The Fires

Qualitative and semi-quantitative analyses presented in this article suggest that the massive fires caused by the crash of the planes into the World Trade Center Towers and the spillage of large amounts of jet fuel inside the buildings played a major role in their quick collapse on September 11, 2001. It is argued that the WTC fires, while unprecedented in form, magnitude and extent, resembled massive compartments fires in which the primary fuel the jet fuel spilled over a large area, ignited almost immediately, supported the formation of huge fireballs that extended outside the crash zones, and triggered very large-scale secondary fires that engulfed all available combustibles contained within the floors surrounding the impact area. These post-flashover fires, which sent thick smoke plumes a long distance downwind over lower Manhattan's previously cloudless skies, continued to burn long after the catastrophic collapse of the buildings. The analysis presented in this article relies on models of compartment fires to estimate the burn rate and the resulting fire and structure temperatures, incorporating rational assessment of the crash damage on the exterior and the interior of the Towers that were created by the plane impact. Using these models, scenarios for the fires during their different stages are developed, and approximate rates of overall heat release and the prevailing temperature history within the buildings are obtained. It is shown that the fire power, measured in terms of total heat release rate, was of the order of gigawatts, the fire temperatures may have exceeded 1000° C, and the structural steel elements attained dangerously high temperatures for an extended period of time. While these estimates are approximate and preliminary, they remain relatively unchanged when varying some of the assumptions and numbers used to define the burning conditions over ranges supported by available data, and confirm the assertion that the fired played a major detrimental role in the quick collapse of the Towers on that tragic day.