After a bomb exploded under the World Trade Center in 1993, power was lost and communications halted, even the generators were shut down for safety reasons. This affected the Fire Departments rescue efforts to maneuver through unlit, smoke filled stairwells and the firefighters inability to use their radios in such large buildings. Millions of dollars were spent to address the shortcomings displayed after the bombing. Working under the guidelines of the 1968 performance building codes of New York City, enhancements to the power sources, exits signs, and the fire alarm systems were made. Plans to improve the fire emergency preparedness and operations were also implemented by conducting bi-yearly fire drills and creating a new position, the fire safety director. This person was in charge of the deputy fire safety directors, who were routinely stationed in the lobbies of both towers and would communicate with the building tenants during an emergency (Natl. Comm’n on Terrorist Attacks Upon the U.S. 280).
In the eight o’clock hour of September 11, 2001, American Airline Flight 11 struck the north tower at a rate of approximately 500 miles per hour (Longman 52). Upon impact, the hijacked plane severely damaged the 93rd to the 98th stairwells of the North Tower, leaving people trapped on floors and in elevators. The building swayed back and forth from the initial collision. Reports of a change in air pressure, bombs exploding, and screams were documented by 911 operators (Avery).
The plane left a gapping hole on the outside of the building, severing many of the weight bearing columns and forcing the columns adjacent to the damaged area to pick up the exterior load to keep the building erect. As the plane ripped through the interior core, fuel leaked down the shaft and burst into flames, igniting other combustible materials. Drywall was knocked loose from its framing and was on fire. Drywall enclosed the elevator shaft and stairwells, and unfortunately when this material is exposed to high heat, it becomes very weak. The spray-on fire retardant had been blown off the structures skeleton from the initial impact, leaving the bare steel of the floor trusses exposed to the elements. The sprinkler systems had been compromised, allowing the fire to spread at will. The intense heat from the fire caused the steel to buckle, weakening the sagging floor trusses. This unaccounted for force applied extra tension on the trusses and caused the bolts to snap. The floor truss connections had failed, the fireproofing was jeopardized, and the interior core could not cope any longer and finally collapsed. The intense force of the interior core falling pulled the exterior walls along with it. A total of 10 seconds is all it took for the building to collapse in on itself. In the event, approximately 1,400 people perished in the north tower (Nova).
United Airlines Flight 175, at a rate of approximately 500 miles per hour, hit the South Tower at three minutes past nine o’clock (Longman 58). Upon impact, the hijacked plane banked as it hit the building, crashing through floors 77 through 85 (Natl. Comm’n on Terrorist Attacks Upon the U.S. 293). Portions of the building were not damaged and one stairwell remained unscathed. Since the plane hit the middle section of the building, more pressure was put on the lower, undamaged base to support the upper stories. “The only survivor known to have escaped from the heart of the impact zone described the 81st floor- where the wing of the plane had sliced through his office-as a “demolition” site in which everything was “broken up” and the smell of jet fuel was so strong that it was almost impossible to breathe” (Natl. Comm’n on Terrorist Attacks Upon the U.S. 294). Crippling smoke and fires were running amok. Many of the same instances and variables involved occurred in the south tower as occurred in the north tower; drywall was knocked loose from its framing and was on fire, the spray-on fire retardant had been blown off, the sprinkler systems had been compromised, and the bare steel floor trusses were completely exposed to the elements. After some time the exterior columns could no longer hold and eventually bent outward, destroying more floor trusses. The South Tower fell differently than the North Tower. The exterior walls toppled over like a peeled banana, bringing down most of the interior core with it. It was the second building to be struck but the first to collapse. A total of 10 seconds is all it took for the building to collapse in on itself. In the event, approximately 600 people perished in the south tower (Nova).
