and the damage to the structure, partitions, thermal insulation materials, and building contents.
2. The evolution of multi-floor fires.
3. The heating and consequent weakening of the structural elements by the fires.
4. The response of the damaged and heated building structure, and the progression of structural component failures leading to the initiation of the collapse of the towers.
For such complex structures and complex thermal and structural processes, each of these steps stretched the state of the technology and tested the limits of software tools and computer hardware. For example, the investigators advanced the state-of-the-art in the measurement of construction material properties and in structural finite element modeling. New modeling capability was developed for the mapping of fire-generated environmental temperatures onto the building structural components.
The output of the four-step simulations was subject to uncertainties in the as-built condition of the towers, the interior layout and furnishings, the aircraft impact, the internal damage to the towers (especially the thermal insulation for fire protection of the structural steel, which is colloquially referred to as fireproofing), the redistribution of the combustibles, and the response of the building structural components to the heat from the fires. To increase confidence in the simulation results, NIST used the visual evidence, eyewitness accounts from inside and outside the buildings, laboratory tests involving large fires and the heating of structural components, and formal statistical methods to identify influential parameters and quantify the variability in analysis results.
· Combination of the knowledge gained into probable collapse sequences for each tower,2 the identification of factors that contributed to the collapse, and a list of factors that could have improved building performance or otherwise mitigated the loss of life.
· Compilation of a list of findings that respond to the first three objectives and a list of recommendations that responds to the fourth objective.
Summary of findings
Objective 1: Determine why and how WTC 1 and WTC 2
collapsed following the initial impacts of the aircraft.
· The two aircraft hit the towers at high speed and did considerable damage to principal structural components (core columns, floors, and perimeter columns) that were directly impacted by the aircraft or associated debris. However, the towers withstood the impacts and would have remained standing were it not for the dislodged insulation (fireproofing) and the subsequent multi-floor fires. The robustness of the perimeter frame-tube system and the large size of the buildings helped the towers withstand the impact. The structural system redistributed loads from places of aircraft impact, avoiding larger scale damage upon impact. The hat truss, a feature atop each tower which was intended to support a television antenna, prevented earlier collapse of the building core. In each tower, a different combination of impact damage and heat-weakened structural components contributed to the abrupt structural collapse.
· In WTC 1, the fires weakened the core columns and caused the floors on the south side of the building to sag. The floors pulled the heated south perimeter columns inward, reducing their capacity to support the building above. Their neighboring columns quickly became overloaded as columns on the south wall buckled. The top section of the building tilted to the south and began its descent. The time from aircraft impact to collapse initiation was largely determined by how long it took for the fires to weaken the building core and to reach the south side of the building and weaken the perimeter columns and floors.
· In WTC 2, the core was damaged severely at the southeast corner and was restrained by the east and south walls via the hat truss and the floors. The steady burning fires on the east side of the building caused the floors there to sag. The floors pulled the heated east perimeter columns inward, reducing their capacity to support the building above. Their neighboring columns quickly became overloaded as columns on the east wall buckled. The top section of the building tilted to the east and to the south and began its descent. The time from aircraft impact to collapse initiation was largely determined by the time for the fires to weaken the perimeter columns and floor assemblies on the east and the south sides of the building. WTC 2 collapsed more quickly than WTC 1 because there was more aircraft damage to the building core, including one of the heavily loaded corner columns, and there were early and persistent fires on the east side of the building, where the aircraft had extensively dislodged insulation from the structural steel.
·
The WTC towers likely would not have collapsed
under the combined effects of aircraft impact damage and the extensive,
multi-floor fires that were encountered on
·
NIST found no corroborating evidence for
alternative hypotheses suggesting that the WTC towers were brought down by
controlled demolition using explosives planted prior to
Objective 2: Determine why the injuries and fatalities
were so high or low depending on location, including all technical aspects of
fire protection, occupant behavior, evacuation, and emergency response.
· Approximately 87 percent of the estimated 17,400 occupants of the towers, and 99 percent of those located below the impact floors, evacuated successfully. In WTC 1, where the aircraft destroyed all escape routes, 1,355 people were trapped in the upper floors when the building collapsed. One hundred seven people who were below the impact floors did not survive. Since the flow of people from the building had slowed considerably 20 min before the tower collapsed, the stairwell capacity was adequate to evacuate the occupants on that morning.
