|MadSci Network: Earth Sciences|
Determining the size of an explosion is not an exact science because there are a wide range of variables. For example, the size of crater produced by an explosion depends on a variety of factors, specifically how strong is the material subjected to the blast, what is the distance from the explosive to the ground, and what are the characteristics of the explosive. So, looking at the size of a crater isn't necessarily the best way to determine the size of an explosion. When an explosive detonates, it generates a pressure wave which expands more or less spherically from the point of the explosion. The pressure wave decreases to the third power with distance from the source of the blast, i.e., double the distance from a blast and the overpressure, or pressure higher than atmospheric pressure decreases by a factor of 8. The following link: http://www.fas.org/man/dod-101/sys/dumb/fae.htm presents some simple formulas for calculating blast overpressures. Of course, buildings, hills, and other features can interact with the blast wave, causing overpressures to increase or decrease. Overpressures developed by nuclear explosives have been studied extensively. The following link: http://www.nbc-med.org/SiteContent/MedRef/OnlineRef/FieldManu als/amedp6/PART_I/chapter3.htm provides a description of the effects of a nuclear blast. Table 3-II in that reference shows the overpressures necessary for certain types of damage to occur. For example, an overpressure of 3 to 7 kPa results in glass being shattered. So, if investigators are attempting to determine the size of a specific blast, they can measure the distance how far away from the blast that windows are broken and then back calculate to determine the approximate size of the blast. There are computer models available to predict the size of a blast and its effect on structures which enable structural engineers to design oil platforms and chemical processing equipment to be safer to operate. These models are also used to determine safe distances for storing explosives so that in the event of an accident, an explosion doesn't propagate from one cache of explosives to the next. Thanks for giving me the chance to talk about explosives. It was a blast.
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