Floor after floor smacked down on top of the next to bring a 110-story building to its knees in seconds, the South Tower was reduced to rubble and shortly afterward the North Tower fell just as swiftly. “The towers fell in free fall speed, shatter and explode outward over 500 feet. Concrete is pulverized into dust.” The Twin Towers crumbled as if a planned implosion was scheduled. At Columbia University’s observatory in Palisades, NY the South Tower collapse registered as a 2.1 earthquake and the North Tower collapse registered as a 2.3 earthquake (Avery). “Twenty four thousand gallons of jet fuel caused a fire of 1500 to 2000 degrees F which weakened the steel and caused the collapse”, forever changing the New York City skyline. (Dunn)
Just hours after the World Trade Center collapsed, the dimensions of the site were mapped out. This and other compiled data were entered into geographic information system software. The digital maps provided varying information from smoke density and underground fires to power outages in order to help rescue and recovery personnel stay safe (Geographica). The neighborhood of TriBeCa, located just north of ground zero, became a beckoning for the injured, the mourners and the respite workers (Maitland 122). The rubble and twisted steel was relocated to another sight so that forensic scientists could investigate for clues as to what caused the collapse. Video clips were also gathered so that experts could review which parts of the towers failed.
A lack of universal radio communication and knowledge of what was occurring inside of the towers played a major role in unnecessary causalities. The evacuation of emergency response teams and building occupants was greatly improvised; no one had attempted a full-scale evacuation of the WTC during a fire drill. The majority of able-bodied people evacuated the North and South Towers below the point of impact. “At most 2,152 individuals died at the WTC complex who were not (1) fire or police first responders, (2) security or fire safety personnel of the WTC or individual companies, (3) volunteer civilians who ran to the WTC after the planes’ impact to help others, or (4) on the two planes that crashed into the Twin Towers.” Glow strips applied to handrails and stairs, were credited by some as the reason for their survival and making it possible to navigate through low visibility conditions. Compared to the evacuation time of four hours in 1993 to less than one hour for most of the occupants in 2001, indicates the revisions made to the buildings 8 years prior were life saving (Natl. Comm’n on Terrorist Attacks Upon the U.S. 316).
A New York City Deputy Chief, Vincent Dunn, believes that “a skeleton steel frame high rise would not suffer a cascading total pancake collapse of the lower floors in 8 and 10 seconds.” Stronger walls might have allowed more people to get down the stairwells of the Twin Towers (Nova). In conjunction with stronger walls, a more robust flooring system was also needed in the North and South Towers. If the fireproofing had not been lost, there is an increased chance that the buildings could of stabilized. Under normal conditions, structure fires do not end in a total collapse of the building.
How can a structure be built to withstand such a devastating impact? If the interior core had been constructed with concrete (hardening the stairwell) in lieu of drywall, it may have withstood much of the damage and enabled more occupants to evacuate the premises (Nova). Concrete will not burn until extremely high temperatures reach 3000 degrees Fahrenheit, creating a safer escape for the building occupants. Extra fireproofing should be applied to all major connection points of the skeleton to ensure the building is held together. Of all the recommendations given, most importantly is what types of back up systems should be employed in case key components fail? If the towers were connected by a double-decker pedestrian bridge, like that of the Petronas Towers, this application would create another exit point for occupants unable to evacuate from their own building (Petronas Towers). Or what about rooftop evacuations? There should be a way to extend a crane-type mechanism, positioned on the roof, up towards the safety of a helicopter rescue if the rooftop is too crowded for a heliport.