· In WTC 2, before the second aircraft strike, about 3,000 people got low enough in the building to escape by a combination of self-evacuation and use of elevators. The aircraft destroyed the operation of the elevators and the use of two of the three stairways. Eighteen people from above the impact zone found a passage through the damaged third stairway (Stairwell A) and escaped. The other 619 people in or above the impact zone perished. Eleven people who were below the impact floors did not survive. As in WTC 1, shortly before collapse, the flow of people from the building had slowed considerably, indicating that the stairwell capacity was adequate that morning.
· About 6 percent of the survivors described themselves as mobility impaired, with recent injury and chronic illness being the most common causes; few, however, required a wheelchair. Among the 118 decedents below the aircraft impact floors, investigators identified seven who were mobility impaired, but were unable to determine the mobility capability of the remaining 111.
· A principal factor limiting the loss of life was that the buildings were only one-third to one-half occupied at the time of the attacks. NIST estimated that if the towers had been fully occupied with 20,000 occupants each, it would have taken just over 3 hours to evacuate the buildings and about 14,000 people might have perished because the stairwell capacity would not have been sufficient to evacuate that many people in the available time. Egress capacity required by current building codes is determined by single floor calculations that are independent of building height and does not consider the time for full building evacuation.
·
Due to the presence of assembly use spaces at
the top of each tower (Windows on the World restaurant complex in WTC 1 and the
Top of the Deck observation deck in WTC 2) that were designed to accommodate
over 1,000 occupants per floor, the New York City Building Code would have
required a minimum of four independent means of egress (stairs), one more than
the three that were available in the buildings.
Given the low occupancy level on
· Evacuation was assisted by participation in fire drills within the previous year by two-thirds of survivors and perhaps hindered by a Local Law that prevented employers from requiring occupants to practice using the stairways. The stairways were not easily navigated in some locations due to their design, which included “transfer hallways,” where evacuees had to traverse from one stairway to another location where the stairs continued. Additionally, many occupants were unprepared for the physical challenge of full building evacuation.
· The functional integrity and survivability of the stairwells was affected by the separation of the stairwells and the structural integrity of stairwell enclosures. In the impact region of WTC 1, the stairwell separation was the smallest over the building height—clustered well within the building core—and all stairwells were destroyed by the aircraft impact. By contrast, the separation of stairwells in the impact region of WTC 2 was the largest over the building height—located along different boundaries of the building core—and one of three stairwells remained marginally passable after the aircraft impact. The shaft enclosures were fire rated but were not required to have structural integrity under typical accidental loads: there were numerous reports of stairwells obstructed by fallen debris from damaged enclosures.
· The active fire safety systems (sprinklers, smoke purge, fire alarms, and emergency occupant communications) were designed to meet or exceed current practice. However, with the exception of the evacuation announcements, they played no role in the safety of life on September 11 because the water supplies to the sprinklers were damaged by the aircraft impact. The smoke purge systems, operated under the direction of the fire department after fires, were not turned on, but they also would have been ineffective due to aircraft damage. The violence of the aircraft impact served as its own alarm. In WTC 2, contradictory public address announcements contributed to occupant confusion and some delay in occupants beginning to evacuate.
· For the approximately 1,000 emergency responders on the scene, this was the largest disaster they had even seen. Despite attempts by the responding agencies to work together and perform their own tasks, the extent of the incident was well beyond their capabilities. Communications were erratic due to the high number of calls and the inadequate performance of some of the gear. Even so, there was no way to digest, test for accuracy, and disseminate the vast amount of information being received. Their jobs were complicated by the loss of command centers in WTC 7 and then in the towers after WTC 2 collapsed. With nearly all elevator service disrupted and progress up the stairs taking about 2 min per floor, it would have taken hours for the responders to reach their destinations, assist survivors, and escape had the towers not collapsed.
Objective 3: Determine what procedures and practices were
used in the design, construction, operation, and maintenance of WTC 1 and WTC
2.
·
Because of The Port Authority's establishment
under a clause of the United States Constitution, its buildings were not
subject to any state or local building regulations. The buildings were unlike
any others previously built, both in their height and in their innovative
structural features. Nevertheless, the
actual design and approval process produced two buildings that generally were
consistent with nearly all of the provisions of the New York City Building Code
and other building codes of that time that were reviewed by NIST. The loads for which the buildings were
designed exceeded the
·
For the floor systems, the fire rating and
insulation thickness used on the floor trusses, which together with the
concrete slab served as the main source of support for the floors, were of
concern from the time of initial construction.
