Dan Boghean
Chris Peterson
Gianny Rodriguez
Luis Marcelino


On February 26, 1993, at 12:17PM, the garage of Tower 1 of the World Trade Center, in New York, exploded due to a car bomb. The plan was to collapse the offices of Tower 1 onto Tower 2 (Figure 1) and cause chaos. The bomb opened up a 98 foot hole in the concrete, but wasn't enough to bring the tower down. Perhaps if the car was parked closer to the supports, there would have been more damage. Nonetheless, 6 people were killed and 1,042 were injured in the ensuing evacuation. The towers lost power and, as a result, people were trapped in elevators; even the stairwells were dangerous as smoke rose up to the 93rd floor. Luckily, the plan was a failure, and the towers were able to continue standing.

Figure 1 - Layout of Tower 1 and 2 (9-11 Commission)


World Trade Center Bombing 1993, car bomb, underground parking, terrorist attack, floor collapse

Events that lead to the bombing

Figure 2 - Terrorists involved in bombing (FBI)
A report on March 16, 1993 by Peter Caram indicated the increased activities of terrorists groups such as the Hezballah and the Muslim Brotherhood (Saudia Arabia, Algeria, and Lebanon). This report, however, was "sent to file and never circulated to the police commands for their information" (Caram, 13). It was obvious that America was becoming more vulnerable to terrorist attacks, and rightly so, the Port Authority believed the transportation system was at risk. The World Trade Center was seen as a prime target. It was "perceived to represent the arrogance of the United States. There were some forty foreign entities located at the complex, including an economic office of the Israeli Government" (Caram, 47). The extremists of the Islamic faith were a result of the confidence the insurgents gained after defeating the Russian communists that occupied Afghanistan with the help of $3 billion from the US. With such a victory under their belts, the insurgents believed they could defeat any superpower, and the United States was a despicable nation in their eyes. This led to the emergence of radical Muslims in the United States that wanted to purge the nation and be rewarded for their faith. It was with this intention that Ahmad Mohammad Aja, Ramsi Yousef, El Sayyid Nosair, Mohammed Abouhalima, and Mohammed Salameh acted (Figure 2). Their idea was to topple one tower on another and show the world what they were capable of (Caram). Despite their failed plan, the security and serenity of the American people was shattered.

Causes of Failure

The causes of failure of the World Trade Center in the bombing of 1993 involve a lot of factors. According to Frank L. Fire's article "The Materials involved in the WTC Bomb" in the Report and Analysis of the bombing, “Nitrourea is a Class A explosive. It also is known as m-nitrocarbamide, N-nitrocarbonide, 1-nitrourea, and N-nitrourea. Nitrourea represents a severe explosion hazard and is stable until detonated.” In other words, Nitrourea is a explosive that can be used and prepared to detonate anything.

Figure 3 - Rubble due to Nitrourea bomb (FBI)
Frank also explains in the same article “Nitrourea produces about 90.5 percent of the gas volume of TNT when detonated and has slightly more than three percent more relative power than TNT. It produces about 97.7 percent of the gas volume of picric acid and has three percent less relative power. Its caloric value (power as described by the number of joules of energy per kilogram of weight) is 34 percent greater than TNT’s and 19 percent greater than picric acid’s.” This is to say that Nitrourea is the main ingredient in many categories of bombs.

Frank also clarifies that the explosion was bigger because there was hydrogen involved in the explosion. In Fire’s article "The Materials involved in the WTC Bomb" he states that "hydrogen is a highly flammable gas. Its flammable range is from four to 75 percent, the second widest range of any common flammable gas. The flame from burning hydrogen has a very high heat content – its flame temperature is 3,700 degrees Fahrenheit. Hydrogen with an almost invisible flame converting all energy into heat energy.” Fire is trying to let the reader know that Hydrogen was a key factor in this fire for the fact that anything that Hydrogen touch would create immense heat and create structural damage to the building.

Physical problems that contributed to the failure in the tower were the load and weight of the concrete falling down after the explosion (Figure 3), as well as the fire creating cracks and openings for the smoke to travel around the building. The tower floors were made out of concrete, and one factor that allowed failure is that concrete isn’t good in tension. The explosion of pipes, and the hydrogen in air made things even harder for firefighters. The hydrogen traveled all around the area creating that great heat. Even though the fire did not reach certain places, the heat created by the hydrogen reached columns, walls, windows, and damaged them as well as blowing some windows out. (Manning)

The van driven by the terrorists was parked at the B2 sub level of the parking garage next to World Trade Center A. When detonated in Feb. 26, 1993, the explosion destroyed the 15 ft long, 1.5 in thick steel cross bracing, cracked the adjacent column, and bowed the bracing on the other side of the column. Without sufficient supports, the concrete floor above collapsed. This caused critical failure of the aforementioned floor above, the B1 level, and the floor under the car, B2 level. The debris of the concrete slabs broke through the B3 and B4 floors and stopped at the B5 sub level, ruining the refrigeration system of the complex that provides chilled water to the World trade center between the B3 and B5 levels. The explosion created a nearly 55 m long crater, 38 m wide.

Could the failures have been prevented?

