The National Institute of Standards and Technology (NIST) is conducting a two year investigation of the World Trade Center disaster. Among numerous tasks, computer simulations of the fires are being conducted to provide structural engineers with a detailed description of the gas and steel temperatures. In support of the computer simulation, large scale fire experiments are being conducted to both validate the model and to generate input data describing the thermal properties of the contents of the buildings. The results of the calculations are being compared to photographs and videos of the fires. Thousands of pictures and hundreds of hours of videotape have been analyzed to produce a detailed window-by-window timeline of the fires' progress.