NIST found no technical basis or test data on which the thermal
protection of the steel was based. On
· Based on four standard fire resistance tests that were conducted under a range of insulation and test conditions, NIST found the fire rating of the floor system to vary between 3/4 hour and 2 hours; in all cases, the floors continued to support the full design load without collapse for over 2 hours.
· The wind loads used for the WTC towers, which governed the structural design of the external columns and provided the baseline capacity of the structures to withstand abnormal events such as major fires or impact damage, significantly exceeded the requirements of the New York City Building Code and other building codes of the day that were reviewed by NIST. Two sets of wind load estimates for the towers obtained by independent commercial consultants in 2002, however, differed by as much as 40 percent. These estimates were based on wind tunnel tests conducted as part of insurance litigation unrelated to the Investigation.
RECOMMENDATIONS
The tragic consequences of the
While there were unique aspects to the design of the WTC towers and the terrorist attacks of September 11, 2001, NIST has compiled a list of recommendations to improve the safety of tall buildings, occupants, and emergency responders based on its investigation of the procedures and practices that were used for the WTC towers; these procedures and practices are commonly used in the design, construction, operation, and maintenance of buildings under normal conditions. Public officials and building owners will need to determine appropriate performance requirements for those tall buildings, and selected other buildings, that are at higher risk due to their iconic status, critical function, or design.
The topics of the recommendations in eight groups are
listed in Table 1. A complete listing of
the 30 recommendations is provided in Appendix A. The
ordering does not reflect any priority.
The eight major
groups of recommendations are:
· Increased Structural Integrity: The standards for estimating the load effects of potential hazards (e.g., progressive collapse, wind) and the design of structural systems to mitigate the effects of those hazards should be improved to enhance structural integrity.
· Enhanced Fire Endurance of Structures: The procedures and practices used to ensure the fire endurance of structures should be enhanced by improving the technical basis for construction classifications and fire resistance ratings, improving the technical basis for standard fire resistance testing methods, use of the “structural frame” approach to fire resistance ratings, and developing in-service performance requirements and conformance criteria for sprayed fire-resistive material.
· New Methods for Fire Resistant Design of Structures: The procedures and practices used in the fire resistant design of structures should be enhanced by requiring an objective that uncontrolled fires result in burnout without local or global collapse. Performance-based methods are an alternative to prescriptive design methods. This effort should include the development and evaluation of new fire resistive coating materials and technologies and evaluation of the fire performance of conventional and high-performance structural materials.
· Improved Active Fire Protection: Active fire protection systems (i.e., sprinklers, standpipes/ hoses, fire alarms, and smoke management systems) should be enhanced through improvements to design, performance, reliability, and redundancy of such systems.
· Improved Building Evacuation: Building evacuation should be improved to include system designs that facilitate safe and rapid egress, methods for ensuring clear and timely emergency communications to occupants, better occupant preparedness for evacuation during emergencies, and incorporation of appropriate egress technologies.
· Improved Emergency Response: Technologies and procedures for emergency response should be improved to enable better access to buildings, response operations, emergency communications, and command and control in large-scale emergencies.
· Improved Procedures and Practices: The procedures and practices used in the design, construction, maintenance, and operation of buildings should be improved to include encouraging code compliance by nongovernmental and quasi-governmental entities, adoption and application of egress and sprinkler requirements in codes for existing buildings, and retention and availability of building documents over the life of a building.
· Education and Training: The professional skills of building and fire safety professionals should be upgraded though a national education and training effort for fire protection engineers, structural engineers, architects, regulatory personnel, and emergency responders.
The recommendations call for action by specific entities regarding standards, codes and regulations, their adoption and enforcement, professional practices, education, and training; and research and development. Only when each of the entities carries out its role will the implementation of a recommendation be effective.
The recommendations do not prescribe specific systems, materials, or technologies. Instead, NIST encourages competition among alternatives that can meet performance requirements. The recommendations also do not prescribe specific threshold levels; NIST believes that this responsibility properly falls within the purview of the public policy setting process, in which the standards and codes development process plays a key role.
NIST believes the recommendations are realistic and achievable within a reasonable period of time. Only a few of the recommendations call for new requirements in standards and codes. Most of the recommendations deal with improving an existing standard or code requirement, establishing a standard for an existing practice without one, establishing the technical basis for an existing requirement, making a current requirement risk-consistent, adopting or enforcing a current requirement, or establishing a performance-based alternative to a current prescriptive requirement.
