9/11, 2001: A Case Study

September 11, 2001 was a defining moment in American history, as well as a defining moment in the history of the fire service, when 343 fire fighters were lost in the 2 largest building collapses in recorded history (Brannigan & Corbett, 2015). The mechanism of the collapse of these structures has become a source of debate. NIST analyzed the collapse and arrived at a conclusion as to the contributing factors of the collapse of the buildings. Some of the factors include dislodged fire proofing, weakened columns with increased loads, fires on multiple floors, and sagging floors leading to pull-in forces on perimeter columns. Two air craft impacted the towers at high speeds causing severe damage to the structures. The impact of these aircraft caused the fireproofing on steel beams to become dislodged (Brannigan & Corbett, 2015). After the impact and subsequent dislodging of the fire proofing, fires began to heat the unprotected steel beams of the towers. In both towers the impact of the aircraft removed fire proofing on both the columns
These forces pulled the perimeter columns inward reducing their ability to support the building above (NIST, 2011). These columns and neighboring columns quickly became overloaded by the added stress and damage and buckled. After the perimeter columns bulked the top sections of the buildings tilted and the buildings began their decent. All of these factors combined caused the subsequent collapse of both towers. The damage caused by the impact of the aircraft and fires generated destroyed and damaged key elements of the structure that allowed the chain of events that brought down the buildings. In the absence of structural and insulation damage, a substantially similar to of less intense than that of the fires encountered, likely would not have led to the collapse of the WTC towers (NIST,