After a three-year investigation of the collapses of the Twin Towers, the National Institute of Standards and Technology (NIST) recommended building code changes that required tall structures to be more resistant to fire and more easily evacuated in emergencies. Several recommendations were approved by the International Code Council (ICC) and will be incorporated into the 2007 supplement to the International Building Code (IBC). “The proposals addressed areas such as increased resistance to building collapse from fire and other incidents, use of sprayed fire-resistive materials (commonly known as “fireproofing”), performance and redundancy of fire protection systems (i.e. automatic sprinklers), fuel oil storage/ piping, elevators for use by first responders and evacuating occupants, the number and location of stairwells, and exit path markings.” The approved model code changes will require: 1) the addition of another exit stairway for buildings more than 420 feet high, 2) a minimum of at least one fire service access elevator be present in all buildings more than 120 feet high, 3) an increased bond strength for all fireproofing products (to be approximately three times stronger than what is currently required for buildings 75-420 feet in height and seven times stronger for buildings taller than 420 feet high), 4) additional field installation requirements for fireproofing to ensure that: a) it fulfills the manufacturer’s instructions on installation, b) that the surface area being fireproofed is clean and no condition is present to prevent full adhesion, c) that testing is administered to show the required adhesion is maintained for the specified material, d) and that the final state of the fireproofing, once properly cured, does not expose any part of the substrate, 5) conduct field inspections of fireproofing to verify that it still meets specified requirements after the rough installation of mechanical, electrical, plumbing, sprinkler and ceiling systems are done, 6) increase the fire-resistance rate of structural components and assemblies in buildings higher than 420 feet by one hour, 7) adopt the “structural frame” concept towards fire resistance ratings that require the dominant members of the structural frame to exhibit a higher fire resistance rating. Members of the structural frame to which this pertains to includes: columns, girders, beams, trusses, spandrels, and any subsequent members that are connected to the columns or used to carry gravity load, 8) an exit path delineated by luminous markings to aid in full evacuations of buildings be present in buildings more than 75 feet high, which includes all passageways and vertical exit enclosures (Newman).
Plans for a new building and a memorial to honor those that were lost have been in the works for some time. The architects were faced with presenting a building that would make a statement, yet appease the concerns and recommendations for a safer, more secure structure. The Freedom Tower will be the first office building constructed on the sight of Ground Zero, and is said to contain all of these elements in a beautiful display of glass and steel. The Freedom Tower will act as a springboard for all future buildings to come. It will be located on the northwest corner of the World Trade Center site along with two reflective pools as a memorial, which will be known as Reflecting Absence. New York City Governor, George Pataki, said, “together we faced the challenge of redesigning the Freedom Tower and today we see the result is a better, safer, and prouder symbol of freedom for our skyline. This new design reflects a soaring tribute to freedom and a bedrock commitment to safety and security” (Design Plan for Freedom Tower). “The robust, redundant steel moment frame, consisting of beams and columns connected by a combination of welding and bolting, resists lateral loads through bending of the frame elements. Paired with a concrete-core shear wall, the moment frame lends substantial rigidity and redundancy to the overall building structure while providing column-free interior spans for maximum flexibility.” The exterior walls of the base of the tower will be fashioned from a composite, blast resistant, mixture. The life safety system will exceed the minimum required by New York City. “In addition to structural redundancy and extra strong fireproofing, the building includes biological and chemical filters in the air supply system. To assume optimum egress and firefighting capacity, extra wide pressurized stairs, low-level emergency lighting and concrete protection for all sprinklers and emergency risers are being provided, in addition to interconnected redundant exits, additional stair exit locations at all adjacent streets and direct exits to the streets from the tower stairs. All of the building’s life-safety systems-stairs, communications, risers, sprinklers, elevators- are encased in a core wall that is three feet thick in most places. This building is being designed to facilitate emergency response with enhanced emergency communication cables, together with a dedicated stair for use by firefighters. These are used in conjunction with enhanced elevators housed in a protected central building core that serve every floor of the building. In addition, “areas of refuge” are located on each floor” (Design Plan for Freedom Tower).
The modern skyscraper built on the soils of Ground Zero will have some large shoes to fill. People may be reluctant to work or even have their business located on the site. A long time resident of TriBeCa, Pete Hamill, states, “The emotions of awe, horror, rage were gone quickly, replaced by a shared sense of vulnerability. That is what remains: vulnerability. And from vulnerability there has emerged a tough fatalism. We all learned, that terrible morning, that we could die while reaching for a piece of toast at breakfast. Where I live, that knowledge has made us more human” (124). New safety measures will aid in easing the minds of some while visiting or working in the Freedom Tower or any other future high-rise building. There is a basic human understanding that nothing is ever foolproof, yet with tighter security measures and the enactment of better building concepts a brighter future will exist.
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