NEXT STEPS
We have strongly urged that immediate and serious consideration be given to these recommendations by the building and fire safety communities in order to achieve appropriate improvements in the way buildings are designed, constructed, maintained, and used and in evacuation and emergency response procedures—with the goal of making buildings, occupants, and first responders safer in future emergencies.
We are also strongly urging building owners and public officials to (1) evaluate the safety implications of these recommendations to their existing inventory of buildings and (2) take the steps necessary to mitigate any unwarranted risks without waiting for changes to occur in codes, standards, and practices.
We are urging state
and local agencies to rigorously enforce building codes and standards since
such enforcement is critical to ensure the expected level of safety. Unless they are complied with, the best codes and standards cannot protect occupants,
emergency responders, or buildings.
I have assigned top
priority for NIST staff to work vigorously with the building and fire safety
communities to assure that there is a complete understanding of the
recommendations and to provide needed technical assistance in getting them
implemented. We have identified specific
codes, standards, and practices affected by each of the recommendations in its
summary report for the WTC towers and already begun to reach out to the
responsible organizations to pave the way for a timely, expedited consideration
of the recommendations. Toward this end,
we held a conference
We have also has awarded a contract to the
National Institute of Building Sciences (NIBS) to convene a panel of building
code experts to turn appropriate recommendations into code language suitable
for submission of code change proposals to the two national model code
developers.
In addition, we will
implement a web-based system so that the public can track progress on
implementing the recommendations. The
web site will list each of the recommendations, the specific organization or
organizations (e.g., standards and code developers, professional groups, state
and local authorities) responsible for its implementation, the status of its
implementation by organization, and the plans or work in progress to implement
the recommendations.
We are releasing
the final versions of the 43 reports on its investigation of the WTC towers,
totaling some 10,000 pages, today. Our current
plans are to release next spring an additional five reports as drafts for pubic
comment on the investigation of WTC 7.
Mr. Chairman, I
want to thank you and the Subcommittee again for allowing me to testify today
about NIST’s building and fire safety investigation of the
Table 1.
Topics of NIST recommendations for improved public safety in tall and
high-risk buildings.
Recommendation Group |
Recommendation Topic |
Responsible Community |
Application |
Relation to 9/11 Outcome |
||||||
Practices |
Standards, Codes, Regulations |
Adoption & Enforcement |
R&D/Further Study |
Education & Training |
All Tall Buildings |
Selected Other High-Risk Buildings |
Relateda |
Unrelatedb |
||
Increased Structural Integrity |
Prevention of progressive
collapse and failure analysis of complex systems |
ü |
ü |
ü |
ü |
ü |
ü |
ü |
ü |
|
Estimation of wind loads
and their effects on tall buildings |
ü |
ü |
|
ü |
|
ü |
ü |
|
ü |
|
Allowable tall buildings
sway |
ü |
ü |
|
ü |
|
ü |
|
|
ü |
|
Enhanced Fire Endurance of Structures |
Fire resistance rating
requirements and construction classification |
ü |
ü |
|
ü |
|
ü |
|
|
ü |
Fire resistance testing of
building components and extrapolation of test data to qualify untested
building components |
|
ü |
|
ü |
|
ü |
|
|
ü |
|
In-service performance
requirements and inspection procedures for sprayed fire‑resistive
material (SFRM or spray-on fireproofing) |
ü |
ü |
ü |
ü |
|
ü |
|
|
ü |
|
“Structural frame”
approach (structural members connected to columns carry the higher fire
resistance rating of the columns) |
|
ü |
ü |
|
ü |
ü |
ü |
|
ü |
|
New Methods for Fire Resistant Design of Structures |
Burnout without partial or
global (total) structural collapse in uncontrolled building fires |
ü |
ü |
ü |
ü |
ü |
ü |
ü |
ü |
|
Performance-based design
and retrofit of structures to resist fires |
ü |
ü |
|
ü |
ü |
ü |
ü |
|
ü |
|
New fire-resistive coating
materials, systems, and technologies |
ü |
ü |
|
ü |
|
ü |
ü |
ü |
|
|
Evaluation of high
performance structural materials under conditions expected in building fires |
