September 29, 2005

 

As part of a company-funded study Engineering Analysis Inc. has carried out an analysis of the bombing of the London double decker bus on 7 July 2005. The basic objective of the study was to recreate the three-dimensional scenario of the blast, taking into account the location and yield of the bomb, the characteristics of the bus, and the presence of passengers. The High Explosive Damage Assessment Model (HEXAM), including the HEXDAM Man, and the Vulnerability of Structurally Damaging Impulses and Pressures (VASDIP) software were used in carrying out the analysis.

All data describing the bomb characteristics, the bus configuration, and the number and location of passengers were taken from the news media. No data derived from any official British Government reports were used.

As depicted in Figure 1, the passenger vehicle was a Stagecoach London double decker bus, Number 30, commonly used in London. Based on analysis of available photographic data the dimensions of the bus are provided in Table 1. The bus is assumed to be constructed of corrugated steel with annealed glass windows .157 inches thick. As indicated in Figure 1, the engine compartment is located in the lower rear section. Access to the lower level of the bus is provided by two doors on the left side, one located near the front of the bus and the other located approximately halfway back. Immediately behind the driver, on the right side, a stairwell provides access to the upper level.

Table 1. Bus Dimensions

As shown in Figure 2, on the lower level 22 passenger seats are located, 12 on the left and 10 on the right. On the upper level 34 passenger seats are provided, with 20 on the left and 14 on the right.

At the time of the explosion the bus was full or nearly full, according to eyewitness reports. The passenger carrying the bomb was seated in the rear of the upper level. Although the precise location of where this passenger was seated is unknown, for purposes of this study the assumption is made that he is seated in the aisle seat on the left side of the last row, as indicated in Figures 1 and 2.

The bomb is assumed to be located in the vicinity of the bomb-carrying passenger. For this study the bomb is assumed to be just to the right and behind his right shoulder, as indicated in Figures 1 and 2. According to news reports Scotland Yard estimated the yield of the bomb to be approximately 4.5 kilograms or 10 pounds of TNT. This yield value has been used in carrying out the study.

A number of photographs of the bus after the explosion have appeared in the news media, along with eyewitness accounts provided by bystanders. Based on an examination of available photographs, a summary of the observed structural damage to the bus is provided in Table 2.

Table 2. Summary of Observed Structural Damage

No published data are available as to the exact location on the bus of those passengers who suffered fatal injuries, but all appear to have been located in the rear section of the bus. A total of 14 fatalities were initially reported along with an undisclosed number of injuries. A fifteenth passenger apparently succumbed to injuries after being hospitalized.

 

Based on the problem description derived from the news media, a series of test runs were carried out involving both the VASDIP and the HEXDAM software. First, VASDIP was used to calculate the vulnerability of the HEXDAM Man to a blast produced by a bomb with a yield of 10 pounds of TNT. The resulting vulnerability parameters were assigned to all of the 56 passengers, plus the driver, occupying every seat on the bus. HEXDAM was then employed to predict structural damage and personnel injury.

Structural damage to the bus is depicted in Figure 3. For this figure the color legend is given in Table 3.

Table 3. Damage/Injury Color Legend

As indicated in the figure the entire roof of the bus as well as essentially all the windows on the upper level are destroyed. Most of the rear of the bus is severely damaged. The engine compartment located beneath the bomb is damaged but not destroyed. The rear half of the floor on the upper level is severely damaged while the forward half of the floor survived with slight to moderate damage. About 75% of the glass in the lower-level-windows is blown out. Both the front and side doors on the right side suffer moderate-to-severe damage. Much of the glass on the left side of the front windshield is blown out as is approximately one-third of the glass on right side of the windshield. All four wheels are severely damaged.

Comparison with Table 2 reveals that the predicted structural damage agrees quite well with the observed damage, especially for the roof, upper deck windows, panels, and floor, and the front windshield.

A summary of the injuries produced by blast is provided in Table 4. Included in this summary are the bus driver, who suffered no injury, and the bomber, who suffered fatal injuries. As noted in the table, a total of 17 fatalities were predicted. A breakdown of the injuries causing these injuries is provided in Table 5. The most common types of fatal injury, according to the table, would be severe cervical vertebrae fracture and severe skull fracture. Of the 17 passengers with predicted fatal injures, 4 passengers were on the lower level (2 on the left and 2 on the right) and 13 passengers were on the upper level (6 on the left and 7 on the right). As shown in Figure 4, all such passengers were seated toward the rear of the bus. The color legend given in Table 3 applies to the representation of injuries in the figure. Also included in the figure is the 20 psi overpressure contour.

Table 4. Summary of Predicted Injuries

Table 5. Summary of Predicted Fatalities

The actual cause of death for the 15 reported fatalities, and their individual locations within the bus are not known. However, as already noted, according to available reports, most of the actual fatalities were located at the rear of the bus on both levels. This observation is in very good agreement with the predicted fatalities.

 

In an effort to provide a means of visualizing the blast environment, three-dimensional overpressure contours have been generated by means of HEXDAM as shown in Figure 5. Inspection of these contours reveals that the rear half of the upper deck was exposed to pressures ranging from 10 to 500 psi while the front half of the upper deck was exposed to pressures ranging from 1 to 10 psi. By comparison, the rear half of the lower deck was exposed to pressures from 1 to 100 psi, while the front half of the lower deck was exposed to pressures on the order of 1 psi or less.