Blast seat
A blast seat refers to the point of detonation of an explosive device, marking the area most affected by the explosion. Identifying the blast seat is crucial for investigators, as it offers valuable clues regarding the nature and cause of the explosion. This area, also known as the seat of explosion, blast hole, or epicenter, can vary significantly based on the type of explosive used, its quantity, and its placement. Blast seats can be characterized as point sources, resulting in distinct craters, or diffuse, where explosives are more spread out. The presence or absence of a crater can indicate whether a concentrated explosive or a different type of explosive, such as fuel gas or dust, was responsible for the blast. The surface on which an explosion occurs also influences the characteristics of the blast seat; for example, explosions on soft ground tend to create deeper craters compared to those on hard surfaces. Understanding the blast seat's features is essential for determining the explosion's details and gathering evidence for further investigation.
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Blast seat
DEFINITION: Point of detonation of an explosive device.
SIGNIFICANCE: The blast seat is generally the area that suffers the most damage when an explosion takes place. It is very important that the investigators at an explosion scene locate the blast seat, because that area provides many clues about the nature of the explosion.
After an explosion, prompt identification of the blast seat (also known as the seat of explosion, blast hole, or epicenter) makes it possible for investigators to locate quickly and to determine the type of explosion that occurred. The type of crater formed at the blast seat depends on the type and quantity of explosives used, how the device was placed, and whether the explosives were in a container, such as in a pipe. Depending on the magnitude of the explosion and the amount of explosives used, the process of finding the crater can be easy or difficult.
Blast seats are characterized as either point source, such as when a large crater is produced, or diffuse. This characterization is one of the most important determinations for investigators to make when a major explosion occurs, because it can provide information about what caused the blast, such as whether the explosive materials were concentrated or dispersed. A concentrated explosive will typically excavate the blast seat and form a crater. In fact, a distinct crater is usually a very good indication that an explosive device was used. In such a case, thermal imaging cameras can detect a thermal effect surrounding the blast seat. Other types of explosions, such as those that are caused by fuel gas, vapors, or dust explosives, do not produce craters or have definite blast seats. With dispersed explosives, a thermal effect near the immediate blast seat is also absent.
The type of surface on which an explosion takes place can affect the blast seat that forms. When an explosion occurs on the ground, dirt, rock, and other debris are blasted out to form a crater. These materials land near the top of the crater, with some rock and debris falling back into the crater. When a blast is caused by large amounts of explosives, the debris that falls back into the crater can cover it completely, making it difficult for investigators to find the blast seat. Explosions that take place on hard surfaces such as concrete also produce craters, but these are generally not as deep as the craters formed by explosions on open ground.
Bibliography
Beveridge, Alexander, ed. Forensic Investigation of Explosions. New York: Taylor & Francis, 1998.
Ellis, John W. Police Analysis and Planning for homicide Bombings: Prevention, Defense, and Response. Springfield, Ill.: Charles C Thomas, 2007.
Horswell, John, ed. The Practice of Crime Scene Investigation. Boca Raton, Fla.: CRC Press, 2004.
National Institute of Justice. A Guide for Explosion and Bombing Scene Investigation. Washington, D.C.: Author, 2000.
Thurman, James T. Practical Bomb Scene Investigation. 3d ed. Boca Raton, Fla.: CRC Press, 2021.