ü |
|
|
ü |
|
ü |
ü |
|
ü |
|
Improved Active Fire Protection |
Performance and redundancy
of active fire protection systems to accommodate the greater risks associated
with tall buildings |
ü |
ü |
|
ü |
|
ü |
ü |
ü |
|
Advanced fire alarm and
communication systems that provide continuous, reliable, and accurate
information on life safety conditions to manage the evacuation process. |
|
ü |
|
ü |
|
ü |
|
ü |
|
|
Advanced fire/emergency
control panels with more reliable information from the active fire protection
systems to provide tactical decision aids |
|
ü |
|
ü |
|
ü |
ü |
ü |
|
|
Improved transmission to
emergency responders, and off-site or black box storage, of information from
building monitoring systems |
ü |
ü |
|
ü |
|
ü |
ü |
ü |
ü |
|
Improved Building Evacuation |
Public
education and training campaigns to improve building occupants’ preparedness
for evacuation |
ü |
ü |
|
ü |
ü |
ü |
|
ü |
ü |
Tall building
design for timely full building emergency evacuation of occupants |
ü |
ü |
|
ü |
ü |
ü |
ü |
ü |
ü |
|
Design of
occupant-friendly evacuation paths that maintain functionality in foreseeable
emergencies |
ü |
ü |
|
|
|
ü |
|
ü |
|
|
Planning for communication
of accurate emergency
information to building occupants |
ü |
ü |
|
|
ü |
ü |
ü |
ü |
|
|
Evaluation of alternative
evacuation technologies, to allow all occupants equal opportunity for
evacuation and to facilitate emergency response access |
ü |
ü |
|
ü |
|
ü |
ü |
ü |
|
|
Improved Emergency Response |
Fire-protected and structurally
hardened elevators |
ü |
ü |
|
ü |
|
ü |
|
ü |
|
Effective emergency
communications systems for large-scale emergencies |
ü |
ü |
ü |
ü |
ü |
ü |
|
ü |
|
|
Enhanced gathering,
processing, and delivering of critical information to emergency responders |
ü |
ü |
ü |
ü |
ü |
ü |
ü |
ü |
|
|
Effective and
uninterrupted operation of the command and control system for large-scale
building emergencies |
ü |
ü |
ü |
ü |
ü |
ü |
|
ü |
|
|
Improved Procedures and Practices |
Provision of
code-equivalent level of safety and certification of as-designed and as-built
safety by nongovernmental and quasi-governmental entities |
ü |
ü |
ü |
|
|
ü |
ü |
|
ü |
Egress and sprinkler
requirements for existing buildings |
ü |
|
ü |
|
|
ü |
ü |
|
ü |
|
Retention and off-site
storage of design, construction, maintenance, and modification documents over
the entire life of the building; and availability of relevant building
information for use by responders in emergencies |
ü |
ü |
ü |
|
|
ü |
ü |
ü |
|
|
Design professional
responsibility for innovative or unusual structural and fire safety systems |
ü |
ü |
|
|
ü |
ü |
ü |
ü |
|
|
Education and Training |
Professional cross
training of fire protection engineers, architects, structural engineers, code
enforcement officials, and fire service personnel. |
ü |
ü |
|
|
ü |
ü |
ü |
ü |
|
Training in computational
fire dynamics and thermostructural analysis |
ü |
|
|
|
ü |
ü |
ü |
|
ü |
a. If in place, could have changed the outcome on
b. Would not have changed the outcome, yet is an important building and fire safety issue that was identified during the course of the Investigation.
The standards for estimating
the load effects of potential hazards (e.g., progressive collapse, wind) and
the design of structural systems to mitigate the effects of those hazards should
be improved to enhance structural integrity.
Recommendation 1. NIST recommends that: (1) progressive
collapse be prevented in buildings through the development and nationwide
adoption of consensus standards and code provisions, along with the tools and
guidelines needed for their use in practice; and (2) a standard methodology be
developed—supported by analytical design tools and practical design guidance—to
reliably predict the potential for complex
failures in structural systems subjected to multiple hazards.
Recommendation
2. NIST recommends that nationally accepted
performance standards be developed for: (1) conducting wind tunnel testing of prototype structures based on sound
technical methods that result in repeatable and reproducible results among
testing laboratories; and (2) estimating
wind loads and their effects on tall buildings for use in design, based on
wind tunnel testing data and directional wind speed data.
Recommendation 3. NIST
recommends that an appropriate criterion be developed and implemented to
enhance the performance of tall buildings by limiting how much they sway under lateral load design conditions
(e.g., winds and earthquakes).
