Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Initial Model for Fires in the World Trade Center Towers



Ronald G. Rehm, William M. Pitts, D D. Evans, Kuldeep R. Prasad, Kevin B. McGrattan, Glenn P. Forney


Mathematical models have been used to provide an initial estimate the behavior of the fires in the twin towers of the World Trade Center (WTC) on September 11, 2001. Available photographs and videos have provided an initial estimate of the exterior damage to each building. Profiles of meteorological quantities (wind speed, wind direction, pressure and temperature) as functions of height have been obtained from the Aircraft Communications Addressing and Reporting System (ACARS). Different scenarios for the interior damage and fuel distributionswere postulated. For each scenario, the fire and smoke behavior were simulated using the NIST-developed computational fire model known as the Fire Dynamics Simulator (FDS). Visible fire and smoke behavior outside the towers was then compared with the photographic and video evidence to determine which scenario seemed most appropriate. The collision with each tower produced significant structural damage, generated a spectacular external fireball with some of the jet fuel, and spread widely the remaining fuel, which acted as an ignition source for the combustible material within the tower. The fraction of the jet fuel consumed by the fireball was lost as an ignition source. The subsequent fire in each case produced what appeared to be a quasi-steady buoyant smoke plume carried along by the ambient wind. From the wind speed and the plume trajectory, the simulations allowed us to estimate that the rate at which energy from the fire entered the plume was of the order of a gigawatt (GW). FDS was then used to simulate the fires interior to each tower and to estimate the likely thermal environment. Computations to date indicate that maximum temperatures did not exceed 1000 degrees Centigrade.
NIST Interagency/Internal Report (NISTIR) - 6879
Report Number


computational fluid dynamics, fire simulation, mathematical models, World Trade Center


Rehm, R. , Pitts, W. , Evans, D. , Prasad, K. , McGrattan, K. and Forney, G. (2002), Initial Model for Fires in the World Trade Center Towers, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed June 24, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created May 1, 2002, Updated November 10, 2018