Richard G. Gann, Ph.D.

Senior Research Scientist

Building and Fire Research Labo

National Institute of Standards and Tec

U.S. Department of Commerce

rggann@nist.gov

Federal Building and Fire Safety Inves

of the World Trade Center Disast

Reconstruction of the Fires in 

Towers: Findings and Iss

October 19, 2004
Project Objective Project Objective

Reconstruct, with assessed uncertainty limits, thtemperature, thermal radiation, and smoke fieldCenter 1, 2, and 7 for use in evaluating the behaoccupants and responders and the structural pebuildings
Findings to Date Findings to Date - I

• Loading of building combustibles was on the light side • Mass of aircraft solid combustibles was significant rela

the building combustibles in the impact zone

• Ceiling tiles were likely to have been dislodged throug

floors

• The movement of the fires was complex and varied fro

each building

• View of fires through many windows was hindered by 

well as by steep viewing angles and smoke clouds

• It was possible to discern instances where an internal 

fire spread for an appreciable time

• FDS and FSI can be used with confidence to recreate 

of a given WTC fire event
Findings to Date Findings to Date - II

• The results of FDS modeling were relatively insensitive 

in damage estimates and combustible load in WTC 1

• Both FDS and the photographic evidence indicate that 

the fires was ca. 20 min

• The gross uncertainty in the damage to the core walls 

makes it impossible to obtain information from computthe tenability of the building interiors that is surer than information deduced from the activity of the occupants

• FSI simulations of both towers show high (dominant) s

structural element temperatures to the presence or ab

• The predictions of maximum temperatures reached by 

columns in FDS/FSI simulations are consistent with thfrom the analyses of the actual columns
Findings to Date Findings to Date - III

• WTC 1: 

• The oxygen-limited fires spread both counterclock

from the initial locations on the north side, taking mbecome established along the south face.

• By the end of an hour, there were many severely h

members on the south end of the core, complemeheated or impact-damaged core elements to the n

• WTC 2: 

• There was steady burning in the northeast quadra• Within an hour, there had been severe heating of n

perimeter and core columns and floors on the east floors

• There was little heating of the structural elements 

the building, where damage to the SFRM was not 
Issues - I

• Predictive tools for design-based fire scenarios th

• Computational code for determining the fire c

combustibles to fire scenarios

• An accurate model for predicting the performa

in fires, including open doors and window bre

• Mechanisms of and models for floor-to-floor f
Issues - II

• Availability of standards and codes, methodology

design tools, and practical design guidance to pefire as a design condition for the structure as a w

• Broad training opportunities for rigorous use o

fire dynamics and thermostructural analysis to

• Method for rating the fire resistance of structu

barriers for realistic design-basis fire scenario

with furnace conditions)

• Structural principles education for fire protect
Richard G. Gann, Ph.D.

Senior Research Scientist

rggann@nist.gov

Federal Building and Fire Safety Inves

of the World Trade Center Disast

Reconstruction of the Fires in 

Towers: Findings and Iss

Thank you