The procedures and practices
used to ensure the fire endurance of structures be enhanced by improving the
technical basis for construction classifications and fire resistance ratings,
improving the technical basis for standard fire resistance testing methods, use
of the “structural frame” approach to fire resistance ratings, and developing
in-service performance requirements and conformance criteria for sprayed
fire-resistive materials.
Recommendation 4. NIST
recommends evaluating, and where needed improving, the technical basis for
determining appropriate construction classification and fire rating
requirements (especially for tall
buildings)—and making related code changes now as much as possible—by
explicitly considering factors including:
·
timely
access by emergency responders and full
evacuation of occupants, or the time required for burnout without local
collapse;
·
the
extent to which redundancy in active
fire protection (sprinkler and standpipe, fire alarm, and smoke
management) systems should be credited
for occupant life safety;
·
the need
for redundancy in fire protection
systems that are critical to structural integrity;
·
the
ability of the structure and local floor systems to withstand a maximum credible fire scenario without
collapse, recognizing that sprinklers could be compromised, not
operational, or non-existent;
·
compartmentation requirements (e.g., 12,000 ft2 ([1]))
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;
·
the effect of spaces
containing unusually large fuel concentrations for the expected
occupancy of the building; and
·
the extent to which fire
control systems, including suppression by automatic or manual means, should be
credited as part of the prevention of fire spread.
Recommendation 5. NIST
recommends that the technical basis for the century-old standard for fire resistance testing of components, assemblies, and
systems be improved through a national effort.
Necessary guidance also should be developed for extrapolating the
results of tested assemblies to prototypical building systems. A key step in fulfilling this recommendation
is to establish a capability for studying and testing the components,
assemblies, and systems under realistic fire and load conditions.
Recommendation
6. NIST recommends the development of criteria,
test methods, and standards: (1) for the in-service
performance of sprayed fire-resistive materials (SFRM, also commonly
referred to as fireproofing or insulation) used to protect structural
components; and (2) to ensure that these materials, as-installed, conform to conditions in tests used to establish the
fire resistance rating of components, assemblies, and systems.
Recommendation 7. NIST
recommends the adoption and use of the “structural frame” approach to fire
resistance ratings. This approach requires that structural
members—such as girders, beams, trusses and spandrels having direct connection
to the columns, and bracing members designed to carry gravity loads—be fire protected
to the same fire resistance rating as columns.
The procedures and practices
used in the fire resistant design of structures should be enhanced by requiring
an objective that uncontrolled fires result in burnout without partial or
global (total) collapse.
Performance-based methods are an alternative to prescriptive design
methods. This effort should include the
development and evaluation of new fire-resistive coating materials and technologies
and evaluation of the fire performance of conventional and high-performance
structural materials.
Recommendation 8. NIST
recommends that the fire resistance of structures be enhanced by requiring a
performance objective that uncontrolled building fires result in burnout
without partial or global (total) collapse.
Recommendation 9. NIST
recommends the development of: (1) performance-based standards and code
provisions, as an alternative to current prescriptive design methods, to enable
the design and retrofit of structures to resist real building fire conditions,
including their ability to achieve the performance objective of burnout without
structural or local floor collapse: and (2) the tools, guidelines, and
test methods necessary to evaluate the fire performance of the structure as a
whole system.
Recommendation 10. NIST
recommends the development and evaluation of new fire-resistive coating materials, systems, and technologies
with significantly enhanced performance and durability to provide protection
following major events.
Recommendation 11. NIST recommends that the performance and
suitability of advanced structural steel, reinforced and pre-stressed concrete,
and other high-performance material systems be evaluated for use under conditions
expected in building fires.
Active fire protection systems
(i.e., sprinklers, standpipes/hoses, fire alarms, and smoke management systems)
should be enhanced through improvements to design, performance, reliability,
and redundancy of such systems.
Recommendation 12. NIST
recommends that the performance and possibly the redundancy of active fire
protection systems (sprinklers, standpipes/hoses, fire alarms, and smoke
management systems) in buildings be enhanced to accommodate the greater risks associated with increasing
building height and population, increased use of open spaces, high-risk
building activities, fire department response limits, transient fuel loads, and
higher threat profile.
Recommendation 13. NIST
recommends that fire alarm and communications systems in buildings be developed
to provide continuous, reliable, and accurate information on the status of life
safety conditions at a level of detail sufficient to manage the evacuation process in building fire emergencies; all
communication and control paths in buildings need to be designed and installed
to have the same resistance to failure and increased survivability above that
specified in present standards.
