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Officials
at the Commerce Department's National
Institute of Standards and Technology (NIST) today made
public its second status update on the agency's federal building
and fire safety investigation into the World Trade Center
(WTC) disaster of Sept. 11, 2001. At a press briefing in New
York City (NYC), NIST
Director Arden Bement Jr. reported solid progress by the
investigation team at the one-third mark of the ongoing 24-month
effort and thanked the many private citizens and organizations
who helped the team to date.
"As our investigation moves into its next stages, NIST
will need to work even more closely with those individuals
and groups who can provide us with the information and materials
critical to reaching our overall goal—improvements in
the way people design, construct, maintain and use buildings,
especially high-rises," Bement said. "That includes
some New York City agencies, WTC survivors, first responders
and families of victims."
At today's
briefing, NIST released a progress
report on the WTC investigation (pdf*),
its second since the effort began in August 2002.
This interim report does not include any conclusions or
make any recommendations, since the investigation is still
in its early stages.
Key points in the progress report are available in the
attached fact sheet.
As a
non-regulatory agency of the U.S. Department of Commerce's
Technology Administration, NIST develops and promotes measurement,
standards and technology to enhance productivity, facilitate
trade and improve the quality of life.
Note: NIST has set up a special Web site for those who want
to participate in interviews or provide photos, videos or
documents detailing the WTC disaster at: http://wtc.nist.gov/media/provide_info.htm
Individuals can contact the WTC Investigation Team by writing
to NIST, 100 Bureau Dr., Stop 8610, Gaithersburg, Md. 20899-8610;
sending an e-mail to wtc@nist.gov; or faxing (301) 975-6122.
Remarks
by Dr. Shyam Sunder, lead investigator, at the May 7, 2003
news briefing. (PowerPoint file*)
Key
Points of NIST’s May 2003 Progress Report on the
Federal Building
and Fire Safety Investigation of the World Trade Center Disaster
Status of Data Collection Efforts
NIST is basing its review, analysis, modeling and testing
work for the investigation on a solid foundation of technical
evidence. This requires access to critical data such as building
documents, video and photographic records, emergency response
records and oral histories, in addition to the WTC steel
recovered.
NIST has received considerable cooperation and large volumes
of information from a variety of organizations and agencies
representing the WTC building designers, owners, leaseholders,
suppliers, contractors and insurers. Additional important
data have been provided by local authorities, other federal
agencies and the news media. The progress report lists specific
types of materials that NIST has received.
However, some vital pieces of information are still needed.
Among the materials still sought are: 9-1-1 tapes and logs
plus transcripts of about 500 first responder interviews;
the original project specifications for the WTC 1 and 2 towers;
the complete as-built drawings of the WTC towers and WTC-7;
and original design documents related to the ability of the
WTC towers to withstand aircraft crashes. A complete list
of the requested materials is available in the progress report.
As for visual materials, NIST has assembled a searchable
computerized database that contains more than 3,100 still
photographs and 3,400 video clips. Many items were provided
to NIST as a result of its December 2002 public request for
visuals of the WTC disaster. NIST continues to seek visuals
and is especially interested in obtaining: close-up details
of fire conditions in all three buildings (WTC 1, 2 and 7);
shots of the airplanes approaching and entering the WTC towers;
images of WTC-7, especially the south side; and views from
the south and west faces of the WTC towers.
At its May 7, 2003, press briefing, NIST demonstrated how
these visuals are being used to learn more about the aircraft
impacts and the fires.
Interim Report on Fireproofing of the WTC Floor System
As part
of its progress report, NIST has included an interim report
that documents the procedures and practices used to provide
the passive fire protection (fireproofing) for the floor system
of the WTC towers. Nothing in the interim report—based
on a review of factual data in documents obtained by NIST—should
be taken to imply that the floor trusses played a critical
role in the collapse of the WTC towers. The fireproofing issue
is a key component of the ongoing NIST investigation.
Major findings about the floor system fireproofing include:
- Early
in the design phase of the WTC towers, the Port Authority
of New York and New Jersey decided to comply
with NYC building code (the 1961-1962 revision of the NYC
building code was in effect at the time).
- In 1965,
the Port Authority revised its plans to comply with the
second and third drafts of what became the
1968 edition of the NYC building code; that code required
a 2-hour fire rating (the length of time that a structural
element can withstand a standard fire in a test) for the
floor system.
- Limited
information (all from the first 38 floors of WTC 1) from
surveys conducted in 1990 as part of an asbestos-related
litigation and subsequent measurements made in 1993 reported
that the fireproofing thickness on the floor joists (the
supports for the floors of WTC 1 and 2) was consistently
about one-half inch or more, with an average of about three-quarters
of an inch.
- Both
WTC towers were retrofitted by the early 1990s with sprinkler
systems.
- Based
on a 1995 study, guidelines were issued in 1999 to upgrade
the fireproofing requirements for floors
undergoing construction or renovation.
- By 2000,
the floor joists of about 30 floors in the two towers had
been upgraded to
1-1/2 inch thickness, and construction audit reports suggest
that these minimum
requirements were met.
- There
were problems with the original spray-on fireproofing remaining
in place, and it was found to be more
effective to replace it with new fireproofing material than
to patch existing fireproofing.
