Building and Fire Safety
Response to the World Trade Center Disaster
S. Shyam Sunder
National Institute of Standards and Technology
About the Lecture
On September 11, 2001, terrorists attacked the World Trade Center in New York City crashing commercial aircraft into the 110-story towers. The damage to the buildings caused by the aircraft impacts combined with the ensuing fires ignited by the jet crashes, led both buildings to collapse killing in all 2823 people. The death and destruction was unprecedented in the United States and the worst building disaster in human history.
The National Institute of Standards and Technology has proposed a response plan consisting of three key program elements to be conducted in parallel. These are:
First, a 24-month building and fire safety investigation into the factors contributing to the probable cause of the collapse of the Twin Towers and WTC 7 – and the associated loss of life and injuries.
Second, a multi-year research and development (R&D) program to provide the technical basis for improved building and fire codes, standards, and practices.
Third, an industry-led dissemination and technical assistance program (DTAP) that will provide practical guidance and tools to better prepare facility owners, contractors, designers, and emergency personnel to respond to future disasters.
The talk will describe the NIST response plan in the context of the events of September 11, 2001and the lessons expected to be derived to reduce future vulnerabilities.
About the Speaker
S. Shyam Sunder is Chief of the Materials and Construction Research Division in the Building and Fire Research Laboratory at NIST and Lead Technical Investigator for the pending building and fire safety investigation into the World Trade Center disaster. He received a Doctor of Science degree in Structural Engineering from the Massachusetts Institute of Technology in 1981 where he held a succession of faculty and staff positions until joining NIST in 1994. From June 1996 to December 1997, he was on assignment to the Program Office, the principal staff office of the NIST Director. He was chief of the Structures Division from January 1998 until June 2002 when the Building Materials Division and the Structures Division were merged into the Materials and Construction Research Division.
President Collins called the 2148th meeting of the Philosophical Society of Washington to order at 8:20 p.m. on September 13, 2002. The Recording Secretary read the minutes of the 2146th meeting and they were approved.
The speaker for the 2148th meeting was S. Shyam Sunder of the National Institute of Standards and Technology. The title of his presentation was, “Building and Fire Safety: Response to the World Trade Center Disaster.”
Just about a year ago, on September 11, 2001, terrorists attacked the World Trade Center in New York City crashing commercial aircraft into the 110-story World Trade Center towers. The damage to the buildings caused by the impacts combined with the ensuing fires ignited by the jet fuel, led both buildings to collapse killing more than 2800 people. More than 350 fire and emergency responders were among those killed. This was the largest loss of life for this group in a single incident. The death and destruction was unprecedented in the United States and the worst building disaster in human history.
The National Institute of Standards and Technology (NIST), at the request of the Federal Emergency Management Agency and in consultation with local New York City authorities, initiated an effort to understand what led to the structural failure and subsequent progressive collapse of the World Trade Center buildings and use the lessons learned to better protect people and property in the future, enhance the safety of fire and emergency responders, and restore public confidence in the safety of tall buildings nationwide.
To this end, NIST proposed a response plan consisting of three key program elements to be conducted in parallel.
First, accomplish a 24-month building and fire safety investigation into the factors contributing to the cause of the collapse of the Twin Towers and World Trade Center 7 – and the associated loss of life and injuries.
Second, do a multi-year research and development program to provide the technical bases for improved building and fire codes, standards, and practices.
Third, perform an industry-led dissemination and technical assistance program to provide practical guidance and tools to better prepare facility owners, contractors, designers, and emergency personnel to respond to future disasters.
The speaker described the background for the NIST plan in the context of the events of September 11, 2001 and the lessons expected to be derived to reduce future vulnerabilities. The initial NIST analyses included reviews and assessments of photos and videos and used relatively simple mathematical calculations. The size and shape of the smoke plume helped to identify the strength of the source of the fire, on the order of estimated at a giga watt which is about the same as a typical output of a central power station. The size of the initial fireballs was used to determine how much of the jet fuel landed on the outside of the buildings of the WTC and burned off in a matter of minutes. It was this initial fuel burn that ignited the building contents, such as carpets, paper, furniture, etc. This provided most of the heat that weakened the remaining structures and led to eventual collapse.
The initial analysis results showed the 110 story towers collapsed due to damage induced by the high-speed impact of the aircraft and the weakening effect of the subsequent fires. Here, the first impact was at about 400 mph and the second at 500 mph while flying at an altitude of about 1,000 feet. The first tower collapsed after 56 minutes and the second after 1 hour and 43 minutes. Seismic readings showed that it took about 13 seconds for the buildings to collapse. The speaker pointed out that a rock would fall from a corresponding height in about 9 seconds. Thus, the buildings were essentially in free fall, indicating near total lack of structural resistance.
The massive damage extended to World Trade Center 7, a nearby 47-story building which burned and collapsed at 5:20pm. Ironically, this building housed offices of the New York City Office of Emergency Management and emergency generators with several fuel tanks which ignited. The resulting fire caused pivotal structural members to fail and the total collapse of the building. This was the first building in history to collapse due almost solely to fire. Similarly, World Trade Center 5, a 9-story building and the 22-story nearby Marriot Tower were destroyed. In all about, more than 20 million square feet of commercial rental space were lost.
NIST has identified areas where research and development is needed such as those related to emergency response and evacuation procedures. This includes changes in guidance for the use of elevators during emergencies. Currently, it takes about a full minute for a fireman with a 60-pound pack to climb one floor. Thus, more than one hour could pass before help arrives for people on the 60th floor or above. Similarly, changes in guidance for the use of communication equipment were also discussed. Here, it was found that the communication equipment used by the Fire Department of New York didn't work, whereas the equipment used by the New York Police Department did work.
In closing, the speaker cited anecdotal evidence that over the past year an increasing number of tenants were now leaving the Empire State Building. Mr. Sunder then closed his presentation and kindly answered questions from the floor. President Collins thereupon thanked Mr. Sunder for the Society, welcomed him to membership, announced the next meeting and made the usual parking announcement. He then adjourned the 2148th meeting to the Social Hour at 9:42 p.m.