Recommendation 14. NIST
recommends that control panels at fire/emergency command stations in buildings
be adapted to accept and interpret a larger quantity of more reliable
information from the active fire protection systems that provide tactical decision aids to fireground commanders, including
water flow rates from pressure and flow measurement devices, and that standards
for their performance be developed.
Recommendation 15. NIST
recommends that systems be developed and implemented for: (1) real-time off-site secure transmission of valuable
information from fire alarm and other monitored building systems for use by
emergency responders, at any location, to enhance situational awareness and
response decisions and maintain safe and efficient operations; and (2)
preservation of that information either off-site or in a black box that will survive a fire or other building failure for
purposes of subsequent investigations and analysis. Standards for the performance of such systems
should be developed, and their use should be required.
Building evacuation should be
improved to include system designs that facilitate safe and rapid egress,
methods for ensuring clear and timely emergency communications to occupants,
better occupant preparedness regarding their roles and duties for evacuation
during emergencies, and incorporation of appropriate egress technologies.
Recommendation
16. NIST recommends that public agencies,
non-profit organizations concerned with building and fire safety, and building
owners and managers develop and carry out public
education and training campaigns, jointly and on a nationwide scale, to
improve building occupants’ preparedness for evacuation in case of building
emergencies.
Recommendation 17. NIST
recommends that tall buildings be designed to accommodate timely full building evacuation of occupants due to
building-specific or large-scale emergencies such as widespread power outages,
major earthquakes, tornadoes, hurricanes without sufficient advanced warning,
fires, explosions, and terrorist attack.
Building size, population, function, and iconic status should be taken
into account in designing the egress system.
Stairwell capacity and stair discharge door width should be adequate to
accommodate counterflow due to emergency access by responders.
Recommendation 18. NIST
recommends that egress systems be designed: (1) to maximize remoteness of egress components (i.e., stairs, elevators,
exits) without negatively impacting the average travel distance; (2) to
maintain their functional integrity and
survivability under foreseeable building-specific or large-scale
emergencies; and (3) with consistent layouts, standard signage, and guidance so
that systems become intuitive and obvious
to building occupants during evacuations.
Recommendation 19. NIST recommends that building owners,
managers, and emergency responders develop a joint plan and take steps to ensure that accurate emergency
information is communicated
in a timely manner to enhance the situational awareness of building occupants
and emergency responders affected by an event.
This should be accomplished through better coordination of information
among different emergency responder groups, efficient sharing of that
information among building occupants and emergency responders, more robust
design of emergency public address systems, improved emergency responder
communication systems, and use of the Emergency Broadcast System (now known as
the Integrated Public Alert and Warning System) and Community Emergency Alert
Networks.
Recommendation
20. NIST recommends that the full range of
current and next generation evacuation
technologies should be evaluated for future use, including
protected/hardened elevators, exterior escape devices, and stairwell descent
devices, which may allow all occupants an equal opportunity for evacuation and
facilitate emergency response access.
Technologies and procedures for emergency
response should be improved to enable better access to buildings, response operations,
emergency communications, and command and control in large-scale emergencies.
Recommendation 21. NIST recommends the installation of fire-protected and structurally hardened elevators to improve emergency response activities in tall buildings by providing timely emergency access to responders and allowing evacuation of mobility impaired building occupants. Such elevators should be installed for exclusive use by emergency responders during emergencies. In tall buildings, consideration also should be given to installing such elevators for use by all occupants. The use of elevators for these purposes will require additional operating procedures and protocols, as well as a requirement for release of elevator door restrictors by emergency response personnel.
Recommendation 22. NIST recommends the installation, inspection, and testing of emergency communications systems, radio communications, and associated operating protocols to ensure that the systems and protocols: (1) are effective for large-scale emergencies in buildings with challenging radio frequency propagation environments; and (2) can be used to identify, locate, and track emergency responders within indoor building environments and in the field. The federal government should coordinate its efforts that address this need within the framework provided by the SAFECOM program of the Department of Homeland Security.
Recommendation 23. NIST
recommends the establishment and implementation of detailed procedures and
methods for gathering, processing, and delivering critical information through integration of relevant voice, video,
graphical, and written data to enhance the situational awareness of all
emergency responders. An information intelligence sector[2]
should be established to coordinate the effort for each incident.
