On September 11th, 2001 at 8:46 am hijackers deliberately crashed American Airlines Flight 11, carrying 87 passengers and crew, into floors 94-98 of the North Tower (1 WTC). At 9:03 am United Airlines Flight 175, carrying 60 passengers and crew crashed into floors 78-84 of the South Tower (2 WTC). At 9:59 am the South Tower collapsed. That was just 56 minutes after the plane struck the tower. Then at 10:28 am the North Tower collapsed. These 110 story buildings were not supposed to collapse like they did or as fast as they did. Why physically did the World Trade Center eventually collapse after being struck by the airplanes?

When the planes hit the towers that day they were full of jet fuel. The fuel in the planes caused a fire. The fire was so hot that it caused the metal beams supporting the buildings to weaken. It was not hot enough to melt the metal but the fire did make the metal weak, which caused it to bend. The weakening of the metal structure caused one story to collapse. Once one story collapsed all floors above would fall with it. The huge mass of falling structure would gain momentum, crushing the floors below, resulting in failure of the entire structure. While the columns at say level 50 were designed to carry the static load of 50 floors above, once one floor collapsed and the floors above started to fall, the load of 50 stories above is very much greater, and the columns at each level were almost instantly destroyed as the huge upper mass fell to the ground. Because of the collapse not all of the people in the towers were able to evacuate in time. It is said that the attacks took the lives of around 3,000 innocent people. We wonder why this happened. We also wonder if there was anything that could have been done to prevent the collapse of the towers.

The towers were built in the 1970’s. During this era asbestos was added to flame-retardant sprays used to insulate steel building materials, particularly floor supports. The insulation was intended to delay the steel from melting in the case of fire by up to four hours. In 1971, New York City banned the use of asbestos in spray fireproofing. In result to this ban the towers only had the insulation up to about the 40th floors. After that a different insulation not containing asbestos was used to finish the buildings. The planes struck above the 40th floor where there was a different insulation. Some people believe that if the asbestos insulation was used through out the whole building, it would have prevented deaths. Those people believe that the asbestos insulation would have made the buildings stand up longer. I don’t know if anyone will ever really know if it would have made any difference. All we know is that we lost people in a horrible attack on our nation.

Annotated Bibliography

(2009, June). The World trade center - asbestos use in construction. Retrieved from http://www.asbestos.com/world-trade-center/asbestos.php This was about the asbestos used as insulation in the World Trade Center. This article talked about how the non asbestos insulation used would have been less effective than products that contained asbestos, which ultimately shortened the time that the people had to escape. This was helpful to me because it told me about the asbestos in the WTC, but it was also focused on asbestos exposure and what to do if you have exposure. I also do not know how reliable this source is because I could not find an author.

Thompson, P. (2004). The Terror timeline. Harpers Paperback. The Terror Timeline offers a complete and thorough history of the many roads that converged on 9/11. It traces the actions of every important figure in the war on terror, both before and after 9/11. This was helpful to me because I wanted to give background information on that day. This source was very reliable.

Walker, J. (2006). The Flying circus of physics. Wiley; 2 Edition. This book features more than 700 thoroughly intriguing questions about relevant, fun, and completely real physical phenomena. Detailed explanations and references to outside sources guide your way through the problems. It was very helpful because I got my question and answer from this book. This source was very reliable.