In 2005, a six-member jury of the State Supreme Court found the Port Authority of New York and New Jersey guilty of negligence in protecting the World Trade Center bombing of 1993. The trial was mainly based around a report by the Office of Special Planning, an anti-terrorist task force established in 1985. This report concluded that "a time-bomb-laden vehicle could be driven into the W.T.C. and parked in the public parking area. The driver would then exit via elevator into the W.T.C. and proceed with his business unnoticed. At a predetermined time, the bomb could be exploded in the basement. The amount of explosives used will determine the severity of damage to that area." Eerily, that is exactly what happened on February 26, 1993. The Port Authority deemed that the economic losses that would occur due to the closing of the public parking would be too great, and thus, refused to take any preventative measures (Hartocollis). In fact, the Port Authority "allegedly spent $10,000 on a study on how to increase revenue from public parking instead of limiting access" (Caram). Taking advantage of this fact, the terrorists exploited the weaknesses of the World Trade Center in an attempt to bring down the towers. Fortunately, the attempts were a failure because the design was able to take the impact, but the fact remains that if the Port Authority had listened to the experts, perhaps the 1993 bombing could have been entirely avoided.

Lessons and Changes due to the bombing

The industry learned that we must always stay as up to date on safety prevention as possible, especially for densely populated buildings of such importance as the World Trade Centers. Efficient means of evacuation are a must for all buildings, and because of the 1993 World Trade Center bombing, more care was put into those evacuations including better stairwell lighting and clearer signage pointing towards the evacuation routes (Smith).
Figure 4 - 600 pound bomb mitigators (NYS Education)

The 1993 World Trade Center bombing brought the instance of terrorism farther into the light. As a response to it, extensive fire and bomb safety improvements were made. “Blast mitigators” were placed in and around the World Trade Center Plaza that would assist bomb technicians in the event of the discovery of a bomb. These 600 pound small structures (Figure 3) (about 2/3 the height of an average human, and approximately 3-4 feet in diameter) provided places to insert the bomb so the blast would be directed upward instead of outward (A Preface). This would completely prevent injury (unless an unfortunate bird was to be passing by). Also, the Port Authority’s police in New York were given training as bomb technicians would in order to improve protection of the World Trade Center.
Lessons that were not learned were to increase the durability of fireproofing. The fireproofing was lost in the 1993 blast (Anatol), but the support column that the exploded van was next to fortunately did not buckle. In the 2001 attack, the fireproofing was also lost on most of the steel supports, which resulted in them becoming soft due to the flames.


"A Preface to September 11, 2001". <http://www.nysm.nysed.gov/wtc/about/preface.html>.
The site explains the steps taken to try to fix the problems that came about due to the WTC Bombing.

Anatol, Longinow and Mniszewski, Kim. (February 1996). "Protecting Buildings from Vehicle Bomb Attacks". Pract. Periodical on Struct. Des. and Constr. Volume 1, Issue 1, pp. 51-54.
This article uses the WTC and other buildings as examples on how to protects against vehicle bomb attacks.

Caram, Peter. (2001). The 1993 World Trade Center Bombing: Foresight and Warning, Janus, London, Great Britain.
This book talks about some of the warnings of the attacks from the perspective of a Port Authority Police Officer.

Hartocollis, Anemona. (October 27, 2005). "Port Authority Found Negligent in 1993 Bombing". The New York Times. <http://www.nytimes.com/2005/10/27/nyregion/27wtc.html>.
This newspaper article explains that the 1993 bombing could possibly have been avoided if the authorities would have heeded the warnings.

Manning, William A. (February 1993). "The World Trade Center Bombing: Report and Analysis". U.S. Fire Administration/Technical Report Series.
This is an indepth report and analysis of the bombing of the WTC as provided by Homeland Security.

Puri, Satinder. (1994). "Trapped in an Elevator during the World Trade Center Bombing: A Personal Account". ASCE Publications. 217-228.
This article is about the personal accounts of a person that was trapped in the elevator during the bombing of the World Trade Center. It is a view into the damage experienced from an inside perspective.

Ramabhushanam, Ennala and Lynch, Marjorie. (November 1994). "Structural Assessment of Bomb Damage for World Trade Center". J. Perf. Constr. Fac. Volume 8, Issue 4, pp. 229-242.
This article explains the structural damage to the WTC and the steps taken to keep it up.

Smith, Sandy. (September 10, 2004). "1993 WTC Bombing Probably Saved Lives on 9/11". <http://ehstoday.com/news/ehs_imp_37185/>. EHS Today.
This article talks about the lessons learned from the WTC bombing and the effects it had on the attacks of September 11th.

Usmani, A.S. (June 2005). "Stability of the World Trade Center Twin Towers Structural Frame in Multiple Floor Fires". J. Engrg. Mech. Volume 131, Issue 6, pp. 654-657.
This article talks about the structural frame of the WTC during fires, similar to what might have happened during the 1993 bombing.

Wald, Matthew L. (March 2, 1993). "CRISIS AT THE TWIN TOWERS: Repairs; Damage to the World Trade Center Is Called Limited". The New York Times. <http://www.nytimes.com/1993/03/02/nyregion/crisis-twin-towers-repairs-damage-world-trade-center-called-limited.html?scp=17&sq=%22World%20Trade%20Center%22%201993&st=cse>.
This newspaper article explains the damage caused by the bomb and the attempt to fix it.