Recommendation 24. NIST recommends the establishment and implementation of codes and protocols for ensuring effective and uninterrupted operation of the command and control system for large-scale building emergencies.
The procedures and practices
used in the design, construction, maintenance, and operation of buildings
should be improved to include encouraging code compliance by nongovernmental
and quasi-governmental entities, adoption and application of egress and
sprinkler requirements in codes for existing buildings, and retention and
availability of building documents over the life of a building.
Recommendation
25. Nongovernmental and quasi-governmental entities that own or lease buildings—and
are not subject to building and fire safety code requirements of any
governmental jurisdiction—should provide a level of safety that equals or exceeds the level of safety
that would be provided by strict compliance with the code requirements of an
appropriate governmental jurisdiction.
To gain broad public confidence in the safety of such buildings, NIST
further recommends that as-designed and as-built safety be certified by a qualified third party, independent of the building
owner(s). The process should not use self-approval for code
enforcement in areas including interpretation of code provisions, design
approval, product acceptance, certification of the final construction, and
post-occupancy inspections over the life of the buildings.
Recommendation 26. NIST
recommends that state and local jurisdictions adopt and aggressively enforce available provisions in building codes to ensure
that egress and sprinkler requirements are met by existing buildings. Further, occupancy requirements should be
modified where needed (such as when there are assembly use spaces within an
office building) to meet the requirements in model building codes.
Recommendation 27. NIST
recommends that building codes should incorporate a provision that requires
building owners to retain documents,
including supporting calculations and test data, related to building design,
construction, maintenance and modifications over the entire life of the
building[3]. Means should be developed for offsite storage
and maintenance of the documents. In
addition, NIST recommends that relevant building information should be made
available in suitably designed hard copy or electronic format for use by
emergency responders. Such information
should be easily accessible by responders
during emergencies.
Recommendation 28. NIST recommends that the role of the “Design Professional in
Responsible Charge”[4] be
clarified to ensure that: (1) all
appropriate design professionals (including, e.g., the fire protection
engineer) are part of the design team providing the standard of care when
designing buildings employing innovative or unusual fire safety systems, and
(2) all appropriate design
professionals (including, e.g., the structural engineer and the fire
protection engineer) are part of the design team providing the standard of care
when designing the structure to resist fires, in buildings that employ
innovative or unusual structural and fire safety systems.
The professional skills of
building and fire safety professionals should be upgraded though a national
education and training effort for fire protection engineers, structural
engineers, and architects. The
skills of the building regulatory and fire service personnel should also be
upgraded to provide sufficient understanding and the necessary skills to
conduct the review, inspection, and approval tasks for which they are
responsible.
Recommendation 29. NIST
recommends that continuing education
curricula be developed and programs should be implemented for (1) training
fire protection engineers and architects in structural engineering principles
and design, and (2) training structural engineers, architects, fire protection
engineers, and code enforcement officials in modern fire protection principles
and technologies, including fire-resistance design of structures, and (3)
training building regulatory and fire service personnel to upgrade their
understanding and skills to conduct the review, inspection, and approval tasks
for which they are responsible.
Recommendation 30. NIST
recommends that academic, professional short-course, and web-based training
materials in the use of computational fire dynamics and thermostructural
analysis tools be developed and delivered to strengthen the base of available
technical capabilities and human resources.
1 NIST is a nonregulatory agency of the U.S.
Department of Commerce. The purposes of
NIST investigations are to improve the safety and structural integrity of
buildings in the
2 The focus of the Investigation was on the sequence of events from the instant of aircraft impact to the initiation of collapse for each tower. For brevity, this sequence is referred to as the “probable collapse sequence,” although it includes little analysis of the structural behavior of the tower after the conditions for collapse initiation were reached and collapse became inevitable.
[1] Or a more appropriate limit, which represents a reasonable area for active firefighting operations.
[2] A group of individuals that is knowledgeable, experienced, and specifically trained in gathering, processing, and delivering information critical for emergency response operations and is ready for activation in large and/or dangerous events.
[3] The availability of inexpensive electronic storage media and tools for creating large searchable databases make this feasible.
[4] In projects
involving a design team, the “Design Professional in Responsible
Charge”—usually the lead architect—ensures that the team members use consistent
design data and assumptions, coordinates overlapping specifications, and serves
as the liaison to the enforcement and reviewing officials and to the owner.
The term is defined in the International Building Code and in the ICC
Performance Code for Buildings and Facilities (where it is the Principal Design
Professional).