ROLE OF FIRE RESISTANCE ISSUES IN THE COLLAPSE OF THE TWIN TOWERS

The twin towers of the World Trade Centre suffered significant damage from the impact of the planes, however, they withstood the impact. The severe fires that followed the impact brought down the twin towers, WTC 2 and WTC 1, at different intervals - 59 and 89 minutes respectively following the impact. Thus, fire issues played a major part in the collapse of the twin towers and the role of the various fire resistance issues is examined in this paper. While the jet fuel from the aircraft was burned off within the first few minutes, the fire temperatures attained in the twin towers was not significantly different from other building fires. However, the fire intensity and heat output generated in the twin tower fires was very much higher than typical building fires. The intense fires ignited by jet fuel, loss of fire defence mechanism, damaged fire proofing and the stressed state of the structural system were the main factors that contributed to the collapse of the towers. The twin towers, comprising WTC 1 (North Tower) and WTC 2 (South Tower), were the primary components of the seven building World Trade Center (WTC) Complex in Manhattan, New York City. These towers, built in the late 1960's were 110 stories above grade and were the world’s tallest buildings for a while. The full occupancy of the towers was about 50,000 people and the tenants included many prominent multinational financial service companies. Therefore, these towers were a major landmark and financial center in New York City.