- Construction
audit reports associated with the fireproofing upgrade
to 1-1/2 inch suggest that the minimum
bond strength requirement for the spray-on fireproofing was
met; the ability of the fireproofing materials used in the
WTC towers to withstand shock, vibration, and impact is unknown
at this time.
- NIST
has been unable to locate any fire endurance tests conducted
on the WTC floor system to determine its
fire rating. The Architect of Record and the Structural Engineer
of Record stated in 1966 and 1975, respectively, that the
fire rating of the floor system of the WTC towers could not
be determined without testing.
- Based
on existing fireproofing conditions, a property condition
assessment in 2000 stated that "the rating of the structural
fireproofing in the Towers and subgrade has been judged
to be an adequate 1-hour rating considering the fact that
all Tower floors are now sprinklered," and noted the
at-that-time-ongoing program to upgrade the fireproofing
thickness to 1-1/2 inch in order to achieve a 2-hour rating.
- From
the documents reviewed, NIST has not been able to determine
the technical basis for the selection of
the fireproofing material for the joists, and the determination
of the thickness of fireproofing to achieve a 2-hour rating.
Fire Model Validation Experiments and Fire Testing of the
WTC Floor System
NIST
is using a combination of analytical, experimental and
numerical tools to analyze the various collapse scenarios
hypothesized for the WTC buildings. The progress report details
the key factors that NIST is considering in this analysis;
the elements required to simulate the thermal and tenability
(survivability) conditions in the buildings during the fires;
and the experiments being conducted to provide data for and
validation of computer models (including studies of the
mechanical
properties of recovered WTC steel, the thermal-insulating
properties of WTC fireproofing materials, the dynamics of
the fires in the buildings and their effect on the response
of the various WTC structural components, and the fire endurance
testing of a typical WTC floor system and individual steel
members).
The WTC
building fires will be modeled using NIST-developed software
that has been used for nearly a decade and has been validated
against experimental data for a variety of applications. A
series of fire tests was conducted by NIST to assess the accuracy
of the modeling software in predicting the thermal environment
in a burning compartment, and provide a reference set of data
to validate the software's ability to predict temperature
rise in steel components similar in geometry and cross-sectional
dimensions to those used in the WTC towers. The progress report
details these experiments and their preliminary results.
NIST plans fire endurance tests of a typical WTC steel-concrete
composite floor system and individual steel members under
the fire conditions prescribed by current standards (ASTM
E 119).
Assessing the Most Probable Structural Collapse Sequence
A number of hypotheses have been publicly considered for
the sequence of events that led to the collapses of WTC Buildings
1, 2 and 7. Based on an initial assessment of the expert
studies conducted as part of recent litigation and other
relevant data, NIST still considers it premature to exclude
any of these theories.
Appendix
5 of the progress report released on May 7, 2003, details
the integrated approach that NIST will use to identify the
most probable of the technically possible collapse sequences.
This approach combines three assessment methods in parallel—physics-based
mathematical modeling, statistical and probabilistic—to
evaluate and compare the plausible collapse scenarios.
Status of the Recovered WTC Steel and Its Analysis
NIST
has nearly 250 pieces of steel recovered from the WTC site—a
number adequate for the purposes of this investigation. Among
the types of pieces in hand are columns, rectangular box beams,
wide flange sections, truss sections, channels and bolts.
The recovered steel—representing roughly 0.25 to 0.5
percent by weight of the 200,000 tons used in the WTC towers—includes:
- twenty-eight
perimeter and 11 core columns for which locations have
been identified;
- several
columns from areas impacted by the hijacked aircraft;
and
- samples
of all 14 steel strengths used in the different components
of the towers.
Numerous chemical and mechanical analyses have been conducted
on the recovered steel. Preliminary results indicate that
the yield strength (ability to resist stress) of the different
steel types satisfied applicable specifications and that
most of the structural elements were made from steel with
higher-than-required yield strengths.
First-Person Data on Occupant Behavior, Evacuation and Emergency
Response
At an April 8, 2003, public forum in New York City, NIST
presented its plans for studying the WTC evacuation and emergency
response by collecting first-person data from survivors (both
WTC occupants and first responders), families of victims,
and individuals with operational and command authority during
the WTC disaster. The study will involve 750 face-to-face
interviews, 800 telephone interviews and 15 focus groups.
NIST believes
that it is possible to learn from the WTC disaster and to
improve public safety through the collection and analysis
of first-person accounts. This is an ambitious undertaking
and will need the active participation of WTC employers, occupants,
first responders and victims' families.
Other Items in the Progress Report
The progress report also includes sections detailing the
following items:
- the
implementation of the National Construction Safety
Team (NCST) Act under
which the NIST WTC investigation
is being conducted;
- the
establishment and first meeting of the NCST Advisory
Committee;
- funding
status of the WTC investigation, as well as the parallel
R&D and dissemination and technical assistance programs
in NIST's response plan for the WTC disaster; and
- a
summary of contracts solicited and awarded for
work on the investigation.
* the
pdf file requires Adobe Acrobat Reader to be viewed. Download
it free. The PowerPoint file requires Microsoft PowerPoint
to be viewed. Please contact inquiries@nist.gov if you are unable to view these files and would like to request
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